ampeg svt-3 pro bass problem

[JerseyJake]

I also got a SVT 3 PRO off ebay for a wit gator flght case. I had it for a year now played out in some big clubs here. Once playin out it died I banged the top of the gator case it came back well it started happing more n more now I can't push the amp @ all or it clips out a bang on the top it comes back. I have a clasic 4 10s cab I changed all the tubes last week still clips out. I have had SVTs for 40 years now never had any problem does Ampeg suck now? this Pro 3 says made in USA is it?

[JerseyJake]

Does anyone know if there is a reliable fix for these amps? I just bought another cause I love the sound I plan on racking 2 SVT 3 and use 1 for a backup.

[Mark Black]

Probably would be better form to start a new thread rather than tacking on to an old one but I will say:

Those amps (and indeed most of the amps from Ampeg & Crate, especially of that era) suffer from fairly poor factory soldering made even more troublesome by the use of single-sided PC boards. The fact you can change the behavior of the amp by whacking it is a classic sign of cracked solder joints.

Best thing that can be done for those amps is to have a competent tech go through and re-solder ALL of the joints at ALL: Jacks, switches, controls, LED's, multipin headers, heatsink-mounted devices, driver transistors, all large and/or heat-producing PCB-mounted components, and at any joints seen along the way that look solder-starved or otherwise suspect. This should be done regardless of whether the joints look cracked visually (though I'd bet with some inspection via magnification a whole lot of them WILL turn out to be cracked). Don't just fix the cracked ones - do it right for reliability sake.

There can certainly be other problems but taking care of the solder work will solve the greatest percentage of issues and give a good starting point for any further troubleshooting.

[ImEX82]

hey cheers for getting back to us!
yeah im totally new to all this forum stuff, its really good for a lot people to get solid information with out having you bank balance being violated
and im not sure how to start a new thread
i manged to get the Ampeg to amp tech, he had look at it and he got to the conclusion that "the last person who had it put the tubes in, he put them in wrong section and it blew most of the components which was the reason of the mass lack of volume" so he replaced the tubes with JJ tubes and cleaned it all up!

i took it to the studio and then plugged it up to a 1'15 harkte cab at 8 ohms and it did sound better but still the lack of volume was present!
my previous head what i was using was a Ashdown ABM EVO II at 500 watts! which compared to the Ampeg is a different beast, so im thinking i mite have to re sell it, which was something i really didn't want to do as the time and money what i have put into it!!!!
cos for years have wanted to own a Ampeg, and when i saw it on E bay it was 2much of a deal to throw away!!

The music i play is Melodic Death Metal and i reckon the Ampeg suits more Rock typed metal rather then that!
there is nothing wrong with the amp cos its bin surly checked it and and through the scope now its reading just under 300 watts at 8ohms and just under 500 watts at 4 ohms!!

i am massively gutted!!!!!

[JerseyJake]

Probably would be better form to start a new thread rather than tacking on to an old one but I will say:

Those amps (and indeed most of the amps from Ampeg & Crate, especially of that era) suffer from fairly poor factory soldering made even more troublesome by the use of single-sided PC boards. The fact you can change the behavior of the amp by whacking it is a classic sign of cracked solder joints.

Best thing that can be done for those amps is to have a competent tech go through and re-solder ALL of the joints at ALL: Jacks, switches, controls, LED's, multipin headers, heatsink-mounted devices, driver transistors, all large and/or heat-producing PCB-mounted components, and at any joints seen along the way that look solder-starved or otherwise suspect. This should be done regardless of whether the joints look cracked visually (though I'd bet with some inspection via magnification a whole lot of them WILL turn out to be cracked). Don't just fix the cracked ones - do it right for reliability sake.

There can certainly be other problems but taking care of the solder work will solve the greatest percentage of issues and give a good starting point for any further troubleshooting.

Thanks Mark I'll start a new tread on this too.

[JerseyJake]

hey cheers for getting back to us!
yeah im totally new to all this forum stuff, its really good for a lot people to get solid information with out having you bank balance being violated
and im not sure how to start a new thread
i manged to get the Ampeg to amp tech, he had look at it and he got to the conclusion that "the last person who had it put the tubes in, he put them in wrong section and it blew most of the components which was the reason of the mass lack of volume" so he replaced the tubes with JJ tubes and cleaned it all up!

i took it to the studio and then plugged it up to a 1'15 harkte cab at 8 ohms and it did sound better but still the lack of volume was present!
my previous head what i was using was a Ashdown ABM EVO II at 500 watts! which compared to the Ampeg is a different beast, so im thinking i mite have to re sell it, which was something i really didn't want to do as the time and money what i have put into it!!!!
cos for years have wanted to own a Ampeg, and when i saw it on E bay it was 2much of a deal to throw away!!

The music i play is Melodic Death Metal and i reckon the Ampeg suits more Rock typed metal rather then that!
there is nothing wrong with the amp cos its bin surly checked it and and through the scope now its reading just under 300 watts at 8ohms and just under 500 watts at 4 ohms!!

i am massively gutted!!!!!

I am sorry Im new to this I havta figer out how 2 start new tread

[spy]

I'm resurrecting this thread as I also have a problem with this amp. When I switched it off it makes a loud POP that it doesnt's seem normal. And, the pot "Tube Gain" doesn't work.
The weird is that I can't find the Master Volume and the Tube Gain pots at the schematics? Am I missing something?

[Jazz P Bass]

Come on Spy, you should know better.
Start a new thread.
Anyway, Tube Gain is on Preamp Sheet #1. Test Point 4
Master Volume is on Preamp Sheet #2. Top left, between TP12 & TP14.

[spy]

Ok, maybe I'll start a new thread! Just didn't want to start a same one.

The amp has two Gain pots. One is just "Gain" and the other one is "Tube Gain". I'm reffering for the second one.
I don't have Preamp Sheet 2! Maybe there's the Tube Gain. Can you post it or send it by e-mail?

By the way, any idea about the POP?!

[Jazz P Bass]

Ampeg SVT3 Pro

For the schematic, look at Enzo's post aboce. #7.

I do not see a Tube Gain pot.
Just Gain.
Strange!
The gain pot labeled on the schematic is working the tube.

Don't know about the POP.
Troubleshoot it.
Is it on the FX out?
Is it on the input to the power amp?
Pull V3 & see if it stops.

[spy]

OK! Didn't know that the schematics have 3 pages each! I was checking only page one!

The Tube Gain pot is the "Plate Voltage" pot and it works just fine. Just expecting a different sound difference when you turn it. But as it's adjusting plate voltage the difference will be less audible and in relation with the Gain/Volume.

About the POP, I feel that it's the normal pop all amps are doing when you turn them off. It's like the relay is arcing or something like that. I'm not sure if it's a problem or not. It's only at the output and not at the FX out.

EDIT: Just pull off V1 and when I switch the amp off there's no pop!? What does this mean?

[km6xz]

I must live in a sheltered world but I can't figure out why anyone would rebuild a different amp section, and layer it with mods when it just needs repair. Seems lile a good way to ruin any resale value of an amp. If the OP wanted to give up on it, he should have sold it to a Ampeq lover and bought an amp that he does not think needs mod'ing to work as intended. I sense that they assumed the fault was a design, rather than a repair matter, that can be a costly and wrong assumption.
The amp might be complex to repair but it works just fine as designed.

[J M Fahey]

EDIT: Just pull off V1 and when I switch the amp off there's no pop!? What does this mean?

That the output MOS power pak has no gain, follows what's fed to it, and is quite symmetrical, all of which usually helps in the Pop business.
It doesn't even have feedback, works open loop.
It acts so passively that they had to add a DC servo to keep offset off.
This *is* some kind of feedback, as was pointed out, but since its time constant is 2M2+.047uF it doesn't do much if at all above a couple Hertz.
Worst case, it would cause someting similar to motorboating or a very slow tremolo.

[spy]

Thanks for the info J M Fahey!

Is there any chance to get rid of it?

[J M Fahey]

Maybe, but I don't think the "Pop" is caused by it.
I think that's the common garden variety Pop caused by a small spark in the power switch, coupled and amplified into the audio section, because when you break that chain (by pulling the 12AU7) it disappears, yet the servo is still there.
The output relay doesn't help because it switches the speaker off *after* it.
I usually solve it in the few cases my amps get into different kinds of Temples, Yoga or meditation classes, small Theaters where actors do not use amplification (amp only supplies low volume background music), etc., where the smallest Pop is unacceptable, because it ruins the mood, simply by adding a "standby" switch, which actually switches output jacks on and off.
*Always* works .
My last such amp went into a Federal Prison for Women, close to our Ezeiza Airport, chock full of *gorgeous*, man-starved female prisoners.
My customers are into Guru Maharaj-Ji and go there to let them "see the Light" , including DVDs by him.
Who are these gorgeous prisoners?
Air Stewardesses which are caught smuggling Cocaine, who wrongly believe their airline uniform is some kind of shield.
1/3 of them tried to smuggle into Europe (mainly Spain) but an astonishing 60 to 70% are beautiful South Africans.
I guess that by the geographically isolated position of S.A., the only practical way for this kind of "trade" is by air, so they are offered good money.
They get 5 years for it.
Oh well.