Help! Massive squeeling and feedback in HBE mode.

[Blackie08]

Dave,

I bought a JCM800 2203 Reissue that you had modded for somebody a while ago. It has BE,HBE,JBE,SAT,C45,MODERN,FULL Clean, dual footswitchable masters/gains and a marsha OT. The HBE mode is on a toggle switch. My problem is if im in HBE mode with the gain at more than say 12:00, i get some serious squeeling and feedback. I have replaces the HBE tube and still it continues... Is this normal to have that kinda feedback with the gain at say 3/4 in HBE mode?? Here is the amp in question

Thanks,

-Dustin

 

[charveldan]

No, not normal.

 

[mikehickey]

could be microphonic pickups, that would be my first thought.

 

[charveldan]

could be microphonic pickups, that would be my first thought.

I had one do that, i wax-potted it, that helped.

Blackie are you playing a guitar with covers over the pick-ups?

 

[Blackie08]

could be microphonic pickups, that would be my first thought.

I had one do that, i wax-potted it, that helped.

Blackie are you playing a guitar with covers over the pick-ups?

nope. guitar is a Charvel So cal pro-mod with the stock non covered pups. (evo neck, ToneZone bridge)

If it was a microphonic pup, wouldn't it squeal with the gain dimed in BE mode as well???

 

[Blackie08]

Just tried it with my dimarzio area loaded strat. same thing happens in HBE. Gain at 12:00 = no noise, gain dimed=massive feedback/squeeling/hissing....

 

[RACKSYSTEMS]

Squealing with the guitar on or just by itself? The HBE is high gain how close are you to the amp?

 

[londaxe]

While I can't speak for Dave, just thought I'd throw this out there. Did you replace V1? (not sure what one that is - usually it's on the far left, but I see your amp is setup differently)

I assume that affects the whole amp, so maybe it only squeals in HBE because that's much higher gain?

 

[Blackie08]

Squealing with the guitar on or just by itself? The HBE is high gain how close are you to the amp?

You can hear the faint hiss by itself that most high gain amps have with the guitar vol off, then it becomes more apparent as u turn up the volume on the guitar, im probably 5-10 ft away from the amp.

 

[Blackie08]

While I can't speak for Dave, just thought I'd throw this out there. Did you replace V1? (not sure what one that is - usually it's on the far left, but I see your amp is setup differently)

I assume that affects the whole amp, so maybe it only squeals in HBE because that's much higher gain?

Maybe dave can shed some light on to where V1 actually is ( i thought V1 was the furthest to the right and the HBE tube was in the back on the left). I put a new tube in V1 and swapped the old V1 tube with the HBE tube...

 

[steve_k]

Every modded Marshall I own from various chop shops will squeal like a stuck pig with the gain dimed and especially those with as much gain as the HBE circuit. While I can't imagine playing with the gain more than around 1:00 or needing too, it is something to contend with. If you need to play with the gain that high, I would suggest a 30' cable and face the opposite direction of the amp and let someone fiddle with the settings while you play and find where you like it. My Marsha was this way and I fully expect the KS to be that way when it arrives.

Also, you really need to know the tube assignments. Different modders do it different ways when a tube is added. Some will move the input to the new tube position, and some will leave it as is. With most Marshall's and their mods, there will be a cathode follower tube and you need to differentiate this from the rest when changing tubes. Call or email Dave so he can advise you of the positions or look under the chassis and follow the circuit. Also, a good high gain tube will be better in the HBE spot and V1, something like a Ruby HG+ or some Gen 8 Chinese tubes. A good strong, balanced PI tube helps too when running full on.

Steve

 

[glip22]

I would swap all the pretubes just to see. Also it probably won't make a difference, but when I had my Dave modded JMP with HBE, I shorted the unused half of the added tube's Plate, Grid and Cathode with a piece of bus wired soldered to the pins. This did make it quieter and eliminated the slight hum I had. I would also make sure none of the input jacks leads were touching and that the lead wire going to the first pretube was done with shielded wire. Mine was but I am not sure they all were.

 

[RACKSYSTEMS]

Hbe tube is the one to the left closest to the back panel. Sounds to me like you are just getting pickup noise in the room you are in.

 

[charveldan]

My HBE is pretty quiet, i sent Dave a NOS tube to go with the mods when he did my amp, but that tube was a little noisey, it's been replaced and the amp has no issues.

 

[glip22]

maybe you sitting to close in front the amp while your playing with higher volume. Check the amp with another guitar.

Definietely check that its not pickup noise. Another thing in a room that will cause feedback is if you are playing the amp loud. The sound bounces off of things and goes back into the speakers. This is my problem. I play way to loud for my cave.

 

[Blackie08]

maybe you sitting to close in front the amp while your playing with higher volume. Check the amp with another guitar.

It still happens when I play my dimarzio area loaded strat....

 

[glip22]

maybe you sitting to close in front the amp while your playing with higher volume. Check the amp with another guitar.

It still happens when I play my dimarzio area loaded strat....

Is it happening with the amp volume
lower?

 

[Blackie08]

maybe you sitting to close in front the amp while your playing with higher volume. Check the amp with another guitar.

It still happens when I play my dimarzio area loaded strat....

Is it happening with the amp volume
lower?

The amp is only on about 2...but yes it does occur when it is lower then that..

 

[Blackie08]

it sounds like the howling in this vid around 2:00..

 

[glip22]

it sounds like the howling in this vid around 2:00..

Yes the amp must have an issue