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Ampeg Heritage 50th Anniversary SVT issue
- Thread starter TechnoTurian
- Start date
TechnoTurian: Did you get a satisfactory resolution to the amp's buzz issue, as per the Psionic Sound video? I just got one of these amps and it has the same buzz issue. Did Ampeg have a fix for it, or did you get a replacement amp without buzz?
oberkampf: My new SVT Heritage 50th has about the same fan noise as yours, which I can live with. But it also has the constant preamp buzz identified in the Psionic Audio video linked by TechnoTurian, which I really don't like. I can keep the SVT fan away from a mike; I can't keep the SVT buzz out of my mic'd speaker cab. Fortunately, your video of your amp shows me what a quiet SVT Heritage 50th should sound like.
I am hoping there is a fix for this buzz issue that does not involve disabling the standby switch on the front or other circuit surgery.
My early '90s SVT-II (same guts with diff form factor) gets buzzy when I plug it in at home. But when at a venue it is dead quiet. These amps are very sensitive to dirty power. At band volume it is never an issue. Same with the fan, whoosh is immediately absent when you play. Bedroom is not the ideal environment. My onstage industrial cooling fan is muuch louder!
I called Ampeg Technical Support (818)-575-3600 ("TS") today about the buzz/standby switch issue I was having, which is the same issue identified by the OP and in the Psionic Audio video. It is experienced by others, from the various complaints on the internet by other users I have read while looking for a solution. Here's a summary of my dialogue with Ampeg TS today:
Me: is Ampeg aware of this buzz issue? TS: yes.
Me: does Ampeg has a fix for it? TS: no. Ampeg "has not investigated the issue."
Me: what does "not investigated" mean? These amps have been in production for a few years now and the issue is widely reported. TS: Ampeg has not investigated the issue and does not have a fix for the issue.
Me: what should I do with my buzzing SVT? TS: return it to the vendor and ask for a replacement SVT and the vendor will take care of you.
Me: how I can be assured the vendor won't send me another SVT that also buzzes? The vendor said this one was fine. TS: the vendor should take of you.
Me: can I take my buzzing SVT directly to Ampeg in Calabasas for diagnosis/repair, since I live nearby? TS: no, Ampeg does not do repair work, it is handled by authorized service centers.
Me: can TS recommend an Ampeg service center who has a fix for the buzz issue. TS: no, there is no fix, so you should return the SVT to the vendor.
Me: If I exchange it for another SVT that develops the same buzz issues in a few months, what can I do? TS: the vendor will take care of you.
Me: it seem that this is an Ampeg design defect that Ampeg has not resolved, and so purchasers have to take their chances that the SVTs they get are not the ones that buzz. Is that how it is? TS: (pause) "I hear you and I am sorry about the situation."
I have to say, I found this exchange with Ampeg's TS very disappointing. The 50th Anniversary SVT is Ampeg's most expensive product, and much touted by Ampeg for its made-in-USA engineering and build quality. The 50th Anniversary SVT was launched 3 years ago, at the 2019 NAMM show, so there has been ample time for Ampeg to address this defect. Moreover, Yamaha owns Ampeg and obviously has the technical and financial resources to deal with "investigating" and resolving this issue. For Ampeg to continue production of an amp with an apparent design defect and no fix for it does not speak well of how Yamaha/Ampeg deals with customers. Ampeg TS throwing the buzz issue back to the vendors to provide replacements is problematic.
If the particular Ampeg TS person I spoke with is misinformed, or I misunderstood, and Ampeg does have a fix for this problem I would love to be corrected. Until then, IMHO, 50th Anniversary SVT buyers beware.
Me: is Ampeg aware of this buzz issue? TS: yes.
Me: does Ampeg has a fix for it? TS: no. Ampeg "has not investigated the issue."
Me: what does "not investigated" mean? These amps have been in production for a few years now and the issue is widely reported. TS: Ampeg has not investigated the issue and does not have a fix for the issue.
Me: what should I do with my buzzing SVT? TS: return it to the vendor and ask for a replacement SVT and the vendor will take care of you.
Me: how I can be assured the vendor won't send me another SVT that also buzzes? The vendor said this one was fine. TS: the vendor should take of you.
Me: can I take my buzzing SVT directly to Ampeg in Calabasas for diagnosis/repair, since I live nearby? TS: no, Ampeg does not do repair work, it is handled by authorized service centers.
Me: can TS recommend an Ampeg service center who has a fix for the buzz issue. TS: no, there is no fix, so you should return the SVT to the vendor.
Me: If I exchange it for another SVT that develops the same buzz issues in a few months, what can I do? TS: the vendor will take care of you.
Me: it seem that this is an Ampeg design defect that Ampeg has not resolved, and so purchasers have to take their chances that the SVTs they get are not the ones that buzz. Is that how it is? TS: (pause) "I hear you and I am sorry about the situation."
I have to say, I found this exchange with Ampeg's TS very disappointing. The 50th Anniversary SVT is Ampeg's most expensive product, and much touted by Ampeg for its made-in-USA engineering and build quality. The 50th Anniversary SVT was launched 3 years ago, at the 2019 NAMM show, so there has been ample time for Ampeg to address this defect. Moreover, Yamaha owns Ampeg and obviously has the technical and financial resources to deal with "investigating" and resolving this issue. For Ampeg to continue production of an amp with an apparent design defect and no fix for it does not speak well of how Yamaha/Ampeg deals with customers. Ampeg TS throwing the buzz issue back to the vendors to provide replacements is problematic.
If the particular Ampeg TS person I spoke with is misinformed, or I misunderstood, and Ampeg does have a fix for this problem I would love to be corrected. Until then, IMHO, 50th Anniversary SVT buyers beware.
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I wonder who that actually was you spoke to. I've known the folks at Yamaha and Ampeg and I've spoken to a few over the years and none of them deadpan answers like that. That just sounds like a junior-front-line call-taker.
Do we have a running tally of the total number of complaints vs number sold? It doesn't sound like there are actually that many issues.
Do we have a running tally of the total number of complaints vs number sold? It doesn't sound like there are actually that many issues.
Reading between the lines….They want to avoid paying for a rework on all the Heritage VR amps. It would be a major hit. As they said, warranty repairs will be dealt with. They don’t want to say anything more.
I spoke with the person who answered the phone at Ampeg Technical Support, who I called using the phone number provided in the SVT's owner's manual. I didn't take down his name. He was polite and professional. He repeated the "Ampeg has not investigated that issue" several times, while also saying that neither Ampeg nor Ampeg's service centers had a fix for the issue.
I want to add this: I played my SVT through a full-range Bergantino HT322 cab and heard the buzz distinctly. When I turned the control for the HT322 high frequency driver all the way off, however, the buzz was greatly reduced. The Bergantino frequency range spec for the HT322 is 36hz - 18khz. Ampeg's spec for a Heritage SVT cab 40Hz - 5kHz, so perhaps the SVT cab rolls off the buzz a bit so it is less noticeable?
I have an SWR Henry 8x8 and a Bag End 4x10 I will try with the SVT. But why should I have to turn down the treble driver to mask the SVT's buzz? (When I run my Trickfish Bullhead 1K through the Bergantino HT322 there is no buzz at all with the treble driver maxed.)
Just got an used but pristine SVT-AV SLM 2005 (for a good price). Had a buzz at high volume: goodbye all Sovtek’s OEM 12xx7’s and welcome to the quietest tubes of my stash. No more buzz and a big difference on noise floor/hiss/white noise.
Then yesterday, green light wouldn’t want to lit on right side accompanied by a worrying hum that immediately tells that me something is not well balanced current wise on one of the 6550’s trios (Sovtek originals).
A quick swap of the power tubes almost randomly and it cured itself. Readjusted the BIAS without the fan, running volume and gain at full blast to be able to hear the least amount of hum. There’s a slight tiny region of the pots rotation where the LED’s are green but only one more tinier point where the residual hum is the lowest, at idle after 15-20 minutes obviously.
I guess that by shuffling the tubes it cleaned pins or sockets/and/or/balanced equally the two sides. Quite a bit sophisticated circuit BIAS but I prefer the multimeter way personally. Not recommended with the SVT’s as you have to:
- disassemble the beast;
- poke your hand (the other in the pocket please) in circuits that can kill you (700 volts).
As for the fan, mine is a jet engine, worse than the last posted YouTube vid.
Upon recommendation by @agedhorse in another thread, I’ve opted for this: Low Noise Fan For SVT-AV
I know that the Heritage one is bigger and not on the front but God, this was way too loud for me. Measured at 60 dB’s with two iPad apps (not the same as the dBA figure they use for standard specs measurement, thanks again @agedhorse for clarification) but still… It rattles all the chassis! It’ll be for studio use only.
Threads: MTI SVT Fan Replacement. (80mm front fan mainly);
Low Noise Fan For SVT-AV (120mm?).
Then yesterday, green light wouldn’t want to lit on right side accompanied by a worrying hum that immediately tells that me something is not well balanced current wise on one of the 6550’s trios (Sovtek originals).
A quick swap of the power tubes almost randomly and it cured itself. Readjusted the BIAS without the fan, running volume and gain at full blast to be able to hear the least amount of hum. There’s a slight tiny region of the pots rotation where the LED’s are green but only one more tinier point where the residual hum is the lowest, at idle after 15-20 minutes obviously.
I guess that by shuffling the tubes it cleaned pins or sockets/and/or/balanced equally the two sides. Quite a bit sophisticated circuit BIAS but I prefer the multimeter way personally. Not recommended with the SVT’s as you have to:
- disassemble the beast;
- poke your hand (the other in the pocket please) in circuits that can kill you (700 volts).
As for the fan, mine is a jet engine, worse than the last posted YouTube vid.
Upon recommendation by @agedhorse in another thread, I’ve opted for this: Low Noise Fan For SVT-AV
I know that the Heritage one is bigger and not on the front but God, this was way too loud for me. Measured at 60 dB’s with two iPad apps (not the same as the dBA figure they use for standard specs measurement, thanks again @agedhorse for clarification) but still… It rattles all the chassis! It’ll be for studio use only.
Threads: MTI SVT Fan Replacement. (80mm front fan mainly);
Low Noise Fan For SVT-AV (120mm?).
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See my reply, it’s not supposed to buzz, even with levels fully cranked. Try to at least swap or reseat the two preamp 12AX7’s on the front. You also have a third one (located on the right when viewing the back) you could swap with the others. Beware however that I’m not sure it couldn’t mess the BIAS. To be confirmed. Do not swap the 12AU7’s neither with the 12AX7’s or you’ll be in for a surprise!
BTW, one of my strong 12AX7 (RCA) was a no go in the power amp section: big hum and BIAS completely messed up…
Someone could confirm that all three 12xx7’s in the power amp section have an impact on BIAS adjust?
I’ve always heard about the two 12AU7’s needing a BIAS adjust if replaced (or busting the BIAS if toasted/bad quality) but was surprised to see that the last 12AX7 before the drivers looks to have an impact too…
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Oh, an another source of buzz (and what a buzz!) I just experimented myself. Loos input jack that won’t short once cable disconnected. I had to use a pair pliers to tighten the metal tabs on the 0dB input jack a few minutes ago. Scared the hell of me as I started the amp @full blast!! BZZZZZZ x 300w!
A little squirt of Deoxit too (very little!).
A little squirt of Deoxit too (very little!).
Yes I would advise resetting the bias if the 12AU7s are replaced. AFAIK the 12AX7 should have no impact on bias. Only the second section of each driver tube should be involved in bias.
The 50th AV webpage lists the small signal tubes in the power amp as one 12AX7 and two 12AU7s. The webpage calls all of them drivers tubes, but I don't think this is correct. I have not seen a schematic for the 50th AV, but I believe it is essentially a lightly modded SVT VR. In the VR, the 12AX7 is the phase inverter and the 12AU7s are driver tubes.
This image is from the VR schematic:
I put red circles around the bias controls. One side of the bias controls are tied to -150V and the other side is tied to ground (OV). The bias controls determine the voltage passing along the red paths to the grids of the J3B and J5B. Notice that capacitors block this voltage from traveling back through the circuit to J3A or J5A. The voltage from each bias control sets the operating point of the J3B and J5B. Making the voltage more negative will reduce current in these tube stages (shown in green). Making the voltage less negative will increase current.
The cathode of these tube stages is also connected to -150V through a 47k resistor. The plates are connected to 305V. The bias (shown in orange) is essentially the voltage drop across the 47K resistors subtracted from the -150V supply. This voltage drop varies with current flow through the associated tube section.
Since the bias is approximately -48V and the supply is -150V, the voltage drop is +102V...(I.E. -150+102=-48V).
The current flow for this voltage drop is found with the formula I=V/R (I = 102V/47K=2.17mA)
So the bias controls are adjusted so J3B and J5B pass approximately 2.17ma at idle.
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Ah, Thanks! This old 12AX7 was so noisy and splattering that the BIAS LEDs were flickering between red and green fastly. Dumb me, quite obvious as it was like a music signal (not really musical…)!
I must have a good one, because mine is working flawlessly. Played an outdoor gig last night with heat indexes in the 90’s. Sound check at 5 and it was taking direct sunlight on the back. Played 3 hours plus the sound check and it sounded fantastic. Have played another outdoor gig (at 2 ohms) and a 3 hour indoor dance gig with it in the past 2 weeks. No issues, no buzz, no anything except sweet tone.
I did replace the 12ax7 that pushes the au7’s and V1, V2, and V5 with ANOS tubes from my stash. Really happy with this amp!
I did replace the 12ax7 that pushes the au7’s and V1, V2, and V5 with ANOS tubes from my stash. Really happy with this amp!
simple: don't buy one of the new versions. i've owned two from the magnavox era, both reliable & dead quiet with only simple and infrequent maintenance.
I have an 80's SVT and a Berg HT322.
It's not a compatibility issue as mine is dead quiet with the tweeter between 25% - 50% on.
My SVT-AV is (now) dead quiet apart the fan, that’ll be replaced anyway.
As @Jim C mentioned, my tweeter is also around 50% and it’s an insane amount of time quieter than my ‘74 V4…
This pic goes to my files right now, thanks!
No yellow however on the SVT-AV…
**Great explanation by the way. Just trying to grasp the concept in my little head…
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Just to clarify: The information posted in this thread about getting rid of noise in various SVT models is helpful to other SVT users and I appreciate it. But this thread is specifically about the 50th Anniversary SVT amp head, not other current or discontinued SVT models that have different designs and noise issues. The apparent design defect/issue that Psionic Audio identified in the linked video specifically concerns the 50th Anniversary SVT's circuit layout, in which the AC voltage on the standby switch is too close to the preamp circuit board and induces the constant buzz that concerns me. Psionic Audio explained that when he detached the standby switch and moved it away from the preamp board the buzz went away.
As such, the identified buzz for at least some 50th Anniversary SVTs is likely not the result of poor preamp tubes, poor preamp tube pin connections, poor tube bias, etc., and they are probably not effective solutions for that issue with this model amp. (But, I may try them anyway because I have been wrong plenty of times before.)
Psionic Audio's suggested fixes for the issue with this amp include disconnecting the AC to the standby switch on the face of the amp, leave the switch in place for cosmetic reasons, and install a new standby switch on the back of the SVT, away from the preamp circuit board. Alternatively, using the existing standby switch to trigger a relay installed to operate the standby function, so that the voltage to the standby switch to operate the relay is much less than the 120 AC volts and does not induce a buzz.
Others have suggested fabricating a metal shielding box to put around the standby switch to reduce its effect on the preamp board of the SVT-VR. Ampeg SVT-VR Ch 2 Buzz/Hum - Music Electronics Forum
Anyone have a better idea?
As such, the identified buzz for at least some 50th Anniversary SVTs is likely not the result of poor preamp tubes, poor preamp tube pin connections, poor tube bias, etc., and they are probably not effective solutions for that issue with this model amp. (But, I may try them anyway because I have been wrong plenty of times before.)
Psionic Audio's suggested fixes for the issue with this amp include disconnecting the AC to the standby switch on the face of the amp, leave the switch in place for cosmetic reasons, and install a new standby switch on the back of the SVT, away from the preamp circuit board. Alternatively, using the existing standby switch to trigger a relay installed to operate the standby function, so that the voltage to the standby switch to operate the relay is much less than the 120 AC volts and does not induce a buzz.
Others have suggested fabricating a metal shielding box to put around the standby switch to reduce its effect on the preamp board of the SVT-VR. Ampeg SVT-VR Ch 2 Buzz/Hum - Music Electronics Forum
Anyone have a better idea?
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