Roland Jazz Chorus JC-120 preamp

[Sensei Tim]

has anyone here built this successfully?

i've built two and i've tried using 2sk117 transistors and j201s but i get the same result.   my test tone is fine through Q1, Q2, and the tone stack but then something weird happens like my test tone drops an octave and i can hear it pulsing along with severe background whine.  I get my original test tone on the output, but the volume is significantly lower than the input volume, even with the volume pot at max.

I've tried replacing the 15k biasing resistors with trimmers but it didn't help.

I'm using a 24V laptop-style power supply.

If it only happened on one board i'd say i screwed up somewhere, but i'm getting the exact same behaviour on two different builds.  Could it be the power supply is injecting noise?

I've tried running one of those 60 and 100watt class D power amps with the same power supply and when i connect my test tone straight to the input it's clean as a whistle.  i've also run a Dr. Boogie with the same PS and it's been fine.

[Sensei Tim]

ok more trouble shooting last night and i'm 95% sure that it's my power supply that's creating the noise.

I was thinking of adding a cut along row 1 and adding a 47R which would form a low pass filter with the 100u cap so the corner frequency would be 33.9Hz - more than good enough to get rid of whatever that hum is.

if that fails, i already have a 9V regulator in there to send 9V to the reverb unit and i figured i could tap off that 9V and send it to an 18V charge pump to drive the JC120 circuit. hopefully that will eliminate the noise if the LPF doesn't.

[Sensei Tim]

So I finally fixed it

Had to power the jc120 from an 18v charge pump to “isolate” it from the 24v power supply

For some reason that’s what was creating all the noise.  Adding the 47R resistor did nothing.

[Kirkus]

Hey Sensei Tim!
I'm having the exact same problem...
The signal does go through but the output volume is so much lower than the input...
I also get some noise like whining
Adding a charge pump after your power supply fixed all of those problems for you?
Please help me out mate it's been 2 weeks I've been struggling to get this to work!
Using a random 22 volt power supply from a Thomson router right now...