Adding balance input and outputs to a fuzz?

[Chugs]

A friend who works part time at a recording studio has asked me to make him a fuzz with balanced input and outputs to use in the studio. I plan to make a a fuzz with a buffered high impedance input and a low output impedance. But I have never add balanced XLR inputs and outputs to a pedal before. What is a good way to go about this? What should I be aware? What impedances issues, if any, will there be?

[Mark Hammer]

Why?  I understand the desire for balanced ins/outs as a way to minimize noise.  But once we move into the realm of fuzzboxes, noise starts to become a matter of things other than whatever can get picked up over the interconnecting cables.

I'm not saying your friend is wrong in his motivation, but will it really make any difference in this instance, or is it simply a matter of convenience?

[Chugs]

I am not sure why he specifically wants balanced inputs and outputs, he just does. Patching convince perhaps?

[PBE6]

What is your friend going to be using it for, vocals, other instruments, maybe re-amping? Also, are you going to be making a Fuzz Face-style fuzz or an overdrive/distortion pedal? I think each case would have its own ideal impedance and preamp requirements, although as Mark says noise is unlikely to be an issue if you're clobbering the signal with a Fuzz Face.

[PBE6]

Lots of info here:

http://sound.westhost.com/articles/balanced-2.htm

http://sound.westhost.com/balance.htm

[deafbutpicky]

also making a fuzz input impedance high will make it necessary to simulate something guitar like right after the input buffer
to keep it sounding good.

http://www.muzique.com/lab/pickups.htm

[PBE6]

deafbutpicky has a good point about the input impedance. Another thing to consider is that the output will likely not be going through a guitar amp, so it's going to sound unnaturally bright and harsh unless it's being run into a cab simulator or EQ of some sort.

[Chugs]

Thanks for the links.

I am not worried about the fuzz sound being different after it has been buffered. I often add buffers to fuzz pedals that I make.

My impedance question relates to whether adding balanced inputs/outputs to the fuzz and it being used with studio gear meant that impedances different from typical guitar high in/low out might be more appropriate.

Also, just the basics: what is the best way to sum the two inputs from a balanced input to the mono signal for the fuzz, etc.

Looks like the link have some good info.

[PRR]

> sum the two inputs from a balanced input to the mono signal for the fuzz

A "balanced input" is ONE signal.

The one signal is passed on TWO wires (plus usually a shield) out-of-phase so outside interference (in-phase on both) can be rejected.

If the studio dude wants to Sum a Left and a Right to one mono fuzz, he has a mixer for that.

[Quackzed]

I am not worried about the fuzz sound being different after it has been buffered. I often add buffers to fuzz pedals that I make.

a valid point... but all the same, you are probably going into a guitar amp with its own high end taming filters/tonestack/speaker high frequency roll-off etc...
as long as your friend knows that a fuzz running direct into a full frequency mixer or recording interface WITHOUT those high end taming filters and roll-offs is gonna sound alot different;
mainly much brighter-harsher-fizzier...
he may intend to 're-amp' with it, running it into various amps/modelers etc... that DO have some high end taming. but i would want to find out a little bit of his intended use to know whether or not to include some sort of high end filtering; either cab sim or pickup sim/ impedence matcher or some sort of treble filtering... something he could switch in to keep it from sounding too bright/harsh when being used without any external high end taming...like into a recorder or digital interface...

[Chugs]

He runs stuff like vocals through various pedals often so he is aware of the differences between using an amp and desk in regards to the sonic differences.

[Chugs]

> sum the two inputs from a balanced input to the mono signal for the fuzz

A "balanced input" is ONE signal.

The one signal is passed on TWO wires (plus usually a shield) out-of-phase so outside interference (in-phase on both) can be rejected.

If the studio dude wants to Sum a Left and a Right to one mono fuzz, he has a mixer for that.

Apologies, misuse of terminology on my part.

Apart from rejection of possible outside interference what advantages, if any, is there of using balanced over unbalanced for the purpose of plugging into a distortion unit in a recording application?

[bool]

Another POV:

With a bareback, single-ended unit, there will always be an interaction with the source and the load. IOW, your fuzz will never quite "sound the same" when plugged into different things.

With adding a balanced I/O's, you will be forced to sort these impedance (signal levels, etc) issues within the unit itself. IOW, you will in effect be adding a "protection layer" wrt. the outside world and much of the previous interaction will be gone. The unit will act more predictably, but much of the "wildness" will be gone also. Which may be a good thing for your friend ...

[ashcat_lt]

Apart from rejection of possible outside interference what advantages, if any, is there of using balanced over unbalanced for the purpose of plugging into a distortion unit in a recording application?

Honestly, aside from noise, there kind of aren't any.

Depending on how it's balanced to begin with (at the source) and how it gets unbalanced (between the source and the pedal), you might lose up to 6db from basically throwing away half the signal, but that kind of raises a new point:

Nominal line level is a bit hotter than typical guitar signals.  A decent signal coming off the board or recorder is going to pound that little fuzz box pretty hard.  Yes, he's probably got knobs for that, but attenuating at that end makes it even more susceptible to noise along the way.  Most interfaces nowadays apply 9-10db gain to any input marked "Instrument", and it seems to be a reasonable rule of thumb.  You might think about a switchable pad even if there's an input level knob.

I find myself also wondering why you're not asking about balancing the output run back to the board/recorder.

I personally wouldn't bother with any of it.

[PRR]

> what advantages, if any, is there of using balanced over unbalanced for the purpose of plugging into a distortion unit in a recording application?

In small studios (audio does not go outside the room), un-balanced can work very fine.

But balanced-to-unbalanced connections can be problematic.

And "balanced" interfaces are now 38-cent chipwork. (Though these are one reason that balanced-to-unbalanced connections can be problematic.)

So studio operators have generally standardized on Balanced. Anything else may have problems with random patching.

The interface circuits are now fairly standard and found on the usual websites.

Going from Guitar Level to Studio Level -- assume studio level is 5 times larger than guitar level. So you fuzz input will need roughly 5:1 cut-down, and this should be wildly adjustable so that board signal hits the fuzz at a user-preferred distortion point. At the output you probably need 1:5 of gain so the fuzzed signal comes into the board at a reasonable level. This may not need a user-control since the board may have a FX return knob.

[ashcat_lt]

At the output you probably need 1:5 of gain so the fuzzed signal comes into the board at a reasonable level.

I was going to say something about that, but doesn't a transistor fuzz usually swing pretty close to the rails?  Even 6V p2p is a greater than 0dbVU in most studios.

[mth5044]

This may be helpful?

http://sound.westhost.com/project51.htm

[PRR]

> doesn't a transistor fuzz usually swing pretty close to the rails?

Most have some knock-down at the end. Otherwise the output would be so strong that the amplifier would fuzz before the fuzz fuzzed.

Yes, in specific cases you could trim-back the knock-down and avoid a gain stage. But in most cases you still need a chip to drive the possibly medium/low impedances of studio gear inputs, and the knock-down may also do tone-shaping, so why get too clever?

But they are all different, and Chugs has not specified his technique, so this has to be worked out between breadboard and final studio product.

[PRR]

me> some knock-down at the end

For example-- the FuzzFace:
http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacepnpschematic.gif

The Collector swings about 8Vpp. But we take output across just 470/8,670 of the Collector resistance load. So 8Vpp becomes about 0.39Vpp or "around 0.14Vrms" (not that a 2.828 factor can be applied to a fuzz-wave).

OK, that's not small and we know it can't get higher. Some mixers are happy taking 0.1V external feeds. Others prefer signals arrive more like a half-Volt.... there may not be enough spare gain, or the operator may not like to turn pots to "10" (board-ops have knob superstitions just like guitarists do).

Yes, we could tap-up. Change 470+8.2K to say 1.5K+7.5K or 2K+7K. In this case, if nobody is looking, I might. But you have to think what comes after, if the impedance change from 470 to 2K matters. Here it probably doesn't. I do think you want the 0.01u+500k loading to trim the sub-sonic thumps as the transistor flips-out, but with 500K at the end a change from 470 to 2K is minor. The 500K sure will need buffering from the ~~10K inputs of many modern boxes, and as-said most studios are set up for "balanced" patching so you need an inverter to create equal-but-opposite signals.

So just be aware you may need some gain (trimmed on first trials) as well as the buffering and balancing. All this needn't add much cost.

At the input-- if you power the unit with just 9V, you may need to be clever in case some ijiot sends a +20dBu (7Vrms) signal. Hmmmmm.... this plan should take the biggest signals a console could put out (even if +/22V or 44V power) and get them into a 9V system with gain from unity to zero.

[PRR]

me> this plan should take the biggest

Where it says "50K", of course I would grab 47K nearest standard value. This isn't a rocket to Mars.

ASS-uming fuzz starts at 20mV (typical for many fuzzes), input specs can be claimed:

Input type: differential (balanced)
Input impedance: 100K
Sensitivity (adjustable)--
Input for edge of fuzz: -30dBu (20mV) to +10dBu (2.5V)
Input for gross fuzz: -16dBu (120mV) to +24dBu (12V)
Maximum safe input: +36dBu (50V)

(maximum output likely from studio gear is +28dBu, so ample margin)
(if you use 1/2W input resistors it can stand being plugged to a 125V wall-outlet, but do not tell them)