SVT-3 Issue

WhoDidTheElf · #1 06-09-2011, 05:14 PM

Hey guys,

So I just my SVT-3 Pro in the mail today from a fellow TB'er and I'm having some issues...

The biggest issue is volume. There is almost none of it. For it to even be audible the master hast to be at about 1 o'clock, and the gain well over 12 o'clock.

I checked inside, all the tubes are in place, and they all light up when the amp is on. The fan spins and everything seems to be in place, but no volume. When I run just one 8ohm cab it seems to be a bit louder, but when running 2 8ohm cabs it gets quieter.

I tried different cables, basses, cabs, ect... all to no avail.

Alex1984 · #2 06-09-2011, 05:17 PM

As I'm sure JimmyM would chime in to say, the SVT 3 Pro likes the gain HIGH. The LED is more of a signal light rather than a clip light, so you actually want it to be lit.

WhoDidTheElf · #3 06-09-2011, 05:19 PM

Even if the gain is full tilt and the lights solid on regardless of what I'm doing, the volume is almost inaudible.

I'm not talking about "oh this isn't 450 watts worth of volume" I'm talking like there is no volume what so ever.

Alex1984 · #4 06-09-2011, 05:23 PM

Can you tap the preamp out to test whether the problems in the preamp side or the MOSFET side?

WhoDidTheElf · #5 06-09-2011, 05:34 PM

Quote:

Originally Posted by Alex1984

Can you tap the preamp out to test whether the problems in the preamp side or the MOSFET side?

Just did, ran my WA's preamp out to the power amp in on the Ampeg and the volume was low and it was distorted out of the cabs powered by the Ampeg.

JimmyM · #6 06-09-2011, 05:40 PM

Driver tube busted, maybe? They can still light up and not be working.

rodl2005 · #7 06-09-2011, 05:44 PM

Oh the 3pro is notoriously under powered ;-)

WhoDidTheElf · #8 06-09-2011, 05:46 PM

Quote:

Originally Posted by rodl2005

Oh the 3pro is notoriously under powered ;-)

Nah I know how loud and SVT-3 Pro is, I've used them before. This isn't the normal "this isn't 450 watts of volume" this is NO volume.

Quote:

Originally Posted by JimmyM

Driver tube busted, maybe? They can still light up and not be working.

Possibly. It just distorts really easy. Aside from being extremely quiet.

JimmyM · #9 06-09-2011, 05:48 PM

Distorting really easily is often a sign the MOSFETs need biased as well. I'd try getting a couple tubes, one of each, and swapping them around one at a time till you find the culprit. If there is no culprit, you'll have to take it in to get it repaired and/or biased.

Alex1984 · #10 06-09-2011, 05:49 PM

Quote:

Originally Posted by rodl2005

Oh the 3pro is notoriously under powered ;-)

I thought the 4 Pro was even more notorious.

JimmyM · #11 06-09-2011, 05:53 PM

All BS, this underpowered stuff. I had a 3 Pro for a few years and have played many 4 Pros, and they're not underpowered at all.

WhoDidTheElf · #12 06-09-2011, 05:56 PM

Quote:

Originally Posted by JimmyM

Distorting really easily is often a sign the MOSFETs need biased as well. I'd try getting a couple tubes, one of each, and swapping them around one at a time till you find the culprit. If there is no culprit, you'll have to take it in to get it repaired and/or biased.

Yeah from what I've read, it sounds like MOSFET biasing.

Sigh...

Could they have become unbiased over delivery? (clueless about the subject)

prd004 · #13 06-09-2011, 06:09 PM

Input gain should be way up, I have a hot bass and still I run mine at 3:00 all the time.
The plate voltage/tube gain knob is key too, where is yours set? It's a tricky knob that in IMO is severly mis-labeled! People turn it down thinking it's some kind of distortion level, but it's more like a compressor. If you turn it way down your amp will have little to no output. Try cranking that one way up too (3:00 or so), and see what happens. If you're input is at 3:00, your plate voltage/tube gain is at 3:00 you should be able to rock the house with the master around 12:00......................
If that doesn't help then look into biasing.

WhoDidTheElf · #14 06-09-2011, 06:11 PM

Tube gain is full tilt, other wise it literally is inaudible regardless of my settings.

prd004 · #15 06-09-2011, 06:12 PM

Quote:

Originally Posted by JimmyM

All BS, this underpowered stuff. I had a 3 Pro for a few years and have played many 4 Pros, and they're underpowered at all.

Amen, this is like an old wives tale that has no basis in reality but somehow won't go away.
I've used an SVT-III PRO for nearly two decades and it's NEVER been underpowered in any situation, and I've been in some loud ones.

prd004 · #16 06-09-2011, 06:15 PM

Sorry to hear that, seems like a repair is in order.

The bias issue seems to come up quite a bit on this forum, can anyone elaborate? I would just like to know what causes it, what it means, and what is involved in fixing it.

Thanks

redhed · #17 06-09-2011, 06:19 PM

Quote:

Originally Posted by prd004

Input gain should be way up, I have a hot bass and still I run mine at 3:00 all the time.
The plate voltage/tube gain knob is key too, where is yours set? It's a tricky knob that in IMO is severly mis-labeled! People turn it down thinking it's some kind of distortion level, but it's more like a compressor. If you turn it way down your amp will have little to no output. Try cranking that one way up too (3:00 or so), and see what happens. If you're input is at 3:00, your plate voltage/tube gain is at 3:00 you should be able to rock the house with the master around 12:00......................
If that doesn't help then look into biasing.

Man, I've never had to crank mine that high - ever. I run mine through a 810 or a 115 ( or even two aggie 112's ) - never had a problem with volume.

prd004 · #18 06-09-2011, 06:25 PM

Quote:

Originally Posted by redhed

Man, I've never had to crank mine that high - ever. I run mine through a 810 or a 115 ( or even two aggie 112's ) - never had a problem with volume.

LOL, maybe mine needs biasing too!!!!!!! it's seventeen years old and seen a lot of mileage. I haven't heard any problems though.

WhoDidTheElf · #19 06-09-2011, 06:27 PM

I don't know if it makes a difference or not...but the amp is at least 10 years old.

And the original owner said the tubes have never been replaced so...

redhed · #20 06-09-2011, 06:32 PM

Quote:

Originally Posted by prd004

LOL, maybe mine needs biasing too!!!!!!! it's seventeen years old and seen a lot of mileage. I haven't heard any problems though.

I do however put the tube gain all the up - thats just the way I like it.