The Phonoclone and VSPS PCB Help Desk

[woodturner-fran]

I could be wrong here, but in the past I've only heard "hiss" referred to being from the opamps - kind of a rushing sound. Most around here have had hum problems, but not hissing.

Maybe you have the opamps set to ve high gain within the VSPS?


Only a shot in the dark, but maybe it might help


Fran

[juluska]

My equipment:
Goldring GR-1 with Elektra capsule, without ground connection. The interconnect cable is not shielded.
Passive preamplifier diy, a symple alps potentiometer and a selector.
Two diy LM3886TF monoblocks from chipamp.com.

the vsps has 40db gain

I think it's probably a problem with rca ground or with the ground connection in the case.

Thanks

[Akita]

May be your chasis grouding point. I saw 3 wire connected to the chasis. One should be your amp ground to chasis, 2nd might be from psu 0v, Where is the yellow wire from? Ac to chasis ground?

Try not to connect your 'AC ground to chasis' at the same point with your amp 'grouding to chasis'.

You can try to twist the RCA cable a bit if you suspect the hiss is from there.

Or you may read a little story of my troubleshotting at
http://skycoral.com/?p=49

[ahaja]

>juluska
Too long signal wires.
Too long signal pathes on pcb.
Transformer should be far away from phono pcb, specially from RIAA network.

Ground should be also short as possible. From PSU to phono board. From v stabilisation (phono board) to chassis thru 10-22R resistor.

Every RCA should be isolated from chassis!

Regards K

[juluska]

Thanks. Changing the AC grounding point, twisting the cables and using shielded interconnect cables the high frequency noise is almost gone. I can only heard some mild hiss at very high volumes. But, after hours of hearing several lps I found that sound is worse that I espected, distorted and obscure. Is it possible that using metal film resistors 732k and 105k in RIAA eq can affect in that way the sound. I read carbon film resistors are better. Its true? And the long signal path in the protoboard, the distance between 1nF caps, or the big 4,7 uF coupling caps, can affect in that way the sound?
I'm considering to repeat the board. What are the best components to use and where can I buy them.

[mavallarino]

hello juluska: all your suspects may, could, can be, are...

RIAA correction is very sensitive and condensers should be polipropreline (or of high quality) and the resistors are all carbon and nothing metal... metal sounds metal. You can use nice Mcaps for the coupling or nice blackgates or other. Even if you didn't have mechanical problems (grounding, twisting the signalling wires etc...) I don't think you could enjoy the sound quality of this phono stage.

Only use the best quality and matched components for signal path manipulations. Plan once, be happy, or moderately content, and then improve on the design.

The problem with this design is that there are OpAmps therefore this phono stage can't, and probably will never sound Hifi. So the hissing will probably never go away... believe me, I have sensitive speakers and this causes me nightmares and hallucinating schizophrenia.

So I am working at a special solution to modify this design. I doubt that 47 Labs has used (all) OpAmps... If they have for sure they have stabilised them (or it) with the help of... (more to come after my little experiments).

Hope this helps,
MV

[juluska]

Following your suggentions, i repeated the board and the result is impresive, now it really sounds hi-fi as i espected, without hissing nor humming problems and very good sound. i think distance really influence in sound. the shorter signal path and smaller capacitors sonds better.

Thank you so much for your help and comments.

[juluska]

.

[mavallarino]

Nice work. Maybe the caps can be placed closer to the OpAmp. I use Phonoclone, not VSPS so you have lower gain (less hiss).

Which are the new values?

Cheers,
MV

[ahaja]

Hola.
These tricks much improve the sound.
VSPS and also Phonoclone.