Third layout down...

[HiGain]

Check out the 250pF cap/100k R to ground, followed by the 470k/22k VD, followed by they 68k grid stopper. This arrangement is not on any of the schematics, is it?

...and a big thanks to Omar and everyone who conributed files!!!!

Jake

[glasman]

That network is from an ODS-Reverb (actual HAD schematic) that was floating around a while back. It trims the top and bottom end before entering the OD stage. I have never tried it so I have no idea how well it works.

Gary

[Funkalicousgroove]

Do you have a copy of that you'd share?? I have a Layout of that amp but it's tough to read. To me the values look like a 220K bypassed with a 33pf to ground, a 3M3 across the whole network and a 33K to ground on the other side

[glasman]

Do you have a copy of that you'd share?? I have a Layout of that amp but it's tough to read. To me the values look like a 220K bypassed with a 33pf to ground, a 3M3 across the whole network and a 33K to ground on the other side

Unfortunately mine is just as bad. I doubt that 3.3M is really that big, it would kill all the signal to the ovredrive stage. I just looked at that section of the schematic and I really can't read the values.

220K over 100K trim works pretty good. If you want to cut a little more bass lower the 100K to 50K or so. This really helps the OD sound.

Gary

[Funkalicousgroove]

The 3M3 in paralell with the other 2 becomes a much smaller value, at any rate I like it with a trimmer there anyway.

[tonelab2]

The values there are 470k,100k,22k, the 100k bypassed with 250pf cap, junction of 100k + 22k grounded, try a pot between this junction and ground to control how much clean signal is fed to O.D. stage. 250pf cuts treble, lower values less cut. This was the '70s setup, moved to a 100k trimpot for 80's models.

[HiGain]

OK, so here is a schematic. Basically, it seems like it would form a subtle bandpass filter, in addition to reducing overall gain.

EDIT: updated schm to refelct tonelab2's comments. Thanks.

[oldmacman]

I've found that the standard 220K resistor into 100K lin pot, as found in the '77 schematic here, sounds as good as anything I've been able to do with this circuit.

You can tweak the resistor values to change the impedance of this network to adjust how much bass gets rolled off at the entrance to the OD.

[tonelab2]

Sorry that should have read 220k not 470k, too many late nights.