Impedance, Levels, and Pedals (oh my)

[SMcD]

Part 3 of the "Shaun asks dumb questions about tech that he should've learned a decade ago" series.

 

I'm beefing up my rig (monitoring, effects, instruments, the works), and it's led me to finally start learning about the more "technical" side of audio: levels, gain staging, balanced vs. unbalanced, all of those buzzwords. Turns out that stuff matters when you want to mix and self-monitor a bunch of different instruments with a bunch of different specs.

 

To this end, two things are stumping me with the new rig, and despite the SEVERAL dozen Chrome tabs worth of research I've done, I haven't quite been able to cobble together a straight'n'complete answer.

 

1. I've ordered a Hammond Pro-44HPv2 melodion. Unlike most melodicas, this one has a "pickup" built in, so I'm planning to connect it to a multi-effects unit like the Boss GT-1 and get weird with it. However, the "pickup" on the Pro-44HPv2 is actually a built-in dynamic microphone, and from what I've read it has the kind of low output level you'd expect from something that's mic-level. Presumably, the Boss GT-1 is expecting an instrument-level signal, since it's built for guitars. 
2. On the suggestion of brother @Jim Alfredson, I've ordered a Lounsberry Wurly Grinder pedal to use with my Hammond SKX. I've got a few other pedals I like using with the SKX, and my intended chain is [SKX -> Crybaby wah -> EHX Frequency Analyzer (ring mod) -> Wurly Grinder]. However, it's recently come to my attention that the line-level output from the SKX might be too much for the first two pedals, since they're made for guitars (I've never paid attention to these things when using pedals in the past, but now I'm wondering how much better my sound could've been if I had). I could get a reamp to bring the Hammond down to instrument level for the first two pedals, but I imagine the Lounsberry expects a line-level input since it's built for keyboards. Plus, for the sake of good signal/noise ratio I want to run things somewhat hot into my mixer. That leads me to believe I should find something to put between the ring mod and the Grinder to bring an instrument-level signal back up to line level.

 

So it seems to me that I need three additional "boxes" here: one to bring the melodica from mic-level up to instrument-level, one to bring the SKX from line-level down to instrument-level, and another to take the SKX back up to line level. And ideally, I achieve all of this without introducing a bunch of noise. Am I correct here, or is this overkill?

 

Part of my uncertainty here is that I'm not entirely clear on what the pedal outputs will do to the levels. For instance: if I just ran the SKX straight into the guitar pedals without a reamp, will the pedals output at instrument level on their own? How about when I hit the bypass buttons? Do the answers change if we're talking true bypass (the ring mod has it, and I'll probably mod the wah pedal to have it too)?

 

Then there's the matter of impedance, which I barely understand. I know guitars have lots of it, while mics and most line-level stuff doesn't. How will the various pedals and preamps and reamps modify this, and how should it be modified? Does it really matter?

 

Hoping someone can make sense of all of this without me having to take a whole physics course. Thanks!

 

EDIT: I have looked into the possibility of using DI boxes for some of this, but converting a line-level signal to mic-level (or vice-versa, if you reverse it) is just slightly different from what I actually want to do here. Plus, [something something impedance]

[Winston Psmith]

Guitar guy here, so take what I say from that perspective  . . .

 

Most Guitar-oriented pedals are designed so the Output Impedance won't tend to overload the Input Impedance of the next pedal in line, so you're generally safe chaining Guitar effects pedals; that's the simple answer on Guitar pedals. Less sure about the Output from the Hammond SKX, particularly as it was designed with onboard effects.

 

While looking quickly at the specs for that Hammond SKX, it seems to have most of the effects you'd be looking to augment with Guitar pedals, including Wah & Ring Mod, while the website for the Melodica model specifically mentions that the onboard mic makes it easy to plug into outboard effects. That would suggest the Melodica, at least, is safe for use with outboard effects.

 

I have a Boss GT-1, among other Boss MFX, and I've run various Synths and MonoSynths through it, with no issues. IMHO, it's not entirely sure if it wants to be an entry-level MFX, or something more, in which case, it falls short. Tera Echo is interesting.

[SMcD]

The SKX does have a decent selection of onboard effects, but I find the wah and ring mod a little lacking compared to the sound I get out of my pedals. Plus, I find them easier to control externally.

 

With the melodica, it's less about safety and more about getting sufficient signal. Ditto for the output from the ring mod (a guitar pedal) into the Wurly Grinder (a keyboard pedal). Cranking the gain at the mixer creates a lot of noise, so I want to make sure things are suitably hot earlier in the chain.

[Winston Psmith]

With every Boss MFX I've owned and used, I've found that turning Off the Compressor in the Factory Presets cuts the noise level considerably. It is possible to dial in a more-or-less clean Boost with the GT-1, and there is a Full Range Amp Model available, which have less tone coloration than most of the Guitar Amp models.

 

If you haven't already got a GT-1, I might suggest looking into the GT-1B Bass MFX. It has Ring Mod & Bass Synth effects onboard, which the GT-1 doesn't.

 

[stoken6]

I've always understood that it's fine to connect low-impedance outputs into high-impedance inputs. So [something something impedance] shouldn't be an issue in the use cases you describe. You might need [something something gain-staging optimised levels] but there's no harm in trying what you want with just what you've got. If you find you need to turn gain really high or really low, we can talk again.

 

Cheers, Mike.

[Docbop]

Sounds to me like you guys are mixing your use of level and impedance.    Most mic's these days are low impedance and low output but a high impedance mic's are still low output like guitar pickups and most musical instruments.    High level in general means something is putting out Line Level output like a preamp.   

[Baldwin Funster]

Funny thing. Many and probably most guitar players are obsessed with whether or not a pedal changes their precious guitar/amp "tone". That's why you constantly see the term true bypass or transparent overdrive and other laughable oxymoronic terms. I've never heard a hammond player or Rhodes player worry about this. 

[SMcD]

1 hour ago, Docbop said:

Sounds to me like you guys are mixing your use of level and impedance.    Most mic's these days are low impedance and low output but a high impedance mic's are still low output like guitar pickups and most musical instruments.    High level in general means something is putting out Line Level output like a preamp.   

 

Yeah, my understanding was:

 

Mic level: low signal (i.e. voltage), low impedance

Instrument level (guitar pickups): medium signal, high impedance

Line level (most keyboards): high signal, low impedance

 

On the second-last page of the manual for the Pro44HP, it has "information to choose amplifiers or external effects", then lists "input impedance: over 10K Ohms". I assume this is a recommendation (i.e. try to find an amp with input impedance at least this high). If so, that'd imply that the mic is a standard low-impedance one.

 

Certainly it's safe to connect a low-Z source to a high-Z input, but my understanding is that this isn't optimal for sound, and when the mismatch is significant it can weaken the signal relative to noise. Is that true? It seems to me that there must be some such downside to plugging everything into high-Z inputs: otherwise, why wouldn't every mixer have exclusively high-Z inputs, even for mics and line-level sources?

 

Now, both of the Boss MFX units we've discussed here have an input impedance of 1M Ohms, as you'd expect for a guitar pedal. So if I'm using it with the melodica, the above concern applies, does it not?

 

Seems to me that I need something between the melodica and the pedal to ensure a decent signal-to-noise ratio. Will it be enough to bring up the melodica's level, or will I also need to independently address the impedance?

 

[PianoMan51]

Way back in the day (late 60s) there was a sea change from high impedance to low impedance mics on stage. That meant for me that the new good low-z mic that you just bought would not work well well with the band’s Shure Vocal Master mixer that had high-z inputs.

 

So, you bought an impedance matching transformer. I still had my Shure AO5UF in a box of 30 year old unused crap. And then I got a Hammond 44. A low-z unbalanced mic, not a pickup. Yes, it could plug into a guitar input,  but not optimally. So I tried the matching transformer. Just what I needed. You can find new versions on Amazon for $20 or so.

 

BTW, the signal flow is:

Hammond 44 to transformer to iRig to iPhone to mixer.

 

Out from Hammond is 1/4” unbalanced. Use an adapter to plug into transformer’s XLR female input.

 

The iRig is a cheap I/o for getting an electric guitar in and out of an iPhone/iPad with audio connector. The output of the iRig is 1/8” female stereo.

 

The iPhone hosts a bunch of inexpensive Eventide plug-ins.

[SMcD]

Thanks for the tip!

 

Okay, so I get one of those transformers for cheap, and that takes care of the impedance mismatch. But what about the levels? Even if you run a low-Z mic through such a transformer, will it still have insufficient gain to get enough sound from the guitar pedal?

[PianoMan51]

The transformer was designed to take the input from a low impedance dynamic mix and output it into a guitar amp. I don’t know the design specifics for the transformer turns, but it appears to add voltage gain in my case.

[SMcD]

Gotcha. Thanks for the tips!

 

Looks like those transformers are pretty readily available, but all of them have XLR at the low-Z end. Which means I'll have to get a second (neutral) adapter to convert the 1/4" melodica output to XLR, plug it into the transformer, and immediately convert it back to 1/4". 😑

[PianoMan51]

I bought a cable to connect the melodica to the transformer.

 

1/4” unbalanced at one end, XLR male at the other. 
 

The output end of the transformer is already 1/4” and can go directly into your pedal boxes. Unfortunately the transformer is hanging physically on the pedal’s input Jack.

 

So I usually use a 1/4” female to 1/4” female (mono) adapter and a second 1/4” cable to move the transformer off the pedal Jack. 
 

It’s still a kluge. Maybe that’s why the Hammond 44 marketing materials never show a transformer being used.

[JohnDoe]

Could this be of any help?

https://www.radialeng.com/product/stagebug-sb6

[SMcD]

3 hours ago, JohnDoe said:

Could this be of any help?

https://www.radialeng.com/product/stagebug-sb6

It very well might! Especially since, with all the pedals in the SKX chain, I'm running a considerable amount of unbalanced cable (from the SKX down to my foot for the wah pedal, then back up so I can manipulate the knobs on the other pedals). Thanks!

 

7 hours ago, PianoMan51 said:

I bought a cable to connect the melodica to the transformer.

 

1/4” unbalanced at one end, XLR male at the other. 
 

The output end of the transformer is already 1/4” and can go directly into your pedal boxes. Unfortunately the transformer is hanging physically on the pedal’s input Jack.

 

So I usually use a 1/4” female to 1/4” female (mono) adapter and a second 1/4” cable to move the transformer off the pedal Jack. 
 

It’s still a kluge. Maybe that’s why the Hammond 44 marketing materials never show a transformer being used.

 

I did find listings for a couple of transformers with female 1/4" ends, which just slightly reduces the klugery. As you'd expect, 1/4" female end is intended for putting a guitar into a mic input (i.e. the opposite of what we're talking about here). But I assume there's no downside to running one of these things "backwards"?

[PianoMan51]

Make sure. The transformer is hi-z on one side and low-z on the other. The traditional design has the XLR on the “low-z mic” side and the 1/4 male on the “guitar “ side.  It’s just a transformer inside. Different numbers of windings to create voltage and impedance shifts. Yes, it can work backwards. Just make sure it’s working in the right direction for you.

[Jim Alfredson]

I think all you really need to worry about is the output of the melodica, which will be mic level. It might work fine into the Boss or it might need an impedance matching transformer in front of it. Something like this should work:

https://www.sweetwater.com/store/detail/A85F--shure-a85f-line-matching-transformer

 

I would try it straight in first and see if there's enough gain.

Regarding the SK into the pedals, you might need to add gain between the ring mod and the Wurly Grinder, as you said. For that, I'd use something like this: 

https://www.sweetwater.com/store/detail/TubeMPps--art-tube-mp-project-series-tube-preamplifier

As you can see, it has a switch for mic or instrument level. It will be instrument level coming out of the ring mod pedal. Then you can boost the gain into the Wurly Grinder. 

From the output of the SK into the wah wah, just adjust the output via the volume knob on the SK. Should be fine.