Showbud D15 steel SS amp hiss

[g1]

Mouser's got the J305 for $3, just ordered a couple

I think you will have to reverse gate and drain pins, but otherwise should be a good sub.

[loudthud]

I think you will have to reverse gate and drain pins, but otherwise should be a good sub.

Pin Info:




JFET protection:

[mozz]

You may be better off with 2n5457 if they are still available. Or 2n5484. This is experience talking from building EP3 echoplex preamps that originally had TIS58. The printing on those ones doesn't even seem correct.

[g1]

Pin Info:

I don't disagree about S and D being interchangeable for a jfet, but the datasheets call them out as SGD for the TIS58, and SDG for the J305 (Interfet brand). And to further confuse things, other brands of J305 have different pinouts. Fairchild is GSD.

[LarBal]

I don't disagree about S and D being interchangeable for a jfet, but the datasheets call them out as SGD for the TIS58, and SDG for the J305 (Interfet brand). And to further confuse things, other brands of J305 have different pinouts. Fairchild is GSD.

Oh wow thanks Loudthud, that was very helpful for you to make that substiution diagram. I just got my J305 and was sitting down to work all this out.

These are Interfet, and are SGD. So I'll put the G of the J305 where the middle pin of the TIS58 goes on the board, then D/S in the other two and report back. Thank you for the headsup g1

[loudthud]

If you are having trouble getting things to work, check the link I posted in post #3 for how to check JFETs with an Ohm meter.

[LarBal]

Well , I decided just to do one side, and check, and the JFET sub works, but it didn't solve my problem, still a lot of hiss, and I could be totally wrong, but that channel now seems a little quieter than the fx channel.
It actually seems like there's more noise now

[loudthud]

What type resistors were used on the input circuit. Carbon composition ? There is a 22Meg a 1.5Meg and two 47K ? One thing to try is to touch a capacitor across the 1.5Meg resistor. That will tell us if one or more of the resistors on the input is creating the noise. Be sure the cap is discharged before touching it across a live circuit.

[mozz]

Freeze spray.

[LarBal]

What type resistors were used on the input circuit. Carbon composition ? There is a 22Meg a 1.5Meg and two 47K ? One thing to try is to touch a capacitor across the 1.5Meg resistor. That will tell us if one or more of the resistors on the input is creating the noise. Be sure the cap is discharged before touching it across a live circuit.

Yep the 22M and 1M5 are CC, the 47Ks look like film. I'm assuming an electrolytic cap across the 1M5 ?

[loudthud]

Yep the 22M and 1M5 are CC, the 47Ks look like film. I'm assuming an electrolytic cap across the 1M5 ?

No, a film cap perhaps 0.022uF to 0.1uF or so. It's just an experiment to see if it kills the hiss.