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Upgrading Clock , I/V stage and regulators on a DAC

Mogami Cables

sachi

Active Member
Joined
Aug 4, 2006
Messages
518
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28
Location
Portland, Oregon
Hi guys,

I am undertaking a few mods to my DIY DAC which is based on the PCM 1704.

1> I have just ordered parts for a JFET I/V stage to replace the OPA627BPs... The JFET board also comes with a discrete regulator power supply section for the I/V stage which will replace the 7812 and 7912 already on duty. This JFET stage is basically a clone of the I/V stage on the Pass Labs D1 DAC.

Further upgrades that I am looking to make are to the clock, its power supply and the supply to the DACs itself.


2> Currently the power supply to the clock and the receiver chip is being fed through a single archaic 7805. I want to make the power supplies separate as a starting point.

3> Next step up would be to replace the Seiko clock module with a tentlabs XO.

4> I am also going to be replacing the 7805, 7912 and 7812 (which also supply the +/- 12V to the LM317, LM337 adjustable regulators used to derive the +/-5V supply to the DACs ) with a high quality shunt regulator.


5> One final upgrade that I am currently thinking about is having another input to feed I2S signal directly into the DAC. BUt there a alot of logistics i need to work out for this mod before I know it can be made possible. Mainly to do with the input switching from a SPDIF signal to an I2S input and back.

I am expecting huge improvements with some upgrades and smaller ones with a couple others.

I however wanted some first hand input on the tentlabs clock upgrades?

Would appreciate if anyone can shed more light on this.
How big was the difference if at all you did use any of his clock products in your gear?

Thanks,
Saachi
 
Last edited:

sachi

Active Member
Joined
Aug 4, 2006
Messages
518
Points
28
Location
Portland, Oregon
You'd get more responses to your specific question on the other forum.

For I/V, I would suggest holding off till the Twisted Pear Counterpoint is ready - fully discrete (but does not include power supply) bipolar I/V.

To replace the 7805, Tent Regs are a good starting point, but you can get much cheaper and similar performance with the GregBall regulators. <600 each, but capable only of about 40mA.

Shunt regs are not advisable in analog stages if the load is not more or less constant or consistent. For most DACs, you need to have a low-impedance supply for the analog stages, but for digital shunt regs are absolutely fine. some DACs are picky about Va and Vd sequence, so watch it if you're separating the supplies.

Lastly, I2S can be switched using a couple of relays, or electronically with a few gates. Where are you planning to get the I2S signal from?

Cranky,

Thanks for the info. THisis really helpful .

I did not know about the counterpoint IVY. I actually ust sent an email to RUSS asking about using the same IVY stage i will be using with this DAC for the BUffalo.

I guess, I will just go for the Counterpoint along with the buffalo when it comes out in a few weeks.

The current IVY stage that I am have ordered the parts for are about 60$ in total ,so worth a try.

I am not using shunt regs for the analog stage. I guess i mixed that up in my write up. I haven't heard about the Gregball regulators (though 40mA will almost definitely not cut it)..could you provide me some info on it.

I plan on using my ESI Juli@ for the I2S signal.
 
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