advertisement


Phonoclone 3 Phono Stage

"As for the choice of op-amp - the OPA27 is a precision low-noise device and no doubt was chosen carefully for this particular application. IOW, another device might not work as expected..."

It also has a very low input offset voltage. I'd be careful what I let my cartridge connect to in a similar configuration. What is happening here is that you have a topology that is naturally low offset combined with a low offset device. The AD797 is a far more quirky op amp so, if it works as U2, I wouldn't necessarily take that improvement to U1. In fact, I'm not entirely sure I would do it as U2 either (esp. if it is wired as in the diagram with R1 and R4 sharing a common path to ground. That seems very odd, though it may not be repeated on the board.)
 
MartinC said:
Hi DF,

Actually the PD phono stage is still on my radar too, I have a board design roughed out, but haven't a lot of time to finish at present. The Phonoclone was a stop gap for me but is proving so pleasing that it has slowed my PD board progress!

BTW, are your Teflon caps Russian surplus ones? - I was considering those for the RIAA on the Phonoclone but am put off somewhat by mixed reviews.



Regards
Click to expand...

Hi, yes they are from the seller on ebay. A few people have said they sound good on DIY Audio. I'm in the middle of getting my Salas V1.2r regs to work. I have plenty of polystyrenes that I can substituse them with if I don't like them. I haven't got round to measuring the teflon's yet, but plan on matching the values up using low-value polystyrenes.

David
 
Have you tried the power supply sans capacitors as RJM recommends?

MartinC said:
Just added a second transformer and Hackercap board, so the set up is truly dual mono. The difference from a single transformer is small but I feel tangible. Next step is to try AD797 back in the second stage but with some added ceramic caps fpr supply decoupling on the power pins. Now just awaiting two cases from HiFi2000 and the 'premium' build begins.

Of course RJM have now released an additional buffer board to go after the Phonclone, so that will be on the cards to try once it's released.

Just as with the Buffalo DAC build, it's difficult to know when to stop!

Regards
Click to expand...
 
I would love to attend, but unfortunately I'm in California, so probably not!

Will be trying the 'no added smoothing caps' and 797 changes in the next day or two.
 
James,

Tried with the regs only (no CRCRC filtering after) straight to the Phonoclone, couldn't really tell any difference, so it looks like Richards advice is sound and that you can run right from the regs to the board.

Personally though since there was also no detrement in having the caps there I'm leaving them in, gives me more flexibility if I use the supply for something else later.

Didn't get a chance the try alternate opamps in U2, and have family visiting this next week so will be delayed in these trials.

Regards
 
How come you have crcrc after regulators anyway? All my psu's go rectification - crcrc or equivilent and then regs, why is this different?

Stefan
 
Thanks Martin, thats good to know

MartinC said:
James,

Tried with the regs only (no CRCRC filtering after) straight to the Phonoclone, couldn't really tell any difference, so it looks like Richards advice is sound and that you can run right from the regs to the board.

Personally though since there was also no detriment in having the caps there I'm leaving them in, gives me more flexibility if I use the supply for something else later.

Didn't get a chance the try alternate opamps in U2, and have family visiting this next week so will be delayed in these trials.

Regards
Click to expand...
 
orangeart said:
How come you have crcrc after regulators anyway? All my psu's go rectification - crcrc or equivilent and then regs, why is this different?

Stefan
Click to expand...

Stefan,

The CRCRC smooting/filtering is after the rectifier diodes but before the Phonoclone board. The Phonoclone board then has some smoothing/filtering on board before it's own regulators.

The Phonoclone board designer feels that having any additional smoothing prior to the board is unnecessary. I didn't find and significant difference either way, but prefer to have any power supply lines between the PSU box and the Phono stage carrying DC only, since eventually my plan is to place the phonoclone boards inside my Linn,

Regards
 
Not to kill the fun: The RJM phonoclone design is significantly different from the 47 Labs PhonoCube. The PD (Peter Daniel) phonoclone is closer to the 47 Labs unit, but it is also not the same. None of these designs is low-noise, but that should not distract from other strengths.
 
No fun killing here - if the RJM in standard form is better than my Linto I'm happy! Certainly noise is not as low as the Linto, but I would class it, at least with the OPA27 as low noise, since with headphones and full volume there is only minimal noise on the output. An order of magnitude lower than Naim stages.

As an update I have been playing around with the second stage opamp, trying an AD797 again this time with better PS bypassing (0,1uF ceramics at the power pins). This improved noise with the 797, and although there definetely were some differences, with the detail, weight and bass seeming to be slightly improved, my perception was that this was offset by some form of higher register distortions. Looking at removing the socket and mounting the opamp directly as well as adding the distortion reduction cap from pin 8 to the output (though in theory this shouldn't make any difference at these frequencies).

I didn't think that Daniels design was significantly different but will have to look.
 
Why not try OPA 627? It will provide you with excellent detail.

**

The PD design has completely different opas, regulators and parts.
 
slawney said:
Why not try OPA 627? It will provide you with excellent detail.

**

The PD design has completely different opas, regulators and parts.
Click to expand...

Thanks, is that a hint ;)

The current boards are 'mules', I have new ones ready to go, complete with tantalum resistors for the RIAA and other signal paths and some rather nice coupling capacitors.

RIAA caps are up in the air - current build has sytrene, though RJM prefers silver mica. Can't find any suitable teflons in the values requires, either way, cap values will be measured for accuracy and channel matching.

Regards

OK - just saw the price of the OAP627 - is it gold plated... I though that the AD797 was pricey!
 
I will try and build mine using LME49720 or LME49710. As ever there is alot of debate as to the "best" op-amp for audio but the LME's are usually near the top of most peoples lists. The input offset looks to be 100nV typical so they look to be fine in that regard. They are a big improvement over OP27 IMO.

I've just finished my V1.2R Salas phono stage with teflon caps - the next phono will be a Phonoclone or a PD phono, both will be built on veroboard. So I might be able to compare them.
 
Thanks to MartinC’s enthusiasm for the Phonoclone I built a ‘standard’ unit. Result –it’s a substantial improvement over my Naim MC board. The said Naim boards had Super Teddy regs. But no question the Phonoclone 3 is quite an upgrade. One of those true upgrades in that the more I play the more I like.
PS Richard (RJM Audio) is a nice helpful guy
 
John - Exactly, superb value. My messing around with opamps is more for fun rather than due to any deficiency!

Df - I actually have a couple of 49710's on order to try out.
 
For extra speed and liveliness, build the PD circuit with matched 0805 SMD resistors and 2.5mm pitch or SMD WIMA MKS caps in the feedback loop with the shortest possible trace lengths, and a nice, thick ground plane surrounding all key pins on the OPAs. ;-)
If you want a more laid-back, high-end sound use the parts Peter recommends (including the OPA 627s).
The longer the feedback loop however, the more susceptible the circuit is to instability and interference.
 
I can't got along with using the Wima MKS range. They are just standard polyester caps. In these sizes it's cheap enough to go for the top and use the FKP polypropylene range which you can get in 100V or 1000V.
 
You must log in or register to reply here.


advertisement


Back
Top Bottom