SVP-PRO, freaking noisy...

[toomanyslurpees]

Ok, so I picked up a used Ampeg SVP-PRO used, I love the sound of it but it is freaking noisy. The buzz is completely independant of the volume so even if i have the preamp gain, drive and master volumes all the way down I have a substantial buzz. I'm waiting on the schematics which I've requested. The only trouble shooting I've done so far is to remove all the tubes and turn it on, and yep, buzz is still there. The only other thing I've noticed is that there's an small audible hum when I turn the unit on, but not sure if it's more than would be expected (possible power transformer issue?)

Anyway, just thought I'ld throw this out there incase any of you have delt with these things before and don't mind pointing me in a probable right direction to look first.

Thanks.

[phsyconoodler]

There are several models of that amp.
  Do you mean SVT-Pro,not SVP-Pro?
If it's a solid state version,the hum is usually caused by a blown output IC and the support resistors and diodes.

It may be an SVT-3,4,5 or 6 Pro .

[jojokeo]

W/out knowing the amp specifically my first thoghts were main filter caps, a grounding issue, and/or bad traces and loose components on the circuit board?

[toomanyslurpees]

The SVP-PRO is a 1u rackmount version of the preamp section of the SVT-IIpro so kinda like an SVT-cl with a drive knob and an eq. I got the schematics today so hopefully I'm make some progress soonish.

[sluckey]

So it's a preamp. What do you have the output connected to?

[toomanyslurpees]

I'm running it into an Aguilar AG500 though I've tried it into my battery powered digital recorder to make sure it's not some weird ground loop issue and the buzz is still very much there.

[sluckey]

Have you tried connecting it directly into a power amp? I don't think it was meant to feed into an instrument level input.

[toomanyslurpees]

Ok, so I have to hang my head in shame.... I'm not going to tell you how long I've been playing, or how much I've messed around with sound gear.... yeh, I suffered from a huge laps of judgement thinking I should be able to run that preamp out into the AG500's input. I pulled out my pa amp and a monitor, and made the discovery that I'm an idiot.... Thanks Sluckey. (no, not sarcasm, really, thanks)

I started out trying to run this preamp into the effects loop ot the AG500 which worked well except the effects loop is post master so every time I changed volumes I had to change all the gain settings on the ampeg, so that didn't last long, then I tried running running the ampeg and the AG500's preamps in parallel but I think this let me push the power amp too hard and trip it's protection mode, so I dropped that. I threw this thing into action pretty quick so most of my experimenting was live, when I finally fired the amp up here in my appartment to try it straight into the input I was trying to figure out how on earth I didn't notice how loud that noise is before, but obviously the adjustable return level took the output of the ampeg better.

So anyway.... tried running it out from the the effects send of the ampeg to the AG500, and as far as playing in my appartment it appears to work pretty good (it takes the signal from before the last tube, I can't get much drive that way, but I don't really use that anyway, I just wanted to use it to warm up my bass rig)

Thanks again.

[phsyconoodler]

Ok,now we are making progress.That preamp has a power supply noise issue that can be corrected by re-routing the internal wiring near the IEC connector and twisting the AC wires.
  We have had a couple that do indeed hum unless you do that.

[Paul_5]

Hi All, I'm an Ampeg user in the UK and have a wonderful (if a little noisy SVP PRO). is there any more information fixing the wiring near the power inlet?

I've retubed, re-transformered and recapped the PSU board, but to no avail.

any advice or diagrams, cake or photographs would be appreciated.

Cheers, Paul

[HotBluePlates]

Hey Paul!

Start up a new thread with this question; you can find the Main Board schematic and Tube Board schematic by clicking the links.

Be sure to include your specific symtpoms, and especially any repairs/changes you've made to date. I'm sure we can help you out.