2. amps-preamps
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Krell FPB300 - mechanical transformer noise.

I have an FPB300 that does not have the pinging issue discussed on another thread - my problem is a noisy transformer. I have measured approximately .75 volts of DC on my incoming line (dedicated 30A) and plan to try a DC trap such as PS Audio's UPC200HB.
The unit makes the most noise and is most noticable when the music stops or when the music transitions from loud to very soft - unit almost growls for several seconds and then fades away. I am assuming that this is related to the class A biasing scheme. Krell had no suggestions even after I asked if DC could be saturating the transformer - they acted like they never heard of toroids and DC issues. I am feeding the amp directly with a Wadia 850 (balanced) and it is driving Apogee Duetta Signatures (Audioquest Midnight Cables) Anyone experience this or have ideas? I am very happy with the combo except for the noise. Thanks in advance for any help.
landshark75
landshark75 OP
8 posts
 
Cytocycle,

I used a Fluke (I believe model 23) multi-meter set on the DC setting with the decimal at the hundreths. On another occasion I opened all the breakers except the dedicated lines to find a possible in-house cause but was interrupted when the wife came home, saw the power was off and gave me one of those looks!
landshark75 OP
8 posts
 
Cytocycle,

To clarify, I measured at the receptacle on the dedicated line. I could be wrong but I still haven't ruled out an in-house cause simply because I have dedicated lines since all circuit neutrals and grounds are tied together at the loadcenter - any electricians out there?
stevecham
3,298 posts
 
You have a grounding problem and you need to get this fixed immediately in order to prevent damage to the amp and other components in your system, humbuster or not.
landshark75 OP
8 posts
 
Stevecham,
Please elaborate on your diagnosis of a grounding problem - The equipment has been operating for months without any problems other than the transformer noise. How does DC on the line relate to the grounding? My understanding is that it can generated from outside by faulty utility equipment or internally by motor loads and low voltage lighting transformers.
Thanks,
Richard
rwwear
2,692 posts
 
Transformer noise usually implies a bad transformer or at least a noisy one. I had to send an amp back to Krell years ago for the same problem. I was told they got hold of some bad transformers from their supplier. Mine was brand new so they replaced the amp. It could also be a bad filter cap but it is not as likely.
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