Preamp Deal of the Century

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?

Yes, that is correct but lets change the terminologies so as not to get confuse.

Lets call what you call "ground" as negative phase. So,on one end, positive phase to + of RCA pin, negative phase connected to the shield together then to the negative of the RCA pin, on the other end negative phase and positive phase connections only on the RCA's.

regards,

Abe.

On my amp, it was the input tube NOS6922 Amperex.
*are you positive it is the pre-amp....not the amp.
*Some amps do not like to be plugged into AC conditioners or voltage stabilizers. It the worst case scenario, it could be a bad or leaky cap.....

I have the same hum issue with my supratek preamp. when i connect the amp to speaker only (no pre amp involveed) i have no hum. connecting pre to amp and to speakers, hum is audible. I then changed a pair of CHEAP monster ic from pre to amp. th e hum decreased significanly. i disclosed the monster ic i learned that the ic conductors are bigger than the other one. Also the monster is not shielded. It is simply twisted. I then ordered a good shielded ic but this pair does not help at all with the hum. Any recommendation? Thanks alot.

Hello,

I have the same hum issue with my supratek preamp. when i connect the amp to speaker only (no pre amp involveed) i have no hum. connecting pre to amp and to speakers, hum is audible. I then changed a pair of CHEAP monster ic from pre to amp. th e hum decreased significanly. i disclosed the monster ic i learned that the ic conductors are bigger than the other one. Also the monster is not shielded. It is simply twisted. I then ordered a good shielded ic but this pair does not help at all with the hum. Any recommendation? Thanks alot.

As I mentioned above, it is good to know what freq of "hum" you are having. Have you tried a different rectifier? This will test if the hum is 120 Hz or not if by using a different rectifier, the hum decreases. If this is the case, remember that our preamp is transformer coupled at the output, then ripple is high on the supply voltage which means that the filter caps after the rectifier could be bad or not doing its function well. Is the hum present on phono only? Or linestage as well?

Phono only, then you can be sure that the grounding scheme of the arm is the problem. Linestage too and there could be several factors. If the ground plane of the preamp(chassis) have a different reference than the ground plane of the amp you are using, hum will be present. Too many ground path and you will have to deal with it also which is commonly known as "ground loop". Have you tried connecting the amp and preamp to the same outlet ground? Have you tried connecting the chassis of the amp to the chassis of the preamp(phono ground lug) using a wire with alligator clip on both ends and hear a difference in hum loudness?

Have you tried taking off all the input components to the preamp and then rotating the orientation of the preamp or moving it further away from the amp and hear any difference in hum level? On this case, we are isolating the preamp and testing for any interference. When the preamp gain is set to high, any interference or signal coupling from transformers or power cords close to the preamp will be amplified greatly.

My suggestions only of course. FWIW, my Chenin is dead quiet on the phono section and linestage section with regards to hum. All I can hear is tube hiss when the tubes, especially phono, are noisy at maximum (fully clockwise) position of the volume attenuator(min attenuation). I can only hear a hum on mine when I connected an SET amp that I know hums with my 100 dB/1W/meter speakers (Altec). I have use my preamp with Magnepans (not likely to have a hum issue), MLogans, and other speakers as I mentioned above on my other post and have no hum problems (thank God!). Maybe I got lucky. BTW, I use a shielded cable from preamp to amp with the shield connected at the preamp side only.

regards,

Abe

abe:

i'm gonna try the cable route first as my yamamoto and cabernet are only connected with cheapie red/white throw away cables. i noticed that when the yamamoto is turned on, the hum starts and the cab only amplifies it due to it's super high gain. if i unplug the rca cables from the yamamoto, the hum is greatly reduced.