Amp problem: Giving an odd sound :(

Mirthoneist · #1 01-04-2011, 09:58 AM

Quick History: A few years ago I bought a new Ampeg 4x10 cab and a used Ampeg SVT-3 Pro head, which worked amazing. I've always left it at my brother's house (drummer), where we had band practice, and one day he had some friends over and they jammed. Next time I go there, it just sounds like ass. I couldn't figure out what was wrong, and during that time found an amazing price on a GK head and an Avatar Cab, so I got those to have some sort of remedy.

Fast forward a few years ahead to now. My Behringer practice combo sucks, and I'd really love to get my Ampeg stuff working, as I have it at home now and the GK/Avatar stuff as my main rig at my new band's place.

I'd never known if it was my cab that was the problem or the head. I finally got the chance to test some combinations out: The GK head with the Ampeg cab sounds nice and normal. The Ampeg head and Avatar cab sounds like ass, just like it does with the Ampeg head and cab. So, I know it has to be the Ampeg head that is the problem. Problem is, I don't know how to fix it. I changed the fuse that's is in a little cover in the back, and that didn't seem to help. (Couldn't tell if the fuse was blown or not, as the glass has a white covering or something). I've opened it up and "looked" at the tubes... I don't know what bad tubes are supposed to look like, but I know they all lit up fine. I've tried other cables, which didn't help, and it sounds bad on all my basses, so I know it's not that.

To describe the sound... Every note sounds lifeless. If you play a note somewhat softly, it sounds lifeless AND sounds like there is static. I've tried different setting, such as tube gain all the way down or middle or up, equalizer on or off, etc, and everything sounds bad.

If anyone has any suggestions or methods that I'm not aware of to test it more, please let me know. I'm not in the financial position right now to be able to pay someone to look at it and fix it, so I'd like to figure it out on my own with you guys.

**pacojas** · #2 01-04-2011, 10:13 AM

re-seat all the tubes. if better great,... if not remove, replace, and re-bias all new tubes. if that doesn't work,.. sell as is and buy a rack that locks. gl.

Jim C · #3 01-04-2011, 11:37 AM

Most common problems are a bad tube in the pre-amp or driver stage or a bad solder joint (my old 3-Pro developed 2 bad solder joints over the 10 years I used it gingerly).
While the SS power amp may need to have a bias adjustment the tubes do not.
If you feel comfortable inside an amp, borrow some known good tubes and try some swapping; if this doesn't fix it, time to see a tech.

Mirthoneist · #4 01-04-2011, 04:42 PM

Thanks for the advice fellas. I'm going to open it up and take a gander inside first thing in the morning or later tonight.

If it is the tubes, do any of you have a recommended site to purchase some from?

okcrum · #5 01-04-2011, 04:46 PM

OP, your bro owes you a trip to the tech. If you're not set up to test a ceramic fuse or tube, you do not want to be poking around inside that amp.

Mirthoneist · #6 01-05-2011, 09:19 AM

Yeah, I think we both learned our lessons, so I'll just take it as an accident and a learning experience.

But I already poked around inside. I reseated all the tubes, and that didn't seem to help. I'm thinking of purchasing one brand new tube and testing it in place of each old tube, one by one. And I guess that all the solder joints are on the bottom side, so I'd have to unscrew the boards to look at the underside. I'll do that after the tube thing.

pbass2go · #7 01-07-2011, 01:54 AM

If your amp has a pre-out and power amp-in, try running the pre-out into your GK... see if it sounds ok. Then go the other way and see what you get.
Thats how i found out my brothers SVT3 Pro had a power amp section that needed work.

Good luck with it..

Mirthoneist · #8 01-07-2011, 08:26 PM

So I bought a new tube, and swapped each one out for the new one, one by one, and I get the same thing. So I suppose that eliminates it being the tubes, unfortunately.

Thank you for the advice, pbass2go, I didn't even think about that, I'll give it a shot!

rickdog · #9 01-07-2011, 10:28 PM

Quote:

Originally Posted by Mirthoneist

Quick History: A few years ago I bought a new Ampeg 4x10 cab and a used Ampeg SVT-3 Pro head, which worked amazing. I've always left it at my brother's house (drummer), where we had band practice, and one day he had some friends over and they jammed. Next time I go there, it just sounds like ass.

Optimistic possibility: vibration upset the very sensitive bias adjustment pot. From your description ("static" on soft notes) I think this sounds pretty likely.

Pessimistic possibility: one or more of the output transistors failed due to abuse.

If your testing with the pre-out and power-in isolates the problem to the power amp, take it to a tech to be rebiased. The tech will notice right away if it an output transistor is blown.

Mirthoneist · #10 01-08-2011, 12:58 PM

Again, thank you guys for the kind advice.

Since I won't be to my GK gear till Thursday, I noticed that my Behringer combo amp has an Amp In and Preamp Out, so I used those to test it with my SVT-3 Pro. In conclusion, it sounded bad with both the Preamp Out or Power Amp In...

So I guess it's something more than needing a rebias, I assume? I apologize for my lack of electrical knowledge. Sounds like I've run out of options minus bringing it to a tech, which I can't really afford not knowing how much it'll cost me.

BassmanPaul · #11 01-08-2011, 01:59 PM

PLEASE stop messing around with potentially lethal equipment! Take the amp to a tech his bill will be less than your life is worth.

No advice that advises opening up a tube amp by someone without technical skills is good advice. Apart from hurting yourself you could well make a $50 repair into a $500 one.