Crackling sound from Ampeg SVT CL

[IronLung1986]

Does the noise go away completely with the master volume off?

So, the crackling noise when I first take it off standby, before I play anything, which happens in that last video, DOES still happen even if the Master is all the way down. If I then start playing with the Master down after those first few seconds, there is no sound or issue at all.

 

[agedhorse]

Ok, if you are lucky, it may be a failing preamp tube.

My suggestion is to take your amp to a qualified, experienced service tech that has the reputation of being honest.

 

[baxter_x]

it may be a failing preamp tube.

If it's just that, why not swapping the tubes?
No bias, and cheap

 

[agedhorse]

If it's just that, why not swapping the tubes?
No bias, and cheap

It’s a possible path, but it’s a fair amount of work in this amp and the other part of this is not to create additional problems.

 

[IronLung1986]

Thank you @agedhorse @Wasnex and everyone else who took the time to help me out on this. I'll be taking the amp to a tech next week. I'll give an update for anyone who comes across a similar issue in the future. Hopefully it's not too bad, fingers crossed.

 

[bassguitarist85]

My money is on a flaky socket/pot somewhere in the preamp. My SVT-CL was dropped in shipping transit to me. Had to glue repair the wood case, fix a broken solder joint on the power tube board, remount the fan, V1 was microphonic, still had a terrible background hum. Fixed the hum when I replaced the aluminum shielding in the wood case that was ripped apart in shipping. After all that repair work plus the standard maintenance deoxit F5, cleaning etc, dead quiet. A tech will get you sorted out I'm sure. These amps are a fair amount of work in general, but worth it.

 

[IronLung1986]

Just tried another little test:

Switched on the power (for first time today so it was completely cold).

Let it sit on Standby for a full 30 minutes before doing anything.

Switched Standby up to play.

No problems at all. No scratchy sound right at the beginning, no crackling when I play. And I played for a half hour or so, pretty loud and it worked perfectly. There was a small swishing sound when I turned the Master, that's all.

Could it be related to it being warm enough?

I'll still be taking it to the tech, just curious what this might mean.

 

[Wasnex]

Could it be related to it being warm enough?

I don't think so.

Some tubes may crackle and pop as they warm. But after they stabilize at operating temperature, it won't make a difference.

Letting the amp run in standby applies power to the heaters. The heaters warm the tube cathodes. The cathodes have to be hot before they can emit electrons.

With an SVT CL, the high voltage power supplies remain off off when the amp is in standby. I think a 15V power supply is activated, which is used to power IC chips. Also I believe the -180V bias supply for the output tubes is activated.

When you set the amp to operate, the high voltage power supplies are turned on and all operating voltages are sent to the tubes so current begins to flow from the cathodes to plates. Pretty sure the tubes will only reach full operating temperature after the tubes actually begin pulling current.

 

[IronLung1986]

I don't think so.

Some tubes may crackle and pop as they warm. But after they stabilize at operating temperature, it won't make a difference.

Letting the amp run in standby applies power to the heaters. The heaters warm the tube cathodes. The cathodes have to be hot before they can emit electrons.

With an SVT CL, the high voltage power supplies remain off off when the amp is in standby. I think a 15V power supply is activated, which is used to power IC chips. Also I believe the -180V bias supply for the output tubes is activated.

When you set the amp to operate, the high voltage power supplies are turned on and all operating voltages are sent to the tubes so current begins to flow from the cathodes to plates. Pretty sure the tubes will only reach full operating temperature after the tubes actually begin pulling current.

Ah ok. Yea I wonder why just letting it run for a bit before playing avoided the issue. At least it's nice to know the issue has a workaround for the time being.

 

[JMacBass65]

Ah ok. Yea I wonder why just letting it run for a bit before playing avoided the issue. At least it's nice to know the issue has a workaround for the time being.

Eh, it avoided it for now. If you are gigging I would make damn sure I had a backup at the ready. I have had similar issues with an old (1976) SVT went away for no apparent reason, only to return at a later date, for no apparent reason, except to say that the original cause was not identified and resolved. Still need to get that head to a tech.

 

[IronLung1986]

Eh, it avoided it for now. If you are gigging I would make damn sure I had a backup at the ready. I have had similar issues with an old (1976) SVT went away for no apparent reason, only to return at a later date, for no apparent reason, except to say that the original cause was not identified and resolved. Still need to get that head to a tech.

Oh yea, no doubt about it. I'll be taking it to a tech next week. I could never just be ok with an issue like this.

 

[B-string]

Eh, it avoided it for now. If you are gigging I would make damn sure I had a backup at the ready. I have had similar issues with an old (1976) SVT went away for no apparent reason, only to return at a later date, for no apparent reason, except to say that the original cause was not identified and resolved. Still need to get that head to a tech.

If your 1976 is still using a 7pin 6C4 in the preamp finding an acceptably "quiet" one can be a real chore. None seem to be really quiet for the last couple decades.

 

[JMacBass65]

If your 1976 is still using a 7pin 6C4 in the preamp finding an acceptably "quiet" one can be a real chore. None seem to be really quiet for the last couple decades.

Yeah, that tube was pointed out to me by several people here. I went and got a couple new ones. It's been a while but I believe I tried them both, and that might have contributed to the "sometimes it works fine, other times not" view. In other words, the symptoms didn't really change, so the results were inconclusive. The last time I used it was at a gig, started giving me trouble a few songs in, I had my trusty 400RB sitting on top of it, ready to go. Made the switch and haven't fired up the SVT since.

I need a trusted tech in the DC/MD/NoVA area (or even Richmond), if anyone has a name, that would be awesome.

 

[B-string]

Yeah, that tube was pointed out to me by several people here. I went and got a couple new ones. It's been a while but I believe I tried them both, and that might have contributed to the "sometimes it works fine, other times not" view. In other words, the symptoms didn't really change, so the results were inconclusive. The last time I used it was at a gig, started giving me trouble a few songs in, I had my trusty 400RB sitting on top of it, ready to go. Made the switch and haven't fired up the SVT since.

I need a trusted tech in the DC/MD/NoVA area (or even Richmond), if anyone has a name, that would be awesome.

Just a little background. Before I left the land of granola (SoCal) I bought into an auction that included "NOS" tubes, chances are they truly were NOS, Included were 28 6C4's of RCA and GE mix. I wound up out of the 28 with 5 "good" (read as very low microphonic) tubes and additional 8 "acceptable. The rest should not go anywhere near an SVT. All fresh that "test" as such, but not for a circuit like the SVT uses.
Being basically 1/2 a 12AU7 I made a few 7 to 9 pin adaptors (all in service) but the retainer that had to be added was pretty ugly. It was not mod for people looking to retain a pristine value. You most likely need to purchase a large quantity to find a mechanically quiet one or buy from a service that "weeds" them out and provides a guarantee of service. Groove Tubes of over two decades ago did have quiet ones and TAD had a few but gave up on the idea quickly. I don't know current re-branders as I stopped offering repairs a few years ago. Loss of a matched pair of RCA 6L6GC's to a nonpayer erected the prepared tombstone.

 

[IronLung1986]

Well, I got the amp back from the repair tech and unfortunately he wasn't able to figure out what it was. He had thought it was the tube socket for one of the phase inverter tubes, and tightened up the little tiny metal sockets that receive the pins on the tube. But, the issue is still happening.



It goes away after the amp warms up or has been on for between 5 - 15 minutes depending. If I turn it on and leave it in Standby for 15 or 20 minutes before playing, it doesn't seem to happen at all usually. That's the only rhyme or reason I can make of it. The colder the amp is - like, the colder it is in the room - the longer it seems to take to go away. I really feel it's related to how long the amp has been on, or how warm it is. I can't deduce any other conclusions about it. The tech said the same, and basically said that the tube sockets must be loose, but as they warm up they change shape slightly and allow better electrical transfer. If I play the amp for a bit and then come back a little while later it doesn't happen as badly, goes away quicker, or won't happen at all. For that reason the issue can only be tested for a very short window once per day, making it very slow and time consuming to troubleshoot.

I really am at a loss at this point. I'm on a waiting list for another tech but they're booked till at least April. At least I have the amp back in the meantime. I guess I'm not real hopeful about this guy being able to figure it out at this point.

The tech suggested that maybe this is working as intended and I just have to let the amp warm up before playing it. I feel this is not how the amp is supposed to work and basically makes it useless for gigging as I typically don't have the luxury of letting my amp idle for 15 minutes before playing.

 

[Wasnex]

The tech suggested that maybe this is working as intended and I just have to let the amp warm up before playing it.

This is non-sense .

 

[IronLung1986]

This is non-sense .

Yea, it is.

I should add that I can't fault the guy too much. He spent a good amount of time and I think got as far as he could with it. His fee was very reasonable and he thought it was fixed when he gave it back to me. It wasn't happening when I went to his shop to pick it up. I tried it right there with him in his shop and it wasn't happening. Then I get it home and the very next day it's happening again. Note that the tech was able to repro the issue many times in his shop, including with me there. It's not like the issue only happens in my basement.

 

[Patrice B]

Well, I got the amp back from the repair tech and unfortunately he wasn't able to figure out what it was. He had thought it was the tube socket for one of the phase inverter tubes, and tightened up the little tiny metal sockets that receive the pins on the tube. But, the issue is still happening.



It goes away after the amp warms up or has been on for between 5 - 15 minutes depending. If I turn it on and leave it in Standby for 15 or 20 minutes before playing, it doesn't seem to happen at all usually. That's the only rhyme or reason I can make of it. The colder the amp is - like, the colder it is in the room - the longer it seems to take to go away. I really feel it's related to how long the amp has been on, or how warm it is. I can't deduce any other conclusions about it. The tech said the same, and basically said that the tube sockets must be loose, but as they warm up they change shape slightly and allow better electrical transfer. If I play the amp for a bit and then come back a little while later it doesn't happen as badly, goes away quicker, or won't happen at all. For that reason the issue can only be tested for a very short window once per day, making it very slow and time consuming to troubleshoot.

I really am at a loss at this point. I'm on a waiting list for another tech but they're booked till at least April. At least I have the amp back in the meantime. I guess I'm not real hopeful about this guy being able to figure it out at this point.

The tech suggested that maybe this is working as intended and I just have to let the amp warm up before playing it. I feel this is not how the amp is supposed to work and basically makes it useless for gigging as I typically don't have the luxury of letting my amp idle for 15 minutes before playing.

Find an authorized certified tech on the Yamaha site…

 

[beans-on-toast]

The problem needs to be broken down to isolate where in the amp the problem originates. Crackling that goes away when the amp warms up can be a bad tube, tube socket contact tension, solder joint, wire connection, even component such as a resistor or a capacitor. So there are many possibilities.

First, plug your instrument into the power amp in. Test. If it doesn’t occur, then chances are the issue is in the preamp. If it’s in the power amp, there was an issue related to cracked power tube solder joints. The service bulletin solution is to install two metal hex standoffs that mount the power tube socket to the power board PCB, this secures the tube socket. Then reflow the solder joints. As a minimum, if the hex standoffs are already in place, as a minimum, reflow the power tube sockets.

If the issue is in the preamp, there are ways to trace the signal that can help. A tech might also use a freezing spray to help reveal the problem. This can’t be used on the tubes.

 

[agedhorse]

Find a more qualified service tech.