Dean Markley Overlord not working

[TarheelTechinTraining]

Ok I've removed ic1 and the voltages are better. +15.8 and -14.3 though the negative is higher now its fluctuating about 1/2v. Any ideas or should I just replace the chip?

[52 Bill]

I would replace the chip.

[Jazz P Bass]

Please, please annotate that one fet.
2N4383.
Make it 2SK30A.

[oc disorder]

Started doodling with this then a few hours passed & ended up redrawn so posted here in case it's of any use ..

EDIT:Q2 changed from 2N4383 to 2SK30A on schematic as advised.

The original overlord schematic showed a 2N4383 transistor next to the symbol of a fet which is wrong!
(Most probably a mistake.. the closest N channel with a similar number is MPF4393...)

[TarheelTechinTraining]

Well Bill. I owe you a stoogie, it was IC1. I put in a fresh jrc4558 and its working great. Now I gotta put Q1&2 back in,lol. One question, what is the purpose of C3&C4? Thanks again for y'alls help,Greg

[Jazz P Bass]

One question, what is the purpose of C3&C4?

C3 & C4 are coupling caps.

They block any dc voltage but pass the ac voltage (signal).

[TarheelTechinTraining]

Well it's working, sorta. When I turn the drive past 5 it starts sounding squeaky. Any ideas?

[52 Bill]

Well it's working, sorta. When I turn the drive past 5 it starts sounding squeaky. Any ideas?

Squeaky?

[TarheelTechinTraining]

Damn auto correct. Squealing

[52 Bill]

C5 is a negative feedback cap that is wired across the gain control to reduce the high frequencies at high gain settings. Is this cap in circuit and the correct value?

Also, have you tried a different tube? Moved the wires around keeping ins and outs separated?

[TarheelTechinTraining]

So c5 is in definitely in circuit, soldered across pin 1&2 ic1. Seems correct value, 121 on cap. Also I did swap in a 12au7 and swapped ic's , 4558 for a tl072. Its better now but when I turn up drive past 7 its still squealing. Also I replaced c3&4 with correct values, 4.7 & 2.2 uf.

[TarheelTechinTraining]

Also I'm considering changing c3&4 to 22uf for both. Think it'll help? Also what about r16, 22k, up to 56k?

[52 Bill]

Also I'm considering changing c3&4 to 22uf for both. Think it'll help? Also what about r16, 22k, up to 56k?

Increasing the value of the caps will allow for lower frequencies to drive the op amp. Increasing the value of r16 will reduce the low frequency response of the tone stack.

Does turning the tone pots alter the oscillation?

[TarheelTechinTraining]

Yes it does, especially the bass. But when I turn all the tone knobs down there's no output, that's normal I think.

[52 Bill]

Yes it does, especially the bass. But when I turn all the tone knobs down there's no output, that's normal I think.

Yes, with all of the tone pots set to zero the entire audio signal is sent to ground.

I know that you will not like this idea, but try removing Q1 and see if the oscillation stops.