The Phono Stage

[BigE]

Originally Posted by tms0425

I had one wire from each phono board over to the insulated ground terminal. TT ground was connected there.

Where is is attached on the phono board? Mine is attached to the GND side of the two caps on the phono circuit. See Peter's photos on post #1

[freebee]

Is it possible to order the full kit through Audiosector?

[Peter Daniel]

Send me an email for current price list.

[freebee]

Thanks Peter. I've just sent you an email via your Audio Sector website.

[Peter Daniel]

Originally Posted by tms0425

No change.

Here is what I did tonight:
- Removed both black phono board ground wires from black ground terminal and also separated them from each other (floated)
- Removed TT ground from isolated black ground terminal (floated)
- Removed AC power to the TT
- Removed AC filter board and input circuitry from the back right of chassis
- Hardwired AC directly to the 2 power supplies in front of the chassis. IEC is fed there to the front instead of the back right.
- Re-dressed all cables to ensure they are separated away from AC sources

There was no change at all from these steps. One channel slightly more hum than the other, but not much. Basically gain is fairly high, to the point where hiss is starting to be evident when the hum starts.

When I remove the input cables from the preamp or remove the headshell all is quiet, which I suppose makes sense. This old Empire tonearm cable and arm wiring does not have any shielding or a separate ground on it. The ground wire from the TT is tied to the plinth/chassis itself, a few inches from the arm base. I have a new TT and tonearm on the way so will replace that very soon.

I guess it's time to separate the power supplies from the phono boards, recheck soldering, and see what happens. It's just a pain because they're both hardwired.

The strange thing is I actually built up a PhonoClone3 without a case and I have a stock Jolida JD9 and neither of them hums with the same TT/arm.

I don't really have any particular advice here, as it seems like the problem is system dependent, however, this is what I observed today in my setup:

I've just built a preamp for a customer and was testing it before shipment. The unit was built exactly as pictured ion a first page of this thread. Chassis is grounded through the earth pin on a power entry module, RCA jacks are isolated from a chassis. I'm using Shelter 901 mounted on SME V tonearm.

There was initially low level hum at maximum volume level on a TVC based preamp. After ground wire from TT was connected to the chassis or one of the RCAs, the hum disappears.

[tms0425]

Originally Posted by Peter Daniel

I don't really have any particular advice here, as it seems like the problem is system dependent, however, this is what I observed today in my setup:

I've just built a preamp for a customer and was testing it before shipment. The unit was built exactly as pictured ion a first page of this thread. Chassis is grounded through the earth pin on a power entry module, RCA jacks are isolated from a chassis. I'm using Shelter 901 mounted on SME V tonearm.

There was initially low level hum at maximum volume level on a TVC based preamp. After ground wire from TT was connected to the chassis or one of the RCAs, the hum disappears.

Thanks Peter. I hope to get back to this problem this weekend. I tried to follow my usual common sense grounding rituals but there still seems to be a little special magic to get it all worked out sometimes. I have a whole new TT/tonearm setup now. It has a slate plinth so there isn't even a metal chassis to ground to other than the tonearm base and the bearing. I'll experiment a bit and see what happens. Hopefully it follows some logic this time ;-)

Tom

[BigE]

When I brought my phono stage to a frieds place, they hummed a bit. Making a better groung connection than an alligator clip solved the problem.

[tms0425]

I switched to the new TT and arm, and to a Zu Denon 103 instead of the 103R which has a lower resistance. Hum is significantly less now, even just using a nest of clipleads to experiment with. Hopefully I can get past it now. Thanks for help.

Tom

[eelind]

Hi Peter. Nice job. When thé LM3875 Will be finished, I think I Will Troy your phono stage. One question: did you think about using an RLC RIAA corrector instead of the R and C network?

Eric

[Peter Daniel]

Originally Posted by eelind

did you think about using an RLC RIAA corrector instead of the R and C network?

If something works good, I prefer not to touch it