Volume Boost/Output Buffer Options

[BennyBoy]

Hey folks,

I am currently working on improving an overdrive design and wanted to pick your brains! After getting some feedback on my drive, people wanted more output volume.


Because of that, I tried adding a clean boost op-amp stage after my tone control. Because I am already using a TL072 for the input buffer and the clipping stage, I figured I would use another TL072 here. This led me to wonder, why not swap the transistor output buffer I have for an op-amp buffer to use the other side of the 72. Any thoughts on potential drawbacks on this compared to the output section I have? Any suggested changes to my added boost stage? Thanks! (Also, please ignore the sloppy schematic drawing and weird resistors in place of pots, I just made this quick on LTSpice to test)

[Clint Eastwood]

I wonder if you can't do without the input buffer. You can connect you guitar directly to the clipping amplifier. Or does the buffer stay in circuit when you switch off the overdrive? if not, you could use that op amp channel to make a fixed gain booster/output buffer. This way you can have all you want with just one TL72.

[GibsonGM]

Yes, per R.G. Keen's "son of screamer" at the bottom of this page:
http://www.geofex.com/article_folders/tstech/tsxfram.htm

Removing the input buffer would free up that '72 section.

[ElectricDruid]

Another +1 for that idea.

That first op-amp buffer is doing nothing, basically. You can get the same input impedance direct into the clipping stage. Just take everything that joins to U1 +ve input, and join it to U2 +ve input instead. U1 and the rest in-between can go.
That gives you a second op-amp to use instead of the output buffer, without needing to add a second TL072. And if you need a bit of gain on that output op-amp to get things back to unity or a bit more after the tone control, then why not?

On another note:
What's going on with that tone control? It looks like a Big Muff style thing, except the top end is just a divider with no cap at all. The bottom is ok - a lowpass.

[antonis]

Can't either get what's going with R19/R20..
(unless it's a Volume pot..)

P.S.
I DO know it's a drawing error but I still don't like to see U4 in such a #@*     wiring state..

[ElectricDruid]

Can't either get what's going with R19/R20..
(unless it's a Volume pot..)

Yeah, it's a "budget LTSpice Pot". R14/R15 is another for Tone. We've all done it. We mostly don't show it off though

[PRR]

more output volume.

Cheapest/simplest/quickest:

[antonis]

Yeah, it's a "budget LTSpice Pot". R14/R15 is another for Tone. We've all done it. We mostly don't show it off though

Should it be a lot of trouble if you inform us about it..??

or else, we are free to consider R11/R12 a 40k 10% pot set at 50% rotation..

[BennyBoy]

On another note:
What's going on with that tone control? It looks like a Big Muff style thing, except the top end is just a divider with no cap at all. The bottom is ok - a lowpass.

Thanks for the advice

The tone control is strange, but I wanted to keep it original to the circuit this is drawn from (the Yamaha OD-10MII). This is the original tone control from that pedal.

[BennyBoy]

P.S.
I DO know it's a drawing error but I still don't like to see U4 in such a #@*     wiring state..

Just noticed that, sorry  I redrew it just to take the screenshot and did it really quick lol.

[BennyBoy]

Yeah, it's a "budget LTSpice Pot". R14/R15 is another for Tone. We've all done it. We mostly don't show it off though

Should it be a lot of trouble if you inform us about it..??

or else, we are free to consider R11/R12 a 40k 10% pot set at 50% rotation..

R11 and R12 are actually part of the wonky tone control from the original pedal. The dividers at R14 and R15 and R19 and R20 are the only pot simulations (for gain I just maxed it out for testing purposes, 100k at R9). Here's my actual schematic from Eagle so you can see what's going on.

[BennyBoy]

Sorry all, didn't mean to start a controversy with my horrible LTSpice schematics! 

[antonis]

This is the original tone control from that pedal.

Similar to Watson's EFY-6 Fuzz Tone control..
(a bit simplified..)

[antonis]

Sorry all, didn't mean to start a controversy with my horrible LTSpice schematics! 

There can't be any serious controversy without duck_arse involvement..
(ElectricDruid is too noble for hassling..)