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everytime I use a fuzz, it effs up my amp???

ruger9

Silver Supporting Member
Messages
9,415
Everytime I use a fuzz (not an OD,boost, or distortion), it seems to F up my amp... the amp loses gain, as if I was running a 12AT7 or 5751 in the preamp instead of a 12AX7 (for lack of a better description)...

And I turn the amp off/on, and it's still that way... effed up. If the amp sits awhile, long enough to cool off, it goes back to normal. Only happens with my Analogman Sunface. WTF is going on???

It's a Genz Benz Black Pearl (basically a hot-rodded AC30 design, EL84s).

At first, I thought I had it sussed, after talking with a tech at genz benz... I had been using a sovtek LPS in the V2, half of which is a cathode follower stage, and he recommended I NOT do that tube in that stage, so I replaced it, and all seemed fine. But then again tonight, everything sounded great, I stepped on the SF, which sounded great, and when I turned it off my amp had lost gain. It almost sounds like the power tubes going bad, but I replaced them when this first started, so it's not the power tubes (actually, I have replaced ALL the tubes in the amp, and there's no LPS in there anymore, so I don't THINK the tubes are the issue). Any ideas??? I'm going nuts here!!!!

It's almost like the fuzz is "over driving" (not overdriving) something into partial-temporary-failure?????
 
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TimmyP

Member
Messages
2,484
Is there a lot of HF fizz to the fuzz? If so, perhaps it's causing the amp to break into oscillation.
 

phsyconoodler

Member
Messages
4,315
Those amps have high cathode voltages in the cathode follower position and you should only use a JJ or chinese tube.
The Black Pearl is also prone to poor grounding on the faceplate.I had one in for repair that had very low volume and I traced it to the pots not grounding properly against the front of the chassis.Poorly designed made in china amps.
Nasty PC board with traces on both sides.An invitation for disaster.
 

Hwoltage

Member
Messages
9,713
I would call Mike about it. The first thing I would check is a leaky output capacitor. This cap couples the collector of Q2 to the volume pot and is the last line of defense against DC leaking into the grid of the amp's first tube stage.

Is the volume pot scratchy when you turn it? If so, this would indicate DC where there should be none.

Does the pedal still effect the amp if there is a second pedal placed after the fuzz (and before the amp)? If not, determine if the fuzz is effecting the second pedal instead.

I think it's possible that when you let the amp "cool off" this is not effecting the amp but rather is letting the capacitors of the pedal discharge. When you hook everything back up, everything is good until you hit the fuzz, the caps charge back up and DC starts leaking again. This continues to occur after you bypass the pedal because, most likely, you are bypassing the signal, not the power supply. The pedal remains powered as you are only turning off the LED and bypassing the circuit. DC will continue to leak in bypass mode for the DC is appearing at the output jack.

Anyhow, my thoughts. Good luck.
 

Structo

Member
Messages
9,556
Could be the impedance mismatch.

But that is weird that the amp misbehaves after the pedal is out of the circuit.
 

ruger9

Silver Supporting Member
Messages
9,415
Those amps have high cathode voltages in the cathode follower position and you should only use a JJ or chinese tube.
The Black Pearl is also prone to poor grounding on the faceplate.I had one in for repair that had very low volume and I traced it to the pots not grounding properly against the front of the chassis.Poorly designed made in china amps.
Nasty PC board with traces on both sides.An invitation for disaster.
Thanks. I have a TungSol (new) in there now.... shouldn't that be fine in the cathode follower position? I talked to a GB tech back and forth for a few days, trying to figure it out once before, and we came to the conclusion it was the LPS in V2, a tube that can't really take the beating of that stage. I put a new TS in, and thought everything was fine, up until last night...

I'll also investigate the pot/grounding thing, but I wouldn't think that's it... since this happens ONLY after I use the fuzz.
 

ruger9

Silver Supporting Member
Messages
9,415
I would call Mike about it. The first thing I would check is a leaky output capacitor. This cap couples the collector of Q2 to the volume pot and is the last line of defense against DC leaking into the grid of the amp's first tube stage.

Is the volume pot scratchy when you turn it? If so, this would indicate DC where there should be none.

Does the pedal still effect the amp if there is a second pedal placed after the fuzz (and before the amp)? If not, determine if the fuzz is effecting the second pedal instead.

I think it's possible that when you let the amp "cool off" this is not effecting the amp but rather is letting the capacitors of the pedal discharge. When you hook everything back up, everything is good until you hit the fuzz, the caps charge back up and DC starts leaking again. This continues to occur after you bypass the pedal because, most likely, you are bypassing the signal, not the power supply. The pedal remains powered as you are only turning off the LED and bypassing the circuit. DC will continue to leak in bypass mode for the DC is appearing at the output jack.

Anyhow, my thoughts. Good luck.
I don't think Mike can help... because the problem remains when the pedal is switched off/out of circuit. When you say "output cap", you're talking on the PEDAL? Because a leaky cap on the AMP was one of my first thoughts.

But you've given me food for thought... thanks, I'll do more experimenting with the SF off the board vs on the board... "not bypassing the power supply"...hmm.... if I recall correctly, the power supply did have something to do with a similar problem I was having with another pedal a few years ago (same amp tho)... hmm... maybe an email to mike is appropriate... thanks.
 
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ruger9

Silver Supporting Member
Messages
9,415
Could be the impedance mismatch.

But that is weird that the amp misbehaves after the pedal is out of the circuit.
Yes. That is exactly what it sounds like... an INTERMITTENT impedance mismatch, but of course that doesn't make any sense?

I actually had this problem, years ago... and it was a pedal causing it... I don't remember which pedal, possibly a big box DMM or something with a tube in it like a vari-drive or echo-drive? Don't remember. I didn't care either, because I sold the pedal, and didn't have the problem anymore lol. Maybe Hwoltage is onto something with his theory above...
 
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ruger9

Silver Supporting Member
Messages
9,415
Does the pedal still effect the amp if there is a second pedal placed after the fuzz (and before the amp)? If not, determine if the fuzz is effecting the second pedal instead.

.
The sunface has pedals on both sides. (only a true bypass pedal before it tho.)
 

ruger9

Silver Supporting Member
Messages
9,415
I think it's possible that when you let the amp "cool off" this is not effecting the amp but rather is letting the capacitors of the pedal discharge. When you hook everything back up, everything is good until you hit the fuzz, the caps charge back up and DC starts leaking again. This continues to occur after you bypass the pedal because, most likely, you are bypassing the signal, not the power supply. The pedal remains powered as you are only turning off the LED and bypassing the circuit. DC will continue to leak in bypass mode for the DC is appearing at the output jack.

Anyhow, my thoughts. Good luck.
So, if this IS the case, would the problem disappear if I unplug the PS from the sunface, then plug it back in?
 

DGDGBD

Member
Messages
7,020
Aren't reisssue TungSol 12AX7's prone to failure in a cathode follower positions? I remember reading not to use them as V2 in the old marshall/5F6A-type circuits.
 

ruger9

Silver Supporting Member
Messages
9,415
Aren't reisssue TungSol 12AX7's prone to failure in a cathode follower positions? I remember reading not to use them as V2 in the old marshall/5F6A-type circuits.
I've never heard that, but if it's true, there's a great likelyhood that's my problem. I do have a chinese 12AX7 I could use, I just don't use them much because they don't have my favorite tonal properties for a 12AX7... but anything is better than what's happening.

I just googled it, and you're correct. Reissue TS not good for high voltage CF positions. I didn't know it, and the tech at Genz Benz didn't know it. Thnks for that. It'll be my first plan of attack on this problem.
 

ruger9

Silver Supporting Member
Messages
9,415
Alright...

Replaced the CF tube (which was an EHX, a tube that Mesa Boogie has stopped using because it's not reliable in CF positions), with a Chinese 12AX7... Oct 2006, not sure what generation, but from what I can dig up, it seems to be 9th gen or later, so it should be good.

So far, so good... the Sunface doesn't seem to be able to cause the problem I was having. I'll keep testing tho... as for the DC leakage proposed as a possible condition above, I have the SF powered from a separate source than the pedalboard... and also have it in a TB loop, hoping if the SF does turn out to be the problem, by hitting the AB loop, I can switch the entire pedal out of the circuit?

But since this problem was solved last time by replacing the CF tube (which was an LPS- not reliable for CF), with the EHX.... and I have now found out that EHX and reissue TS are also not good for CFs, and having replaced it with the chinese, that this problem is solved, and will STAY solved, as long as I have a chinese tube in CF.
 

Chris Scott

Member
Messages
9,145
Played a gig once with my 5F6 Bassman, and I had just replaced V2 with an EH - I'd just ordered a bunch, and popped a few in to try.

Hour into the show and pop, 75% volume drop. Looked in the back, and for some reason went right to that tube - I think I was thinking it looked like the fil was weak - and subbed it with a spare nos, and it ran like a clock for the rest of the evening.

Next day I checked out the entire circuit, and all was rosey posey. Put in a NEW EH, and later that night got through the soundcheck thinking all was good.

4 tunes in, and pop, same deal - I went right to V2 and put the same spare I'd used the night before while the rest of the band continued playing, back in before the end of the tune and all was good for 3 hrs. straight.

It was what everyone is now quite aware of, but a kinda cool way to learn about it for me...
 




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