Effect with balanced in/out

[il_mix]

Hi, everyone!

I'd like to know what's the best way to manage balanced in/out in an effect pedal. Is it mandatory do unbalance->process->rebalance?

Why do I need this?
I'll start a personal project for a fancy "mic". Will be something like an helmet with an integrated mic, and some integrated effects. The idea is to add 2 base and simple effects:
- "lo-fi radio-izer" (cut bass frequencies, boost mids to let it sound like a walkie talkie). Just a couple of RC filters will probably donough
- distorsion; something like the example beginner project will probably be enough. Or maybe something based on 4558

So, I'll have a dynamic capsule in the helmet. Two wires balanced signals comes out from the mic.
First question: two wires comes out, but since the effect will be literally centimeters away from the capsule, will it be ok to just route a single unbalanced wire to the effect? Or do I need to send the balanced signal and then unbalance it before the effect?
The sound will then pass through the effects (or bypass them).
What about the output? If I want a balanced output I need to take the single signal and "duplicate" it before output. Or is it better to just leave it unbalanced, since it will actually be a quite lo-fi mic?

Also, generic questions regarding impedances and signal levels;
- how to dimension the effects input stage for a mic signal? I've just done guitar/bass effects so far...
- how to "restore" the impedance/level on the output side to send a mic-like signal to the mixer? (in case of balanced output)
- if I go for the unbalanced output is it ok to leave the output stage "as is" (output stage of a typical guitar effect) or is it better to let it become something more similar to a line level, so an unbalanced line mixer input will treat the signal better? Notice that if I output an instrument-like signal I can leave the effect output as is, but I'll probably have to do something on the clean sound when the effects are bypassed. Probably better to output a mic-like signal from the effect and leave the clean signal as is.

Thanks for the hints!
(more questions will come...)

[PRR]

> the effect will be literally centimeters away from the capsule, will it be ok to just route a single unbalanced wire

Yes. Or at least assume that Yes is a good first start.

If you have to work with your head inside a Telsa Coil, you will have crap. And balancing alone won't cure it. However anyplace you can use a guitar is probably benign enough for unbalanced mikes. (I have run 50 feet through a church.)

[ElectricDruid]

Is it mandatory do unbalance->process->rebalance?

No, but balanced circuit design is a whole other area that we mostly don't see. You *could* probably design fully-balanced versions of many common pedals, but you'd cutting a new path.

Have a look at this for starters:

https://www.electronicdesign.com/technologies/analog/article/21799356/design-balanced-opamp-circuits-for-performance-and-simplicity

I used to have a link to an interesting article (I think it was TI) about balanced filters, but I can't find it now. If I can turn it up, I'll post it.

Note that there are op-amps that have balanced *outputs* as well as balanced inputs, which makes it much easier to chain these things together. I'd say that once you've gone to a single-ended output, you might as well stay there.

HTH,
Tom

[tubegeek]

(I have run 50 feet through a church.)

"I got to keep movin', I got to keep movin'
Blues fallin' down like hail, blues fallin' down like hail
Hmmm-mmm, blues fallin' down like hail, blues fallin' down like hail

And the days keeps on worryin' me
There's a hellhound on my trail, hellhound on my trail
Hellhound on my trail" - Robert Johnson

As to the OP:

THAT Corp has a whole slew of chips designed as topnotch balanced line receivers/amplifiers and balanced line drivers. Their app notes are wonderfully informative, so, if you are curious, take a look.

Even THEIR guitar pedal designs are unbalanced!

For mics, unless you are adding ungodly amounts of gain or recording into a nearly-silent background, the extra complexity is probably not worth the bother  So, are you recording wind-rustling sound effects in the forest? And do you have all your other equipment up to the task of an ultra-low noise floor?

[il_mix]

If you have to work with your head inside a Telsa Coil, you will have crap.

As cool as it may sound, I doubt I'll ever have a gig in a Tesla coil (...unluckily...).
So I'll go with the unbalanced input. Still, with respect to a regular guitar pedal, I'll have to do some modifications to the input stage to better match the mic input.

Note that there are op-amps that have balanced *outputs* as well as balanced inputs, which makes it much easier to chain these things together. I'd say that once you've gone to a single-ended output, you might as well stay there.

Sound interesting! Any op-amp name? A good (crude ascii) block diagram could be

Code Select Expand



MIC
  |
  |-------
  |       |
  |  (single wire (unbalanced)
  |    on this path)
  |       |
  |  MIC/GUITAR
  |   IMPEDANCE
  |   BALANCING
  |       |
  |      EQ
  |       |
  |    DISTORSION
  |       |
  |    BALANCED
  |     OUTPUT
  |     OP-AMP
  |   - AND/OR -
  | MIC/LINE OUTPUT
  |   IMPEDANCE
  |   MATCHING
  |       |
  |       |
  |       |
EFFECT SWITCH
     |
     |
   OUTPUT

Will read your linked article carefully.

Also, if I got your last sentence correctly, you're saying that it will be probably ok to just output an unbalanced signal. I will still have to match the clean output to the effected output to avoid problems when switching between the two.

THAT Corp has a whole slew of chips designed as topnotch balanced line receivers/amplifiers and balanced line drivers. Their app notes are wonderfully informative, so, if you are curious, take a look.

Uhm.... any more hints on THAT?
(I admit I didn't do any research on commercial pedals. Jumped straight on the DIY. With near-zero experience. Fock yeah!)

For mics, unless you are adding ungodly amounts of gain or recording into a nearly-silent background, the extra complexity is probably not worth the bother  So, are you recording wind-rustling sound effects in the forest? And do you have all your other equipment up to the task of an ultra-low noise floor?

Well, no. As said it will be a lo-fi microphone with lo-fi effects, so picking up noise on the cambe wil probably be the last of the problems.
But, if I can skip the unbalance to balance output conversion,  I still have to work on balancing the output to match the clean mic one. Maybe the balanced output op-amp mentioned by ElectricDruid will also do this without the need of extra components?

[tubegeek]

http://www.thatcorp.com/THAT_IC_Products.shtml

[PRR]

> are you recording wind-rustling sound effects in the forest?

Most forests are low-crap areas. No lights, no power-lines, and radio stations don't get rich by reaching the bears with ads.

Yes, balanced really developed when unbalanced teleGraph lines were un-usable in the big lightning-storms on the prairie. Taking two too-crackly lines and connecting tapper *across* them gave a good signal. Probably some telegraphers died passing messages in storms, but they were cheap.

[merlinb]

Sound interesting! Any op-amp name?

http://www.ti.com/lit/ds/symlink/opa1632.pdf
But it costs >four times more than a regular dual-opamp which can be made to do the same job, so few people use balanced opamps.

I still have to work on balancing the output to match the clean mic one. Maybe the balanced output op-amp mentioned by ElectricDruid will also do this without the need of extra components?

Balancing the output only requires one extra opamp to provide the inverted signal. UNLESS you need it to behave like a real transformer balanced output (i.e., if you short one leg you get twice the output from the other leg), in which case you can use a DRV135 or similar. http://www.ti.com/lit/ds/symlink/drv135.pdf

But in your case you don't need to go balanced at all. You mic is right next to the preamp, and the preamp can send a line level, low Z signal to the outside world. It doesn't need to be balanced any more than the output of a regular guitar pedal.
It wouldn't make sense to amplify the mic, then knock it down and balance it to feed into a mixer mic input, only to be reamplified again.

MIC
  |
(short single wire unbalanced)
  |
CLEAN GAIN
  |       |
  |      FX
  |       |
SWITCH
     |
     |
LINE LEVEL OUTPUT

[il_mix]

Yeah, I think I'll probably output an unbalanced signal. Will focus more on the effects.
Just a clarification; line level vs. instument level output? Do I actually have to think about this? Mixers sometimes have different inputs for line level and instrument level unbalanced inputs.

[ElectricDruid]

Found it!

http://www.ti.com/lit/an/sloa054e/sloa054e.pdf

I don't really recommend using any of this stuff, but it's quite interesting to look at and see how things change when you've got differential outputs as well as inputs.