Phonoclone 3

[kffern]

Originally Posted by northernsky

Hi,

finally I completed my Phonoclone. It worked at my first attempt thank to your help! I could use for the first time a MC cartridge, a brand new Denon DL-103. I have no experience, but for sure the sound is much better when compared with my previous Grado Prestige Green MM cartridge.

The only problem I have, despite the metal case and the shielded wiring for the music signal, I have low level RF noise coming out from the speakers.

Thank you RJM and to everibody here

Renato

Hi Renato,
Is that a shielded cable from the board to the phono socket? If so, try grounding the shield at the phono end.
Regards,
kffern

[northernsky]

Thank you for your reply Kffern. I have not grounded the shield. I will do.

Please tell me if I am right: I'll connect the shield to the RCA input ground.

Since I used the same shielded cable to connect the phonoclone out to the RCA out, do I need, also for this cable, to connect the shield to the RCA out ground?

Thank you again for your help

Renato

[kffern]

Yes, try connecting the shield to the RCA plug ground. If the external cable has a metal shield it should be grounded on one end. I can't remember whether it should be at the preamp or the phono stage. Best to use an ordinary factory terminated cable till the problem is sorted. For such short internal cabling I'm not sure if it's worth using shielded cable. Maybe someone will advise.
Kffern

[rjm]

Re RFI you just have to try a few things to see whether it makes any difference. The OP27 has a bipolar input stage which is more sensitive to RF pickup than sat a FET opamp, so you might try switching opamps, or adding a small (500pF about) capacitor across the + and - input pins of the input opamp. Also try switching phono cables, for example, and making sure that COM is securely connected to the case at the ground lug.

[InSides]

Here is my PhonoClone:







Standard BOM. HiFi2000 cases, Trafomatic potted transformers. Neutrik SpeakOn + AQ power cable for umbilicals.

Mundorf MCap on outputs. I have ZN coming soon...

...what is not standard is my contraption for easy loading. I attached a small PCB with 300, 400, 500, 1000, 1500 and 2000 CNF55 resistors [or close enough values].

Using MB style jumpers, I can select any combination of those in parallel and get a much larger degree of loading steps. Current combination yields ~170ohm which seems quite suited to the Ortofon Rondo Red I have installed.

Initial Thoughts

No perceivable hum or noise on normal listening levels. Some noise after 2PM on the volume dial... still quite negligible. Will give it a few days and see what happens. Happy happy right now.

More to come. I hope.

[rjm]

Insides gets my vote for "phonoclone you would be most likely to pay more than $2000 for".

Nice work. Looks like a million bucks.

[InSides]

Originally Posted by rjm

Insides gets my vote for "phonoclone you would be most likely to pay more than $2000 for".

Nice work. Looks like a million bucks.

Thanks! Means a lot, especially being my second project. First one was a tubed output stage for my HD 990.

Now... I know I had asked this question before, and I did get an answer from RJM, but I keep wondering...

...anyone try any opamp rather than OP27/37? I saw a reference earlier to an issue with the bandwidth on the AD797, but maybe an LT1028?

RJM, I remember you said that you feel the best part for the job is OP27, but a guy wonders...

[rjm]

Christmas, Christmas...

A present for you guys.

I will offer 6 Phonoclone kits for sale at a special price. $100 US including shipping.

Two boards, op amps and sockets, resistors, mica caps for C1 C2, arcotronics for C3, Nichicon KW for the electrolytics.

Email or pm me to reserve.

[rjm]

Another year.

I'd like to share the potential direction the phonoclone circuit development will take in the coming months.

I'm thinking along the lines of the B1 Buffer from Nelson Pass / Firstwatt. A single ended transistor buffer circuit to isolate the op amp output of the phonoclone output stage from the cable capacitance. Some sort of two transistor design, either JFETS or bipolar, creatively wired to the Xreg. The low output impedance of the op amp suggests bipolar.

Note that board space is a bit of a premium, so unless this is made as a separate board (which has its attractions) the parts count has to be kept to a minimum.

Thought and suggestions (links) welcome.

/rjm

[Onvinyl]

Originally Posted by InSides

...anyone try any opamp rather than OP27/37? I saw a reference earlier to an issue with the bandwidth on the AD797, but maybe an LT1028?

RJM, I remember you said that you feel the best part for the job is OP27, but a guy wonders...

Hi,
I said it before, that I liked best the AD797 in the second stage and AD811 in the first, but made it on veroboard, as those are less forgiving than op27. In fact, this combo didn't run smooth with the old v2 (or was it v1?) boards, I got to much offset at the input, never a problem with op27. You might try the opa627 in the first stage, I guess many people would like it, I didn't (too soft and weak bass). The LME49710 might also work good in the 2nd stage, but I didn't try. I didn't like the 1028 in the second stage too much, this one will most probably not run in the old boards, I have no exp. with the actual v3. I never managed to have them in the first stage without problems though (offset, oscillation, strange pops and the like).

Rüdiger