Op Amp distortion box builds too loud

[ninoman123]

This may have been covered but I've been searching threads and goggle and have found nothing so far.  :cry:

So far Ive bread boarded the smash drive and I built up a Dirty Bird and they both use Op amps are they are way too loud. I have a volume control on the dirty bird and only 1/4 of the knob changes the volume, the other 3/4 blows the house down. How could I tame the volume on this thing? Ive tried 5k audios 10k audios and a 100k audio. Should I go even smaller? Or can I add something to the circuit to reduce the output. Thanks for the help

[j0shua]

hmmmm i never build or saw dirty Bird , but i know very well the smash drive, you can use 1k Pot for distortion and 1k to volume, but what version of smash drive you build ? ... are 2 versions , simple and killer version .....

[petemoore]

Voltage divider...
 Like on the Blackfire or is it the Obsidian...
 Just before the output pot is a series 470k, and a 470k to ground.
 I suppose different size resistor could be used, as long as they are the same value, of course different values would give different %ages left after dividing.

[ninoman123]

Blackfire has a 1M to ground and a 10k in series, but either way I know what ur talking about so ill try it out. Thanks for the help!

[ninoman123]

Heh its the vulcan with the 470k combo. Just found it.

[Mark Hammer]

Your pedal doesn't "know" that resistances attached to either leg of a pot are actually different physical objects.  All it "knows" is that there is a combined resistance of some value which is divided in some ratio by the current position of the wiper.

If a fixed resistance is added to the ground leg of a pot, then from the pedal's perspective this is like a pot that can never be turned down below a certain ratio.  Look at the "Sustain" control of a Big Muff for an example of that.

If a fixed resistance is added to the input leg of a pot, it behaves as if the pot can never be turned above a certain level or ratio of resistances.

E.g., Suppose we have a 50k pot.  To the ground leg, we add a 10k fixed resistor.  To the input leg we add a 39k resistor.  This combination now behaves as if it were a 99k pot that can never be turned down below the level set by 89k/10k, and never turned up above the level set by 39k/60k.  In effect, what we've done is taken a smaller percentage of the full hypothetical range of the "pot" and devoted 100% of the rotation to that limited part of the range.  This is extremely helpful when you want to be sure that a) the level/output-voltage never exceeds a certain amount, b) the level never goes below a certain amount, or c) you have enough articulation in the pot to nail a specific level/setting.  This is one of the many reasons why you will often see this sort of arrangements used with trimpots.

[onboard]

Everybody else pretty much covered it, but I have to chime in because when I read the thread title I thought "That's the first time I've ever seen someone commenting that they want *less* volume" out of a distortion build!

That and you're signature made me laugh out loud - eventually they'll stop asking you if you need a cell phone, too...

So did you go with the voltage divider or a series resistor or what?

By the way, what happens to output impedance when you start hard setting the volume level before the pot?

[ninoman123]

Everybody else pretty much covered it, but I have to chime in because when I read the thread title I thought "That's the first time I've ever seen someone commenting that they want *less* volume" out of a distortion build!

True, but its the fact that the bypass volume is way lower than the effect volume. Plus Ive been blowing down the house at level 2 on my amp. Which isnt good.

So did you go with the voltage divider or a series resistor or what?

Havent gotten home yet to try it. But ill try some values and post back if anyone is interested.

Thanks to Mark for all the great information. It all makes sense now!  

[David]

This may have been covered but I've been searching threads and goggle and have found nothing so far.  :cry:

So far Ive bread boarded the smash drive and I built up a Dirty Bird and they both use Op amps are they are way too loud. I have a volume control on the dirty bird and only 1/4 of the knob changes the volume, the other 3/4 blows the house down. How could I tame the volume on this thing? Ive tried 5k audios 10k audios and a 100k audio. Should I go even smaller? Or can I add something to the circuit to reduce the output. Thanks for the help

Nino:

The 386 isn't an op-amp , it's a one-chip audio amp.  Think of it as a tiny PA power amp.  Depending on the resistance across pins 1 and 8, IIRC, you can get gain between 20 and 200.  Damp the gain down and this should make your situation more manageable.

[ninoman123]

Yeah I realized that once I posted heh. :oops: Even still, next time I build the Smash Drive I'll know what to do