Ampeg SVT-VR LOUD static noise when turned on

[Matthew_Vaughan]

I have scoured the internet and this forum, but it seems every post is about a different problem with their SVT-VR.

When I turn my amp on from standby, sometimes there will be a very, very loud static noise coming from it no matter how the volume knob is set. It doesn't do it all the time, but when it does it's loud and scares the crap out of my dog.

It will make the noise with or without a bass plugged into it. When it first started doing this I took it apart, took all of the tubes out, sprayed a bunch of things with contact cleaner, put them all back and that seemed to work for a good while. Yes, I even took the front chassis out and cleaned those two or three tubes hidden away. I don't play this amp all that often. Maybe once a week if I am lucky. The fix lasted for about a couple months. Now it's back.

In all honesty when it first happened it reminded me of a dirty volume pot I had on a guitar amp years ago. I also cleaned that pot with the contact cleaner. I also found a post on here for a different problem and tried plugging a cable between the preamp in and out as a very trustworthy poster suggested as a way of determining a problem. That didn't help, still got the static.

Has anyone else experienced this problem? Is it the tubes? Is it truly a dirty pot? I am at a loss for what it could be. I will most likely take it apart again tonight or tomorrow to clean everything out again, but it would be really nice if I could just figure out what the problem actually is.

Thanks!

 

[tadawson]

If the controls don't affect the noise, that's telling you it's in the power amp section, not the preamp . . .

 

[bobyoung53]

Time for a tech, could be a lot of different things.

 

[Wasnex]

I have scoured the internet and this forum, but it seems every post is about a different problem with their SVT-VR.

When I turn my amp on from standby, sometimes there will be a very, very loud static noise coming from it no matter how the volume knob is set. It doesn't do it all the time, but when it does it's loud and scares the crap out of my dog.

It will make the noise with or without a bass plugged into it. When it first started doing this I took it apart, took all of the tubes out, sprayed a bunch of things with contact cleaner, put them all back and that seemed to work for a good while. Yes, I even took the front chassis out and cleaned those two or three tubes hidden away. I don't play this amp all that often. Maybe once a week if I am lucky. The fix lasted for about a couple months. Now it's back.

In all honesty when it first happened it reminded me of a dirty volume pot I had on a guitar amp years ago. I also cleaned that pot with the contact cleaner. I also found a post on here for a different problem and tried plugging a cable between the preamp in and out as a very trustworthy poster suggested as a way of determining a problem. That didn't help, still got the static.

Has anyone else experienced this problem? Is it the tubes? Is it truly a dirty pot? I am at a loss for what it could be. I will most likely take it apart again tonight or tomorrow to clean everything out again, but it would be really nice if I could just figure out what the problem actually is.

Thanks!

The Power Amp In appears to be a switching jack. So if you plug you bass into it, it should kill the signal from the preamp. You can actually play the amp with your bass plugged into the power amp...it just won't be very loud. If the static goes away, the problem is somewhere in the preamp. There's a good chance it's a bad tube. The preamp uses 12AX7 and 12AU7 tubes...you could swamp in new tubes if you like. Just make sure to replace 12AX7 with 12AX7 and 12AU7 with 12AU7.

Channel 2 is the simplest...it's just V5. (I believe this should be a 12AX7) The volume control is between V5a and V5b. If you pull V5 and the static remains you know the problem is probably not Channel 2. If V5 checks good, use it to troubleshoot Channel 1.

Channel is more complex. It uses a mix of 12AX7s and 12AU7s. I believe this is the signal path; V1a, V2b, Ultra Low/Ultra High switches, volume control, V2a, Bass and Treble control, V3b, Midrange Control, V3a, V4b (The Midrange control is actually implemented between V3b and V4b rather than being inline with the signal path)

Both channels are mixed together in the input of V4a.

V1b is not used. This might prove useful as well. Perhaps the noise is coming from another tube like this one with a bad "b" section.

If you still have static after you plug your bass into the Power Amp In, the problem is in the power amp. The power amp is supposed to have a 12AX7 in the phase inverter and a pair of 12AU7 driver tubes. You could swap one of the 12AX7s from the preamp to see if the static goes away.

If you have spare 12AU7 you could swap driver tubes as well. Before you pull the old driver tubes. Adjust the bias from minimum tube current. Bias procedure can be found in the attached manual.

If swapping the tubes and resetting the bias does not fix the problem, I suggest taking the amp to a technician.

Also, I recommend you don't spray any more contact clean on the amp as using the wrong kind can cause serious problems.

Good luck!

 

[Matthew_Vaughan]

The Power Amp In appears to be a switching jack. So if you plug you bass into it, it should kill the signal from the preamp. You can actually play the amp with your bass plugged into the power amp...it just won't be very loud. If the static goes away, the problem is somewhere in the preamp. There's a good chance it's a bad tube. The preamp uses 12AX7 and 12AU7 tubes...you could swamp in new tubes if you like. Just make sure to replace 12AX7 with 12AX7 and 12AU7 with 12AU7.

Channel 2 is the simplest...it's just V5. (I believe this should be a 12AX7) The volume control is between V5a and V5b. If you pull V5 and the static remains you know the problem is probably not Channel 2. If V5 checks good, use it to troubleshoot Channel 1.

Channel is more complex. It uses a mix of 12AX7s and 12AU7s. I believe this is the signal path; V1a, V2b, Ultra Low/Ultra High switches, volume control, V2a, Bass and Treble control, V3b, Midrange Control, V3a, V4b (The Midrange control is actually implemented between V3b and V4b rather than being inline with the signal path)

Both channels are mixed together in the input of V4a.

V1b is not used. This might prove useful as well. Perhaps the noise is coming from another tube like this one with a bad "b" section.

If you still have static after you plug your bass into the Power Amp In, the problem is in the power amp. The power amp is supposed to have a 12AX7 in the phase inverter and a pair of 12AU7 driver tubes. You could swap one of the 12AX7s from the preamp to see if the static goes away.

If you have spare 12AU7 you could swap driver tubes as well. Before you pull the old driver tubes. Adjust the bias from minimum tube current. Bias procedure can be found in the attached manual.

If swapping the tubes and resetting the bias does not fix the problem, I suggest taking the amp to a technician.

Also, I recommend you don't spray any more contact clean on the amp as using the wrong kind can cause serious problems.

Good luck!

Hey Wasnex!

Thanks so much for the in-depth break down and test procedures. I do have some spare 12AX7's laying around so I can definitely try those if I need to, but I will plug my bass in first to the preamp to see what happens there. I will also stop using the contact spray. Good to know.

Thanks so much and I'll let you all know what happens.

 

[Oliver M]

Hey Wasnex!

Thanks so much for the in-depth break down and test procedures. I do have some spare 12AX7's laying around so I can definitely try those if I need to, but I will plug my bass in first to the preamp to see what happens there. I will also stop using the contact spray. Good to know.

Thanks so much and I'll let you all know what happens.

Hi Matthew, did you solve your problem ? I have the same loud and terrific noise sometimes when I power on my amp ....
Oliver

 

[agedhorse]

Hi Matthew, did you solve your problem ? I have the same loud and terrific noise sometimes when I power on my amp ....
Oliver

Number one, don’t go spraying anything into your amp. That will just cost you more to clean up the mess and additional damage it causes.

Have you considered contacting a QUALIFIED, experienced service tech to correctly diagnose the problem. That way it can CORRECTLY perform whatever repair is necessary.

 

[Oliver M]

Number one, don’t go spraying anything into your amp. That will just cost you more to clean up the mess and additional damage it causes.

Have you considered contacting a QUALIFIED, experienced service tech to correctly diagnose the problem. That way it can CORRECTLY perform whatever repair is necessary.

HI Agedhorse,
I'm such a qualified technician. Do you know the problem? Have you any solution?

 

[Wasnex]

HI Agedhorse,
I'm such a qualified technician. Do you know the problem? Have you any solution?

The symptoms can be caused by a wide variety of problems, which is why you need to take the amp to a qualified technician.

 

[agedhorse]

HI Agedhorse,
I'm such a qualified technician. Do you know the problem? Have you any solution?

If you are really a qualified technician, you shouldn’t need my (or our) help.

you SHOULD know that no professional can remotely diagnose your amp based on the symptoms you describe.