Preamp Deal of the Century

I bought a set of XLR-RCA adapters for the preamp output of my Cabernet to see if it would reduce a hum issue I was having. The adapters did eliminate the hum, BUT it ABSOLUTELY killed the dynamics, bass, and overall volume of the music.

The manual does not state what the xlr pinout is, but I did email Mick and he stated that pin 2 is hot, so I believe the Cabernet follows the USA XLR standard (Pin 1 = Shield ground, Pin 2 = Positive balanced signal, Pin 3 = Negative balanced signal). The XLR-RCA adapter was made to the USA XLR standard according to the maker of the adapter.

I'm connecting the Cabernet to a Yamamoto A-08S. As stated before, I wanted to try the adapter to see if it would effect the hum issue which I have. I had previously built my own RCA to XLR cable (Pin 2 to RCA Center, Pin 1 & 3 to RCA Ground) and I had the same problem with my homemade cable that I had with the adapters - death of dynamics, bass depth, and overall volume. I thought I just botched my cable job, but apparently the problem is different.

I'm guessing the problem is with the Cabernet. Before I received the Cabernet, I had the Yamamoto connected to a Denon receiver and did not have the hum problem that I'm having now. I haven't changed the RCAs, power cords, or speaker cables. The only change was the Supratek.

As far as addressing the hum before the adapters, I have tried floating the ground on just the preamp, just the amp, on both, and on my speakers (Von Schweikert dB99-SE). However, all the ground floating did nothing.

I reconnected the RCA to RCA this morning, but left the adapters still connected to the Cabernet XLR out. I noticed the same reduction in hum as well the constriction of dynamics, bass, and volume. Once I unplugged the adapters, the hum came back, but so did the "life" in the music. If anybody has any suggestions to reduce the hum, I would greatly appreciate it. Thanks much.

Could be a noisy tube......
If you think it is ground loop problem (you have to be sure) fine a dealer and ask for loan of a Ground Zero made by Granite Audio. (if you are in tri-state area - let me know). I had a similar headache just a while ago. Turn out to be a "noisy" tube in one of my amps.

Cheers

Marius:

Which tube out of the bunch would be the likliest culprit? The Cab Dual uses two 101D, two 6SN7, two 6H30, two 5881, and a single 5AR4. I'd be fairly pricey to completely retube the Cabernet as the 101D's aren't cheap. I figure I can start with the 6SN7 first to see. Any other opinions?

Hello Kgturner,

I doubt it if the hum is cause by a tube. Do you have a scope? I ask because you can measure what freq your hum is. 60 hertz and it could be mechanical (tube or transformers vibrating) or filament supply voltage, 120 Hz. and it surely is coming from the rectified voltage of the B+. So which one is it and how much is the amplitude?

One thing to try is to have a shielded cable(shield connected at the preamp side only)from amp to preamp. Try it reverse also and see what happens.

regards,

Abe

Abe:

I don't have a scope nor any access to one that I'm aware of. The hum sounds like a typical ground loop hum to me (60 Hz). I can try the shielded cable route, but I'd likely have to build it. What you're saying is connect the ground and shield at one end of the RCA and just the ground at the other end?