Ampeg SVT-3 "Farting"

[TimSterling1981]

My SVT-3 head is "farting" whenever I use heavy picking or attack. It is a buzzy, loud, distorted "fart" (sorry, but that really is the best description I can possibly compare it to) at the initial attack of the note; sustain and decay are not affected and still sound fine. During lighter playing, it doesn't act up, but once I start hitting the strings hard, that distorted buzz is there again. It's not my cabs doing it, and I have tried several different basses, as well as tried several different gain and volume settings on the head, and it still does it at low volumes. I opened the amp up, as I was thinking that even though the amp is less than a year old, the tubes needed replaced (something I am very comfortable doing myself, and have done in the past). To my surprise, instead of having the standard four 12AX7 tubes (three preamp, one driver) and one 12AU7 tube, every single tube in the amp was a 12AX7 (all EHs, except for one Russian GT in the preamp). I am a bit baffled that this amp came from the factory with the wrong tube configuration. Anyone else have similar discoveries upon popping the top on their SVT-3?

I am aware of the common MOSFET bias issue, which I will be looking into when I get to our rehearsal space tomorrow to install the new 12AU7. If it's still doing the farting act, I'll bust out the multimeter and check the resistors and adjust the trimpot as necessary. Anyone know what type of resistors these are? I know value and such, but I'm talking brand, etc. I know Ampeg uses a 5% tolerance for these resistors, and I would like to replace them with equivalents that are within 1% tolerance if possible.

One last question...is it safe to use a dab of silicone on the top of the trimpot once I get the bias adjusted to keep it from moving during transportation? Sorry for the bombardment of questions, I'm just in love with the sound I get from this amp (when it's working) and would rather do what I can to improve what I have instead of jumping to something else. Thanks!

-=Tim=-

 

[TimSterling1981]

UPDATE: Still doing the farting thing. I also realized it does it on the DI out as well, so wouldn't that mean it's not a problem in the power amp section (power amp wouldn't run to DI)?

Guess it's time to shoot off another PO'ed E-mail to Loud...

My SVT-3 head is "farting" whenever I use heavy picking or attack. It is a buzzy, loud, distorted "fart" (sorry, but that really is the best description I can possibly compare it to) at the initial attack of the note; sustain and decay are not affected and still sound fine. During lighter playing, it doesn't act up, but once I start hitting the strings hard, that distorted buzz is there again. It's not my cabs doing it, and I have tried several different basses, as well as tried several different gain and volume settings on the head, and it still does it at low volumes. I opened the amp up, as I was thinking that even though the amp is less than a year old, the tubes needed replaced (something I am very comfortable doing myself, and have done in the past). To my surprise, instead of having the standard four 12AX7 tubes (three preamp, one driver) and one 12AU7 tube, every single tube in the amp was a 12AX7 (all EHs, except for one Russian GT in the preamp). I am a bit baffled that this amp came from the factory with the wrong tube configuration. Anyone else have similar discoveries upon popping the top on their SVT-3?

I am aware of the common MOSFET bias issue, which I will be looking into when I get to our rehearsal space tomorrow to install the new 12AU7. If it's still doing the farting act, I'll bust out the multimeter and check the resistors and adjust the trimpot as necessary. Anyone know what type of resistors these are? I know value and such, but I'm talking brand, etc. I know Ampeg uses a 5% tolerance for these resistors, and I would like to replace them with equivalents that are within 1% tolerance if possible.

One last question...is it safe to use a dab of silicone on the top of the trimpot once I get the bias adjusted to keep it from moving during transportation? Sorry for the bombardment of questions, I'm just in love with the sound I get from this amp (when it's working) and would rather do what I can to improve what I have instead of jumping to something else. Thanks!

-=Tim=-

 

[fenderhutz]

I went though 5 of the US made SLM ones for the same issue.

Is this the newer Loud model or SLM US one?

 

[TimSterling1981]

I went though 5 of the US made SLM ones for the same issue.

Is this the newer Loud model or SLM US one?

Loud. Vietnam-made, to be exact.

I owned several USA-made SVT-3 Pros in the past with no issue whatsoever. I wasn't too pissed off about this at first, because I figured it was just the common bias issue with the Bourns pot, but now that I realized that the noise is coming through the DI signal as well, I know it's not the bias. And since I bought it refurbished (even though it was through an authorized Ampeg dealer, American Musical Supply), Ampeg didn't seem to be too keen on wanting to cover it under warranty, even after sending them the serial number, my shipping address, full name, copy of purchase receipt, and my first-born (okay, so not my first-born, but still...). Keep in mind that I bought this amp from American Musical in March of last year.

I mentioned that after 15+ years of being Ampeg-loyal, I was strongly considering never purchasing or recommending Ampeg again, and they seemed to be a little more willing to work with me. So we'll see how that goes. Maybe long-time customer loyalty actually DOES still mean something today, despite the company being a far cry from the industry standard that it used to be. Not at all happy with the way this is going, especially having 3 gigs in the next few weeks.

Just curious, what ended up being the problem with yours? I'm pretty keen with electronics, so if I'm better off buying a few parts and replacing them myself than I am playing E-mail Tag with Ampeg, I'll just do it myself.

EDIT: Just noticed you're from Harpers Ferry; I used to live in Martinsburg (from Hagerstown originally). I miss Harpers Ferry a lot--awesome place!