increasing output/volume in the 2nd op amp of a Son-of-Screamer-type circuit

[mordechai]

I'd like to goose the second op-amp in a Son-of-Screamer variant I built up...I'm thinking that taking the 1K between pins 6 and 7 of the IC and upping it to 1.2K or 1.5K might do the trick.  If I have that right...what might I need to do with the tone control (I'm using the standard 220R/220n values) to retain the same frequency response, or would the increased resistor change not really affect that?

[Mark Hammer]

Simply changing that 1k feedback resistor to a higher value will not do anything substantive to the 7:00 Tone-control position, but will do a lot more to the 5:00 full-treble position.  For instance, if you made that feedback resistor 2k2, there would be a gain of 11x at 3.2khz, which I'm pretty sure you wouldn't like.

Realistically, if one wishes to up the output level of a TS-type pedal, without changing the character very much, the best strategy would be to opt for something in SD-1/Timmy territory.  That is, increase the gain of the clipping stage while raising the clipping threshold.

So, stick a schottky or Ge in series with each of the clipping diodes, and change the 4k7/47nf ground leg to 3k3/68nf.  That will keep roughly the same low-end rolloff (709hz vs stock 720hz), but raise the maximum gain from 118x to 169x.  The increased clipping threshold will allow you to get higher output levels, using gain settings that would normally have resulted in more clipping.

In other words, the tone-stage is a bit of a house of cards.  Best to goose the output in the clipping stage in order to maintain a similar character.

[antonis]

(Although posting schematics is strongly recomended..) 

Raising 1k to 1k2 or 1k5 shouldn't have any audible volume result at low treble pot setting but it should dractically result on full treble gain..
(1k resistor in NFB loop doesn't form a 1:1 gain with the 1k resistor right after clipping amp, as you might think - the second op-amp is set as a non inverting buffer independently of R_Feedback value..)

edit: Mark is by far faster.. 

[Mark Hammer]

Well, your message had to come all the way from Greece.  I'm sure you had the idea first, but the transatlantic crossing just makes your post look slower.   

[mordechai]

Thanks for the suggestions.  I've actually already futzed with the clipping section.  I'm using two Green LED's as clippers because I wanted higher output, and lowered the gain resistor from 4.7K to 2.4K (and made the necessary changes to the following cap to keep the same basic frequency response).  It hits unity gain with the volume control at 12, which is **ok**, but I would like a smidge more room to play with that.   I can't remember if I used a 100KA or 100KB volume control...I gave the pedal to a friend who is doing some touring, so I cannot check.  But if it was the former, then switching to the latter would do the trick, I reckon.  If not, though, maybe I just need to live with what it is.  It actually sounds really great (used a nice hi-fi op amp and it made a very nifty difference), so all in all, this is really just a tiny nitpicky issue...

[antonis]

Just wait for Sir Mike to come and propose you a...........
(can anyone guess what..??) 

[MrStab]

if, like the Son of Screamer, your circuit just has a volume control straight before the output, building a non-inverting amplifier with an op-amp after the volume pot would both fix your output impedance and increase the maximum output level. win-win!