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Ampeg SVT-VR hum problem
- Thread starter David Henry
- Start date
Read above. The part that talks about another company running the "name" Ampeg. Not all companies have very good warranty practices after taking over someone elses product.
Do they not ship the "common knowledge books" to CA?....Im joking of course.
Oh man, do you ever have your history screwed up!!! Check your facts before you get so defensive.
For the record, John is fully aware of who Jerrold is. He is also one of the most knowledgeable people on this site. He also knows more about the SVT than anyone on this site bar Jerrold Tiers.
Paul
Hoss,
You are the man!
I completely forgot about that jack and have never used it.
I inserted an instrument cable into the jack with nothing connected to the other end and the noise got louder. It also made even louder noise intermittently when I rotated the cable in the jack. Is that normal?
I then connected the cable to an Avalon U5 output and it did stop the noise almost completely. It sounds like I need to look into the grounding issue as per the article.
Thanks for the great help!
- Feb 16, 2008
- 21,240
- 23,638
- Disclosures
- John K Custom Basses
So far, we seem to know the following.....
1) no controls affect the hum
2) it may or may not go away when plugging into power amp in, which does indeed cut the connection to preamp......
I am not clear if it went all the way away, since the open cord hum would probably be louder, and rotating the plug might intermittently lose ground due to sliding.....
The part about plugging into another unit...... THAT would cut the open cord hum...... did it also cut the "normal" hum? I wasn't totally clear on that part.......
Anyhow, these are good diagnostic steps...... IF it is quiet with the P.A. input terminated, but noisy when allowed to "normal through"..... BUT no controls affect it....
THEN it is in the last part of the preamp..... or the internal interconnect.
the only tube after all controls is half of V4, so if it's a tube, it has to be that one, assuming that no control affects it. The midrange is on the other half of V4 . V4 is a follower, though, with no gain, so the problem would have to be bad, like a heater-cathode leak.
There IS some sort of hum issue with some VRs, which I never was clear on.... it was right before the SLM part of Loud was closed up, and I didn't get involved with it. Maybe I can find out. it might just be the regulator deal..... the original leave out the jumpers part.
AFAICS the OTHER regulator deal is an accidental ground of the regulator heatsink..... there shouldn't be an intentional ground there..... I think I'd have tried a washer to raise the board, since it appears the standoff allows the heatsink to contact the chassis... easy fix, no cutting????
BTW: As for the DI... it's pretty much a mic-level DI, for the board input. So it won't be very high output.
BTW #2, JohnK may know MORE about the SVT... I think he fixes a lot more of them than I do........ Since I have not fixed one after 2007.
BTW #3: As far as I know, in the US warranty is actually repaired on the spot. perhaps they are referring to a board swap? I will ask, as one guy who works for the local repair shop also works at the consulting joint part time
1) no controls affect the hum
2) it may or may not go away when plugging into power amp in, which does indeed cut the connection to preamp......
I am not clear if it went all the way away, since the open cord hum would probably be louder, and rotating the plug might intermittently lose ground due to sliding.....
The part about plugging into another unit...... THAT would cut the open cord hum...... did it also cut the "normal" hum? I wasn't totally clear on that part.......
Anyhow, these are good diagnostic steps...... IF it is quiet with the P.A. input terminated, but noisy when allowed to "normal through"..... BUT no controls affect it....
THEN it is in the last part of the preamp..... or the internal interconnect.
the only tube after all controls is half of V4, so if it's a tube, it has to be that one, assuming that no control affects it. The midrange is on the other half of V4 . V4 is a follower, though, with no gain, so the problem would have to be bad, like a heater-cathode leak.
There IS some sort of hum issue with some VRs, which I never was clear on.... it was right before the SLM part of Loud was closed up, and I didn't get involved with it. Maybe I can find out. it might just be the regulator deal..... the original leave out the jumpers part.
AFAICS the OTHER regulator deal is an accidental ground of the regulator heatsink..... there shouldn't be an intentional ground there..... I think I'd have tried a washer to raise the board, since it appears the standoff allows the heatsink to contact the chassis... easy fix, no cutting????
BTW: As for the DI... it's pretty much a mic-level DI, for the board input. So it won't be very high output.
BTW #2, JohnK may know MORE about the SVT... I think he fixes a lot more of them than I do........ Since I have not fixed one after 2007.
BTW #3: As far as I know, in the US warranty is actually repaired on the spot. perhaps they are referring to a board swap? I will ask, as one guy who works for the local repair shop also works at the consulting joint part time
Thanks for all the help Jerrold,
When connecting to the preamp through the Amp In jack the normal hum almost completely went away to an acceptable level. I am assumming these amps do not run silent.
I can swap the V4 tube to check. Is the tube location listed as V4 on the board?
Anyone have more info on the grounding issues and cures?
Thank you all!
- Feb 16, 2008
- 21,240
- 23,638
- Disclosures
- John K Custom Basses
Youre welcome, Gumbystuff!
As Jerrold mentioned - inserting an open plug will make noise everywhere. The plug MUST be connected to ground/mass. I should have mentioned that.
Best and simplest way to check properly is to connect the cable to your Bass guitar. You can also play and listen to the pure poweramp sound then.
I bet, the noise will clearly disappear. Maybe a very silent deep hum will stay if you listen very closely, thats from the poweramp and nothing to worry about. Try it out to plug, and unplug again. Clearly identify whats the noise and what is gone when plugged. Then rotate - maybe the jack has a loose contact, too.
This kind of slipped past without anyone commenting. Because I virtually no technical knowledge of how this amp works and how to fix it, I can offer my experience with respect to operating noise.
When I bought my VR it had the stock tubes according to the seller. The tube complement was as follows:
Sovtek 6550s
Sovtek 12AX7s relabeled as Groovetubes
Electroharmonix 12AU7s
When I ran the amp in a quiet room in my house and listened very closely, it produced some hiss and a bit of crackle for the first few minutes of operation. There was also a bit of low hum, but barely discernible. All of this was, in my opinion, an acceptable level of noise. I'm not talking anything that could be noticed unless you listen very closely.
I switched out all of the tubes in the amp because I had better ones in my CL. This amp has become my main gigging amp now, so the new tube complement is the following:
Winged C 6550s
TungSol 12AX7s
new EH 12AU7s
Virtually all of the hiss was gone after the tube replacement. There was no crackling whatsoever. The small amount of hum was still present.
In terms of noise, I would have to say that my VR runs VERY quietly and well within my expectations. So far, at gigs, the amount of hum that comes off the amp is completely masked by the ambient noise within the room.
Basically, switching out all of the tubes made the amp a bit quieter, not that it was all that noisy to begin with. Hell, it could have been one tube making the hissing and popping for all I know.
derridiandrift,
Thanks for the tube info!
I really do not expect the amp to be totally silent while at idle.
Well I finally got the chance to get back to the amp diagnostics and here is what I've done:
1. Swapped all 5 preamp tubes one at a time with no change in the hum.
2. Disconnected the ground wire on the preamp chassis with no change in the hum.
3. While checking the hum changes when inserting a cable into the Power Amp In jack I forgot to plug the Avalon U5 into the AC power. The hum goes away to an acceptable level when the Avalon is not on AC power. When the Avalon is plugged into the AC power the hum is barely reduced, almost the same as when nothing is plugged into the Amp In jack.
Jerrold,
I do not know what the internal interconnect is. Is this something I can easily check for problems?
Thanks,
Dave
The internal interconnect is just the various wiring, including the "normal thru" on the jacks....
If the hum goes away with the power amp input "terminated", but not grounded externally anywhere, that's interesting. it suggests that there may be a ground issue, but I'm not entirely sure that it is relevant..... or exactly what it means in this case.... except that the power amp CAN be hum-free.
That's actually good to know, it throws suspicion back on the preamp. And it suggests that nothing horrible is wrong with the power amp.
Does the Avalon have a 2 wire or 3 wire mains cord?
If it is 3 wire, could just be the single-ended connection... that is prone to hum, and hum in that situation probably wouldn't prove anything much.
Another thing to know would be whether the PREAMP OUTPUT has hum if you plug it into a different power amp. Might be hard to determine if the hum is from it or from a 'single ended" connection between units...... (single ended = not balanced ).
it is starting to sound like either wire routing, or a loose jack, or possibly something odder like a return of the hummy midrange coil problem... That last one usually is affected if you turn the mids up and try all the frequencies on the switch..... one or more will give extra hum that the mid control will adjust.......
Are you SURE that NONE of the controls affect the hum?
this is a real longshot, but do you have the channel that you're not using turned down all the way? i know zip about amps, but someone had this problem a couple weeks ago and that cured it.
if so, please ignore me
if so, please ignore me
Please let me apologize for my lack of experience and misguided attempt to diagnose. While listening/testing I had been adjusting the preamp controls with the volumes at or near the full off position with nothing plugged into the instrument input jack.
I have made a new recording of the following noise/hum with the amp volume turned up all the way and nothing plugged into the instrument jack:
http://www.youtube.com/watch?v=yVcB-aEuUQ0
The recording starts with the channel 1 and 2 volumes turned fully down and tone controls at 12:00. Next I turned the channel 1 volume full on with tone controls at 12:00. Then I turned the mids full up and tried all 3 frequencies on the mid switch a couple of times. About half way through the recording I added full treble and tried the 3 mid frequencies again.
I did not record the following:
The bass low end noise increases when fully on and rarely there is a loud pop when swithing the bass switch.
With both channel 1 and 2 volume and tone controls full on, it increases the overall volume, but does not hardly increase the hum noise.
Jerrold:
1. The Avalon preamp does have a 3 wire mains cord.
2. The Ampeg Preamp output to another amp does have the hum.
3. With this new info, is the amp problem more obvious?
Sorry for my misunderstanding and thanks again,
Dave
Also:
I played my bass through the Avalon plugged into the Ampeg Power Amp In jack and it sounds great with no noise.
I played my bass through the Avalon plugged into the Ampeg Power Amp In jack and it sounds great with no noise.
well so much for my idea...sorry
JimmyM,
No need to be sorry!
I can use all the help I can get B4 letting a shop work on this amp.
well i think the bottom line is a shop's going to have to work on it. between jerrold and john, you've done about all the troubleshooting on your own that you can.
have a read here..
http://www.talkbass.com/forum/showthread.php?t=434417&page=2
bad solder on the board??
http://www.talkbass.com/forum/showthread.php?t=434417&page=2
bad solder on the board??
