The Phonoclone and VSPS PCB Help Desk

[Ralph]

Just finished my Phonoclone on the workbench. Before I hook them up to my turntable and amplifier for testing, are there things to measure (i.e. testpoints) to indicate if I made some mistakes? If the tests are OK, I will put them in nice metal enclosures.

BTW: the holes for C1 and C2 were too small for my mica caps. Assembling the other parts went smoothly.

Ralph

[rickmcinnis]

It seems like a good idea.

Any comments?

They are not cheap but would one think they must be good.

Could there be any conflicts in the first stage? Second stage being rather typical, does not seem to matter.

Thanks for any comment and advice.

[Onvinyl]

Originally posted by Ralph
Before I hook them up to my turntable and amplifier for testing, are there things to measure (i.e. testpoints) to indicate if I made some mistakes?

Ralph

You should by all means check for input offset voltage. It should be 0.0mV or very close. Should you have something like 0.6Volts, don't connect a cartridge. It may (and probably will) fry.

Rüdiger

[rjm]

BTW: the holes for C1 and C2 were too small for my mica caps.

Yeah sorry about that. My mica caps didn't fit either. I had to drill out the through holes a little.

With the circuit board there is less worry about making the wrong connections, but with one probe connected to COM, test the voltages at the opamp power pins and IN+. You should see the regulated voltage at the power pins, and zero at IN+.

rjm

[cukkurullo]

Hi,

I am not sure that a "discrete opamp" will make a better sound. It will make the sound different, that's sure.

The most of the sound of any simple-minimalist circuit design depends strongly on the PSU, and in particular by the impedence matching between the PSU and the circuit fed. The psu has it's own impedence, this is a huge point, and this is often sadly forgotten.

I think these blessed guys here have optimized this design for using an LM317-337 type regs with a minimalist psu. So I would not invest all that money to buy somenthing better on the paper that could result in a failure in sound.

Two years ago a friend of mine, a top engineer working in professional audio industry, built an MM phonostage with OP-amps. On the paper the design was top sounding, but the reality was a bit different. The sound was terrible.

Some months later he changed the high specs toroidal trafo, with an expensive C-Core by Bartolini (Italy). Bartolini is one of the best producer trafos for the tube comunity. The result was that the sound changed from night-to-day, and I can say that that phono stage is one of the best MM stage I have ever heard.

So before to struggle with "top-esoteric-high-specs" components at the end of the signal, we should concentrate where the signal starts up to its end.

Bye for now
J. Cukkurullo







QUOTE]Originally posted by rickmcinnis
It seems like a good idea.

Any comments?

They are not cheap but would one think they must be good.

Could there be any conflicts in the first stage? Second stage being rather typical, does not seem to matter.

Thanks for any comment and advice. [/QUOTE]

[cukkurullo]

Hi Guys,

I built prototype of the MM stage before to go for the MC. Richard thanks for this design, it's a bargain for the monney, GOD bless you.

For the moment I am using a R-core trafo (12V/100VA per rail)

First of all I used mil-specs 30uF/30V tantalum caps on the adj pin of the LT317 reg, this makes a big difference. More detail, dynamics and overall musicality. I guess (not sure) some better noise rejection as well.

Than, mantaining the the tantalum on that position I compared the LM317 vs the LT1086, LT1085 regs. It's funny but the LT1085 (3A) sounded the best. With the LT1085 the stage is much bigger, and gained fluidity in mids and higs, while transient response is on a new level.

Impedence and load regulation behaviour of the different regs is important here.

I also tried an IBM laptop psu, you won't believe that, but despite the noise which was somehow loud, the musicality was excellent considering the price of the psu ($7 on ebay)!

I would be delighted to get feedback from all of you.

Bye for now
J. Cukkurullo

[Ed LaFontaine]

cukkurullo,

When you stated

IBM laptop psu, you won't believe that, but despite the noise which was somehow loud

,
were you referring to mechanical noise or induced signal noise?
Could you describe?

[cukkurullo]

Originally posted by Ed Lafontaine
cukkurullo,

When you stated
,
were you referring to mechanical noise or induced signal noise?
Could you describe?

I mean electrical noise. A lot of analougue guys are concearned with noise, but if they are they should change their technology, vinyl produces a lot of noise... but who cares when the SNR is acceptable and the noise is not mdoulated with the frequency!!!!!

Cukkurullo

[rjm]

I think these blessed guys here have optimized this design for using an LM317-337 type regs with a minimalist psu. So I would not invest all that money to buy somenthing better on the paper that could result in a failure in sound.

For he record, no, I did not optimize the phono design for a particular power supply.

Its open-ended in this regard, though I have repeatedly stressed the importance of a high quality power transformer and the minimum amount of filter capacitance.

Power supply design is more trial and error than exact science. Once things get down to the level of which type/value of capacitor to use on the Vreg ADJ pin, your guess is as good as mine. On paper there is no additional advantage putting more than 10uF here, but the impedance characteristics and dielectric losses of different capacitors will surely change the sound slightly.

As I worte earlier, a far more dramatic change would be to experiment with RC stages on the Vreg output.

/R

[cukkurullo]

Originally posted by rjm

...

Its open-ended in this regard, though I have repeatedly stressed the importance of a high quality power transformer and the minimum amount of filter capacitance.

... your guess is as good as mine.

/R

Richard I did not want to say that I was discovering somenthing special. I just wanted to report some findings.

Cukkurullo