Blues Junior Buzz

[PaoloJM]

Hi guys,

I've got a Fender Blues Junior that has a buzz riding on each note.

There is no buzz when unless you're playing, it does not occur while your guitar is silent but turned up.
The noise sounds remarkably similar to the sound you get when you over-drive a cab IR loader with a amp sim on a computer. I sometimes use LePous Lecto with the IR loader in ReValver and having the signal too hot from the LePou plug produces a very similar noise.
The buzz occurs at clean and dirty settings and is not affected by any of the amps controls.

I've tried different guitars, different locations, different cables, double checked each screw on the chassis, Cleaned the valve sockets and plugs, changed the valves with known good ones (from a different amp), tried it with different speakers, removed the power valve retainer, chop stick tested each component, replaced the main filter cap and inspected the others, changed the coupling caps. None of these have shown any faults or produced any results.

Has anyone had a similar problem to this?
Can anyone think of anything else to try other than what I've already mentioned?
Is it time to start re-flowing the solder on every joint? There are no obviously cracked ones but I guess they don't always make themselves obvious!!

Help would be really appreciated.

[52 Bill]

I've seen bad filter caps in the preamp section cause this. Try temporarily adding a new cap in parallel across an existing one and see what happens. This way you don't need to pull the board and replace them until you know that it is a bad cap causing the problem.

[PaoloJM]

I've seen bad filter caps in the preamp section cause this. Try temporarily adding a new cap in parallel across an existing one and see what happens. This way you don't need to pull the board and replace them until you know that it is a bad cap causing the problem.

Cheers, thanks for the quick replay.
I'll give it a go. I did inspect them and founding no signs of leaking or bubbling. Could they still be faulty?

I've a few 350Vdc 22uF caps around. They should be fine as B+ is only around 334Vdc on this amp anyway.
Do you think it would be too risky to use them as a permanent replacement if they do turn out to solve the problem? They're F&Ts and so should be decent quality.

[jpfamps]

I've had several Blues Junior that oscillate, usually around 50 kHz.

In the worst cases this blocks any audio signal passing, but can also cause a nasty modulation of the audio.

The problem is caused by poor lead dress due to the wires from the anode to the output transformer running too close to the grid wires (which are in the first grey ribbon cable on the left as you look at into the back of the amp).

With a chopstick, try moving the ribbon cable into the corner, away from the anode wire (blue).

If you have a 'scope you should can monitor the oscillation.

[Enzo]

Um... hook up a different speaker to the amp and see how that sounds. YOu could be describing a voice coil rubbing.

[Bruce / Mission Amps]

I'm with jpfamps... I've never had one in for repair, tubes, speaker or a mod that didn't self oscillate at some annoying frequency causing all kinds of crap noise ... or at the very least, use up 3-5 watt of power tube energy at frequencies you can't hear and the speaker doesn't reproduce!
Those ribbon cables and tranny leads are all messed up creating this problem.

[PaoloJM]

Um... hook up a different speaker to the amp and see how that sounds. YOu could be describing a voice coil rubbing.

Yeah, I tried that but no joy.

tried it with different speakers

[PaoloJM]

I'm with jpfamps... I've never had one in for repair, tubes, speaker or a mod that didn't self oscillate at some annoying frequency causing all kinds of crap noise ... or at the very least, use up 3-5 watt of power tube energy at frequencies you can't hear and the speaker doesn't reproduce!
Those ribbon cables and tranny leads are all messed up creating this problem.

During my chop stick testing I did try moving them about but it didn't seem to affect the problem in any way.
I'd have expected some change if that was the cause, would that be right?

[PaoloJM]

I've had several Blues Junior that oscillate, usually around 50 kHz.

In the worst cases this blocks any audio signal passing, but can also cause a nasty modulation of the audio.

The problem is caused by poor lead dress due to the wires from the anode to the output transformer running too close to the grid wires (which are in the first grey ribbon cable on the left as you look at into the back of the amp).

With a chopstick, try moving the ribbon cable into the corner, away from the anode wire (blue).

If you have a 'scope you should can monitor the oscillation.

I've just done this and there's no change.
I reinspected the preamp filter caps, no sign of problems and this is not a 50Hz/100Hz problem.

Anyone got any other ideas?

[PaoloJM]

I've since replaced the filter capacitors to double check, no joy.
The buzz still rides on the notes.

I'm stumped.
Can anyone think of anything else, or is it time to blindly start re flowing all the solder joints?

[ChangeYourPickAttack]

Same problem here, tried re-soldering the entire board too - it got worse! I'll post when I find (staying optimistic) the issue.

[jmaf]

Same problem here, tried re-soldering the entire board too - it got worse! I'll post when I find (staying optimistic) the issue.

Maybe you oughta create a new thread for your issue, it'll get better visibility that way...

[PaoloJM]

Maybe you oughta create a new thread for your issue, it'll get better visibility that way...

The problem with the amp I have has still not gone away.
Seems like re-flowing the solder wont be the answer either.

Anyone else experience anything like this?

[Jazz P Bass]

Exactly what test equipment do you have at your disposal.
A signal generator, a scope & a dummy load is what is needed.
If you have this equipment, then you can narrow down the problem.
Such as:
What frequency is the noise.
What circuit is it involved in.
Is the power supply exhibiting the issue.
Is it a global problem.

[ChangeYourPickAttack]

Actually, I think I got it after re-soldering the entire board the other day and checking every single component. There was one bad resistor somewhere in the preamp (don't even remember where and most likely had nothing to do with the noise).

The noise that was on the end of the notes is gone, there is the minor tube rattle and cabinet vibration but that is gone when plugged into a better speaker cabinet.

PaoloJM, I would really recommend just re-soldering the boards, you never know what you might find and it can't hurt it any. Also, when reassembling, make sure the transformers and any other hardware is tight. Good luck.