GK 250ML Chorus Issue

[sweatyk]

The chorus on this amp doesn't sound correct. I'm not sure how to accurately describe it but when playing low notes on the E or A string the swell seems to stretch further then just drops instead of a continuous smooth flow. I have my personal amp here to compare so it definitely has an issue. I've look around inside and at the schematic and there's no trim pot that would adjust it. Looking at the schematic it looks as if U15, U16, and U17 ic chips are affecting this.All 3 are TL-604's. Just looking for some guidance where to start. There's not much info out there other than speaker replacement threads.

[sweatyk]

Here is the section of the schematic involving the chorus.

[Mick Bailey]

I'd start by first checking the +/-15v supplies then take a look at the output of U26. If this looks OK then check that the rest of the wafeforms and voltages are as per the schematic.

[sweatyk]

I'd start by first checking the +/-15v supplies then take a look at the output of U26. If this looks OK then check that the rest of the wafeforms and voltages are as per the schematic.

The +/- 15V is good. I don't have a oscilloscope to check the wave forms. I know someone that does, perhaps I can talk him into it. However I did check the output of U26 with my DVM and it did bounce back and forth voltage wise but I'm sure the wave form is actually more telling in this case correct?

[Mick Bailey]

Yes, I'd be looking to see that the wafeforms are correctly formed, not only off U26, but the others detailed on the schematic . I'm thinking there may an offset or lack of symmetry somewhere that's giving the symptoms described. With chorus circuits that do have an adjustment for waveform symmetry, if it's off in any way you can get a lopsided chorus like it's modulated by a ramp waveform rather than a triangle or sine.