Dealing with pickup squeal at the amp.

[Tone Lover]

Gaz here is a differant perspective . In Merlins pre-amp book is a section on using a cap to stop fret squeel in high gain amps in essence a .01 cap right at the input on the first triod were your 10k is connected to ground . i used it on a high gain amp to remove the fret squeel that was common in this amp and noticed it helped with feedback also . His reasoning was it dumped highs above what were there usefull to ground . it seems to work for fret squeel.
Bill

[Colossal]

Gaz here is a differant perspective . In Merlins pre-amp book is a section on using a cap to stop fret squeel in high gain amps in essence a .01 cap right at the input on the first triod were your 10k is connected to ground . i used it on a high gain amp to remove the fret squeel that was common in this amp and noticed it helped with feedback also . His reasoning was it dumped highs above what were there usefull to ground . it seems to work for fret squeel.
Bill

Yes, this increases the HF rolloff by increasing Miller capacitance. Try 100-470p to ground connecting directly to pin 2 on V1a. If your pickup is really hot and you want to dump some signal at the input, you can also decrease the 1M grid leak to 470k or even 220k.

Rg = 10k, Cg = 100p
ƒ = 1 / (2pi RgCg)
ƒ = 1 / [6.28 * 10,000 * (100 * 10^-12)]
ƒ = 15.9kHz

[matt h]

(deleted)

[crbowman]

I'm still guessing that you've got a problematic preamp tube or driver tube.

[Gaz]

I'm still guessing that you've got a problematic preamp tube or driver tube.

I've tried swapping the first preamp tube, and it made no discernible difference. Why do you think it would be the driver?

[Gaz]

I have "ruled out" the pickups because this problem does not happen if I play DI tracks from my DAW into the amp, or operate the amp into a dummy load and listen via headphones. It's about the relationship between pickups and amp.

Unless I'm missing something, that just "ruled in" the pickups... not ruled out. There has to be a pickup involved for feedback to occur, right? That you're not having the problem with a DI track tells me that your amp, is in fact, stable.

Is there any correlation between the squeal and the setting of the tone pot on the guitar?

Yes, precisely!!! I must pretty bad at explaining myself because that's what I've been trying to convey since my subject line. The problem is the interaction between the pickups and amp. I really just wanted to know if there were any ideas to reduce this interaction besides using EMGs, a noise gate, or reducing the gain/volume.

The Mesa doing it less under the same circumstances is what prompted my curiosity. I honestly think it's because it has less gain. My 10k cathode resistor on the 3rd stage is a huge jump from the 39k, regardless of the Mesa's bypassed 4th stage.

I think the high-ish value cap to ground is worth a shot, and not something I've tried. I'm just wondering where to ground it? The amp is laid out Marshall style and I have the everything grounded at the input jack. It seems to me like it would be a bad idea (noise-wise) to run a long ground wire all the way back to the input jack from the tube socket, right?

[Reeltarded]

Limit the treble pot to around 120k.. That won't help the sqeeky mess, bit still. Try that!!

Pot your pickups. I just had a big argument with dimarzio over 5/6 squealers.

[matt h]

(deleted)

[steveneddy]

This sounds silly - but have you tried shielding the guitar better - with actual foil and everything is grounded properly.

Case in point - kid complains of feedback squeal in his newly built amp. I go through it several times and just can't duplicate the complaint.

I ask him to bring his "Les Paul" in and let me test it with his guitar.

He brings in an Epiphone Les Paul - the $150 model.

After testing I removed all of his wiring - shielded all of the cavities - installed high quality coax between switch and pots - ensured all pots soldered well. Also ensured all grounds were bulletproof.

Finally U made him a new coax cable from guitar to amp out of Mogami 2524 and Neutrik ends. Problems were solved.

YMMV - ensure the guitar is totally ready for those volumes and gain levels.

I love building clean blues amps - but most of my customers are metal heads - I have found through trial and error that the guitar/cable interaction with the amp is very important.

Any stray RF or odd frequency can set an amp off that is on the verge of instability anyway.

My .02

[pdf64]

Finally U made him a new coax cable from guitar to amp out of Mogami 2524 and Neutrik ends. Problems were solved.

That stuff is 130pF/m = 40pF/ft
Quite high capacitance for modern instrument cable and so will load a significant capacitance on to the PUs / roll off more treble than a good commercial Planet Waves etc type.

Nothing wrong with that - whatever works and sounds good, is good.

Just drawing attention to the item that may have had the most significant impact on solving the issue.
Pete

[Structo]

Please!

Just stop playing electric guitars!

All will be revealed later.

But really, just adjust your pickup heights....

[Gaz]

Please!

Just stop playing electric guitars!

All will be revealed later.

But really, just adjust your pickup heights....

What are you talking about?

[bruce egnater]

Is the "squeal" a steady tone or does it change when you move around/away from the speakers? Does the frequency of the squeal change when adjusting the guitar volume knob?

[Gaz]

Is the "squeal" a steady tone or does it change when you move around/away from the speakers? Does the frequency of the squeal change when adjusting the guitar volume knob?

Thanks Bruce. Yes and yes.

[bruce egnater]

Can you record/demonstrate this and email to me at begnater@aol.com? Trying to help determine if the problem is the amp or pickup squeal.