last problem i hope, awful- awful squealing when dimed.

[cooldude666]

I'm trying to debug the final issue with this build. It's got an awful awful very high pitched squeal when dimed, and guitar at 10. With no guitar plugged in the amp is dead quiet but once it's got a hot signal in it it freaks out. If i turn the treble control down I can filter it out. It seems to be dependent on where I'm standing so I'm really feeling like the source is my guitar (the wiring inside is flipping awful). It's one of those Squier Vintage Modified Jazzmasters.
It's going to be fully rewired once I get some full size 1M pots, but is there anything I can do inside the amp to help filter this noise out for other guitars which may also be rats nests? Thank you!

[Jazz P Bass]

It sounds like feedback to me.

Like a howling microphone.

[cooldude666]

It's present even when strings are muted, and it doesn't get louder amplifying itself like the feedback Im used to. I'm not saying it's not, but I play in bands that are 80% feedback, and this is unfamiliar as feedback.

[eschertron]

It seems to be dependent on where I'm standing so I'm really feeling like the source is my guitar!

Can you try a different cable, or a longer one so you can stand farther away from the amp? Can you try a different guitar?
Once the squealing starts, can you stop it by turning the guitar volume down? Can you make it start up again simply by moving closer to the amp?
You didn't say whether it was the treble control on the guitar or the amp you turned down to stop the squeal. Either/or?

I've seen guitar pickups that were microphonic to beat the band, but I'd lay odds on some parasitic oscillations in the amp being the sound source. Eliminating the guitar as the culprit would go a long way to discovering the problem. Finding out that for certain that it is the guitar would be even better

Some amps are supposed to get their golden sound by being on the verge of out of control all the time. Maybe you’ve designed one of these amps? Try chopsticking the amp to see if the squeal is controllable. Also, try putting a 220pF or 500pF cap across grid to ground in front of the first or second stage. Just temporarily, with jumper cables. This can dampen parasitic oscillations at that stage. Any change?

[cooldude666]

If I turn the guitar's volume down, usually just a tiny bit, the squealing stops. In my post I meant that if I turn the treble control on the amp down (not necessarily all the way) I can make it stop. However the guitar's tone knob, turned to 0 has the same effect.

I just ripped apart my guitar to rewire it. After having it open to shield it I couldn't live with the wiring harness inside. It was a thing of nightmares. Once I get this done I'll be back with reports of the experiments you suggested I try.

[Jazz P Bass]

I am not aware of the initial post on this amp.

Does the amp have a negative feedback circuit?

I am wondering if the output transformer primary isn't wired for positive feedback.

[Chuck H]

Your pickups are probably squealing. Even with the strings muted the pickup coils can still vibrate sympathetically. It's pretty common. The pickups are the only thing you remove from the equation when trim the volume on your guitar, so I'm going with pickups. You could "pot" them. Not too hard, but if you've never done it and you're really fond of the pickups maybe better to have it done. Less risk of a mistake causing permanent damage. A lot of guys on the forum could handle it.

EDIT: Try this, take your guitar in the other room while plugged in. Maybe even shut the door between you and the amp. If that stops the squeal, it's the pickups.

[Leo_Gnardo]

Your pickups are probably squealing. Even with the strings muted the pickup coils can still vibrate sympathetically. It's pretty common. The pickups are the only thing you remove from the equation when trim the volume on your guitar, so I'm going with pickups. You could "pot" them. Not too hard, but if you've never done it and you're really fond of the pickups maybe better to have it done. Less risk of a mistake causing permanent damage. A lot of guys on the forum could handle it.

EDIT: Try this, take your guitar in the other room while plugged in. Maybe even shut the door between you and the amp. If that stops the squeal, it's the pickups.

Not just coils but covers. I've wax-potted various pickups & that stopped the squeal all right, but after putting metal covers back on - started squeeking again. Wax dip again with covers on. Some wax stays between the cover and coil, keeping the metal from flexing and participating in the feedback loop.

Of course it's worst when the pickups are right in front of the speakers. Simply turning around can stop that racket - guitar facing away from the speakers now with a body in the way besides, just like real life.

Beeswax - a little sticky - expensive @ $15-20 a pound but a good solution. And a pound will last a long time. Many pickup dippers (including me) go half & half with ordinary white "paraffin" wax. One slight drawback: when playing outdoors in spring summer or fall, honeybees may fly close to your guitar to check it out.

[big_teee]

If you play loud with lots of gain, you need to pot the pickups with the covers on.
Pot them for 10-15 minutes at 140F degrees.
Drain out all the hot wax that will come out.
If they are historic pickups, I wouldn't pot them but put in potted replacements.
I use Gulf Canning wax, thinned with a little Liquid Parrafin Lamp oil, or mineral oil.
I hear of guys using bees wax, but think that it mostly makes good press, most of us pickup makers don't.
GL,
T

[Chuck H]

Not just coils but covers. I've wax-potted various pickups & that stopped the squeal all right, but after putting metal covers back on - started squeeking again. Wax dip again with covers on. Some wax stays between the cover and coil, keeping the metal from flexing and participating in the feedback loop.

For a time Carvin used a comparably large diameter and thin wire gauge spring for mounting their pickups. I had a problem with the actual springs vibrating and feeding back.

[cooldude666]

Confirmed guitar. It must be those shitty squier pickups, or possibly some microphonics from the vibrato or something. I plugged in my Kramer 250G that has Lollar P-90s and while there's still a lot of hum (that guitar is hella noisey), the squeal is gone. I wanted new pickups in the JM anyway. Suppose now might be a good time to order a set. Thanks ya'll.

[big_teee]

Confirmed guitar. It must be those shitty squier pickups, or possibly some microphonics from the vibrato or something. I plugged in my Kramer 250G that has Lollar P-90s and while there's still a lot of hum (that guitar is hella noisey), the squeal is gone. I wanted new pickups in the JM anyway. Suppose now might be a good time to order a set. Thanks ya'll.

With the guitar plugged into the amp, tap on the pickups, one at a time.
If they have a real hot metallic sound, and when you change the switch, you get hot popping, it wiill be the pickups.
A well potted pickup, you can tap on and get a dull thud.
T

[cooldude666]

I just get a thud sound, but it is confirmed to be feedback/something from the guitar. I can walk around and get it to stop without touching controls. My lady's strat does it on the neck and bridge pickups, and the Kramer I have to put the guitar pretty close to the amp to make it happen. That said, is there anything I can do in the amp to help curb the effect? If I order a set

[Chuck H]

That said, is there anything I can do in the amp to help curb the effect? If I order a set

I wouldn't recommend it. Different guitars will behave differently. If you're going to play at volume you'd best learn to control it. Consider stage positioning compared to a closed room, upgrading pickups to suit the issue, etc. The only cure on the amp end would be to trim top end. Usually in the audio spectrum. The solution is using the best pickups (or those provided in the best guitars) or potting (or having potted) those pickups you can't live without. Being able to recognize and understand the problems of performance and prioritizing to make it a reality is the lynch pin that keeps many players/artists from being professional. JM2C on that.

[Leo_Gnardo]

I wouldn't recommend it. Different guitars will behave differently. If you're going to play at volume you'd best learn to control it. Consider stage positioning compared to a closed room, upgrading pickups to suit the issue, etc. The only cure on the amp end would be to trim top end. Usually in the audio spectrum. The solution is using the best pickups (or those provided in the best guitars) or potting (or having potted) those pickups you can't live without. Being able to recognize and understand the problems of performance and prioritizing to make it a reality is the lynch pin that keeps many players/artists from being professional. JM2C on that.

All that ^^^ what Chuck said, and mostly don't stick the pickups right in front of the speakers.