"brightening" a signal in an overdrive

[pinkjimiphoton]

righteous

[mordechai]

Sure.  Water under the bridge.

[Gus]

Look at R4, R5 and C3 you can control gain and add an EQ.  FWIW this was a circuit to see what I could do with one transistor it is bootstrapped, EQed and controlled gain.

[Mark Hammer]

I'm not challenging anything, since I know how much R&D you put into these things.  But the equal value of R4 and R5 perplexes me, given how little I know about these things.  Why would AC "feel" like going to ground through R5 and C3 more than simply going through R4?  Is it their parallel value that becomes important in this application?

Care to elaborate?

[Gus]

Mark  I did a quick sim as an example, this example is like a circuit you can find in textbooks.  The gain of this circuit for small signals is about the collector resistor divided by the emitter resistor 10K/1K(this is at frequencies above the input highpass frequency and below the boost frequency 100hz is a good place to check the curves).  I did not use a guitar cable sim to show more of what the circuit does isolated from the guitar.

The gain will go up with frequency  because of the 1K .22uf cap(1/(2 pi RC)).  The .22uf cap's effect will reach a limit(Think of it as an AC short) and the max higher gain will be 10K/.5K(the two resistor values in parallel).  The gain change does not effect the DC bias.  The resistors can be different values the cap can be changed in value to set the frequency the gain change happens at.  

The other circuit I posted was tuned/built for a fender strat to a brown deluxe for a friend.  The circuit can sound very good or not so good depending on the guitar amp etc but it can be adjusted to taste


Green input Blue output

[Mark Hammer]

The pics don't show up at work, but I'm looking forward to spending some time with them once I get home.  Thanks for taking the time to respond.  Appreciated.

[midwayfair]

Gus, thanks for that explanation. I'd been wondering how this worked recently as I only just started experimenting with bypass caps as a tone control.