What's going on with my Ampeg SVT-3 pro?

[Mark_70]

Any thoughts on what could be going on here?

My specific SVT-3 pro is a bit of an oldie. Bought new (by me) in '95 so just over 20 years old. Played many gigs with it but a while ago it started seriously acting up. I no longer gig it (can't trust it) but kinda miss the sound.

Here's what's happening

When I power on the amp, it hardly produces any sound. A little distorted gurgling when I play..
But then, when I leave the amp on for 30 minutes or so (I guess something is slowly warming up), it starts to do better. It doesn't exactly sound "as new" but at least it produces some clean tones.

Now - obviously I was suspecting the tubes, so replaced all of those. No difference.
The input jack has been replaced and I've hotwired the send/return effect loop (someone smarter than me suggested this may be an issue). Bass has a new 9V battery and is working fine with my other amp (same cable).

I'm at a bit of a loss here.
Any thoughts on what my old girl may be suffering from ?

Thanks in advance,

Regards
Mark

 

[beans-on-toast]

Test the pre and power amp separetly. This can help you determine if the problem lies in the pre or power amp.

Take the pre out and connect it with an instrument cable to the input of another power amp. This will tell you if the issue is in the pre-amp. If you can take the balanced outto a mixer and test for noise there. Next take a pre out from another amp and plug it into the power amp in of the SVT-3 Pro. This will test the power amp.

If you have a footswitch for your amp, try it. If you don't have a dual button footswitch with a TRS plug, try cycling a ¼"plug in and out of the jack several times. Oxidization on this jack can cause a problem similar to what can be seen with the effect send and receive jacks. If the issue improves a bit, have the footswitch jack cleaned.

 

[Mark_70]

Test the pre and power amp separetly. This can help you determine if the problem lies in the pre or power amp.

Take the pre out and connect it with an instrument cable to the input of another power amp. This will tell you if the issue is in the pre-amp. Next take a pre out from another amp and plug it into the power amp in of the SVT-3 Pro. This will test the power amp.

If you have a footswitch for your amp, try it. If you don't have a dual button footswitch with a TRS plug, try cycling a ¼"plug in and out of the jack several times. Oxidization on this jack can cause a problem similar to what can be seen with the effect send and receive jacks. If the issue improves a bit, have the footswitch jack cleaned.

Testing pre/post amp separately; can I put headphones in the "pre-amp out" to check if pre-amp works? And then simply connect something like an iPod to the power amp in to see if the power amp works OK ?

I have a footswitch; will have to look it up in the basement. Thanks for the ideas! I'll report back

Regards
Mark

 

[agedhorse]

The preamp out won't drive headphones, the iPod will work with the power amp in... but this may not work if the effects loop was modified.

 

[Mark_70]

Test the pre and power amp separetly. This can help you determine if the problem lies in the pre or power amp.

Take the pre out and connect it with an instrument cable to the input of another power amp. This will tell you if the issue is in the pre-amp. Next take a pre out from another amp and plug it into the power amp in of the SVT-3 Pro. This will test the power amp.

If you have a footswitch for your amp, try it. If you don't have a dual button footswitch with a TRS plug, try cycling a ¼"plug in and out of the jack several times. Oxidization on this jack can cause a problem similar to what can be seen with the effect send and receive jacks. If the issue improves a bit, have the footswitch jack cleaned.

OK - so it's the pre-amp for sure. I plugged in headphones in the pre-amp out and I'm getting the same gurgle. On the other hand, if I run my bass through a Sonic Spark and into the power amp in, things seem to work fine. Need to find that footswitch next..

Regards
Mark

 

[Mark_70]

If you have a footswitch for your amp, try it. If you don't have a dual button footswitch with a TRS plug, try cycling a ¼"plug in and out of the jack several times. Oxidization on this jack can cause a problem similar to what can be seen with the effect send and receive jacks. If the issue improves a bit, have the footswitch jack cleaned.

Found the footswitch (one of those rare occasions where my eh - filing system - works). Everything looks okay. Both switches (mute on/off and equalizer on/off) respond just fine to the footswitch. Cycled it a couple times but no difference.

So footswitch appears okay, tubes were recently replaced. Effect loop hotwired (but doesn't make much difference), power amp functions OK, input jack replaced
Still getting this odd very low volume crackling growl out of the amp only..

Regards
Mark

 

[beans-on-toast]

Found the footswitch (one of those rare occasions where my eh - filing system - works). Everything looks okay. Both switches (mute on/off and equalizer on/off) respond just fine to the footswitch. Cycled it a couple times but no difference.

So footswitch appears okay, tubes were recently replaced. Effect loop hotwired (but doesn't make much difference), power amp functions OK, input jack replaced
Still getting this odd very low volume crackling growl out of the amp only..

Regards
Mark

To bypass the effcts loop, all you need is an instrument cable patched between effect send and return. This will open shunts in the jacks. Hot wiring will not test those connections properly.

 

[agedhorse]

OK - so it's the pre-amp for sure. I plugged in headphones in the pre-amp out and I'm getting the same gurgle. On the other hand, if I run my bass through a Sonic Spark and into the power amp in, things seem to work fine. Need to find that footswitch next..

Regards
Mark

Not for sure... the preamp out can't driver the headphones without distorting. It MAY be in the preamp, but your test is flawed (like I indicated in my first post).

Take the preamp out and drive the effects return of a known good amp to see if the noise remains.

Is the effects loop modified? If so, that would be the FIRST place to look. IME. modifications often are the cause of problems because a lot of modifications do not look at everything that is going on within a circuit, or mistakes are made.

 

[beans-on-toast]

OK - so it's the pre-amp for sure. I plugged in headphones in the pre-amp out and I'm getting the same gurgle. On the other hand, if I run my bass through a Sonic Spark and into the power amp in, things seem to work fine. Need to find that footswitch next..

Regards
Mark

You've narrowed it down which is progress. Testing the balanced out into a mixer would help. Test the effect send and return jacks with an instrument cable plugged into the two jacks.

If it is in the preamp, although you changed the preamp tubes, it is possible that the issue is with a tube socket that needs cleaning or retensioning the tube socket contacts. There are many other possibilities such as a connector connection, solder joint, or bad component. If this is the case, best to have a tech look into it.

 

[Mark_70]

OK - thanks. Sounds like it's off to the doctor with her.. I'll open it up, see if everything looks okay with the tube placement but other than that, I best turn it over to a pro. Thanks for the advice!

Regards
Mark

 

[beans-on-toast]

OK - thanks. Sounds like it's off to the doctor with her.. I'll open it up, see if everything looks okay with the tube placement but other than that, I best turn it over to a pro. Thanks for the advice!


Regards
Mark

Good plan to see a tech. You've done what you can in an attempt to resolve the issue.

When the amp heats up, metal expands and contacts improve. This can explain what is going on. You can try reseating any cables inside the chassis but it is a long shot. If a tube slips in and out of the socket to easily it is a sign that the contacts need retensioning. But it can just as easily be a bad solder joint or many other possibilities.

 

[Cvdunk]

I used to play the 4pro and 3pro's back in the early 2000's when i was gigging out a lot in an original band. They used to be in and out of the shops regularly. I was told that (at the time) Ampeg (St. Louis Music) used some mighty thin wafer boards and that the constant hustle and bustle of load in and load out would crack solder joints on the board. I ended up going away from Ampeg at that time because of it. I would notice a lot of what you are mentioning. Always worth taking it in to see a tech.

 

[basscapes]

I used to play the 4pro and 3pro's back in the early 2000's when i was gigging out a lot in an original band. They used to be in and out of the shops regularly. I was told that (at the time) Ampeg (St. Louis Music) used some mighty thin wafer boards and that the constant hustle and bustle of load in and load out would crack solder joints on the board. I ended up going away from Ampeg at that time because of it. I would notice a lot of what you are mentioning. Always worth taking it in to see a tech.

That is unfortunate to hear.

I've always had a soft spot for Ampeg gear, dating back to my V2 and V4B (both Magnavox era, IIRC, and the first two amps I owned, in that order!).

Cut to now, where I can't even get them to acknowledge/suggest a mod for getting more output level from my SCR-DI* and all the general badness/variable quality issues I hear about the SVT-CLs... Well, let's just say that I'm dubious as to any further "upward" purchases...

Sad as well that if a product is great, 10% of the people will review/post about it. Whereas if a product is crap/faulty, 90% of the people will review/post about it.

*Even though I offered to either, a; send it to them to mod, or b; sign a disclaimer/confidentiality waiver to do stuff myself, as an Electronics Tech. No dice. With Tech 21 at least, I was able to email/discuss with the designer regarding a mod (he even told me what parts I would need). Oh well...

 

[Cvdunk]

That is unfortunate to hear.

I've always had a soft spot for Ampeg gear, dating back to my V2 and V4B (both Magnavox era, IIRC, and the first two amps I owned, in that order!).

Cut to now, where I can't even get them to acknowledge/suggest a mod for getting more output level from my SCR-DI* and all the general badness/variable quality issues I hear about the SVT-CLs... Well, let's just say that I'm dubious as to any further
upward" purchases...

Sad as well that if a product is great, 10% of the people will review/post about it. Whereas if a product is crap/faulty, 90% of the people will review/post about it.

*Even though I offered to either, a; send it to them to mod, or b; sign a disclaimer/confidentiality waiver to do stuff myself, as an Electronics Tech. No dice. With Tech 21 at least, I was able to email/discuss with the designer regarding a mod (he even told me what parts I would need). Oh well...

Oh, don't get me wrong.. I still love the sound of an Ampeg SVT-CL over everything else. I just recognized the issues he was having as being similar to ones I face many years ago. Believe it or not, I ended up building a rack set up for touring utilizing a SVP-CL, Fender TBP-1, a much beefier Mesa Shockmount Rack, with a QSC power amp and had plenty of reliable success. Originally the TBP-1 was to be a back up, but ended up bi-amping the whole system out to two 810's using both pre-amps (not sure if bi-amping is the correct term or not). Still have that rack set-up (although not being used anymore

 

[basscapes]

Oh, don't get me wrong.. I still love the sound of an Ampeg SVT-CL over everything else. I just recognized the issues he was having as being similar to ones I face many years ago. Believe it or not, I ended up building a rack set up for touring utilizing a SVP-CL, Fender TBP-1, a much beefier Mesa Shockmount Rack, with a QSC power amp and had plenty of reliable success. Originally the TBP-1 was to be a back up, but ended up bi-amping the whole system out to two 810's using both pre-amps (not sure if bi-amping is the correct term or not). Still have that rack set-up (although not being used anymore

My Ampeg-tone-love still runs deep; I just feel so jaded these days with all the "this died after so many gigs/hours" posts, and yet once in a while, I'll see something that goes, "I've been running X for 10 years now, without an issue."

BTW, still loving my 810E, and the TONE my SCR-CI puts out, but I feel like a sharpshooter taking aim- it's WHEN to pull the trigger that counts!

 

[jeff62]

Shot in the dark here.... have you biased the mosfets? There's plenty of discussion here in TB on the issue.

 

[tchristian]

Shot in the dark here.... have you biased the mosfets? There's plenty of discussion here in TB on the issue.

This was my first thought too - easy enough to check - but it depends a lot on the OP's comfort level with testing electronics. Easy enough to let the smoke out too.

Also, agedhorse and beans are much more qualified than me to know if it's even a likely cause.

 

[NKBassman]

I had more than a few broken solder joints in my 2PRO and 3PRO over the years. I attributed it to the crap cabinet I was using at the time, but as always it's best to have it looked over by an experienced tech.

 

[agedhorse]

This was my first thought too - easy enough to check - but it depends a lot on the OP's comfort level with testing electronics. Easy enough to let the smoke out too.

Also, agedhorse and beans are much more qualified than me to know if it's even a likely cause.

Very unlikely.

 

[rickdog]

One more thing to check: the mute switch and footswitch jack. Try cycling the mute switch a few times, try plugging in and removing a phone plug in the footswitch jack. If you've got the lid off, a little bit of contact cleaner spray on those two locations might help the process.