How can i increase the gain of ROG's Odie?

[gigimarga]

Hello,

I've just finished to build the ROG's Odie and i like how it sounds...much better that TS...but i will like it much more if i will increase his gain.
I've listened to the clips from ROG site and i thought that it's possible to increase the gain, but i don't know how (i suppose that i will replace the 250K drive pot with 500K or 1M pot will have no strong effect as in TS).

Can you help me?

Thx a lot!

[petemoore]

  Tweek whatever's there to higher gain or stick another gain stage to it.

[gigimarga]

Thx for your answer...i was interrested if it's possible only the values of some existing resistors/capacitors (as i know, that's possible it i modify the pair resistor/capacitor from the sources of Q1 and Q2, but i don't know how: decreasing resistors and increasing capacitors or in other way?).

[bipedal]

Just to verify, are you looking for more gain (increase in signal level) or more grit/distortion?

Disclaimer: I'm a newb still practicing schematic interpretation, so I offer these as more of guesses/questions than "yep, this will work" suggestions.  Curious if others can verify or correct any of these -- particularly #2   

1)  Audition different transistors in the circuit -- you'll likely notice some differences.

2)  Looking at the Odie schematic, the tone control network (low pass filter between the second and third transistors) causes some signal loss prior to that third transistor.  Scaling the values of the tone control (smaller resistance & larger cap values), or re-positioning the tone control so it's after Q3 might allow Q3 to be hit with a hotter signal.  (Note, changing the signal filtering between gain stages would alter the tonal character of the circuit -- maybe in a way you like, maybe not.)

3)  Add clipping diodes to ground after Q3.  Will reduce output level some, but the right combination of transistor saturation plus a touch of diode clipping might be sonically pleasing.

Again, just guesses for experimentation.  Happy to be corrected if I'm off-track with any of these ideas.

[petemoore]

Thx for your answer...i was interrested if it's possible only the values of some existing resistors/capacitors (as i know, that's possible it i modify the pair resistor/capacitor from the sources of Q1 and Q2, but i don't know how: decreasing resistors and increasing capacitors or in other way?).
  Typical Jfet gain stage:
  Input cap might cut some bass from getting in, large lets more in.
  Source resistor, smaller value [also it's relation to drain resistor] increases gain, a capacitor across the resistor allows ~unobstructed [if large enough value] AC to increase gain, this source bypass cap can reduce bass and adjust gain [depending on value] with the source resistor...let the source sit closer to ground and the gain goes up, bias changes...
  Drain resistor also biases the Jfet as you know.
  The output cap lets out 'x' much bass.
  The first gain stage multiplies, as does the second stage [but it multiplies what the first stage multiplied..hence changes to the first stage may have the differences 'multiplied' by the second stage.
  IiRc the Odie is 2 Jfets, the second is intended to be lightly overdriven by the first.

[gigimarga]

thx a lot both of you...i will try to apply your suggestions

[brett]

Hi
go for high gm (transconductance) JFETs.  The J201 will give lots of gain relative to the 2N5456/7/8s and MPF102s, for example.
cheers

[gigimarga]

All FET are J201

[brett]

Hi
try adjusting the first trimpot for maximum gain instead of Vsuply/2.  It might get you a couple of dB extra.
The Odie should have a fair bit of gain, though.  Approx 400 (20 in each stage).
You could always put a JFET buffer/booster in front (Rd=6.8k, Rs=2.4k, Rg=470k, no bypass cap).
That will give about 3x gain. (ie 1200 when flat out)
cheers

[gigimarga]

Thx for your ideea...i will try to solder it on the same PCB ...i think i still have some space because the PCB is from a Supreaux (i didn't like very much his tone)!