High-pitched squeal from amp - with gain and volume

[RVA]

Mates,

There are a fair amount of threads on this topic out there, but my combo of circumstances is a bit different, so I thought I would ask.

I have a loud, whistling-type, constant feedback when on the clean channel and using high gain pedals
- when there is medium to high gain
- with high volume for this 20W amp
- that is NOT reduced by turning the guitar volume all the way down
- that is NOT reduced by walking approx 25 feet away
- that is NOT reduced by touching the strings
- that DOES breifly go away when actually attacking the strings while playing
- that DOES go away with amp volume reduction (either master or channel)
- it DOES reduce when I turn off delay and reverb

The pickups were stacked Tom Anderson P90s and they are generally dead quiet. The noise does not change when pickups are split or both coils.

It seems that the simple answer would be that it is not the guitar and that this amp simply feeds back with gain pedals at high volume. A less likely thought would be that one or more of the preamp tubes are microphonic.

It is preventing me from using some of my favorite pedals at higher volumes. Any help is greatly appreciated.

 

[DonP]

Tentative diagnosis would be a microphonic valve.

 

[RVA]

Tentative diagnosis would be a microphonic valve.

Thanks. I will do some tapping and swapping.

 

[syscokid]

Which amp?

Thanks. I will do some tapping and swapping.

Besides tapping, gently rock the tubes with a swirly action in their sockets.

 

[RVA]

Which amp?


Besides tapping, gently rock the tubes with a swirly action in their sockets.

The ceriatone I recorded yesterday. As you can hear from those clips, the amp without pedals or with moderate OD is fine. I tried to apply some fuzz and it went ballistic!!While I expect feedback from high gain, it was quite surprising that the squeal occurred when the guitar volume was at zero and regardless of distance from the amp.

 

[syscokid]

Does the feedback happen with any dirt pedal that's heavy on the gain?

Are you testing with just one pedal plugged in at a time?

 

[RVA]

Does the feedback happen with any dirt pedal that's heavy on the gain?

Are you testing with just one pedal plugged in at a time?

I tested a variety of high gain pedals alone and together with the same ear-piercing result. The squeal does not vary. The only way to alleviate it is with a volume reduction on the amp or a significant volume and/or gain reduction on the pedal(s), and then every pedal is usable.

 

[DonP]

What happens if you don't plug anything in? Are there any amp settings that will make it squeal all by itself?

 

[RVA]

What happens if you don't plug anything in? Are there any amp settings that will make it squeal all by itself?

With the guitar "unplugged" (actually, I shut the wireless), the result is the same. I had the amp pretty loud and never had anything approximating this noise, which is a loud, constant, mono-tone, high-pitched squeal which is consistent in volume

 

[DonP]

OK, if you've eliminated microphonic valves, the next suspects are capacitors. What exactly is the amp? I'll dig up a schematic.

 

[DonP]

Next question. Which controls will change or stop the noise when you turn them?

 

[RVA]

Next question. Which controls will change or stop the noise when you turn them?

Any volume related knob on the amp..Volume, Level, Master Volume. I did not mess with the OD trim in the back since it is subtle and difficult to access. I have attached a manual and schematic.

Thanks

 

[RVA]

OK, if you've eliminated microphonic valves, the next suspects are capacitors. What exactly is the amp? I'll dig up a schematic.

I have not messed with them yet, but I will tonight

 

[DonP]

Did you say the amp is much louder, with more gain than you would expect?

 

[DonP]

OK. One really useful test. Can you plug your guitar into the effects loop return socket? I know it's the wrong place, but it effectively disconnects the whole front end, letting us eliminate or implicate that.

 

[DonP]

My focus has shifted to these parts

 

[RVA]

Did you say the amp is much louder, with more gain than you would expect?

No, the amp is very predictable except for this. The volume of the squeal is consistent with the volume of the amp at the time of the issue.

 

[RVA]

OK. One really useful test. Can you plug your guitar into the effects loop return socket? I know it's the wrong place, but it effectively disconnects the whole front end, letting us eliminate or implicate that.

I will do that, into Send I presume. I am not in front of it at the moment (at work unfortunately)

 

[DonP]

ok. and it is still there with the master volume at zero?

 

[RVA]

My focus has shifted to these parts
View attachment 25043

is that presence? I did not notice a change when this was manipulated

ok. and it is still there with the master volume at zero?

No, volume reduction at the amp eliminates the issue (master, channel - and level or ratio if OD channel is selected). So I can only use the pedals at low volumes, otherwise I get the steady, consistent squeal (as opposed to "feedback that can be manipulated)