Ampeg SVT4-Pro Problems

[Steve Conner]

Do you smoke a lot?

Is it damp in wherever you normally keep the amp?

Either can mess up those jack contacts Enzo was talking about.

(currently I play MarkBass F-1 but mainly due to its weight < 2 kg).

also because it has your name on it?

[MarkusBass]

also because it has your name on it?

No, it's just a coincidence. My first name is Marek and when I was trying to choose a nickname on this forum, I found out that MarkBass is available. At that time I didn't own Markbass amp.
BTW: it would be great to play bass on Trace Elliot amp and have exactly this name. I think that Elliot may be a popular first name. Is it?

Mark

[doombilly]

Do you smoke a lot?

Is it damp in wherever you normally keep the amp?

Either can mess up those jack contacts Enzo was talking about.


also because it has your name on it?

Non-smoker. Completely dry where it is.
Guys, I've had 4 "Real guys" look at this thing. It's been a long time since my high school electronics courses. But I think I qualify for at least "half" of a "Real guy." The last fellow, who has worked on many of these amps had it "burning in" in his shop for more than a week and could not find a problem. If the problem does not present itself to them I don't see them fixing it. I don't see me carting it off to one more place. The extended warranty came from Guitar Center. What this involves is Loud getting the amp back for an unspecified time and maybe fixing it, more probably just like everyone else, telling me they don't see a problem. Since I could not do without the amp for an unspecified time, I would likely need to BUY another head to get me through until it is fixed. If I am going to BUY another head to get blown off again by the manufacturer, I'm going to choose another brand, and I'm going to sell this one for what I can. I respect that you may feel if only you could trouble shoot the product it could be fixed. At some point the customer loses faith that it will ever happen. And if it does, any "repair" would be short lived.
Regards,
Eric

[Joedel]

Doombilly, I have owned several classic SVT heads and Cabs thru the year....love em....six years ago I bought an svt pro 4 used from guitar center. great sound, in fact, better than my old classics from the 70's. After about the first year started having problems with the amp all of the sudden both power amp sections would shut down. I took it into an authorized ampeg shop here in seattle and the tech stated how poor the solder joins are with the new tube mosfet ampeg amps. He did some resoldering of a certain area on the main board. After about a year the same problem stated happening. This time I completely disassembled the amp, pulled out the main board with the twin towers of hear sinks still attached put it under a magnifying glass and stated resoldering areas testing then resoldering.. during the testing I found certain occurances that may be connected (no pun intended) to your problem. I noticed in the photo of your wife that she has the amp sitting on top of the cabs. What I found out is that when I took the amp to the tech he put in onto the bench plugged it into a cab sitting on the floor. We could not get the amp to fail...but when I would get the amp at rehearsal or at a gig I would place it directly on the cab...within about 30 minutes it would fail...With 1200 watts producing a ton of cab vibration it would vibrate the very suspect poor production wave solder joint to failure, especially with the tall heat sinks that vibrate unsupported at the top end flapping around causing solder failure at the PCB to Mosfet solder joints. So my fix was to resolder everything and either place a vibration dampening pad under the amp to cab, or move the amp from the cab altogether....hope this helps...ampeg are a great sound especially with old allman bros songs....joedel

[MarkusBass]

I think that this is very old thread and the amp is either fixed, or sold. I'm just worried that , >>4 "Real guys" were look at this thing<< and they were not able to fix it. What "real" means in this case?

Mark

[DrGonz78]

I tend to set up an Ouija board and light some candles. At that point I conjure up some "non-real guys" to enter my repair room and put them to work on the issue. Half of fixing something these days is just trying to find "real guys", so I am bucking the system. Next I am gonna conjure up a sexy black magic woman!!

My old amp tech would never charge for something if he could not reproduce the symptom of the amp in his repair shop. Now that's a real guy! Now I understand that this post had to deal w/ warranty repair so that is a given. Also, I appreciate the explanation that putting a bass head on top of a speaker is gonna vibrate the heck out of the amp. Combo amps is whole different can of worms in this case.

[Enzo]

Venturing to guess, I'd say he meant actual amp techs, as opposed to basement warriors.

[Alex R]

I tend to set up an Ouija board and light some candles. At that point I conjure up some "non-real guys" to enter my repair room and put them to work on the issue. Half of fixing something these days is just trying to find "real guys", so I am bucking the system. Next I am gonna conjure up a sexy black magic woman!!

My old amp tech would never charge for something if he could not reproduce the symptom of the amp in his repair shop. Now that's a real guy! Now I understand that this post had to deal w/ warranty repair so that is a given. Also, I appreciate the explanation that putting a bass head on top of a speaker is gonna vibrate the heck out of the amp. Combo amps is whole different can of worms in this case.

I think no fix no fee is a good rule and I apply it to amps where I can't actually find anything to fix. Saves a lot of trouble. I do have a bench fee in my terms but I very rarely apply it where no fault has been found - only if that possibility was part of the original agreement. Of course if you announce this policy you will get every ghostly fault in the area on your bench, there being such a thing as the imaginary fault, and/or the perceived fault that is an artefact of the nature of human hearing under extreme stress, eg 'my 100w Marshall loses treble after an hour of heavy metal'.

I do often find that amps with a reported intermittent drop in power tend stubbornly to refuse to show a fault on the bench. With this one I'd have been measuring the output of the preamp pretty early on, if checking relays, send/return and speaker jacks didn't reveal a problem. Remembering that the possibility of charging a fee was quickly receding!

[J M Fahey]

Re-reading this incredible thread from the beginning, I don't think we have a problem.
Not a Technical one, at least.
So it can't be solved by a Tech.

Consider the following facts, not individually but as a whole:

1) first complaint: "the amp *seemed* to have lost punch".

In my shop, that immediately raises a red flag.

People buys something, is thrilled; 6 months to 2 years later "it does not sound/have power/etc. like whan it was new".
Yet checking shows it's up to specs, like new.
We are talking measurable power, sensitivity, etc. , not some minor dirty pot or such .
The fact that it's mainly psychological is confirmed by the owner actually "hearing" an improvement.
Happens with new tubes, cables, etc.

He might have been unlucky with 1 tube (and I'm not too sure about that) but 4 in a row is ridiculous.
Specially because after replacement, "they *do* sound good" but within 6 months *all* sound bad.
C'mon, gimme a break !!

2)Ampeg/Loud suggested it, apparently over the phone.

This makes me remember somethig from my youth.

My Dad was a Country Doctor and as such the phone rang any *any* time, day or night.
Some were real emergencies, so he dressed up and went to check it, but others were "non-problems" from fussy customers, already known for that .
Vague undefined "pains" which under scrutiny , tests, XRays, etc. showed nothing, etc.
So, what was the standard answer in such cases?: "have an aspirin, wait 4 hours for it to make full effect, and if not, come see me in the morning".
At reasonable hours, of course.
Well, "replace a tube" sounds like "aspirin" to me.

Also why the heck we keep going through tubes. And if it is not the tubes, why it seems to get better after I change them.

Well, now you know.

OCDisorder seems to parallel my suspicions:

Just wondering if a fresh pair of ears might be worth pursuing.
Another bass player with a different guitar.
Other than that I see no option other than taking it to an authorised
Ampeg repair centre.
The fact that you have changed the pre-amp tubes 4 times and noticed a difference is unusual.

3) the key seems to be related to what I hinted about "New=Exciting vs. Old=Boring

" Now, right after the most recent replacement it just does not have the oomph to compete with my 15w guitar+cabinet played at the same setting we've always done."

Well, there's the key.
I'm sure it means "when just bought, it was so loud that it had to be used with Gain=1 and Master=1 to match my 15W guitar amp"..... and "now that's not enough".

OK Buddy, just use it on 2 (or whatever's necessary".

-"Hey!!! , but 2 years ago it was louder on the exact same setting"
Well, *maaaaayyyybe*, human ear is a very unreliable meter and data recorder so that cdoesn't cut much ice with me.
I'm sure that 2 years ago, say, 200 mV 1KHz with all gain controls on "5" drove it to full power .... and that has not changed.
But we are talking stable test instruments of course.

The *big* unstable variable is the Musician itself.
That plus old strings, different Instrument setup, different pickup height, different finger pressure, etc.

Please avoid the fetish that you must set it to exactly

played at the same setting we've always done.

.
That's why amps come with pots and switches, to be able to adjust it in many different ways and adapt to different players.

That said, I very much doubt a 600W RMS monster, with proper cabinets "doesn't have oomph to match a 15 W amp".
No way.

This seems very "out of order" for 790 watts to not be oomphy enough to keep up !

Same thought here

[soundguruman]

ok, let me start off by professing my ignorance of most in depth electronic gadgetry. I know enough to be dangerous.

My wife/bassist plays a P bass, flat wounds, with her fingers. (So fairly low output passive electronics). She's been using a (purchased new) Ampeg SVT4Pro head for about two+ yrs. We've replaced the pre-amp 12AX7 tubes about FOUR times. This is because after speaking with Ampeg (LoudTech) early on, they suggested it. The amp seemed to have lost it's punch. Each time the problem seemed to correct, but the duration between the need to replace the tubes was less each time. Now, right after the most recent replacement it just does not have the oomph to compete with my 15w guitar+cabinet played at the same setting we've always done. The cabinets (GK BLXIIa 4x10; SWR 1x15) are running dual mono full range. Attached by neutriks. I've tested all the speakers. And they are working. We just took the head to a shop and they tested the outputs of both channels and got 288w (8ohms) from each output (A, B).
After doing some reading I've found that there can be some problems with other SVT hybrid heads wherein they may require some biasing of (what I am guessing is) some part of the solid state power amp section.

Obviously we would want that done if there was any logic to it. Can anyone recommend any tests a novice without a meter or other implements can check?

Please advise. I'm new here, my apologies if I did not format this correctly or have crossed any bounds.
Eric in Charlotte NC USA.

Dear Eric:
To get the consistency of an SVT, start with a real SVT.
The real SVT was made by Magnavox. It was made in USA and weighs 85 pounds.
If the SVT you are frustrated with does not meet this description, then find a real one.