So I finally got the resistors installed and replaced all the top and bottom pre-amp board chips with NE5532P (9 of them). I suppose I did this because I liked the phrase, "low noise." No matter how many I tried.... it didn't change the static. While it is somewhat quieter, it almost sounds like it is picking up interference from a badly tuned in radio that is not quite on the station and the signal comes and goes. Not loudly but not quiet either. I moved it around the apartment to different outlets but that did not help either; still static that comes and goes.

 

Let's stay focused and tackle one issue at a time.

With no guitar input and the MASTER VOLUME set to 0, what sound do you get from the loudspeaker?

 

It does the same whether I plug in on not. It's like a radio station that has lost their broadcast signal in bad weather. You can still hear irregular static on your radio, with the occasional lighting strike crackle and pop; once in awhile. Not loud but not silent either. Thanks again Mr.Chips for your help.

 

Next step.
Remove the top input board (Channel 1 and Channel 3) and the bottom input board (Channel 2 and Channel 4). Put them both aside.

(You can achieve the same effect by unplugging the connection (five red wires) from the main amp board).

Turn the power on.

What sound do you get from the loudspeaker?

 

Speaker thumps at turn on and snaps at turn off. But when on is absolutely quiet.

 

Speaker thumps at turn on and snaps at turn off. But when on is absolutely quiet.

If you go back and examine the posts in this thread you might realized that we took a wrong turn somewhere.
Your post #47 suggests that you are hearing some noise. Same as your post #62.

Absolute quiet is good news, for now.
Let's move on from here.

Install all boards and all connections, including the 5-pin red cables.
Turn the MASTER VOLUME to 0.
No guitars plugged in.

What sound do you hear from the speakers?
(The thump during turn on and turn off is normal. Ignore these.)

 

As I said in 103, It's static.... like a radio station that has lost their broadcast signal in bad weather. You hear irregular static with the occasional crackle and pop; like a bad ham radio signal. Not loud but not completely silent either.

 

Ok, thanks for that reconfirmation.

I know this is tedious on your part but that's the way it is since I am not right there to give you hands on assistance.

Remove the upper board (Channel 1 and Channel 3).
Repeat the same listening test with MASTER VOLUME set to 0.

We are essentially back to where we were at post #63.

 

The next step is I will need to see the components around IC6 in order to identify R73 and R75.



Ok. I have found C44 and R73.

Your next steps (after reporting on post #108) will be to take a short piece of hookup wire and short junction A to junction G shown above.

Conduct same listening tests as before.

 

Same sound. Needed to re-post pictures

 

What was the sound when you short A to G?

What is the sound when you short B to G?

 

Same same. I will probably need to take this up tomorrow but not sure when right now.

 

Ok. When you get a chance, here are three tests, one at a time.

1. Jumper C to G.
2. Jumper D to G.
3. Jumper E to G.

Report the sound for each test. We are looking for no sound, i.e. we are trying to eliminate all noise.

 

C to G = Same
D to G = Same
E to G = Silent

 

So we are back to Q4, 2N5460, and its components, R76, D19, and C48.

Did you already replace Q4 once?
If you remove Q4 does the noise go away?
Have you replaced C48, 47μV/35V?

 

I'm thinking it must be the Q4 because when I removed it and played through the amp it was quiet.
I could not believe it was playing without Q4. I just thought I'd try it and was pleasantly surprised.

The bad news is I checked with Arrow but when that part # comes up it says discontinued. I wonder
what JFET I could replace it with? Arrow did have the spec sheet but I didn't see they offered an
equivalent.

 

If you were to look back at post #63 I did identify Q4 as a #1 suspect.
In post #71 I pointed out that Q4 has nothing to do with the quality of the sound. Its only purpose is to mute the sound during the power up duration.

You have a couple of options.

1. You can run the amp without Q4 installed.
2. You can find a substitute for 2N5460 which is a P-channel FET. Try NTE326

https://www.arrow.com/en/products/nte326/nte-electronics

 

This thread is like watching a high tech procedural TV show! Mesmerizing.

 

Thanks again MrChips, I went ahead and ordered a couple of these but of course I will ditch'em if the noise comes back
after I install it. I'd rather give it to the next person though as close to what the schematic says. Maybe I will make one last report
after that happens. Cheers.

 

Sadly, I need to report that the part I ordered to replace Q4, just made it noisy again. So I'm ditching the NTE326.
Maybe the resistors and caps that MrChips had me install, is the fix that Crate was searching for; because
it is very quiet.... even up loud. Great fix, great help.... Thank you.

P.S. Mr.Chips, I suppose you already know that I have one more amp (only 1), that I am dinking with. If you ever have the time,
I sure could use as much advice as I can get. Joe Jester is doing a great job of course, but our comments back and forth
are very slow. * He probably has a regular job or something. Lol...