Kustom K50 Main PCB Mounted 'Can' Style Diode(?) Help

[J M Fahey]

Finally got a schematic too. ...... R2/22K & Q12N5033/P-JFet.

I think we could answer better if we also could see that schematic.

[El Músico Loco]

Kustom K50 (PC5026) Schematic



Ooopps! Sorry about that. Here is the schematic

[J M Fahey]

Well, it *is* a poor design, not much improvement possible except redesigning it or plain just replacing the full front end.
In the second case you would be losing the klunky diode modulator tremolo, nothing to cry about.
The main problem is that the volume control is at the input jacks, so the preamp after it is always running full blast, happily injecting hiss even with volume on "0".
To further degrade everything, the FET is absolutely wasted because it's driven from a 50K pot, which sets the input impedance to such a low value.
It's functionally equivalent to a PNP transistor.
Your 2N50xx doesn't work because probably the pinout does not match.
I suggest you leave it original; unless you want to rewire it placing the volume pot *after* the input stage; but you'll probably lose the tremolo function or at least it will be impaired.
Not that I'd worry too much about that.
If you want to do that, I'll post a suggested schematic mod.
Good luck.

[km6xz]

The ring modulator will certainly give it a different sound, really rich in harmonic since it produces two sideband spectra according to that wiring diagram. That would be worth keeping but the front end as JM said will be a noise machine most noticed with low level signals and gain settings, because the noise will be constant.
What sort of noise is it? Does it change character with the gain setting? Does it change more with the Bright switch on? If is hiss or or more granular lot shot noise? The noise characteristics would point to the generator of the noise. It the 22k resistor is a carbon comp resistor, listen while squeezing it a little with needle-nose pliers to see it it is the source, a noisy carbon comp resistor will usually have a spitting frying eggs sound, not white noise. A bad JFET can have several noise type. Any bias current on the gate will generate noise in this circuit, but that is easy to hear when moving the gain pot position.

[El Músico Loco]

Hi,
Long time in replying. I swapped out Q1, P-channel fet, with a 2N5460 and after swapping the source and drain which are marked wrong on the schematic and it works great now.
Here is a picture of the fet orientation for any one who has the same problem

Thanks for all the help.
Chris