SVT-3 Pro tube gain question

wallypip · #1 04-09-2010, 03:43 PM

Hi guys! I'm a longtime lurker on this board and I need a little advice. I was testing out a used SVT 3 Pro yesterday and I was pretty happy with it except when I turned the "tube gain" knob it made bad scratchy noises. Also, it didn't actually change the tone once I got it set to a clean sound. The amp had a nice growl in the upper registers that didn't change whether I was all the way up, in the middle or down, so I felt like the tube gain wasn't changing anyway.

This is not just a scratchy pot--I know that when I see it. Something isn't right about it. The guy is offering it pretty cheap ($500) so I am not opposed to anything that requires a simple fix like replacing the tubes. Any ideas on what it could be?

RickenBoogie · #2 04-09-2010, 05:20 PM

That tube gain knob is tricky, at 100, or completely ccw, and with the normal gain and master cranked, you should get some grit, but not alot. The other way, 300, or cw, is clean clean clean. At least, that's how it works on the 6Pro, and supposedly, the 2 amps are very similar, except for the output power difference. Still, sounds like that pot needs a cleaning.

Mark Olson · #3 04-09-2010, 06:32 PM

The tube gain knob has ABSOLUTELY NOTHING TO DO WITH OVERDRIVE WHATSOEVER.

It controls tube compression. Listen more carefully when you put it at minimum and maximum. Personally I liked it at maximum only. Way too "soft" when you turn it down, but hey, that might be what you're looking for. Oh and I got tons of overdrive with it completely clockwise, you just have to crank the amp up, that's the only way to get the overdrive.

Jerrold Tiers · #4 04-09-2010, 09:12 PM

Quote:

Originally Posted by Mark Olson

The tube gain knob has ABSOLUTELY NOTHING TO DO WITH OVERDRIVE WHATSOEVER.

It controls tube compression. Listen more carefully when you put it at minimum and maximum. Personally I liked it at maximum only. Way too "soft" when you turn it down, but hey, that might be what you're looking for. Oh and I got tons of overdrive with it completely clockwise, you just have to crank the amp up, that's the only way to get the overdrive.

Close...........

it controls the voltage to the POWER AMP driver tubes...... IT HAS NOTHING TO DO WITH THE PREAMP, which most people assume it must.

Therefore, it affects the way the power amp overdrives, but you have to already be hitting the power amp hard to have it work and notice a difference. At lower volumes it just isn't noticeable, because you aren't pushing the power amp

JimmyM · #5 04-10-2010, 12:53 AM

Quote:

Originally Posted by Jerrold Tiers

Therefore, it affects the way the power amp overdrives, but you have to already be hitting the power amp hard to have it work and notice a difference. At lower volumes it just isn't noticeable, because you aren't pushing the power amp

jerrold, i know you're the dude from ampeg, but i would have to disagree with you. i found the tube gain control helped out immensely with the tone at quieter volumes as well as louder. sure, i didn't get any drive out of it at the low volumes i play, but tonally i thought it was a big improvement to the clean sound.

RickenBoogie · #6 04-10-2010, 07:50 AM

Since it does seem to be alot like the 6Pro, as I mentioned in my first post, "with the volume cranked", the ccw position will offer more o/d.

mazdah · #7 04-10-2010, 08:04 AM

Strange noises and momentary sound delays/fadeouts during turning the knob is absolutelly normal thing.

Tube gain changes a lot, you just need to listen more carefully.

wallypip · #8 04-11-2010, 06:36 AM

Quote:

Originally Posted by mazdah

Strange noises and momentary sound delays/fadeouts during turning the knob is absolutelly normal thing.

Tube gain changes a lot, you just need to listen more carefully.

I don't think I explained the problem quite right. The knob makes strange noises when it is set at certain levels. I don't mean that I just don't like the sound, I mean that it sounds like the connection to the cabinet is loose or something. Obviously it is not the connection, but I'm trying to describe the overall wrongness of the sound. I hear static and popping noises. Scratchy pot is a good comparison, but usually that only occurs when you are actually turning a pot. This one just gets scratchy and stays that way until spin the knob back and forth.

It is also inconsistant. I can crank it up and it's fine. Then it isn't bad until I turn it down to 3 O'clock. At zero I get nothing and then I can't even make the amp make noise until I turn it back to 12 O'clock. It always sounds great when it's cranked all the way up.

A good cleaning might do the trick, but I want to be sure before shell out the bucks.

Jerrold Tiers · #9 04-11-2010, 07:46 AM

Scratchy pots CAN have settings where they act scratchy even if not being turned..... Clean the pot, and if that doesn't work, it might need replaced.

If the problem was at all settings, it might be something in the voltage control circuit. still might be, if the problem is not at certain settings... if you can't determine for instance that at "2:00" on the dial it is usually noisy.

Jimmy.....

The control does what it does...... which is adjust the driver voltage. That should do little until you actually get close to that signal level, and in fact the usual complaint is that the control "does nothing"......

If you hear it doing a lot at low volumes, OK..... maybe yours is bad in a good way

eyeballkid · #10 04-11-2010, 07:59 AM

yeah, I gotta agree with Jimmy...
i used to have a SVT-3pro... and while it did add a VERY nice overdrive at higher volumes, at low volumes it helped to fill out the sound nicely. It wasnt drastic but definately noticeable and preferred!

mine got more drive going clockwise, as i would expect it to do.

mazdah · #11 04-11-2010, 08:51 AM

When you turn down you'll hear noises for few seconds and then it should work just fine.
Static and popping noises are normal when lowering the tubegain level from about 12 o clock in my amp. After few seconds everything is fine and silent.

Jerrold Tiers · #12 04-11-2010, 09:36 AM

Quote:

Originally Posted by eyeballkid

yeah, I gotta agree with Jimmy...
i used to have a SVT-3pro... and while it did add a VERY nice overdrive at higher volumes, at low volumes it helped to fill out the sound nicely. It wasnt drastic but definately noticeable and preferred!

mine got more drive going clockwise, as i would expect it to do.

Maybe you just hear what most don't. It CAN make a difference , but it's subtle.... most people don't notice.

BTW, the "tube drive" is more effective turned DOWN than UP............. it's really tube voltage........