3 preamps with transformer hum, DC on the line?


Hi everyone,

Searched the first couple of pages around transformer hum but did not find any specific answer around this. I have had the 3 following preamps in my main system with transformer hum, most of them on a dedicated 20 amp line:

- NAD T163 A/V preamp
- Audio Refinement Pre-DSP 2
- Audio Refinement Pre5 (current preamp)

Like I said, all had transformer hum. The problem reproduces with all other main breakers off except the dedicated 20 amp line and the preamp plugged into that dedicated line. I called my power company today requesting that diagnostics on the line into my house be done (check for DC and possibly adjust the AC frequency)? This would be great if this fixed my issue. I have also tried a PS Audio Humbuster III which did remove most of the hum but also killed the high frequencies so I removed it. If the power line diagnostics all check out, would you:

- Try to have the Audio Refinement Pre5 transformer repaired at Audio Plus Services which is USA YBA distributor and service minimum of $250 plus shipping both ways from Seattle to NY. I also have a good local solid state repair shop and I plan on calling them today to see if they can repair this locally. Is repair just a short term band-aid on what could be a tired power supply?
- Try to find a high quality replacement for the Audio Refinement Pre5 transformer. I have no idea what this would cost or how I could find a high quality drop in transformer.
- Have an external high quality power supply made like one from Welborne Labs made.

What does everyone think? The last two options look to be the cheapest route with new parts and warranties vs repairing used parts.

TIA very much,

Scott
sbrownnw
Hi Guys - I am having a DC hum on my cinepro 3K6mk2 amp. I cannot afford a $300 humbuster right now. I'm not an electrician but I do know my way with a soldering gun fairly well. I appreciate any and all advice - thanks.
mark
Airkitty,

If you posted an email address Gbart might contact you..... Not sure what he charges to build a DC blocker.
.
Jea48, I've been contacted ny Airkitty. He has confirmed that he's checked for all possible sources of hum, including a loose transformer mounting bolt. I'm shipping out a DC blocker to him tomorrow. What do I charge ? Not enough I'm afraid. Its hard to justify charging much for a handful of parts in a box. BTW, my e-mail address is sae2300@optimum.net

http://i994.photobucket.com/albums/af67/mr_classe/DC%20blocker/DC_BLOCKER_02.jpg

http://i994.photobucket.com/albums/af67/mr_classe/DC%20blocker/DC_blocker_002.jpg

http://i994.photobucket.com/albums/af67/mr_classe/DC%20blocker/DC_blocker_004.jpg
Gbart,

Thanks for the info. I printed out your post, with email address and links, for future reference.

I suggest others do the same in case the post disappears..... Sure do miss the old Agon email member feature.....
Jim
You might try communicating with PS Audio about their Humbuster in case you had a faulty unit. I've used one before and it didn't roll off the high frequencies whatsoever and I suspect they wouldn't introduce a product that would, if it was functioning by design. Did you measure the reduction in high frequencies and if so, can you be more specific (ie. how many dB and at what frequencies)?