[dave brown]

Just about finished my Coronet just needing to finish the wooden base/plinth.  So far, I think this is a wonderful preamp and the quality of Jim's board and design tremendous.  One problem tho...

I ran it this morning for a few minutes and I seem to have some hum going on.  And, from what I've read on this forum, I suspect it's a ground loop problem.  Can anybody provide some help in sorting this out.

I grounded the AC line underneath one of the transformer mounting screws.  My RCA in/outs are not on the end like Jim's prototype shows; instead, I ran them to the rear.  So the wires to the RCAs and ground lug are about 6" to 8" long.  I'm using the steel chassis (powder coated version).  My RCAs aren't isolated from the chassis although I didn't make an attempt to ensure they are fully conductive with the chassis.  I did make the star grounding mod to C13/C14 per the manual.

Could any of the above things be causing my hum?  

Thanks,

Dave

[hagtech]

Try isolating the RCA jacks.  That would help eliminate the ground loop.  Only ground to PCB should be from the grounded chassis binding post (not from RCA shields).

jh

[dave brown]

Thanks Jim,

That seems to have done the trick.  There still is some hum which I can hear without a record playing, but it is well below the level of record surface noise.

I really like the sound of the Coronet even though not even close to being broken in.  Great tonality, bass is full, and overall the sound is very dynamic.  Now too my Linn LP12 and Souther arm need some TLC and reajusting since they've been sitting unused for over a year.  Then figure out what's wrong with one my Dynaco Mk III amps and get them back in the system.

Anyway, thanks again.

Dave