Have you tried lowering the value of R14 as I described in post #11?

 

Hey gents...I tried lowering R13 by attaching 4.7k across.

Putting a resistance in parallel with R13 *increases* the gain of the circuit. To lower the circuit gain, add a resistance in series with R13. 4.7K would reduce th gain by something like 75%, too large for a first pass. I'd start with something like 1K.

ak

 

Would it be worth while to think about a lower gain op-amp there?

The gain of the opamp itself, called the open-loop gain, is irrelevant. For proper operation, the feedback components assure that the overall circuit gain is much less than the individual opamp gain.

ak

 

This is the second on-going thread about an electric guitar preamp that has a highpass filter that cuts most guitar fundamental low and medium frequencies.
Maybe it makes up for the very poor high frequency response of guitar speakers?

 

Have you tried lowering the value of R14 as I described in post #11?

The only reason I didn't try that; I dont have resistor value...

 

The only reason I didn't try that; I dont have resistor value...

will try to buy something soon...

 

What do you have on hand? Might be able to make something work.

 

What do you have on hand? Might be able to make something work.

dont have anything near 470k...only 2.7 k and some smaller values....
gonna try to add small amount to R13, because I have those smaller values...

 

One thing I noticed are resistors R7A and R8A form a voltage divider that cuts the signal output from U1A by 50%. Reducing the value of R8A will further reduce the signal before getting to U2D and U2C.

 

One thing I noticed are resistors R7A and R8A form a voltage divider that cuts the signal output from U1A by 50%. Reducing the value of R8A will further reduce the signal before getting to U2D and U2C.

Not in both switch positions.

ak

 

Not in both switch positions.

True if the TS requires the bypass. Another thought, add resistor between R12 and C13 to ground.

 

R12 and C13

? ? ?

 

? ? ?

Meant R13 and C12.

 

Meant R13 and C12.

Yes. That will lower the corner frequency of the highpass filter, but it also will decrease the U2C fuzz circuit gain.

ak

 

Yes. That will lower the corner frequency of the highpass filter, but it also will decrease the U2C fuzz circuit gain.

ak

SO, I went from 1.5k to 2.7k for R13. Still too much drive. Should I keep going on R13? I guess I need to get some higher value resistors and try R14, R15 mods....
Thx for the on-going thoughts and suggestions

 

Should I keep going on R13?

No, leave R13 as is and add the resistor circled in RED in the schematic below. Start with a 2.7K

 

No, leave R13 as is and add the resistor circled in RED in the schematic below. Start with a 2.7K
View attachment 309487

I can try that tonight....
Thx for the suggestion

 

So it comes down to this: Basically, there are two different ways to alter the effect of the distortion stage.

1. Change the gain of the stage. This is what happens when you add a resistor in series with R16, or in parallel with R15.

2. Change the amplitude of the signal going into the stage. This is what happens when you add a resistor to GND between R13 and C12.

Note that because of the capacitors around the stage, changing the effective value of any resistor will change the tonal characteristics of the stage, most notably when the Drive pot is set for minimum distortion.

Note also that messing around in the R13-C12 area changes both the signal amplitude *and the gain of the stage*, because those components are the shunt leg of the U2C feedback loop. Adding a resistor to GND obviously attenuates the signal amplitude at that point. BUT, it also reduces the Thevenin equivalent resistance "seen" by the series leg (C13, R15, etc.) U2C feedback network, and this *increases* the gain of the stage. The math for this is not complex, although it is messier because of those pesky capacitors. So the fun question is this: What is the real effect of adding the resistor to GND? Is the net signal amplitude change an increase or decrease ? ? ?

ak

 

I agree with all that above but still think the best way is to reduce the value of R14 as I described in post #11.

 

Years ago I bought an assortment of 1/4W 5% resistors with proper color bands. I am glad I have them.