Ampeg SVT-4 PRO Direct In issiue..

[mLascano]

Hey everybody, this is my first time posting here..

Ever since I bought the thing, every time I play any venue where they want to go direct from the back of my head, they always give up and I end up going through my sansamp or another DI box. Everyone tells me they get a buzz and noise from the jack..

The guy last night asked me If I had a ground or something like that.

I am not very smart on all the sound lingo but I can get the basic logistics of it..

I took it in to a certified ampeg service center and they said they couldn't find anything wrong and i ended up blowing 40 bucks for nothing... Only to find that the next show when I try it still gives noise.

I'm going in to the xlr jack. the middle one.
Can anyone please help me?

[mLascano]

noone can help a guy out?

[PRNDL]

Ever since I bought the thing, every time I play any venue where they want to go direct from the back of my head, they always give up and I end up going through my sansamp or another DI box. Everyone tells me they get a buzz and noise from the jack..

This is not uncommon - both in tube and solid state amps, which is why DI boxes are so useful. The issue is most likely due to grounding, and the ground lift feature on the DI box usually fixes it. There may also be an impedance and cable length issue, which is also solved by the DI box.

I took it in to a certified ampeg service center and they said they couldn't find anything wrong and i ended up blowing 40 bucks for nothing... Only to find that the next show when I try it still gives noise.

The amp may be fine, and still have this problem (BTW - $40 is usually a bargain these days)

You need to find someone that has specific knowledge about using the direct outs on this specific amp. I'm pretty certain, although I'm not an expert, that they'd say the DI box is necessary.

[MarkusBass]

Do I understand correctly that you are using transformer balanced line output jack on the rear of the amp? See page 9 here: http://www.ampeg.com/pdf/SVT4PRO.pdf (items marked 41 and 44). In my opinion the transformer in this amp is separated from the ground (actually there are two transformers, one for each channel). You can verify this with a DMM by checking resistance between pins in this jack and the amp's enclosure. Either the pins are grounded (which is incorrect), or you have problems with the cables you use.

Mark

[PRNDL]

I stand corrected - I was looking at the SVT preamp instead of the SVT4Pro, which has the balanced transformer built in. The Ampeg designers have made improvements.

Does that leave a grounding issue?

[mLascano]

So should I take it ans ask them to check it for grounding issues?

what exactly is a DMM?

[MarkusBass]

Sorry for the shortcut - Digital Multimeter. But you haven't answered to any of my questions . Are you using the output jack I mentioned?
I wouldn't take the amp back to any workshop (you would pay again $40). I would rather take it to a friend who knows something about electronics and is eager to help you.
I would also check other amps of this type (if you have such a possibility, e.g. in a music store). Do they have the same problem?

Mark

[mLascano]

Hey, yeah we tried both of those jacks with an xlr cable and all he gets is a big buzzzzzzzzzzzz