[datman]

I recently received a new DACT CT100 based phono preamp from China.  It seems to be quite good except it hums.  Using the single ended outputs the hum is not too bad.  Using the balanced outputs the hum is LOUD.  If I were to guess at the cause I would say it is coming from the transformer inside the chassis.

What I am thinking of doing is having the existing power supply replaced with the DACT 102 supply.  Since this uses a wall wart ac adaptor, I think this would remove the source of hum.

My question then is this.  Does anyone know of someone in the Los Angeles area or thereabouts who can perform this kind of work?  My problem of having ten thumbs precludes my doing this myself.  Plus I would  like a truly professional job done.

Any help given would be greatly appreciated.

By the way, I am using a London DECCA Jubilee cartridge.

Thanks

Datman

[JoshK]

hmmm....you could have a ground loop problem between your phono and your preamp.   You could try inserting a line (1:1) transformer, such as a Jensen JT11P1 or Cinemag 15-15, this eliminates hum/buzz induced by ground differences (ref: www.jensentransformers/an/an1004 iirc).  But if you are less technical, try lifting ground on your phono plug, a 3 -> 2 prong adapter does this.  

I have also heard that DC blockers before the transformers can sometimes help, but not sure that they are appropriate in this case or not. There are many reasons for why you can experience hum, and I am not expert enough to know which you might have.  I would start process of elimination though, if I were you.

[JoshK]

ok, had another thought.  Is the hum coming from the speakers or the phono stage itself.  This is easy to check and helps narrow it down.

[Tonto Yoder]

The PS Audio site has a good article on hum--
http://www.psaudio.com/articles/hum.asp

They would like to sell you their new Humbuster (which addresses the DC issue that Josh mentions), but there's other info that may be helpful.

[lcrim]

datman:
Both TT's I have use a separate grounding wire on the tonearm assembly to the phono section.  You could try that, then try moving the end on the phono pre to your preamp.  Hum seems more prevalent in phono stages probably because of the high gain there.  It is also more of an issue around tube equipment.   The onboard power supply is definitely a suspect.  Do you hear it w/ music or is it only present w/o music and high gain levels?   What is the rest of your system?   One thing that can help in finding the cause is moving components and lead wires around.  
Good luck