I have a high gain build that functions perfectly, but I noticed it squeals more at high gain volume settings than my band mate's Mesa Boogie Dual Rectifier with same guitar and cab.
I'm certain it's an interaction between the pickups and amp. The squeal/feedback changes when I move, only happens with high gain and volume settings and goes away when the volume is turned down on the guitar. It also changes in intensity with various pickups.
Also, if I do any reamping, running guitar tracks from the computer there's no feedback (since I'm removing the pickups from the equation). There is also no squeal if I run into a dummy load and listen via the line out and headphones.
I'm wondering if this is a matter of my amp having more gain than the Mesa (it very well may), or if lead dress can alter the relationship between the pickup and amp. I'd like to fully understand the relationship before I go tearing up my amp.
Thanks for any advice on the topic.
Dealing with pickup squeal at the amp.
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Cliff Schecht
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Re: Dealing with pickup squeal at the amp.
Need more info on the guitar and pickups. What cables are you using? Is the potting on the pickups OK?
The Dual Rectifier is pretty high gain but is a well controlled and pretty heavily band-limited gain. IME it's a very controlled gain and of course they'll feed back, but at that point you're probably running more gain than necessary.
The input of your amp could be more wide-open (bandwidth-wise) and much pickier about the pickups, cords, connector quality and even the material of anything near the pickup (screws, springs and the infamous ferrous Tele bridge plates). Maybe give us more info on your build as well. We can only give general observations/experiences if we don't know what you are dealing with specifically.
I will say that my main Tele was a nightmare with high gain amps until I switched the bridgeplate from chrome plated crap steel to a non-ferrous stainless steel bridgeplate. Immediately solved all of my issues. Before I would feed back with ANY pickup I had in there, afterwards it was dead quiet (although this also sort of neuters a Tele's twang, but there are ways around that too
).
The Dual Rectifier is pretty high gain but is a well controlled and pretty heavily band-limited gain. IME it's a very controlled gain and of course they'll feed back, but at that point you're probably running more gain than necessary.
The input of your amp could be more wide-open (bandwidth-wise) and much pickier about the pickups, cords, connector quality and even the material of anything near the pickup (screws, springs and the infamous ferrous Tele bridge plates). Maybe give us more info on your build as well. We can only give general observations/experiences if we don't know what you are dealing with specifically.
I will say that my main Tele was a nightmare with high gain amps until I switched the bridgeplate from chrome plated crap steel to a non-ferrous stainless steel bridgeplate. Immediately solved all of my issues. Before I would feed back with ANY pickup I had in there, afterwards it was dead quiet (although this also sort of neuters a Tele's twang, but there are ways around that too
).Cliff Schecht - Circuit P.I.
Re: Dealing with pickup squeal at the amp.
Thanks a lot for the response, Cliff. The particular guitar is an SG with potted PAF style pickups. With every guitar the interaction with the amp is worth with my amp than the Mesa, which is why I chalked up to the amp.
My amp is a modded 4 gain stage SLO style amp (as is the Mesa), but I think mine may have a bit more gain. The feedback only becomes unruly with the potted pickups with the gain past 1 o'clock and the master up to stage volumes, whereas the Mesa is controllable all the way up.
Don't get me wrong, I can get the Mesa to squeal/feedback too, but mine is not really controllable at a certain point regardless of the guitar or where I stand (unless I leave the room with a really long cable).
My amp has a 10K grid stop and a 150p cap to ground as well to simulate a larger grid stopper (as Merlin suggests in his book). I recently just tried a 10p cap from the first stage anode to grid, but that didn't make a difference.
My amp is a modded 4 gain stage SLO style amp (as is the Mesa), but I think mine may have a bit more gain. The feedback only becomes unruly with the potted pickups with the gain past 1 o'clock and the master up to stage volumes, whereas the Mesa is controllable all the way up.
Don't get me wrong, I can get the Mesa to squeal/feedback too, but mine is not really controllable at a certain point regardless of the guitar or where I stand (unless I leave the room with a really long cable).
My amp has a 10K grid stop and a 150p cap to ground as well to simulate a larger grid stopper (as Merlin suggests in his book). I recently just tried a 10p cap from the first stage anode to grid, but that didn't make a difference.
Re: Dealing with pickup squeal at the amp.
Is the amp in a head shell or just a bare chassis wandering about?
Are you using a sheilded bottom?
Miller cap?
One of my amps does this to a degree, when I have it upside-down in a cradle to mod or work on something and I'm close to it with my guitar. (With all its guts exposed) Right side up, I can get right up on it with the guitar and no squealing feedback. This amp also has a 10k stopper.
Perhaps try using a sheilded plane if you haven't already?
Are you using a sheilded bottom?
Miller cap?
One of my amps does this to a degree, when I have it upside-down in a cradle to mod or work on something and I'm close to it with my guitar. (With all its guts exposed) Right side up, I can get right up on it with the guitar and no squealing feedback. This amp also has a 10k stopper.
Perhaps try using a sheilded plane if you haven't already?
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Cliff Schecht
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Re: Dealing with pickup squeal at the amp.
Shielded wire might help and is a better suggestion than what I was going to mention (band-aids - essentially strapping some capacitance across the preamp plate resistors to reduce high frequency response). My suggestion will quite literally neuter an amp however, especially when you get to the point where you are filtering higher order harmonics. Post some pics of the amp, I'm doubting it's your guitar that's the issue now.
Have you tried running say 40ft or more of guitar cable? That will attenuate quite a bit of highs and the impedance of the coax will usually help reduce tendency to feed back.
Also most high gain amps feed back horribly when you float the input connector instead of grounding it when nothing is plugged in. Maybe you have a weak ground connection at the input jack or near that area that is causing excessive sensitivity (when a cable is plugged in).
Have you tried running say 40ft or more of guitar cable? That will attenuate quite a bit of highs and the impedance of the coax will usually help reduce tendency to feed back.
Also most high gain amps feed back horribly when you float the input connector instead of grounding it when nothing is plugged in. Maybe you have a weak ground connection at the input jack or near that area that is causing excessive sensitivity (when a cable is plugged in).
Cliff Schecht - Circuit P.I.
Re: Dealing with pickup squeal at the amp.
Thanks for the replies. The amp is in a shielded head cab and all grids have shielded cable.
I'm really curious how the amp is exactly interacting with the pickups. Is it about gain, shielding, cross-talk between in phase stages? I figured if I could really understand the relationship I could trouble-shoot/redesign my amp in a smart way and learn a bit about high gain design.
I haven't been able to find any info on why one amp might do this more than another besides gain level. My question is really: Is there anything in two amps with the same gain level that could cause one to make a pickup squeal more than another?
I'm really curious how the amp is exactly interacting with the pickups. Is it about gain, shielding, cross-talk between in phase stages? I figured if I could really understand the relationship I could trouble-shoot/redesign my amp in a smart way and learn a bit about high gain design.
I haven't been able to find any info on why one amp might do this more than another besides gain level. My question is really: Is there anything in two amps with the same gain level that could cause one to make a pickup squeal more than another?
Re: Dealing with pickup squeal at the amp.
Here's the schem as it is now. Only difference is I have a 470p across the 2nd stage's plate resistor as well.
The switch that switches the 2nd stage's cathode cap and 3rd gain stage is on a mini DPDT.
The switch that switches between clean and OD in the preamp is a DPDT after the first and 2nd/3rd stages depending on the other switch's position.
When the 3rd stage is switched in, the DPDT is shared by two stages that are in phase with one another (the 1st and 3rd). Could the two in phase signals in close proximity in the relay have anything to do with the pickup squeal?
The switch that switches the 2nd stage's cathode cap and 3rd gain stage is on a mini DPDT.
The switch that switches between clean and OD in the preamp is a DPDT after the first and 2nd/3rd stages depending on the other switch's position.
When the 3rd stage is switched in, the DPDT is shared by two stages that are in phase with one another (the 1st and 3rd). Could the two in phase signals in close proximity in the relay have anything to do with the pickup squeal?
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Cliff Schecht
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Re: Dealing with pickup squeal at the amp.
So you are dealing with a pretty sensitive, wide open input stage. You might just have a lead that need to be moved, maybe in the tonestack or early in the preamp. Think Express, I know it's not that platform but it's the same lineage in a lot of ways. My Express will flat out scream at me still if I turn up the treble and mids past a certain point regardless of the guit-fiddle I put in there. That's good and great for getting the "on the verge of exploding" sound but it makes for an amp that is VERY sensitive to coupling between the leads. Enough with the teasers already, post some pics of the amp!! I wanna see it!! 
Cliff Schecht - Circuit P.I.
Re: Dealing with pickup squeal at the amp.
Haha, yeah I won't be able to try anything on the amp til this weekend which is over at the practice space. I was just trying to do some research, and like I said really understand the relationship between the pickups and amp.
I want to reiterate that the amp is very stable with no guitar plugged in. I can turn the master and gain all the way up with only hiss. The squeal also varies from pickup to pickup (my Dimarzios are the quietest), with guitar volume, and where I physically stand in relation to the amp. The amp is not feeding back by itself. The feedback only happens with high volume settings, and when the gain is cranked. It actually seemed totally normal to me until I played my friend's Mesa.
Speaking of, the Mesa has an even more wide open input stage, so I think we may be barking up the wrong tree there.
Some things I tried last weekend were increasing the grid stop at the input stage and putting a plate bypass on the input stage, but there was no change. I've also tried cutting high end elsewhere and that really only effects tone of the feedback, not the intensity.
All this makes me wonder if I simply have more gain than the Mesa or if there is some lead dress issue I am missing and am getting some positive feedback at a certain gain level. If that were the case, wouldn't that manifest itself when reamping or running into the dummy load, or even with the preamp cranked and master low?
Sorry for rambling, but I'm really trying to understand what could fundamentally cause increased pickup squeal from one amp to another.
I want to reiterate that the amp is very stable with no guitar plugged in. I can turn the master and gain all the way up with only hiss. The squeal also varies from pickup to pickup (my Dimarzios are the quietest), with guitar volume, and where I physically stand in relation to the amp. The amp is not feeding back by itself. The feedback only happens with high volume settings, and when the gain is cranked. It actually seemed totally normal to me until I played my friend's Mesa.
Speaking of, the Mesa has an even more wide open input stage, so I think we may be barking up the wrong tree there.
Some things I tried last weekend were increasing the grid stop at the input stage and putting a plate bypass on the input stage, but there was no change. I've also tried cutting high end elsewhere and that really only effects tone of the feedback, not the intensity.
All this makes me wonder if I simply have more gain than the Mesa or if there is some lead dress issue I am missing and am getting some positive feedback at a certain gain level. If that were the case, wouldn't that manifest itself when reamping or running into the dummy load, or even with the preamp cranked and master low?
Sorry for rambling, but I'm really trying to understand what could fundamentally cause increased pickup squeal from one amp to another.
Re: Dealing with pickup squeal at the amp.
Are your PAF pickups waxed?
It is normal that high gain amps with high volume levels will squeal.
Recto has lots of high end cutoff in preamp and poweramp too, this is why it squeals way less.
It is normal that high gain amps with high volume levels will squeal.
Recto has lots of high end cutoff in preamp and poweramp too, this is why it squeals way less.
Re: Dealing with pickup squeal at the amp.
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Last edited by matt h on Fri Mar 27, 2015 3:57 am, edited 1 time in total.
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Cliff Schecht
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Re: Dealing with pickup squeal at the amp.
Nice point with the PCB amps. That eliminates the conductors themselves (wires) cross-coupling and making unwanted sound. Silver mica and ceramic capacitors are notorious for singing if not dampened properly. Might be something you need to chopstick with the guitar plugged in and the amp on the verge of breaking into oscillation. Might give you some insight into what is working so hard to oscillate.
Cliff Schecht - Circuit P.I.
Re: Dealing with pickup squeal at the amp.
theres some common causes of these things - try these...
1) microphonic pre-amp tube
2) oscillation - lead dress issue
3) inductive capicitance - think TW and wires running parallell and too close
band aids:
- small pf cap on PI plates (aka fender)
- larger grid stopper
- wire wrap/shielding (aka TW)
my take - from your description its not the guitar, its the amps lead dress. High gain amps are difficult to build for a reason, and this is it!
1) microphonic pre-amp tube
2) oscillation - lead dress issue
3) inductive capicitance - think TW and wires running parallell and too close
band aids:
- small pf cap on PI plates (aka fender)
- larger grid stopper
- wire wrap/shielding (aka TW)
my take - from your description its not the guitar, its the amps lead dress. High gain amps are difficult to build for a reason, and this is it!
it really is a journey, and you just cant farm out the battle wounds
Re: Dealing with pickup squeal at the amp.
Are you comparing your amp and the Mesa with the same speaker cab?
The response of speakers have numerous peaks and troughs; my understanding is that the charts we're used to seeing have had averaging / smoothing applied, and even then they're all over the place.
Then combine that with the peaks / troughs that will inevitably result if there's multiple drivers in the cab, due to phase cancellation / lobing.
Then add in room effects, reflections from hard surfaces etc.
Unless all relevant significant variables other than the item in question are eliminated, then the comparison may be questionable.
Pete
The response of speakers have numerous peaks and troughs; my understanding is that the charts we're used to seeing have had averaging / smoothing applied, and even then they're all over the place.
Then combine that with the peaks / troughs that will inevitably result if there's multiple drivers in the cab, due to phase cancellation / lobing.
Then add in room effects, reflections from hard surfaces etc.
Unless all relevant significant variables other than the item in question are eliminated, then the comparison may be questionable.
Pete
My band:- http://www.youtube.com/user/RedwingBand
Re: Dealing with pickup squeal at the amp.
Thanks for all the replies.
First, when comparing, the only thing that changed was the amp. My amp fedback easier at various settings in comparison to the Mesa.
Everyone keeps asking about my pickups as well, and what I was trying to say is that with any given pickup/guitar, my amp fedback more than the Mesa. My Dimarzio Super 3's were the least susceptible likely because they have the best potting. 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.
So, yes the problem is pickup squeal, but I'm wondering if there is anything that can be done to abate it besides lower the gain (which is the only thing that has worked so far). That's why I keep wondering about have two in phases signal sharing the same DPDT relay, and the input stage (since it's connected to the pickup).
The amp's not oscillating or anything like that. I think I could probably get away with less gain actually, but I'm just not sure where the smartest place would be to bring it down. After comparing the schems some more, I I'm pretty sure my amp just has more gain in the preamp with the 10K cathode resistor.
First, when comparing, the only thing that changed was the amp. My amp fedback easier at various settings in comparison to the Mesa.
Everyone keeps asking about my pickups as well, and what I was trying to say is that with any given pickup/guitar, my amp fedback more than the Mesa. My Dimarzio Super 3's were the least susceptible likely because they have the best potting. 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.
So, yes the problem is pickup squeal, but I'm wondering if there is anything that can be done to abate it besides lower the gain (which is the only thing that has worked so far). That's why I keep wondering about have two in phases signal sharing the same DPDT relay, and the input stage (since it's connected to the pickup).
The amp's not oscillating or anything like that. I think I could probably get away with less gain actually, but I'm just not sure where the smartest place would be to bring it down. After comparing the schems some more, I I'm pretty sure my amp just has more gain in the preamp with the 10K cathode resistor.