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DIY Fun With Transformers
#3048967 06/15/20 11:45 AM
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I mentioned starting a DIY "little gadgets" topic, and Kuru, in the "Vocal Chain" discussion, fed me (us) suggested an application for parts in his junk box that might get the ball rolling. Saving things that you're never sure what you're going to do with is such a wonderful things, and leads to many opportunities to experiment.

Originally Posted by KuruPrionz
I've had a pair of Beyer mic to tube transformers for many years. I read up on them and a mic can easily saturate them, they are small. Supposedly very good frequency response. I have some paperwork with them including schematics and test traces.
Supossedly they were used by Ampeg and Studer.

That would be Ampex, and they may be the transformers that are in the Ampex record/repro electronics chassis, part of what makes the Ampex 350 and 351 electronics popular to use as a Phat Toob mic preamp. Do they look sort of like this?


[Linked Image from thumbs.worthpoint.com]

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I thought of just hooking the input wires on one tranny to an XLR mic jack, then hooking like colored secondary wires together on both trannies and the primary wires on the second tranny to an XLR output jack.

Well, if one transformer is good, two transformers isn't necessarily better. I get that you want to get the mic's level and source impedance back so that you can see how it sounds with your assortment of preamps, but I have a better suggestion - Use the transformer for what it was designed. Connect the primary (low impedance) winding to a female XLR, and connect the secondary side to a TRS phone plug. Plug that into a line or instrument input on your preamp or interface. That will give you the closest you can get to the sound of the transformer.


Quote
I've also got a slightly larger transformer that says Packard Bell on it, not sure which wires do what to be honest. And a couple of transformers that came out of boxes that were supposed to go inbetween a guitar amp and the speaker and tap off a line out for direct in to the PA. There are all kinds of vintage transformers around but that means a custom product, maybe it's a prototype?

Probably a custom product. The way to identify transformer leads or terminals is with a multimeter. Low impedance windings will have a low resistance, high impedance windings will have a high resistance. By measuring resistance between various pairs of pins, you can identify which ones go to which windings. There may be a wire that shows resistance to more than one other pin. That means you have a tapped winding, most commonly a center tap if it's an input transformer. Speaker output transformers typically have multiple taps on the secondary (speaker) side to accommodate speakers of different impedances.

If you don't have a multimeter, get one. It doesn't have to be expensive. Get some connectors, a few feet of mic cable, and have some fun.

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Re: DIY Fun With Transformers
Mike Rivers #3048981 06/15/20 02:11 PM
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I hear from a reliable source, the famous mixer (Neve 8028) from Sound City had 9 transformers in the path from front to end. 😁

Re: DIY Fun With Transformers
Mike Rivers #3048987 06/15/20 03:07 PM
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Awesome thread, Sir Mike!!!!
Photos attached. The second tranny is a Stromberg Carlson, not a Packard Bell. I can take another photo with a penny for a size reference, since these are vague in that regard. Cheers, Kuru

Parts numbers on the Beyers is TR/BV 351 006, I'll double - check to make sure those are both the same.

Attached Files IMG_1903.JPGIMG_1905.JPG
Last edited by KuruPrionz; 06/15/20 03:09 PM.

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Re: DIY Fun With Transformers
Mike Rivers #3049022 06/15/20 07:14 PM
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Yup, those are the mic input transformers for the Ampex 300/301. In case your documentation doesn't have it (and yours are the same as the Ampex part, the red and black wires are the primary, the yellow and blue are secondary, the brown is a Faraday shield which is, I believe, also connected to the case. The red (primary) and blue (secondary) wires are both the "start of the winding," which means that in order to maintain the polarity through the transformer, if you make them XLR-XLR, connect the red wire to pin 2 on the input and blue wire to pin 2 on the output. If you wire the secondary to a TRS plug, connect the blue wire to the tip.

As to what to do with Pin 1, connect the brown wire to the input XLR. You can experiment with connecting Pin 1 of the output XLR or the sleeve of the TRS plug to Pin 1 of the input. See which way you get less hum. If you find a useful arrangement, you'll eventually want to put it in a metal box for some shielding.

The sound of an Ampex without the flutter.

Re: DIY Fun With Transformers
Mike Rivers #3049037 06/15/20 08:30 PM
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Thanks Mike!!!! Now I have a simple project to play with. I'll see what parts I have on hand, probably most if not all of them.

And you were correct above about using the two transformers to get back to mic impedence.
The Quantum will want to see a TRS plug, that auto-selects a Line In configuration. XLR defaults to mic in and does not want to be switched.

The Focusrite has XLR Line In which I think bypasses the transformer. The HHB Radius has XLR Line in and no input transformer so that's a another possibility.

Any harm in wiring an XLR and TRS output jack in parallel and just using one or the other?


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Re: DIY Fun With Transformers
KuruPrionz #3049050 06/15/20 10:43 PM
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Originally Posted by KuruPrionz
you were correct above about using the two transformers to get back to mic impedence.
The Quantum will want to see a TRS plug, that auto-selects a Line In configuration. XLR defaults to mic in and does not want to be switched.

Although it will load the transformer differently than what it expects - which means it will sound different than when connected to a high impedance input - you could could connect the secondary to an XLR and plug it into a mic input. The level will be pretty hot but there should be enough range on the input gain control to keep it from clipping.

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Any harm in wiring an XLR and TRS output jack in parallel and just using one or the other?

None at all. If you build it into a box, having two connectors could be convenient. Though what I'd do, probably, is wire a TRS jack directly to the output (Hi-Z) side of the transformer, then make a 20 dB pad with a few resistors to bring it down closer to mic level and present a higher impedance load on the transformer so it behaves more like it was intended.

Re: DIY Fun With Transformers
Mike Rivers #3049054 06/15/20 11:01 PM
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Thanks again! Since it is relatively simple I think I'll try the easiest thing first and see if it needs tweaking.

Sounds like a bit bigger box will make it easier to experiment and it could find a more compact home once the details are worked out.

Since I have 2 of them, any thoughts on using the secondary as the input for guitars/basses with active (EMG) pickups for a DI, with the primary going to a mic pre?
I can get specs if it is a feasible idea.


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Re: DIY Fun With Transformers
KuruPrionz #3049067 06/16/20 01:42 AM
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Originally Posted by KuruPrionz
Since I have 2 of them, any thoughts on using the secondary as the input for guitars/basses with active (EMG) pickups for a DI, with the primary going to a mic pre?
I can get specs if it is a feasible idea.

It wouldn't hurt to try, but because these are so small, while they can have good frequency response and low distortion when driven at mic level, active pickups might be hot enough when driving the high impedance side so that you'd get into saturation too soon. But since this is all about making what comes out sound different than what goes in, why not give it a try? It'll only take a few minutes to hook it up.

Re: DIY Fun With Transformers
Mike Rivers #3049069 06/16/20 02:08 AM
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Originally Posted by Mike Rivers
Originally Posted by KuruPrionz
Since I have 2 of them, any thoughts on using the secondary as the input for guitars/basses with active (EMG) pickups for a DI, with the primary going to a mic pre?
I can get specs if it is a feasible idea.

It wouldn't hurt to try, but because these are so small, while they can have good frequency response and low distortion when driven at mic level, active pickups might be hot enough when driving the high impedance side so that you'd get into saturation too soon. But since this is all about making what comes out sound different than what goes in, why not give it a try? It'll only take a few minutes to hook it up.


Nice. The output of the guitar or bass can be varied with the volume pot so you could dial for a sweet spot as far as saturation goes.
Unlike passive guitar pickups, EMGs are not loaded by the pot and don't need a small bleed cap on the pot to keep a full frequency response.
I do adjust mine lower than most people, since they are very quiet I prefer the sound of them backed off from the strings.

It could be a second item for the "product line" perhaps.

Will be "parts surfing" either tonight or tomorrow to see what's on hand.


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Re: DIY Fun With Transformers
Mike Rivers #3049184 06/16/20 06:51 PM
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Poking around in the "stash", I found a good candidate - pix attached.

I've had this for a many years and never did one thing with it.
I guess it would be fair to clean the jacks and plug it in, it may have it's own merits - there is a transformer.
Somehow, I doubt it, at least not with the gear I have around here. I don't use LIne Out audio gear for the most part, mics and guitars are more interesting. Active bass might be enough signal to perk things up.

It might have to die so other experiments can live. So it goes. This already has all the jacks for the first step project.

Looks like disemboweling the gizzards woudl be easy enough. I have some NOS Switchcraft TRS jacks so that's easy too.

I could make a male to male XLR patch cord if I want to try an active guitar into the secondary. I already have a female to female adapter if I need it for anything else insane.

Attached Files IMG_2157.JPGIMG_2158.JPG

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Re: DIY Fun With Transformers
Mike Rivers #3049217 06/16/20 10:54 PM
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Take out the the two screws on the back of the circuit board and let's see what's on the other side of it. I'll bet it's a transformer, maybe one so good that it doesn't sound like a transformer, maybe one so good that it does sound like a transformer. It looks like the circuit board is soldered directly to the XLR terminals so you'll probably have to take out the two screws on the front that hold in the XLRs (and the circuit board).

From the traces on the board, I can see that the two XLRs are wired in parallel like it says, so you can use either a male or female cable connector. You could rewire them so one is the input and the other is the output, and replace the TS jack with a TRS jack so you could use that to go to or come from either a balanced gozinta or gozouta.

The trick, and it shouldn't be much of one, is to identify the transformer terminals. I'll bet it's the two on the left and the three just to the right of them.

Or if you can get the board unsoldered from the XLRs - which could be a bugger if you don't have a solder sucker - it will make a fine chassis for housing your transformer collection.

Re: DIY Fun With Transformers
Mike Rivers #3049238 06/17/20 12:22 AM
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I took the screws out of the XLR mounts on the top and the board dropped out. The two screws in the bottom of the board appear to be there to secure the XLR jacks, probably for a wave soldering process.
There is a transformer, with a part number. See attached photos.

I might have mentioned above - I also have a couple of transformers that came out of older "guitar amp speaker out to line in" boxes that sounded terrible in that application. Speakers are inefficient and gulp down high frequencies that we do not like.

Attached Files PV_Trans_1.jpgPV_Trans_2.jpg

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Re: DIY Fun With Transformers
Mike Rivers #3049239 06/17/20 12:24 AM
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And, I do have a solder sucker and some solder wick braid. I repair guitars, those are handy tools sometimes.

Update - I put the Peavey box back together and will try to test it tomorrow.

I can run a mic in and 1/4" unbalanced out to a DI, and I can run a guitar in to a Mic/Line input.
The problem I forsee with that approach is that I don't have a "control" setting.

I can't compare a mic through the box to a mic into the DI unless I use one of my straight XLR to 1/4" unbalanced cables and that will probably require considerable adjustment to the gain setting, so it won't be a valid comparison.

The same is true for running the guitar straight into a Line in unless I make a new cable and again, the gain setting will be different.
I'll do it anyway, maybe it will be obvious.

Since there are both male and female XLR, I can hook up a Beyer inbetween them and A/B that with a mic plugged straight in.
Mike, you mentioned resistors in the ciruit to adjust the resistance. One of the photos I posted shows the "top" side of the PC board and inbetween the XLR plugs there are resistors mounted. Those appear to go to traces running back to the transformer.

Last edited by KuruPrionz; 06/17/20 04:11 AM.

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Re: DIY Fun With Transformers
Mike Rivers #3049330 06/17/20 03:44 PM
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I was trying to figure out where in the circuit those resistors go, but can't tell just from the photo. They may be a voltage divider across the Hi-Z (1/4") output.

As far as control goes, the mic is going to drive the transformer at whatever level it puts out. What you need to do is set the gain on the preamp/interface (mic or line in, depending on what you're using) so that it's about the same as you get for either input. You could use a signal generator (a phone app if you don't have anything else) as a substitute for the mic and calibrate the gain setting that way, but you really just need to match by ear.

You can cut traces to separate the two XLRs and adding wire jumpers to connect them to the transformer. I'd suggest wiring the female one to the Low-Z (3 terminals) side of the transformer and the male one to the Hi-Z side. That way you'll have a male gozouta and a female gozinta.

Re: DIY Fun With Transformers
Mike Rivers #3049503 06/18/20 04:27 AM
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As always, many things need done! I'll be back to this project, hopefully by Friday.
I found two more small transformers from when I gutted a couple pieces of terrible sounding gear to get the XLR jacks ro my rack project.

Plenty of options to play with. My money's on the Beyer trannies sounding the best. I guess we'll find out soon.

Still a Fun thread, love it!!!!


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Re: DIY Fun With Transformers
Mike Rivers #3049917 06/20/20 05:22 AM
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First, I want to thank Craig for the Shure SM58 hack thread, it has led to this wild goose chase!!!! laugh

Did some more testing, including new "junk drawer finds" or as I call them - "the equipment stash." Some of this stuff has been sitting around for a LONG time. I use the Whirlwind IMP 2 all the time, it's a good all around bullet proof DI.

I recorded somed experiments and listened back. No plugins were used. Photos are attached.

First, the "control" track. I did a vocal track using a Heil PR40 into a mic channel on the Quantum.

Next, I plugged the Heil into a female to female XLR adapter and into a Whirlwind IMP 2. There are 2 1/4" TS jacks in parallel so I plugged one straight into Quantum DI #2 and one into a Tech 21 Tri-AC, from there into Quantum DI #1.
Did another 2 vocal tracks, using both channels. I had the Tri-AC in Tweed and just a bit of grit. It has a 3 band EQ, slight treble boost.

The clean output of the Whi\rlwind is pretty boring, I didn't hear that "magic transformer" sound. The control track sounded much better. The Tri-AC track is a different animal, there is lots of potential there. I used a battery, which keeps the noise down considerably, noise really wasn't a problem. If you had a better sounding parallel track to blend with it, it could really deliver a subtle but unmistakeable bit of "tube amp tone". It is a Sansamp, one of the best solid state tube emulation circuits by far - (Peavey's TransTube is the other best for analog in my book). One option with this rig would be to run the other output to one of my Peavey Vypyr amps and mic that. One of these days I'll try that.

I did another track with the same rig but I switched the Tri-AC to Calif, which is a Boogie. I put as much evil into it as the noise floor would allow, which was quite a bit. I could hear blending that in somewhere too, it was pretty cool.

Then, I hooked up the Peavey 1:1 Balancing Line Transformer that got me into this project in the first place. I plugged the Heil into the femaie XLR jack and used the TS 1/4" jack into the Quantum DI. It works OK but not inspiring, again the control track sounded better.

Next up was a Shure Line Balancing Transformer - Model No A9SUF, I've had this since before they invented catfish. Super easy, plug the mic cable in and plug it into the DI. This does have some transformer "mojo" to it. It's fairly subtle but it sounds good. I like it. I may try it straight into the Tri AC or worse yet, into a TC Electronics Flashback Delay X4, then one side into the Tri AC/DI and the other into the DI. That's crazy world, I can hang. The Shure is a winner.

Then, using the female/female XLR, I hooked up a Radio Shack 274-017C to the Heil on one end and the Quantum DI on the other. Balanced XLR line to unbalanced TS 1/4" out. The tiny drawing on the label indicates a transformer here too. And it's good. Very clear sounding and definately a transformer tone. Because it has a male XLR it appears to be intended to use as a DI for a high impedance source. I'll have to try it with bass and guitar.

Conclusion is that I will unsolder the circuit board in the Peavey 1:1 box and see what one of the Beyer transformers does wired into that space. Since I was planning on parallel outputs with one XLR and one 1/4 unbalanced, maybe I can use the Tri-AC in parallel

Attached Files DIY_Tran_1.jpgDIY_Tran_2.jpg

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Re: DIY Fun With Transformers
Mike Rivers #3049959 06/20/20 01:37 PM
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Good set of experiments, though lots of combinations. Don't confuse the simulated tube sound with a transformer that's not really going into saturation, but is probably dropping off some highs (or the SansAmp is accentuating them).

You might get some more transformer "action" with a source with more low end then your voice, like an acoustic guitar or bass.

Re: DIY Fun With Transformers
Mike Rivers #3049980 06/20/20 03:43 PM
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Originally Posted by Mike Rivers
Good set of experiments, though lots of combinations. Don't confuse the simulated tube sound with a transformer that's not really going into saturation, but is probably dropping off some highs (or the SansAmp is accentuating them).

You might get some more transformer "action" with a source with more low end then your voice, like an acoustic guitar or bass.


I do know the difference between a "tube amp" sound (tubes and transformers) and a tranformer sound, which is much cleaner, but full and "euphonic" for want of a better word. Set the way I had it, the SansAmp clamps down on dynamics harder and has more harmonic content. That was intentional, I wanted to see what it did. I'm an electric guitarist, it's second nature to push things harder!!! laugh

I can try a bass over the weekend.
The proximity effect of the Heil is pretty unreal and I was intentionally very close to the mic. Again, pushing the mic too. I just cannot be stopped!!!!

It seemed to me that the smaller transformers in the Shure and Radio Shack widgets were wound for microphone impedance and were probably a much better match for a mic. They certainly got closer to what I am looking for soundwise. Both were clear and punchy, but had something "extra" that the mic straight in did not have.

The Beyer is a mic tranny too, no?

Not sure what the tranny in the Focusrite looks like but it has an immediate audible effect on vocals/microphone even when I am not pushing the gain too hot or singing too close. But it's a Lundahl tranny and probably one of the most expensive components in that mic pre.

So comparing it to a tranny that came in a Peavey or Whirlwind widget that can handle line level signal without distortion is probabaly apples and oranges? They were wound for a different purpose.
Sort of like trying to get a good lead guitar tone out of bass amp? Yes, it can be done but there will be hearing damage!!!!! Ever crank an SVT? I have, it is a glorious ear destroyer!!! A 50 watt Bassman with 4-10s is pretty scary too.


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Re: DIY Fun With Transformers
KuruPrionz #3050233 06/21/20 07:45 PM
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Originally Posted by KuruPrionz
It seemed to me that the smaller transformers in the Shure and Radio Shack widgets were wound for microphone impedance and were probably a much better match for a mic. They certainly got closer to what I am looking for soundwise. Both were clear and punchy, but had something "extra" that the mic straight in did not have.

The Beyer is a mic tranny too, no?

Well, yes. That's its application in the Ampex recorder that it came out of. But it was just designed as an off-the-shelf transformer that Beyer figured somebody could put to good use - like to match a mic to a tube grid.

50 years later it would probably make a pretty good re-amp box as long as the low impedance side could take the level you're feeding it without saturating, which, coming from a mixer or DAW audio interface output, will be considerably greater than mic level. Or, maybe letting it saturate gives what's sending back to the amp some extra guts that you like what you're hearing when you record it again.

Transformers look simple, but they're really pretty complicated little buggers. While the impedance of the primary and secondary may be specified, the impedance is "transformed" from one winding to the other. The actual load impedance that the primary presents to the source connected to it (a mic, for instance, if that's what you're using it for) depends on the turns ratio and the load connected to the secondary.

For example, let's say I have a transformer (I do, in a DI, on my workbench, with test equipment connected to it) that's specified as a "line output" transformer - appropriate for a DI because you connect it to a high level source (the amplifier), don't want to load it very much, but, want to get a mic level signal out the other end with a source impedance that looks at least sort of like a mic. Now, let's say I want to use it as a mic input transformer, to step up the voltage out of the mic so that it's high enough to drive the first active stage of the preamp.

When I connect a test generator to the "mic" side, with nothing connected to the "line" side, the generator tells me that the input impedance is about 5 kΩ, not particularly what I'd like to connect a mic to. But when I put a load on the "line" side, I find that when it's loaded with about 25 kΩ, the load on the generator comes down to 600 Ω, a decent "fake mic."

A preamp designer knows where the secondary of the transformer is going, so he can specify or design a transformer that will present the load impedance to the microphone that he wants. He does this by picking the right turns ratio between the primary and secondary windings. But there are other things to consider, and transformer designers have learned that the material that the that the metal that the core that the wires are wound around can make a difference in sound. So can the DC resistance of the windings, which affects the number of turns you need in order to get the ratio you want. And the coils have inductance and capacitance, which can be tweaked by using exotic methods of winding the coils.

Back in the good old days, like with tape recorders, the design goal was to make things sound as transparent as possible, choosing their tradeoffs to suit the product they were making. Today we have all sorts of choices, so you can get your preamps with a Jensen, a Sowter, a vintage Carnhill, or a Korean copy of a Radio Shack transformer.

The point of all this is that by knowing the electrical characteristics of a transformer - its design impedance and turns ratio, you can find one that gets you the right gain (or loss) but when it comes to "color" there are only some generalizations, like which core material saturates at the lowest current. But the original designers didn't expect the transformer to be driven into saturation in its normal operation, so they just made sure that it had the right core material and type of winding to remain transparent.

It's just that all you rock'n'roll guys decided that you liked it better when it was messed up. So fortunately there are some choices that you can pick from.

And, as I've said before, there's nothing wrong with experimenting. If you find something you like, don't worry about impedances or core material, just go for it. You won't blow anything up.

Last edited by Mike Rivers; 06/21/20 10:01 PM. Reason: Oh, there's always something else
Re: DIY Fun With Transformers
Mike Rivers #3050258 06/21/20 09:57 PM
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Originally Posted by Mike Rivers
It's just that all you rock'n'roll guys decided that you liked it better when it was messed up. So fortunately there are some choices that you can pick from.

Another great post, most informative! I do have a rudimentary understanding of presumably simpler inductors - guitar pickups. These offer their own set of options and variables, making them complex in different ways - some of these variables are controllable by the guitarist or their tech (me).

Since we are having fun with transformers, I'll leave guitar pickups for another thread.

I've done a bit of searching the interwebz for information about the Beyer transformers I have and a couple of posters chimed in that they seem to overload more easily than other input transformers. At a guess, perhaps they were designed for ribbon mics, which are lower output? Certainly with some of the newer microphone designs the output has increased.
I have some dynamic mics that use neodymium magnets and/or have larger diaphrams that previous models.
One of the reasons I chose the Heil PR40 is the higher output. I am not a particularly loud singer, nor to I have a "big sounding" voice so I like mics and signal chains that make me sound "bigger."

There is a wide range of "messed up" in recording history. Digital offers a cleaner, lower noise signal path and now with LUFS tables becoming part of the listening environment it's possible to make records with more dynamics and better signal to noise. This is all good but many people like things "messed up" a little or there would not be so many options available for us to do so, no?

I'll be back to this soon, spent some time yesterday upgrading my mic isolation box instead of melting lead. Cheers, Kuru


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Re: DIY Fun With Transformers
KuruPrionz #3050346 06/22/20 02:10 PM
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Originally Posted by KuruPrionz
I've done a bit of searching the interwebz for information about the Beyer transformers I have and a couple of posters chimed in that they seem to overload more easily than other input transformers. At a guess, perhaps they were designed for ribbon mics, which are lower output?

Ribbon mics and tube condenser mics were the most common in the days of the Ampex 350, so the mic input transformer was designed to step up the level of a ribbon mic to what the record input needed. Generally the tube mics were connected directly to the line input of the recorder, bypassing the transformer and preamp.

Because that little transformer doesn't have a lot of metal in the core, (it's often called a "peanut") it will saturate at a lower current than a beefier transformer.

Quote
I'll be back to this soon, spent some time yesterday upgrading my mic isolation box instead of melting lead. Cheers, Kuru

Take your time. I don't have a Beyer peanut here, but I've been curious to see if I can plot the saturation characteristics of something similar. If I can come up with an interesting test setup, lend me one and I'll plot it out to see just what it takes to make it poop.

What I'm expecting is to see a 2nd or 3rd harmonic appear when saturation begins, and then see higher order harmonics come along as it's driven harder. Looking at the RMS output (as you would for expressing THD), I expect that a plot of output level vs. input level would look like a compressor's characteristic curve, but what would make for interesting study, I hope, is to see what harmonics add up to make that RMS output level.

[Later]
Now that I think about it, I probably do have some Beyer peanut mic input transformers here, in my Ampex MX-10 mixer. While I'm not eager to take the mixer apart to get directly to the transformer leads, it wouldn't be too difficult to run a signal through it and see what happens first - transformer saturation or clipping the first tube stage. I'm not making any bets yet.

But it might be harder than I think to saturate a transformer. I tried the saturation experiment using the DI, feeding the mic level side from a generator, and I was unable to get any sort of saturation with an input level of +18 dBu, which is where my generator ran out of steam. So this isn't a very good example of a mic transformer saturating. The peanut would be a better bet.

But, you know, if your information from the webz about saturation is anecdotal, is anyone actually measuring the transformer? Or are they just hearing what they think is saturation with a transformer in the signal chain - which might be something else saturating or, if a tube, just "soft clipping" from being fed a hotter than expected signal.

Last edited by Mike Rivers; 06/22/20 04:49 PM. Reason: Inspiration
Re: DIY Fun With Transformers
Mike Rivers #3051918 06/30/20 09:30 PM
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OK, I'm back!!!! I used a Heil PR40 for all testing and a couple of known good mic cables. I recorded a few samples on my DAW so I can listen more subjectively later tonight.

I started by trying the simplest thing, XLR to XLR - mic pre in. Very low output, not very good sound. Some noise, lots of noise if the level was brought up. Impedence mismatch?

I don't have resistors laying around, a few capacitors is the extent of my electronic parts stash (well, and a bunch of pots, switches and jacks). Guitars don't use resistors to any great degree. So I didn't add one to the circuit as advised. I also tested it to an XLR Line In on my HHB Radius, low output and noisy - the channel strip donated some noise, it's not a premium quality piece of gear and the gain was higher than I would usually use because the output was very low.

Touching the metal case of the input plug made it hum. I tried running a buss wire across both Pin 1 connections, it didn't solve that but it didn't make it worse and it was easier to solder the ground from the TS output jack - which was the next addition since it was handy.

XLR input to TS jack into a DI on either the Quantum or the Focusrite sounds really good.
I tried the mic pre on the Quantum and compared the output with the DI at the same setting - 45. The DI was louder but they both sounded good.

I am not sure I heard any saturation. When I ran it into the DI on the Focusrite, that uses a transformer as well and it sounded like it.

I can certainly send you a Beyer peanut for testing. You wanna goof around with the Stromberg Carlson trannie too? PM me with a shipping address and I'll send them along.

Progress, we have something that works and it is not a disaster (yet).
I'll try hookng up a TRS jack and going into the Quantum Line In. I have a couple other 1/4" Line In Options to try as well.


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Re: DIY Fun With Transformers
KuruPrionz #3051929 06/30/20 11:24 PM
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Originally Posted by KuruPrionz
OK, I'm back!!!! I used a Heil PR40 for all testing and a couple of known good mic cables. I recorded a few samples on my DAW so I can listen more subjectively later tonight.

I started by trying the simplest thing, XLR to XLR - mic pre in. Very low output, not very good sound. Some noise, lots of noise if the level was brought up. Impedence mismatch?

Is this using the Peavey box? Were you using an XLR-1/4" adapter? Which was connected to the mic?

Quote
Touching the metal case of the input plug made it hum. I tried running a buss wire across both Pin 1 connections, it didn't solve that but it didn't make it worse and it was easier to solder the ground from the TS output jack - which was the next addition since it was handy.

XLR input to TS jack into a DI on either the Quantum or the Focusrite sounds really good.

That sounds like the signal path that Ol' Hartley intended.

Quote
I am not sure I heard any saturation. When I ran it into the DI on the Focusrite, that uses a transformer as well and it sounded like it.

Like I said before, it's darn hard to saturate a transformer. And you were hearing the sound of the Focusrite DI which I suspect has some coloration capability built into it, which might or might not involve its input transformer.

Quote
I can certainly send you a Beyer peanut for testing. You wanna goof around with the Stromberg Carlson trannie too? PM me with a shipping address and I'll send them along.

Keep experimenting and take notes. When you figure you've tried everything you can, send me some stuff including that Peavey box and I'll see what I can learn and measure.

Re: DIY Fun With Transformers
Mike Rivers #3051947 07/01/20 01:51 AM
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Originally Posted by Mike Rivers
Originally Posted by KuruPrionz
OK, I'm back!!!! I used a Heil PR40 for all testing and a couple of known good mic cables. I recorded a few samples on my DAW so I can listen more subjectively later tonight.

I started by trying the simplest thing, XLR to XLR - mic pre in. Very low output, not very good sound. Some noise, lots of noise if the level was brought up. Impedence mismatch?

Is this using the Peavey box? Were you using an XLR-1/4" adapter? Which was connected to the mic?

Quote
Touching the metal case of the input plug made it hum. I tried running a buss wire across both Pin 1 connections, it didn't solve that but it didn't make it worse and it was easier to solder the ground from the TS output jack - which was the next addition since it was handy.

XLR input to TS jack into a DI on either the Quantum or the Focusrite sounds really good.

That sounds like the signal path that Ol' Hartley intended.

Quote
I am not sure I heard any saturation. When I ran it into the DI on the Focusrite, that uses a transformer as well and it sounded like it.

Like I said before, it's darn hard to saturate a transformer. And you were hearing the sound of the Focusrite DI which I suspect has some coloration capability built into it, which might or might not involve its input transformer.

Quote
I can certainly send you a Beyer peanut for testing. You wanna goof around with the Stromberg Carlson trannie too? PM me with a shipping address and I'll send them along.

Keep experimenting and take notes. When you figure you've tried everything you can, send me some stuff including that Peavey box and I'll see what I can learn and measure.

Too many quotes above, will answer consectively. I removed the XLR jacks and the 1/4" TS jack and cable from the PCB. I wired the female XLR (input) with leads from the Beyer - red to pin 2, black to pin 3 and brown to pin 1. On the male XLR (output), I put blue on pin 2 and yellow on pin 3. That was my starting point. I probably should have cut the traces like you recommended, would have kept the components between the two jacks in the circuit. I did not use any adapters. Mic was connected to a mic cable going to the input jack.

Yes, probably Hartley's doing. An important and overlooked figure in the sound of modern music.

Most of us never really hear a transformer by itself, which is what the "prototype" is at this point. It is an important component, interaction with other components is certainly a big factor in the way some gear sounds. Guitar amps come to mind, you can ruin one by putting too nice an output transformer in it but it's not just the transformer. An efficient speaker will change the sound of an amp too, or swapping in a higher/lower gain V1.

Sounds good, I'll play around with it and see what comes of it. I want to try a bass for one thing.


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Re: DIY Fun With Transformers
Mike Rivers #3051987 07/01/20 11:46 AM
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OK, so it's just the Beyer transformer in line with the mic. First thing to check is the gain or loss through the transformer. Establish a benchmark. Connect the mic directly to the preamp or interface. Play a steady tone through a speaker into the mic (put a weight on a key on a keyboard) and set the input gain for a mid-scale reading on your DAW's input meter, say around -16 dBFS.
Then put the transformer into the circuit, and, without changing the gain, read the meter.

Re: DIY Fun With Transformers
Mike Rivers #3052033 07/01/20 05:01 PM
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It took some thought to come up with a reasonable alternative for a constant sound since my only keyboards are MIDI controllers.

Then, the neighbor upstairs gave me an idea by vacuuming their carpets.

I could mic my vaccum cleaner!!!! It emits a constant (and annoying) sound, sort of a filtered pink noise if you will. I'll just wear headphones to mitigate it.

I can tell you right now that the mic connected through the transformer into the mic-pre has a serious loss of volume. This is probably a mis-match based on the components you mentioned adding to that circuit (and / or the stuff Hartley put into his circuit).

I am pretty sure that board is still laying around, I'll take a look at it. Maybe I can cut traces and solder wires to add it back into the circuit and see what that does.

On the other hand, the mic through the transformer and into the DI via 1/4" TS worked fine, the gain was set to a reasonable level and there was plenty of volume for recording a vocal. That input would be high impedence and more sensitive to input voltages.


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Re: DIY Fun With Transformers
KuruPrionz #3052059 07/01/20 06:51 PM
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Originally Posted by KuruPrionz
It took some thought to come up with a reasonable alternative for a constant sound since my only keyboards are MIDI controllers.

Then, the neighbor upstairs gave me an idea by vacuuming their carpets.

Now that's creative. I have a bunch of genuine hardware signal generators here, but I have a signal generator app on my phone, and when I go in the field, I carry a cable with a mini phone plug to connect to the phone and a few adapters to plug the other end into an XLR, 1/4", or phono jack and I have a test signal.

Quote
I can tell you right now that the mic connected through the transformer into the mic-pre has a serious loss of volume. This is probably a mis-match based on the components you mentioned adding to that circuit (and / or the stuff Hartley put into his circuit).

On the other hand, the mic through the transformer and into the DI via 1/4" TS worked fine, the gain was set to a reasonable level and there was plenty of volume for recording a vocal. That input would be high impedence and more sensitive to input voltages.

I'm pretty sure that what's going on is that the transformer is stepping up the voltage, and, in the process, stepping up the impedance. So what you have when you connect the 1/4" output to the low input input impedance of the mic preamp, even though you start out with a higher open circuit voltage going in, you have a big voltage divider consisting of the maybe 25,000 ohm output impedance of the transformer in series with the 1,500 ohms or so of the preamp's input. That'll get you about a 25 dB loss of level and probably more at the high frequency end due to the inductance of the transformer.

[Later on]
I should have thought of this sooner, but I was getting hungry. When I suggested that your cobble up an adapter to plug the transformer output (1/4" jack) into the mic input to compare to the mic level, I was being unfair to the comparison. As I wrote above, the mic into the mic input is loaded by an impedance that it expects. The transformer output into the mic input is being abused by the lower than expected loading. What we really want to compare is the open circuit output to the open circuit input, and the closest we can get to that is to connect both the mic and the mic-through-transformer to the DI input. The closer they are to giving you the same DAW level, the closer the transformer is to being a 1:1 ratio, but I don't think that's what you'll find.


This is why it's good to figure out what the transformer is doing.

Last edited by Mike Rivers; 07/01/20 08:01 PM.
Re: DIY Fun With Transformers
Mike Rivers #3053942 07/13/20 06:58 AM
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And... I'm back.

I set up the test for the level of attenuation provided by the Beyer transformer wired directly from an XLR input to XLR output in the Peavey box as above.
I mic'ed up my vacuum cleaner with a Heil PR40 mic plugged straight into Presonus Quantum and set up my DAW to meter the output at -5 db. Then I plugged the mic into the transformer interface and plugged that directly into the same input with the same level setting. It showed -22db. 17db less output. Not an exacting test, the vacuum cleaner did have minor volume spikes here and there. Still, probably reasonably accurate. Certainly there is attenuation.

Since I wanted to see if I could drive the transformer into saturation I tried a couple of bass guitars - one tuned to EADG and one to BEAD. I dug around in my stash of EMG stuff and found an old BTC = Bass Tone Control. It is a battery powered 2 band EQ. The low frequency band is broad and with a pair of 9v batteries running 18 volts, it can push a broad swath of low frequencies up to 12 db hotter.

I put the BTC in another project box, using a TRS output jack as the on/off switch. Then, I realized my predicament - both the bass and the BTC were 1/4" phone plug. I have a Switchcraft 384A, which is an adapter from 1/4" female jack to XLR male plug with no transformer, the signal was feeble and noise level was high using the adapter. I suspect it is shorting pin 3 of the primary coil to ground. I am not sure how or if that can be rewired to solve that issue so I went to Plan B:

I used both a Whirlwind IMP 2 DI box and a Radio Shack 275-017C inline DI - 1/4" TS to XLR Male plug. Either way, there were 2 transformers in the signal path - a DI to go into the Beyer Box and the Beyer itself. If the resulting recording had saturation it could be either or both of the transformers. For that reason, it cannot be a conclusive test.

I need to listen again to those tracks, it seemed when I was playing that I was hearing a subtle form of compression but the waveforms in the DAW stayed well below 0db so there was no digital overloading - I wasn't crashing into my headroom. I didn't hear the typical subtle enhancement of the trebles that adding harmonics usually generates but the harmonics might have been created from low frequencies so that could be a factor.

The results did sound good, I am just not sure that they were notable. If there was a definite change that I could clearly and easily hear I would not be trying to couch it in such subtle language.

I think it is time to ship the transformer project box to Mike Rivers and see what he comes up with. It is certain that he will observe some unseemly soldering technique in the build. I "tack-soldered" to pins that were meant for a PCB, if I were committed to a circuit I might have taken aother measures - that's as good an excuse as I can come up with!!! laugh

From Mike's post above - "This is why it's good to figure out what the transformer is doing." I agree and I will defer to somebody who has the experience and knowledge to do better than my bumbling about and guessing what is going on. Cheers, Kuru


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Re: DIY Fun With Transformers
Mike Rivers #3053970 07/13/20 02:48 PM
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I think you have to remember these transformers were designed NOT to color the sound. So while they contribute some non-linearity that is easily measurable they shouldn’t change the audible results much if at all.

Now you could design a system that purposely drives the snot out of them. Or you could just get a fuzz box wink.

Re: DIY Fun With Transformers
dboomer #3053980 07/13/20 03:27 PM
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Originally Posted by dboomer
I think you have to remember these transformers were designed NOT to color the sound. So while they contribute some non-linearity that is easily measurable they shouldn’t change the audible results much if at all.

Now you could design a system that purposely drives the snot out of them. Or you could just get a fuzz box wink.

This is true. I allowed myself to be mislead by forum posters (not on MPN) that mentioned the Beyer transformer in their Ampex preamps was easily overdriven but thinking on it later I don't recall them mentioning what they were micing or how they knew it was the transformer and not the tube it was connected to?

The big bass boost I hit the trannies with mentioned above was intended to "drive the snot out of them." It did sound great but it was still clean. Not looking for fuzz box tones, I have other options for that. Just a bit of color. And this topic came up with a couple of wizards chiming in so I tossed in my bait and now I am here... I like MPN for the potential to learn from generous and interesting people (and the opportunity to share my own knowledge - primarily 50 years of guitar tech-ing). Cheers, Kuru


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Re: DIY Fun With Transformers
dboomer #3053983 07/13/20 03:53 PM
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Originally Posted by dboomer
I think you have to remember these transformers were designed NOT to color the sound. So while they contribute some non-linearity that is easily measurable they shouldn’t change the audible results much if at all.

That's what I said early on in this discussion, but there seems to be folklore on the net that there's some magic to the distortion when a transformer begins to saturate. Actually, I think that "saturate" is a much-misued term in these parts, but it's one that's become accepted so I guess we have to live with it. Saturation of the core - where it just can't take any more magnetism - does take a lot of poop. A couple of mic-to-line transformers I found around here needed to be driven upwards of +25 dBu before the linearity curve - the (ideally) straight line plot of input to output level - began to look like the start of a compressor's "knee" curve. And there are other electrical characteristics of a transformer that can cause distortion besides core saturation.

There's lots of other things between a mic and an output that cause distortion that people love, and while transformers are well known contributors to the "tube" sound, in circuitry where a transformer is the best design choice, for solid state circuitry, a transformer is often a designer's or manufacturer's choice for a combination of excellent common mode noise rejection and marketing. In truth, these days the THAT chips do CMRR better than coils of wire, and cost less. And of course nothing says "marketing" like "fully Class A," but in order to get that in a mic preamp these days you need to go to something like a Jensen 990 module (Radial makes a preamp with that) to achieve it.

Re: DIY Fun With Transformers
dboomer #3053997 07/13/20 05:40 PM
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Originally Posted by dboomer
I think you have to remember these transformers were designed NOT to color the sound. So while they contribute some non-linearity that is easily measurable they shouldn’t change the audible results much if at all.

Now you could design a system that purposely drives the snot out of them. Or you could just get a fuzz box wink.

The less sane you are about driving them, the easier it is to saturate the core smile But I think an important point is that the distortion is inversely proportional to frequency, which is why my preferred transformer abuse is with bass. Also, the distortion caused by hysteresis, which doesn't depend on excessive levels, is also in the low frequencies. I don't hear much difference in mids on up. For example, the average transformer doesn't do much with voice, as far as I can hear; if someone wants to use a transformer to change the vocal quality, they'll probably be disappointed.

Re: DIY Fun With Transformers
Anderton #3054038 07/13/20 09:08 PM
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Originally Posted by Anderton
Originally Posted by dboomer
I think you have to remember these transformers were designed NOT to color the sound. So while they contribute some non-linearity that is easily measurable they shouldn’t change the audible results much if at all.

Now you could design a system that purposely drives the snot out of them. Or you could just get a fuzz box wink.

The less sane you are about driving them, the easier it is to saturate the core smile But I think an important point is that the distortion is inversely proportional to frequency, which is why my preferred transformer abuse is with bass. Also, the distortion caused by hysteresis, which doesn't depend on excessive levels, is also in the low frequencies. I don't hear much difference in mids on up. For example, the average transformer doesn't do much with voice, as far as I can hear; if someone wants to use a transformer to change the vocal quality, they'll probably be disappointed.

Curiosity - what transformer are you using and is it just the transformer or is there a circuit with other components?

A couple posts back I mention that it seemed like there was some compression, this is because running straight in with the bass and the same setting on the BTC - bass cranked and treble attenuated slightly - and it was super bassy (as we would expect). Using the transformer(s) it sounded more "even" with the bass attenuated a bit and the trebles audible but not to the point of revealing my less than perfect bass technique.

I looked inside the Whirlwind IMP 2 and there are two 1/4" TS jacks, 1 XLR male output jack, a transformer and a ground switch. The Radio Shack DI has a schematic drawing on the label, just the jacks and a transformer. I am assuming those bore the brunt of the bass and BTC since they were next in the signal chain.

Now I need to dig around and see what other cables I have, I remember seeing an XLR to 1/4" TS cable that I need to try to get the bass and BTC to go directly to the Beyer. Otherwise I can't really tell much as to what it sounds like. I may have to change the XLR plug, depending on if male or female. I have the parts.

If that is feeble I'll suspect that the Beyer really wants to see a microphone or similar load at the primary instead of whatever is coming out of the BTC (or the bass, which I will also try).

While I am by no means sane, this isn't exactly like running with scissors - "You could put out an eye!!!!!." laugh


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Re: DIY Fun With Transformers
KuruPrionz #3054137 07/14/20 01:24 PM
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Originally Posted by KuruPrionz
I think it is time to ship the transformer project box to Mike Rivers and see what he comes up with. It is certain that he will observe some unseemly soldering technique in the build.

Bring it on. While I don't think we're going to find anything in the way of "saturation," there are, as I've said, plenty of other effects that transformers can cause, including just plain ol' frequency response rolloff and resonance due to inductance and capacitance that are unavoidable when making a transformer from coils of wire/

Re: DIY Fun With Transformers
Mike Rivers #3054216 07/14/20 08:52 PM
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I'll try to get it out this week, will keep you posted.

I am here to learn, what is the better word if "saturation" is not satisfactory?


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Re: DIY Fun With Transformers
KuruPrionz #3054219 07/14/20 09:36 PM
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Originally Posted by KuruPrionz
I am here to learn, what is the better word if "saturation" is not satisfactory?

For my two cents, there's nothing wrong with "distortion." But let's see how much and what kind. I suspect that as input level goes up, the first we'll see is second harmonics, then as the level increases further, higher order harmonics will be added to the mix.
Hysteresis, I believe, is, in essence, slew rate distortion, which translates to intermodulation distortion.

Take your pick, or some of everything.

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