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Low line level #3004646 08/23/19 11:14 AM
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dazzjazz Offline OP
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Hi
I have a keyboard that has balanced line outs, but the level is on the low side. When I use it with a powered speaker with the input set to ‘line’, I rarely get enough volume. So I’ve taken to using the ‘mic’ position, but been unhappy with the tone, probably due to impedance issues.

So, seeing as I have a very nice Radial JDI Direct Box, I’ve had the idea of using it to drop the level down to actual Mic level and running the input on Mic to match. I’ve tried it and it was a great sound and tonnes of volume. Is this a reasonable fix or is there some kind of potential issue with running the signal chain like this?

Darren


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PhD in Jazz Organ Improvisation.
BMus (Hons) Jazz Piano.
1961 A100.Leslie 45 & 122. Kawai K300J. Yamaha CP4. Viscount Legend Live.
Re: Low line level [Re: dazzjazz] #3004669 08/23/19 02:29 PM
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There should not be any issue at all using the Radial. If for some reason the line going to the powered speaker is quite long, it would be best to place the Radial close to the speaker instead on the other end (high level going most of the way, then converted to lower level), but for short runs (under 50 or so feet), placement won't matter all that much.
Only issue I see is if you are willing to carry the small amount of extra gear. You already have the device instead of having to buy one (I have the Radial Pro D2 which is quite similar just a lower priced transformer). Smaller and easier than having to carry a separate mixer to get some additional level.


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Re: Low line level [Re: dazzjazz] #3004681 08/23/19 03:15 PM
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Sounds like the powered speaker has impedance issues that loads down the output of the keyboard. The JDI probably solved the problem because it is acting as an isolation device.

Re: Low line level [Re: dazzjazz] #3004682 08/23/19 03:15 PM
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Originally Posted by dazzjazz
Is this a reasonable fix or is there some kind of potential issue with running the signal chain like this?

Darren


Well, if it works, then it's a reasonable fix smile I don't see any technical reason why there would be a problem. However, it does seem odd that you can't get enough level from the keyboard to drive the powered monitor. I'm sure you've double-checked your system, but maybe there's something like a defective cable...if one of the balanced line leads isn't connected and you're therefore going in single-ended, you're likely losing 6 dB of potential level.

Re: Low line level [Re: dazzjazz] #3004724 08/23/19 06:24 PM
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Almost every self powered speaker I’ve run into will drive to full power with a very low line input level so that seems odd. Also I can’t imagine any impedance issues with any modern keyboard equipment. If you run your keys into the line input ... can you EVER light up the clip LED?

Specifically which keyboard and speaker are we talking about.

Re: Low line level [Re: dazzjazz] #3004725 08/23/19 06:30 PM
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Have a QSC K10 and have noticed running a 1/4" into it that my Kronos won't drive it to high enough stage volume in a loud band on the LINE setting and the MIC setting is too hot and creates hiss. I use a small line mixer in between, partially because I need to squeeze 3 sources into the K10's 2 inputs, but it also gives me the ability to get enough gain to drive it at an adequate volume.


Dan

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.
Re: Low line level [Re: dazzjazz] #3004739 08/23/19 08:28 PM
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Originally Posted by dazzjazz
Hi
I have a keyboard that has balanced line outs, but the level is on the low side. When I use it with a powered speaker with the input set to ‘line’, I rarely get enough volume. So I’ve taken to using the ‘mic’ position, but been unhappy with the tone, probably due to impedance issues.

So, seeing as I have a very nice Radial JDI Direct Box, I’ve had the idea of using it to drop the level down to actual Mic level and running the input on Mic to match. I’ve tried it and it was a great sound and tonnes of volume. Is this a reasonable fix or is there some kind of potential issue with running the signal chain like this?


It's hard to argue with success. It's also hard to believe that you're having this problem, but sometimes you just have a square peg that you're trying to put into a round hole. There's more than one configuration of "balanced output" and, while you may not have an impedance problem, you may have a wiring problem. What type of connectors are you trying to connect? XLRs? 1/4" phone plugs? One of each?

It's OK to name names around here for troubleshooting purposes. What's the make and model of the keyboard and the powered speaker? Web links to a spec sheet or manual would be helpful. If I know specifically what you're trying to connect I might be able to offer you a less expensive solution than the DI box.

Re: Low line level [Re: dazzjazz] #3004759 08/23/19 11:21 PM
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Thanks for all the input everyone.
The keyboard is the Viscount Legend organ and the speaker is a Yamaha DXR10. The organ is renown for being a great clone, but many users find the output level low and I believe Viscount are working on a fix.

The organ has balanced jacks out, so I have a Hosa-Brand balanced jack to XLR cable. The DXR10 does give some hiss using the above mentioned setup, but it's not going to be noticeable when the band is pumping.

I'm just glad I don't have to buy any more gear!


www.dazzjazz.com
PhD in Jazz Organ Improvisation.
BMus (Hons) Jazz Piano.
1961 A100.Leslie 45 & 122. Kawai K300J. Yamaha CP4. Viscount Legend Live.
Re: Low line level [Re: dazzjazz] #3004762 08/24/19 12:23 AM
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The XLR inputs jacks on the DXR10 do expect a standard +4dB line level input which keyboards do not put out. However the 1/4” jacks marker “line” are only looking for -10dBu. So a properly wired unbalanced xlr to 1/4” should work nicely. Then just use the level control next to the jacks.

This Hosa cable should work fine.

Last edited by dboomer; 08/24/19 12:28 AM.
Re: Low line level [Re: dazzjazz] #3004767 08/24/19 12:53 AM
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dazzjazz Offline OP
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Ah that reminds me DBoomer, when using the balanced jack out of the organ to the unbalanced line level jack input on the DXR10, I was getting a weird kind of digital noise. That’s what started this whole saga.


www.dazzjazz.com
PhD in Jazz Organ Improvisation.
BMus (Hons) Jazz Piano.
1961 A100.Leslie 45 & 122. Kawai K300J. Yamaha CP4. Viscount Legend Live.
Re: Low line level [Re: dazzjazz] #3004776 08/24/19 02:08 AM
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Are you positive that the XLR jack on that Viscount is actually a balanced output?

The ARP synths had XLR jacks but (with the exception of the Chroma) they were NOT balanced outputs, they were single ended and no better than the 1/4" output.

There are many variations of balanced line drivers, and balanced line receivers. The wrong combination can screw up the tone and level. Some do not follow the AES convention and assign the positive polarity to pin 3 not pin 2, which can really mess up the sound.

Re: Low line level [Re: dazzjazz] #3004793 08/24/19 06:21 AM
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Noise is an entirely different issue. I’d have to know a lot more about your system.

I wouldn’t expect flipping polarity would cause any difference to tone, although it may make a difference in level depending on how things are configured.

Re: Low line level [Re: dazzjazz] #3004801 08/24/19 11:12 AM
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Mike Rivers Offline
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Originally Posted by dazzjazz
Thanks for all the input everyone.
The keyboard is the Viscount Legend organ and the speaker is a Yamaha DXR10. The organ is renown for being a great clone, but many users find the output level low and I believe Viscount are working on a fix.

The organ has balanced jacks out, so I have a Hosa-Brand balanced jack to XLR cable. The DXR10 does give some hiss using the above mentioned setup, but it's not going to be noticeable when the band is pumping.
!


I found what I think is a manual for your keyboard (the English version starts on page 26). Is that it? I couldn't find any detailed specifications, but I don't have any reason to believe that the audio output jacks are balanced. If they're unbalanced and you're using a TRS-to-XLR cable, you're connecting the audio signal from the keyboard between pins 2 (+) and 1 (ground) of the speaker's XLR input, leaving pin 2 (-) not connected to anything. That's not good, and can explain why you're having symptoms of low gain and noise.

I'd suggest using an unbalanced TS-TS cable (like a guitar cable) between the keyboard output and the Line 2 L/MONO jack on the speaker. That will give you the proper signal and shield connections and input sensitivity with the working range of the keyboard. I'd suggest starting out with the keyboard volume control set to maximum and the input level control set to minimum. Then, as you play, adjust the speaker's input level control for a volume a little louder than you'd ever expect to need. Then fiddle with the keyboard volume and speaker input level controls so that you'll be able to give you the best compromise between noise (there's bound to be some) and the ability to control the volume from the keyboard.

I have an article on my web site that explains a lot of this stuff. The Ins and Outs of Gozintas and Gozoutas

Re: Low line level [Re: Mike Rivers] #3004876 08/24/19 11:09 PM
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dazzjazz Offline OP
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Yes that's the manual. Thanks for doing this.
I was told by Viscount service that the outputs are balanced. When I started using a balanced jack to XLR cable, the digital noise issue went away. I was initially using the TS-TS cable as you suggest, but this results digital noise, a little like USB noise that can happen when connecting audio and USB from a keyboard and audio interface.

I hope I have answered all questions.

Much appreciated.

Originally Posted by Mike Rivers


I couldn't find any detailed specifications, but I don't have any reason to believe that the audio output jacks are balanced. If they're unbalanced and you're using a TRS-to-XLR cable, you're connecting the audio signal from the keyboard between pins 2 (+) and 1 (ground) of the speaker's XLR input, leaving pin 2 (-) not connected to anything. That's not good, and can explain why you're having symptoms of low gain and noise.

I'd suggest using an unbalanced TS-TS cable (like a guitar cable) between the keyboard output and the Line 2 L/MONO jack on the speaker.


www.dazzjazz.com
PhD in Jazz Organ Improvisation.
BMus (Hons) Jazz Piano.
1961 A100.Leslie 45 & 122. Kawai K300J. Yamaha CP4. Viscount Legend Live.
Re: Low line level [Re: dazzjazz] #3004904 08/25/19 04:54 AM
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Your digital noise issues could be ground loop related - much like what happens with a USB audio interface on a laptop and when you unplug the power supply and run off battery it goes away. As an experiment, cut the shield/ground wire at one end of the cable (TS cable) and see if it goes away. As long as the shield is grounded at one end you will maintain shield and break the ground loop. There are better permanent ways to fix the problem if that's what it is, but at' a quick way to check.


Dan

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.
Re: Low line level [Re: J. Dan] #3005047 08/26/19 04:43 AM
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Originally Posted by J. Dan
Your digital noise issues could be ground loop related - much like what happens with a USB audio interface on a laptop and when you unplug the power supply and run off battery it goes away. As an experiment, cut the shield/ground wire at one end of the cable (TS cable) and see if it goes away. As long as the shield is grounded at one end you will maintain shield and break the ground loop. There are better permanent ways to fix the problem if that's what it is, but at' a quick way to check.


I’m confused here. If you cut the shield how are you getting a return line? It takes 2 conductors to make the signal flow. Maybe you are confusing this with a telescoping shielding system in which a separate wire carries the common signal and the shield only shields the pair conducting the signal. But even in this case it does not remove the ground loop.

And while ground loops can cause some noise (and you always have ground loops when running unbalanced), the noise in your example with the computer is almost certainly a result of the switch mode power supply (wall wart) powering the laptop and not a ground loop. SMPS power supplies do not have a ground reference so your audio output on your computer is ungrounded until it hits the receiving end (which hopefully is grounded).

Last edited by dboomer; 08/26/19 04:45 AM.
Re: Low line level [Re: dazzjazz] #3005048 08/26/19 04:57 AM
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Originally Posted by dazzjazz
Yes that's the manual. Thanks for doing this.
I was told by Viscount service that the outputs are balanced. When I started using a balanced jack to XLR cable, the digital noise issue went away. I was initially using the TS-TS cable as you suggest, but this results digital noise


Ok ... first there is no particular problem using the DI if it fixes the problem. Running into the mic input will have a tiny bit more noise that if you could make the balanced line ins work. But if it works for you there is no reason to change it.

You didn’t answer my question as to whether under any circumstances have you ever flashed the clip LEDs?

Not that I suggest you actually run this way. But if you use xlr to xlr cables to run from the organ to the speaker and you turn up the volume knob al, the way AND you turn up all your tone controls to +12, volume control to max and pull out all the drawbars... at that point can you trip the clip lights?

I too checked the owner manual and there are no real tech specs tp let us know what’s going on. Possible you have what’s called an impedance balanced output, which generally doesn’t have as much output as a fully balanced output. Alternately you may have some funky wiring scheme on the organ output wiring.

Re: Low line level [Re: dboomer] #3005063 08/26/19 11:07 AM
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Originally Posted by dboomer


I’m confused here. If you cut the shield how are you getting a return line? It takes 2 conductors to make the signal flow.


A "ground loop" means that you have two (or more) connections between the signal reference point in two devices that you're connecting audio between, typically one through the audio cable shield and the other resulting from the chassis from both being connected together by the safety ground pin on their power plugs. If that's the case, you can disconnect the shield and you still have a return path for the signal. So disconnecting the shield to fix a ground loop problem works because you had a ground loop. But that doesn't solve the problem in all cases.

Quote
Maybe you are confusing this with a telescoping shielding system in which a separate wire carries the common signal and the shield only shields the pair conducting the signal. But even in this case it does not remove the ground loop.


If the two chassis are connected through their power plugs and the cable shield and nothing else (if they're both in the same metal rack, that's another ground path between them), disconnecting the shield does indeed remove the ground loop. But, on the other hand, it leaves a hole in the shield for EMI to get in, so while you may fix one problem you may have caused (or still have) a different problem.

Quote

And while ground loops can cause some noise (and you always have ground loops when running unbalanced), the noise in your example with the computer is almost certainly a result of the switch mode power supply (wall wart) powering the laptop and not a ground loop.


I don't recall there being a mention of a computer in this case, but wall warts can indeed be a source of noise, and if I remember correctly, that's the kind of power supply the keyboard uses.

Oh, and you mentioned "impedance balanced" outputs. I hadn't thought about that when I questioned whether the keyboard outputs were really balanced. Sure, they could be, for about an extra two bits (or about 400 lira if you still have some). And for suppressing radiated EMI, they work nearly as well as a transformer, but only if they're connected through a balanced cable to a differential input with good common mode rejection. "Balanced" isn't defined by voltage, it's defined by impedance. All balanced outputs have the same impedance between each of the two signal leads and "ground." That's how and why they work.

"Impedance balanced" is a term that someone had to invent when balanced outputs became a marketable part of price-point-driven audio equipment design. The concept was in use long before Mackie et al.

As usual, there's an article or two about this on my web page, or for the full story, the whole June 1995 issue of the AES journal was devoted to grounding and shielding.

Re: Low line level [Re: dboomer] #3005090 08/26/19 02:08 PM
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Originally Posted by dboomer

I’m confused here. If you cut the shield how are you getting a return line? It takes 2 conductors to make the signal flow. Maybe you are confusing this with a telescoping shielding system in which a separate wire carries the common signal and the shield only shields the pair conducting the signal. But even in this case it does not remove the ground loop.

And while ground loops can cause some noise (and you always have ground loops when running unbalanced), the noise in your example with the computer is almost certainly a result of the switch mode power supply (wall wart) powering the laptop and not a ground loop. SMPS power supplies do not have a ground reference so your audio output on your computer is ungrounded until it hits the receiving end (which hopefully is grounded).


Balanced vs unbalanced has nothing to do with ground loops and you don't always have a ground loop with unbalanced. Balance cables address induced noise. Since the input is differential and you have 2 lines of opposite polarity, the noise is induced equally on both lines and cancels out at the input on the other end because of common mode rejection. There is still a 3rd ground wire that can can complete a ground loop. A ground loop simply occurs with the ground potential of 2 interconnected device is other than 0 volts. The reason why it goes away when you unplug a laptop and run off battery is because you are disconnecting the ground reference at the power supply end and causing the entire system to use the ground reference of the connected device. It would be easier to explain if I drew a sketch, but there isn't an easy way to do that on here without doing something in some other program on my computer, hosting I think somewhere and linking to it. Sorry I'd like to help but I'm not quite THAT dedicated, lol.


Dan

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.
Re: Low line level [Re: dboomer] #3005246 08/27/19 05:26 AM
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I haven't been able to see the clip lights overload yet. If I get time on Thursday's gig, I will test that out.


www.dazzjazz.com
PhD in Jazz Organ Improvisation.
BMus (Hons) Jazz Piano.
1961 A100.Leslie 45 & 122. Kawai K300J. Yamaha CP4. Viscount Legend Live.
Re: Low line level [Re: J. Dan] #3005263 08/27/19 10:27 AM
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Originally Posted by J. Dan

Balanced vs unbalanced has nothing to do with ground loops and you don't always have a ground loop with unbalanced. Balance cables address induced noise.


I think that what you're trying to say here is that noise can be induced in both balanced and unbalanced connections. A balanced connection minimizes this noise, but there are other ways that noise can get into the system. But it sounds like you have a good handle on the concept.

Quote
There is still a 3rd ground wire that can can complete a ground loop. A ground loop simply occurs with the ground potential of 2 interconnected device is other than 0 volts. The reason why it goes away when you unplug a laptop and run off battery is because you are disconnecting the ground reference at the power supply end and causing the entire system to use the ground reference of the connected device.


The problem isn't that there's a potential difference between grounds on two interconnected devices. That's something that's difficult to avoid. The problem is with what happens to that potential difference inside the box. If the reference point for signals inside the box (usually the 0v terminal of the power supply) is connected to ground through other than a really low impedance path, the signal reference point will follow the unwanted "ground" signal and will be added to every signal in the box.

You can cut the shield lead and break a loop, but there can still be a potential difference between the two chassis from the ground pin on the AC power cord. In my "workshop for expenses" that I've given in a couple of places, I jokingly address this issue as "If you have hum, pick a shield and cut it. If the hum decreases, leave it cut. If the hum increases or doesn't change, put it back together and move on to the next shield. Repeat this process until either the hum goes away or you get electrocuted." However, in today's high EMI environment I don't encourage breaking shields, but rather, find the real problem and fix it. This is often not trivial.

Re: Low line level [Re: dazzjazz] #3005309 08/27/19 03:45 PM
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Note that in my original suggestion, I indicated that it wasn't the best solution, or a good long term solution, but an easy way to diagnose the problem.


Dan

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.
Re: Low line level [Re: dazzjazz] #3005359 08/27/19 07:16 PM
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The thing with XLR connectors is that there are two different grounds - circuit ground and chassis ground. For audio balanced circuits, circuit ground is on pin 1 and chassis ground on the shell. The two should never be shorted in the XLR connectors. That mistake can lead to ground loops. I have built my own balanced cables for over 30 years, and I always leave chassis ground unconnected and connect the wire shielding to pin one circuit ground at both ends. When my cable is plugged in, the shell connects to chassis ground which shields the connector but not the cable and chassis ground is isolated between the two devices. This has yet to fail me.

Not every manufacturer follows the XLR wiring convention, and some short pin 1 to chassis ground at the XLR jack. That is asking for trouble.

Re: Low line level [Re: The Real MC] #3005373 08/27/19 08:07 PM
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Originally Posted by The Real MC
I have built my own balanced cables for over 30 years, and I always leave chassis ground unconnected and connect the wire shielding to pin one circuit ground at both ends. When my cable is plugged in, the shell connects to chassis ground which shields the connector but not the cable and chassis ground is isolated between the two devices. This has yet to fail me.


Well, then, you've been lucky. Some XLRs, particularly the Chinese imports, have pin 1 tied to the shell. The standbys - Switchcraft and Neutrik, have a solder tab connected to the shell that you can leave floating, tie it to Pin 1, or connect the shield to it and use three conductor cable. That's the real he-man way to do it but three conductor shielded cable is kind of hard to find. Gotham GAC-3 is nearly a dollar a foot from Redco. Neumann recommends this cable for many if not all of their mics, and a couple are notably hum-prone when used with any arrangement of 2-conductor cable.

The thing about the cable shield is that it acts like a metal tube with a metal box solidly attached at both ends. This is what you need to keep EMI out of the cable. A differential input or transformer on a mic preamp does a good job of cancelling common mode noise at audio frequencies, but isn't worth a hoot at a couple of gigahertz. That's where you need the metal to keep it from getting in. By keeping pin 1 isolated from chassis ground, you avoid the ground loop formed by the shield and the Pin 1 wire, and that's a good thing. You can do that by disconnecting it at one end or both ends (unless you need it to carry DC for phantom power) as long as the shield is connecting the two boxes, which it does if it's wired to the connector shell.

Re: Low line level [Re: dazzjazz] #3005376 08/27/19 08:10 PM
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In balanced audio, what you're calling "circuit ground" isn't ground, it's negative. It's the same signal as the positive except opposite polarity, each of which is referenced to ground. If you tie it to ground, you've made it unbalanced. The ground is in fact the circuit ground and in most equipment, circuit ground is the same as the case ground.


Dan

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.
Re: Low line level [Re: dazzjazz] #3005382 08/27/19 08:40 PM
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"Circuit ground" is the reference point for all signals, positive and negative. With a symmetrical source (output) when the voltage on one signal lead is positive with respect to the reference, the voltage on the other signal lead is negative with respect to the reference by the same amount. The destination sees twice the voltage measured between either signal lead and the reference point. But this in itself doesn't make the source balanced. The impedance between each signal lead and the reference point must be identical.

With a singled-ended balanced output, the voltage between what we call the "hot" signal lead - conventionally Pin 2 on an XLR and the Tip of a TRS connector - and the reference point is the voltage that the destination sees. The voltage between what we call the "low" or "cold" signal lead - conventionally Pin 3 or Ring - and the reference point is zero because there's nothing driving it. It becomes balanced when the "cold" signal lead has a resistor between it and the reference point equal to the source impedance measured between the "hot" lead and the reference point.

The reference point, which is conventionally the "return" point for the power supply outputs, is typically connected to chassis ground some place, but it doesn't have to be. But it must be the reference point for all signals in the box.

My articles about the subject are available for free for anyone who cares to learn:
Balanced and Unbalanced Connections
Grounds and Shields

Re: Low line level [Re: Mike Rivers] #3005389 08/27/19 09:32 PM
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Originally Posted by Mike Rivers
Originally Posted by The Real MC
I have built my own balanced cables for over 30 years, and I always leave chassis ground unconnected and connect the wire shielding to pin one circuit ground at both ends. When my cable is plugged in, the shell connects to chassis ground which shields the connector but not the cable and chassis ground is isolated between the two devices. This has yet to fail me.


Well, then, you've been lucky.


I'm an BTEE with over 30 years experience in audio electronics and studio/road work. "Lucky" is hardly the word. I suspect you are also an EE.

Originally Posted by Mike Rivers
It becomes balanced when the "cold" signal lead has a resistor between it and the reference point equal to the source impedance measured between the "hot" lead and the reference point.


Correct term for this configuration is impedance balanced but it is not differential. The differences are, there is no driver for the "cold" pin 3 lead, and it is incapable of driving a true differential line over long distances (not even 15 ft). I found this out the hard way when the direct outputs of my mixing console were described as "balanced" but the schematic revealed it was actually impedance balanced, which is a crucial detail.

Re: Low line level [Re: The Real MC] #3005414 08/27/19 10:51 PM
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Mike Rivers Offline
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Originally Posted by The Real MC

I'm an BTEE with over 30 years experience in audio electronics and studio/road work. "Lucky" is hardly the word. I suspect you are also an EE.


I also have an EE degree, but I didn't learn about balanced/unbalanced connections in school. I barely learned about transistors. Experience with audio came later (if you don't count that in elementary school, I was the one who cued up and started the record for the orchestral background for the school chorus).

I'll skip another lecture about what balanced and unbalanced means. Either you get it or you don't. You're at least half way there, so let's move on to your problems.

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Correct term for this configuration is impedance balanced but it is not differential. The differences are, there is no driver for the "cold" pin 3 lead, and it is incapable of driving a true differential line over long distances (not even 15 ft). I found this out the hard way when the direct outputs of my mixing console were described as "balanced" but the schematic revealed it was actually impedance balanced, which is a crucial detail.


OK. I might be the one who coined the term "impedance balanced." It hadn't become common jargon when I was writing an article about balanced and unbalanced connections in the 1990s and I needed a shortcut to writing "single ended non-symmetrical balanced". Mackie was the first manufacturer to use that term in their design documents, but their literature and manuals just said "balanced," which is correct.

As for a problem driving long cables - exactly what was the problem you encountered? If it was a fairly old piece of gear, one with a transistor or an early IC driving the output, what you may have been doing is trying to drive a long cable from a source with too high an impedance, or from an op amp that breaks into oscillation when driving a capacitive load. That has nothing to do with whether the source is differential or single-ended. Modern op amps have an output impedance of nearly zero ohms, and there's usually a 50 to 100 ohm resistor in series between the output of the op amp and the output connector to protect it against shorts. They can easily drive a 600 ohm load. Op amps from the late 1980s weren't happy with a load of less than about 10 kΩ and didn't like to see a capacitor tied across them. And with their relatively high output impedance, there will be more voltage drop at the end of a long cable than one with an output impedance of 50 ohms.

I had a TASCAM Model 5 console that used 4558 op amps, which was about a 10 year old device when the console was designed. I figured that I could get better transient performance with a more modern op amp, so I swapped them out with the hot dual op amp of the day, a TL072. It sounded better in the shop, but when I put it back in the control room where it had to deal with about 30 feet of cable to and from the patchbay. It sounded terrible out there, and when I looked at the output at the load end with a scope, I saw that it was oscillating at the full rail-to-rail voltage at about 1.5 MHz. I replaced the TL072s with 5532s and that worked find and sounded better than the original op amps.

For what it's worth, there are many microphones that have single ended balanced outputs, and mics typically connect to preamps through 25 feet or more cable, and often through 100 feet or more.

Re: Low line level [Re: Mike Rivers] #3005426 08/28/19 12:40 AM
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Originally Posted by Mike Rivers
Originally Posted by The Real MC

I'm an BTEE with over 30 years experience in audio electronics and studio/road work. "Lucky" is hardly the word. I suspect you are also an EE.


I also have an EE degree, but I didn't learn about balanced/unbalanced connections in school. I barely learned about transistors. Experience with audio came later (if you don't count that in elementary school, I was the one who cued up and started the record for the orchestral background for the school chorus).


Ah, good. I could tell by other posts you wrote.

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I'll skip another lecture about what balanced and unbalanced means. Either you get it or you don't.


I read your informative documents from your website, which agrees with my understanding. Good articles!

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Quote
Correct term for this configuration is impedance balanced but it is not differential. The differences are, there is no driver for the "cold" pin 3 lead, and it is incapable of driving a true differential line over long distances (not even 15 ft). I found this out the hard way when the direct outputs of my mixing console were described as "balanced" but the schematic revealed it was actually impedance balanced, which is a crucial detail.


OK. I might be the one who coined the term "impedance balanced." It hadn't become common jargon when I was writing an article about balanced and unbalanced connections in the 1990s and I needed a shortcut to writing "single ended non-symmetrical balanced". Mackie was the first manufacturer to use that term in their design documents, but their literature and manuals just said "balanced," which is correct.


I'm not at home, but I'm pretty sure the impedance balanced topology dates back further than that. It might be in my 1976 edition of Audio Cyclopedia.

Quote
As for a problem driving long cables - exactly what was the problem you encountered? If it was a fairly old piece of gear, one with a transistor or an early IC driving the output, what you may have been doing is trying to drive a long cable from a source with too high an impedance, or from an op amp that breaks into oscillation when driving a capacitive load. That has nothing to do with whether the source is differential or single-ended. Modern op amps have an output impedance of nearly zero ohms, and there's usually a 50 to 100 ohm resistor in series between the output of the op amp and the output connector to protect it against shorts. They can easily drive a 600 ohm load. Op amps from the late 1980s weren't happy with a load of less than about 10 kΩ and didn't like to see a capacitor tied across them. And with their relatively high output impedance, there will be more voltage drop at the end of a long cable than one with an output impedance of 50 ohms.


It was years ago and I don't remember the specific combination of devices, but the devices were modern (2005 and later) and the impact on fidelity was detrimental enough that I wrote off impedance balanced outputs as not being suitable for long cable runs. Works fine with 9ft cables to my Alesis HD24.

Just when you think you know it all, you find another combination that doesn't work. Never ends.

Quote
I had a TASCAM Model 5 console that used 4558 op amps, which was about a 10 year old device when the console was designed. I figured that I could get better transient performance with a more modern op amp, so I swapped them out with the hot dual op amp of the day, a TL072. It sounded better in the shop, but when I put it back in the control room where it had to deal with about 30 feet of cable to and from the patchbay. It sounded terrible out there, and when I looked at the output at the load end with a scope, I saw that it was oscillating at the full rail-to-rail voltage at about 1.5 MHz. I replaced the TL072s with 5532s and that worked find and sounded better than the original op amps.


The 5532 worked for two reasons. Its power bandwidth is ~150Khz depending on output conditions. If you study the graph of large signal frequency response on its spec sheet, the 5532 tops out at ~100Kz. It isn't capable of oscillating at 1.5Mhz. Every opamp is a compromise. The 5532 is very good for low noise and has improved power capacity (IE driving long cables), but at the expense of bandwidth and slew rate (but still has better slew rate than 4558). Also the 5532 can operate on power rails up to 22VDC, important for (+)4dBu systems.

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For what it's worth, there are many microphones that have single ended balanced outputs, and mics typically connect to preamps through 25 feet or more cable, and often through 100 feet or more.


No dispute there. Key attributes are low impedance and low pf/ft capacitance rating of the cable(s).

Re: Low line level [Re: The Real MC] #3005438 08/28/19 02:00 AM
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Mike Rivers Offline
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Originally Posted by The Real MC
[About a problem using impedance balanced connections]

It was years ago and I don't remember the specific combination of devices, but the devices were modern (2005 and later) and the impact on fidelity was detrimental enough that I wrote off impedance balanced outputs as not being suitable for long cable runs. Works fine with 9ft cables to my Alesis HD24.

Just when you think you know it all, you find another combination that doesn't work. Never ends.


That's what keeps this interesting. There's never a dull moment once we got away from transformers on every input and output. wink

I had a client with a problem connecting the inputs of his ADAT (the tape one) to the direct outputs of a newly acquired but used TASCAM 512 mixer. There was very little headroom and the input stage (but not the console output) would start clipping at around -20 dBFS on the ADAT meters. Turned out that the input jacks were connected directly to the input pins on the A/D converter chip and it didn't like having one side tied to ground, or nearly to ground through the "low lead" resistor. The problem was solved by disconnecting the low side and feeding the ADAT between tip and ground, leaving the ring floating. This made for an unbalanced connection, but that didn't cause any problems, and fixed the one keeping the system from working.

This was probably different from your problem, though. Cable length didn't contribute to the problem. at least not the 20 feet or so going route from console to patchbay to recorder.

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