Ampeg SVT-4 Pro Ground Lift Issues

Depending on what model that is, it DOES have a ground lift, and it is lifted. The outputs asre transformer coupled, and there is NO connection between the chassis of the amp and the mixer.

In that case, any hum etc would have to come either from a defect in the mixer, a defect in the DI transformer, or hum induced in the transformers from outside, like something else nearby in the rack.

 

Then my suspicion is that the internal transformers in teh 4 pro are for some reason turned in such a way as to pick up hum.

They aren't shielded like mic transformers, and I seem to recall something like that. I thought it was with very new ones, and not older ones, but then I don't know how old yours is.

Anyway, there is zero way for the setup to hum due to any form of "loop", since it is "permanently ground lifted" in the design.

 

I'll be interested to see what the resolution to this problem is since my 4pro has the exact same problem.

 

Read this. If there's a loop one or more of the described issues is in play.
http://www.rane.com/note110.html

 

this prob have been addressed before as it seems don't have solution, Jerrold as always is been more then helpful helping others( thanks man!!). I use a di in the 1/4 output, a very cheap way to solve this issue , but other then that I love this head.

 

OK

#1, no "ground loop" can exist, the landing gear, oops I mean the circuit, has no thru connection between chassis in any recent 4PRO

#2 BOTH DI outputs are fully transformer isolated, eleiminating ANY wire connection to the 4PRO chassis.


So... The problem is virtually certain to be induced hum.

I seem to recall that certain of the 4PRO units actually had the transformers oriented in a way that allowed the internal power transformer to induce hum right in. naturally that makes it part of the signal, and you'll never get rid of it in that case. The transformers need to be turned differently.

If an external DI fixes it, that is NOT the problem.

SOME 4PRO, probably very early, MIGHT have had a non- transformer output, in which case a DI external will fix it. I don't have a schematic handy which shows that, and I may be recalling the wrong unit.

 

Obviously, there is. Pinning it down is the problem. Try using an XLR with the cable shield not connected to pin 1 or the shell at the amp (send) end, with only pins 2 & 3 connected to the conductors.

 

Yah... but pin 1 is NOT SUPPOSED TO BE CONNECTED ANYWHERE in the unit............

So opening it had better not make any difference.

If it does, that would be interesting.

I'm Ok with everything up to the part where "the external DI fixes it".........

I'll have to check with others who may recall the specific deal.

 

Has there ever been a solution for the hum problem?

Basically all the XLR DI outputs hum. All the 1/4" DI outputs are clean, but you need a DI box to make it XLR tho.

 

So I have the same exact problem in my shop. Kid used it at a gig and the sound guy got the hum from the balanced outputs. Hooke it here, amp only and had the hum. The only thing not mentioned is that it has the hum with the amp off, like a ground short somewhere. unplugged the cable to the transformer board on the side of the chassis and it went away. Betting on a transformer being bad but I'm not an electrical type. Checking into a replacement board.

 

Hi, the ground loop is for ground chassis to ground wall, basically is a bad design from ampeg in this model because used jump between signal ground to chassis. I suggest use 1/4" out to DI.

 

Don't want to bump this old thread but I had the same problem with the same amp. My solution was to rund XLR to a DI box. That took away the hum. Is this ok to do. Should I do 1/4" out to a DI box? I didn't want to start a new thread with the same issue.

 

No problem, either way.