Do I understand gain properly?

[Joecool85]

here's an analogy ...

the open-loop gain of a typical op amp is similar to the utmost maximum RPM of a typical car engine .... our typical overdrive/distortion/fuzz guitar stompbox usually uses an op amp with closed-loop gain .... closed-loop gain, as R.G. described, can be controlled ... when you drive your car, your RPM goes up to a certain point, and then the transmission switches to a higher gear, and your RPM goes down to a more manageable level ... ( and climbs back up again if you're stepping on the gas ) ... just as you would never want to run your car in 1st gear at the engine's maximum RPM ( which would seriously stress your engine's working parts ), you wouldn't want to run an op amp 'wide-open' ...

when you step on the gas, you're controlling RPM, which eventually translates to car speed ... miles/per/hour ...

when you turn the "drive" knob on many overdrives/distortion/fuzzbox units, you're controlling the closed-loop gain of an op amp ...

Ok, so how do I get enough mph out of a pedal to make it have the same gain as a black coffee pedal?

[anchovie]

Ok, so how do I get enough mph out of a pedal to make it have the same gain distortion as a black coffee pedal?

Diode clippers! You don't just want to amplify, your aim is to (heavily) chop the tops and bottoms off the waveform as well.

[petemoore]

 Ok, so how do I get enough mph out of a pedal to make it have the same gain as a black coffee pedal?
1a. Copy the BC, exactly.
It's tricky to explain..how to talk about gain.
Lowpass, highpass, fullband attenuation...bandpass 'n boost amount is worth investigation.
If you cut the highs [LP Filter] it can take out the fizz, try a two pole filter to keep midrange out of it's biz.
When lows are cut much, the amplitude it carries is much, so signal strength diminishing is a greater consideration as such.
 All these things tend to interact.
 A look at the BC schematic would reveal the balancing act it's designer created.
 

[petemoore]

 'tone' requires voicing [which relates to signal attenuation], often combined with full-band attenuation and bandpass boosting
 /...I just threw together a hypothetical possibility, not real clear on any of it:
 Tone...you'll want this, requires voicing before and/or after the clipping or other stages, guaranteed the BC has thought through voicing and has boost/attenuation which 'balances' everything out.
 Terms for thought/study:.
 Attenuation:
 HF [by way of LP filter].
 LF [by way of HP filter].
 When a frequency's amplitude is reduced, overall signal amplitude is reduced [somewhat].
 Fullband attenuation: Volume control, passive resistor or adjustable resistive divider, refers to volume pot.
 Bandpass = HF + LF filters...cut the highs and the lows..what remains ? Middle range frequencies.
 

[Mark Hammer]

A big part of what can make some pedals sound so "intense" is the EQ.  Try a Superfuzz, or one of its many variants, some time.  The Superfuzz has a two-position tone switch.  One imposes a big midscoop that makes the deep low end and upper mids dominate, and the other has no scoop, attenuating the overall signal enough to produce approximately equal output levels compared to the scooped setting.  The Cramps' Poison Ivy describes the Superfuzz as sounding "like death", and in the scoop setting, I'd say I have to agree with her.  In the non-scoop setting, it doesn't.  But here's the thing: there is absolutely NO difference in "gain" between the two settings, only EQ.

So, part of the perceived intensity lies in what you allow the user to hear.  Obviously, there has to be enough gain to produce it, but you can have some pedals with surprisingly high gain that don't sound all that intense.  A Rat has a max gain in the thousands for content over 1.5khz, but if you roll back the Filter, it just sounds like a smooth overdrive with good sustain.  A Distortion+ has a max gain of 213x and can sound quite intense in the right hands, largely because it applies that gain to stuff from 720hz up and makes precious little attempt to trim the top end.

There is also the magic of double-clipping, and its variants.  Here, you can apply gain so as to elicit clippping from one set of diodes, then apply a bit more gain to the resulting signal to bring it back up to a level where distortion is again elicited from yet another set of diodes.  What you're left with after the first set of clipping diodes may not be enough to produce clipping in the second set, but it may not take all that much gain whatsoever to get it back up to that level.  And believe me, whether the combined cumulative gain is 2000x or 750x (250x, followed by 3x), getting harmonics of harmonics tends to make the sound "intense".

The Boss HM-2 heavy Metal pedal uses double-clipping but of a different sort.  It places a pair of back-to-back germanium diodes in series with the signal to produce crossover distortion, before applying clipping in a subsequent stage.  Crossover distortion of this type occurs when the signal must be above some minimum for the diode to conduct, and the resulting output trims the lead-in and lead-out of the signal, effectively "clipping the sides", rather than the top.  This changes the marmonic structure, but has no bearing on the amplitude of the peaks, which means you can clip them without having to add much more gain.  And of course, with both the sides and the tops clipped, you end up with a near-square (thought really more like a 30-40% duty-cycle pulse) that, with a tiny bit of EQ tweaking sounds quite intense.

All of this is to say that the perceived intensity of a fuzz is a product of more things than flat out gain.

[Joecool85]

Very interesting reads here.  Looks like I will need to do a LOT more reading, playing with circuits and researching them before I will totally "get it."  But at least I'm on my way, thanks guys!