5E3 whistling noise until warmed up

[rdh006]

Do you have a scope?

No, 'fraid not -- just a humble multi-meter.

[The Dude]

If you don't have a scope, try pulling V1. See if the noise goes away. If not try V2. See if you can at least isolate what stage the noise is coming from.

[rdh006]

If you don't have a scope, try pulling V1. See if the noise goes away. If not try V2. See if you can at least isolate what stage the noise is coming from.

Pull V1 = noise still there, unchanged
Pull V2 = all noise gone

[dstrat]

do you have a schematic or what did you build the amp from?

[nickb]

The Normal volume has little effect on the noise.
The Bright volume has much more effect on the noise.
The volume controls are somewhat interactive on this amp which confuses the issue to some degree.
The noise goes away altogether with the tone control turned down -- but then the whole amp is shut off anyway.


If I allow it to warm up, turn off and then on again, it is the same before and after -- the noise is still there, to the same degree, as far as I can tell. If I turn it off and back on while the noise is there, the noise is still there. If I turn it off and back on while the noise is gone, the noise is still gone.

Thanks for helping.

OK quick test - try subbing the 0.1uF coupling cap in the bright channel.

[rdh006]

do you have a schematic or what did you build the amp from?

I built the amp from the layout provided by Bruce at Mission amps, which I can't post. However, the amp is basically the original 5E3 circuit as shown on the Fender schematic and layout which is out there on the internet. I'll find a link when I have some spare time later today.

[rdh006]

OK quick test - try subbing the 0.1uF coupling cap in the bright channel.

Thanks -- I'll try that a little later today.

[rdh006]

I built the amp from the layout provided by Bruce at Mission amps, which I can't post. However, the amp is basically the original 5E3 circuit as shown on the Fender schematic and layout which is out there on the internet. I'll find a link when I have some spare time later today.

5E3 schematic
https://cdn.instructables.com/F8P/XH...DN7.MEDIUM.jpg

5E3 layout
https://cdn.instructables.com/F4X/D8...DN8.MEDIUM.gif

Some of the component values are slightly different. The filter caps are 22uf and the coupling caps are .047uf

[rdh006]

I changed the coupling cap in the bright channel, as per nickb's post above. Noise appears to be gone. I had been intending to reduce that cap from .047 to .022 to cut a little of the lows, so killed two birds with one stone. The amp sounds great.

Hopefully that's it. Thanks nickb for the fix, and thanks to everyone who helped here. Learned some stuff and got my amp back together -- what more could I ask?

[nickb]

I changed the coupling cap in the bright channel, as per nickb's post above. Noise appears to be gone. I had been intending to reduce that cap from .047 to .022 to cut a little of the lows, so killed two birds with one stone. The amp sounds great.

Hopefully that's it. Thanks nickb for the fix, and thanks to everyone who helped here. Learned some stuff and got my amp back together -- what more could I ask?

Woo Hoo!

[Chuck H]

Woo Hoo!

I hope I'm not the only curious one here... How did that fix the problem and how did you know it would?

[nickb]

I hope I'm not the only curious one here... How did that fix the problem and how did you know it would?

dstrat pointed out the probable general cause in post 12. The test with the controls in post 13 narrowed it to the bright channel. There just the one cap with large DC across it. Plus luck of course

[Mick Bailey]

I just love it when these thinks work out. I'm sitting here smiling - I can't think of any other forum where so much expertise, patience, understanding and care goes into helping someone fix their problem.

[Chuck H]

dstrat pointed out the probable general cause in post 12. The test with the controls in post 13 narrowed it to the bright channel. There just the one cap with large DC across it. Plus luck of course

So do you suppose it was a microphinic cap or a leaky cap. I didn't suspect a leaky cap because it's a newer amp and I didn't suspect a microphonic cap for the same reason. I don't think I've ever seen a newer microphonic film cap. Anyway, this is something I wouldn't have caught for a while longer yet. So good instincts.

[rdh006]

I just love it when these thinks work out. I'm sitting here smiling - I can't think of any other forum where so much expertise, patience, understanding and care goes into helping someone fix their problem.

Amen to that. You guys are brilliant. I used the amp at a gig last night -- no issues and the amp sounded great.