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SVT-4 Problem

V

Varkatzas

Oct 21, 2008
37
0
#1
Recently my band was on tour, and at one of the shows the bass kept cutting in, and cutting out. It would play fine for about 15 seconds, then cut out and be 0 sound, then after a minute it would come back, then just repeat.

We packed up, went to our next show, and now as soon as we turn the amp on, the peak light is on at all times and we get absoultuly no sound of it. Tried different speaker cables, instrument cables, basses, everything, but it just says its peaking and there is no sound.

Can anyone please help me diagnos the problem? :help:
 
#2
you can buy mine, its for sale! lol, but seriously!

um, i had that happen once, i accidentally plugged my tuner into the mute switch on the back once and the red light stayed on. another issue, if youre using any preamp stuff in a rack, make sure everything is plugged in hard. i had a few times where some cables got loose and the head would just peak like that.

other than that, it might be a preamp tube issue but im not super familiar with that. somebody will know though.
 
#4
I have posted the problems with SVT-4PRO's numerous occasions. Search on 4PRO overheating problems.

The problem is the amp circulates air from left to right and not out the front. The symptom you describe is the amp going into temp overload. It is now broken.

It says right in the manual, provide three inches on each side of the amp for cooling. My guess is your rack does not provide this clearance.

If it doesn't you need to provide a way to circulate the air artificially. Unfortunately NOW your repair is going to be VERY COSTLY.

For instance my rack only has 1" of clearance on each side and I utilize a bunch of blowers to move air into and out of the rack. You may look at my profile for a picture of my rack.

BOB
 
#5
rbonner said:
I have posted the problems with SVT-4PRO's numerous occasions. Search on 4PRO overheating problems.

The problem is the amp circulates air from left to right and not out the front. The symptom you describe is the amp going into temp overload. It is now broken.

It says right in the manual, provide three inches on each side of the amp for cooling. My guess is your rack does not provide this clearance.

If it doesn't you need to provide a way to circulate the air artificially. Unfortunately NOW your repair is going to be VERY COSTLY.

For instance my rack only has 1" of clearance on each side and I utilize a bunch of blowers to move air into and out of the rack. You may look at my profile for a picture of my rack.

BOB
Click to expand...

Ive never seen a rack that provides 3 inches of space on the sides... we have a 10 space with just that and a 1 space power conditoner... I can't see how it would overheat.

How costly are you talking?

edit: I am going to de-rack the head tonight and hope to god it works :(
 
#6
Does sound like overheating, in the beginning.....

Question is why, since I agree, the clear space and lack of other stuff tends to make the cooling less of an issue (but not "no issue").

besides, overheating to the degree allowed by the temperature circuit, if it is working, is a stress, but not generally a fatal stress. The temp is set specifically NOT to be a fatal problem, it goes off just before you get into problem territory.

There is, IMO, a possibility that the temp cutoff circuit, or some other part of the circuit which runs the relays, has a problem, and that there MAY not be a serious problem at all. It MIGHT be stuck in a "fault" that really does not exist, because the fault circuit is bad and declaring a fault when there is no fault.

There is also a chance that there really is a bad problem. Can't tell from here.

I suspect a chance of teh less expensive problem because usually if the temp circuit cuts off the sound, it will play LONGER than 15 seconds before going off again. The circuit cuts off at one temp, but requires the amp to cool down to a lower temp before cutting in again. Then it has to warm up again before cutting off. That takes a while, there is a lot of aluminum heatsink to heat up.

Have a reliable tech look at it, then you'll know. the rest of us are guessing....... I designed the amp that was adapted from, so if I don't know from the info so far, nobody else is likely to either.
 
#7
I de-racked it last night, and it still just has the peak light on the whole time, no cutting in or out at all. I took off the top, and changed the preamp tubes just to make sure, and it is still doing it. I don't know much about the construction of amps, but all of the solders and wires seemed to be okay, so it must be something I can't see. I really hope it is a cheap fix because this is the 3rd Ampeg head that has gone to **** for such a stupid reason ;/
 
#8
Hi.

Sorry to hear that You couldn't solve the problem by swapping the tubes.

Like Jerrold said above, if he can't diagnose it from the distance, good chances are that no one else here can either. And even if the problem is diagnosed correctly, it still takes a tech to perform the repair.

Unfortunately it's tech time and hopefully it doesn't mean a new amp.

Like BOB said, look for 4PRO threads and You'll get a rough estimate what are the most common problems with that particular design and that particular circuit. Won't make You happy, but at least you'll know what to expect.

Regards
Sam
 

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