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

Autor

Beitrag

Savyasaachi
Inventar

#1 erstellt: 19. Jan 2009, 02:18

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

[Beitrag von Savyasaachi am 19. Jan 2009, 02:52 bearbeitet]

Savyasaachi
Inventar

#2 erstellt: 19. Jan 2009, 23:53

Here's another mod that might be a possibility.

Replacing the CS8414 digital receiver chip with the newer DIR9001 from TI.

Cost is approximately 25$ shipped...

http://img.ruten.com.tw/s2/b/bc/12/11080123452434_223.jpg

however, i would need to use it in 24 bit I2S mode unlike the CS8414 which does not have a fixed bit length and varies from 16 to 24 bit I2S based on other inputs which would be made largely useless by using the DIR9001.

i haven't checked yet, but I may have to change the clock to a diffferent freq too.

[Beitrag von Savyasaachi am 20. Jan 2009, 00:09 bearbeitet]

Savyasaachi
Inventar

#3 erstellt: 22. Jan 2009, 06:58

I just came upon these interesting discussions on I/V stages (both passive and active)...

http://www.diyhifi.org/forums/viewtopic.php?t=798

http://members.chello.nl/~m.heijligers/DAChtml/Analogue/IV.html

I should be expecting my Pass Labs clone I/V stage arriving soon. Class A output via John Curl's Jfet source follower.

The replacement of the CDS8414 with the DIR9001 seems to be a give and take thing.

The converter board is using on board regulators LM117 from the same family as the LM337 for supplying power to the DIR9001. So it is like a double regulator stage. I could of course remove the on board LM117 regulators and bypass them and hook up the DIR9001 directly to the new discrete regulator I will be putting in place.

The only caveat is that the receiver chip would be used exclusively in 24 bit I2S mode unlike the variable bit rate on the CS8414...

Then of course there is the problem of removing the CS8414 carefully and soldering this board on without destroying the pads..risky

But of course I could always replace the entire receiver board with something like the one from Twistedpear audio..which uses a wolfson receiver chip which has the same jitter rating as the DIR9001. This is for $75 and might actually be a better idea.

However, it would be great if I could find a receiver kit/board that is full fledged and not based on glue logic and instead with a separate re sampler chip after the receiver chip.

[Beitrag von Savyasaachi am 22. Jan 2009, 07:16 bearbeitet]

aks07
Stammgast

#4 erstellt: 22. Jan 2009, 07:10

Would a tube find a place somewhere in there ?

Savyasaachi
Inventar

#5 erstellt: 22. Jan 2009, 07:18

aks07 schrieb:

Would a tube find a place somewhere in there ?

Aks07,

I am so glad you asked me...

You know I would love to put in a tube on the output stage..But I am lost when it comes to tubes. Maybe a tube buffer after the I/V stage ?

Suggest me something as to where I could put a tube in that chain and guide me

as to how I would have to go about it.

[Beitrag von Savyasaachi am 22. Jan 2009, 07:21 bearbeitet]

aks07
Stammgast

#6 erstellt: 22. Jan 2009, 07:33

I have absolutely no idea on dac. My Shanling CDP has a tube buffer and I am contend to just tweak that.

But I have seen many articles on web describing a tube buffer for dac. To me the tube part looks a million times less daunting then the digital part of such designs. So I am sure it will be easy to implement should you desire to do so.

I think Shri Sivat will be able to offer valuable advice on such a plan. He seem to have done a few.

sivat
Stammgast

#7 erstellt: 22. Jan 2009, 07:36

Use a passive I/V stage and a good tube output stage.

This will give you better benefit that an clock upgrade ..

The prioiryt will be the DAC's ability to interface well with a amp/preamp and drive it without any problem. This is more important and has a more drastic sonic impact ...than the problem of Jitter..

Savyasaachi
Inventar

#8 erstellt: 22. Jan 2009, 07:56

Thanks for replying Siva.

A passive I/V stage means using a transformer (or a resistor network)and the PCM1704 DAC chip has an output of 1.2mA. Are tehre any specific transformers that you can suggest to you use with this DAC. I see the LunDahl 7903 being mentioned a few times among others..But they usually implement it as the output stage as well by using a 1:4 or higher turns ratio to get some gain.

The problem however then becomes the input impedance of the next stage. Specifically a 50k pot or sometimes a 10k pot, which would attenuate the signal a bit.

But you suggest that after the transformer I/V stage (maybe with no gain 1:1 turns ratio), to place a tube buffer stage?

If so what transformers and tube stages should i be looking at?

[Beitrag von Savyasaachi am 22. Jan 2009, 07:57 bearbeitet]

Savyasaachi
Inventar

#9 erstellt: 22. Jan 2009, 08:06

I wonder if any of you have seen this page?

http://www.lampizator.eu

i am pretty sure Siva probably has..?

http://www.lampizator.eu/lampizator/Lampizator.html

[Beitrag von Savyasaachi am 22. Jan 2009, 08:10 bearbeitet]

sivat
Stammgast

#10 erstellt: 22. Jan 2009, 10:20

The passive I/V stage is quite simple incase of 1704...just use a resistor value of around 100ohms. The effective output from such I/V sill be decent enough for a tube o/p stage.

Try the resistors alone....then if you feel you need more improvement to sound, you can always add a transformer (this will be expensive) and lower the I/V resistor to around 50 ohms..or even lower.

Yes. you can try the Lundhal...i've not tried them...but many people recommend them. The idea is to use this transformer for some gain...i do not think there is any point using a transformer here otherwise.

square_wave
Inventar

#11 erstellt: 22. Jan 2009, 14:19

The Lampizator dude thnks quite highly about the buffalo dac by twisted pear.
Of course,he takes it through the Lampization process

http://www.lampizato...0DAC/BuffaloDAC.html

[Beitrag von square_wave am 22. Jan 2009, 14:19 bearbeitet]

Savyasaachi
Inventar

#12 erstellt: 22. Jan 2009, 18:14

square_wave schrieb:

The Lampizator dude thnks quite highly about the buffalo dac by twisted pear.
Of course,he takes it through the Lampization process

http://www.lampizato...0DAC/BuffaloDAC.html

Yeah Vinny.

I actually almost bought the Sabre last month when it was available the first week or so.

But, knowing that the newer Sabre32 design was coming out made me stop. I will be building the Sabre32 once it is released.

Siva,

Thanks for the info. I will definitely give the passive I/V a try. I just don't think I could fit a tube output stage in my current DAC case. BUt,here's a photo of my DAC..tell me if you think I could squeeze one in including a PSU + transformer for it of course.

http://picasaweb.goo...qkwQ?feat=directlink

Thanks,
Saachi

square_wave
Inventar

#13 erstellt: 23. Jan 2009, 08:53

Savyasaachi schrieb:

square_wave schrieb:

The Lampizator dude thnks quite highly about the buffalo dac by twisted pear.
Of course,he takes it through the Lampization process

http://www.lampizato...0DAC/BuffaloDAC.html

http://picasaweb.goo...qkwQ?feat=directlink

Thanks,
Saachi

Great

Looking forward to this one.

Amp_Nut
Inventar

#14 erstellt: 25. Jan 2009, 04:22

The ESS Sabre is probably the best specification DAC i the world... currently avaiable.

There is a long an comprehensive thread on the DIY Audio forum on this DAC. As I have been tom-toming ....The Twisted Pear Audio site provides this as a kit, at a Very attractive price.

The notreworthy features of the ESS Sabre8 are :

Not 2, Not 4 but EIGHT high quality DACs on the ESS Sabre8 single chip. This permits it to be used in 7.1 systems and Blu Ray players etc, which target quality performance.

For us audiophiles, the 8 DAC can be configured into (an awesome) "Stereo Quad Balanced" mode, using 4 DACs per channel !

Built in High-precision, low-jitter clock, with built in reclocking. Also has a facility to disable the internal clock and accept an external clock.

INPUTS:
Direct DSD (SACD),

I2S ( The Ideal for DACs)

and S/PDIF ( For universal interface )

Full 24-bit/192kHz support for the highest (current) popular audiophile quality bit rates.

I2C header for remote uC interfacing - can provide a digital volume control, quite easily !

The ESS Sabre8 sadly lacks only an external USB / Firewire input, which will have to be assembled separately...

Also very well reviewed.

Incidentally, PEACHTREE Audio ( No Idead if associated with Twisted pear audio !

) launched - at CES 2009, a DAC + Amplifier, using this DAC chip and 11 individual power supplies, feeding various stages separately. Clearly a well thought out product, for about US $ 1 K..

Arj
Inventar

#15 erstellt: 25. Jan 2009, 04:37

AN, witout the intent to sound cheeky (

), any idea on how it sounds ?

Amp_Nut
Inventar

#16 erstellt: 25. Jan 2009, 05:31

Hi Arj,

That IS the Million $ question.

Note that I have restricted my comments Sharply to tech matters Only !

I too am trying to find reviews of this DAC.

The few that there are.... are all praise. I have not read a single review that says this DAC was bettered by another... but then, there are precious few who have reviewed it.

Forum guys, would appreciate any other links of good or bad reviews of this DAC, specially an A/B comparision with other DAC chips...

Savyasaachi
Inventar

#17 erstellt: 25. Jan 2009, 07:00

ampnut, arj,

I have already made up my mind on building one. I have been in touch with Brian and Russ about the new boards coming out (in the next few weeks or so).

They are working on multiple projects..
1> new I/V stage (discrete)
2> new DAC based on Sabre32
3> New Joshua tree attenuator

I have funds ready for the DAC> I will be using my own power supply and regulators, already bought the transformer, MIght go for a different I/V stage but haven't decided yet. Definitely there is going to an I2S input so I can use my ESI Juli@ I2S signal out.

Been following diyaudio.com thread for a while now...interesting stuff.

Back to my PCM1704 DAC, i just disconnected the old I/V stage, so the DAC is non-functional now. Ordered transformer and power supply parts for the I/V stage. GOing to try and finish whis up next week.

Amp_Nut
Inventar

#18 erstellt: 25. Jan 2009, 07:14

That is GREAT, Savyasaachi

Just wondering .... why the Joshua tree attenuator instead of the "Volumite" ?

I also see that their USB to I2S board is out of stock. Any idea if something new is cooking in this direction ?

Any Firewire to I2S ?

I guess the new Sabre32 DAC kit will be Atleast 3 months away .... ?

[Beitrag von Amp_Nut am 25. Jan 2009, 07:16 bearbeitet]

Savyasaachi
Inventar

#19 erstellt: 25. Jan 2009, 07:53

Amp nut...

I don't think there is going to be a Firewire interface.

Most items are out of stock.

I am guessing there will be no further improvements to the USB receiver.

All enhancements seem to be centered around the I/V stage and the new board to implement the 32 bit DACs.

I am actualy a bit apprehensive abou tthe newer 32 bit DACs..I mean who really needs that much resolution.

I would rather be content with the 24 bit DAC.

But, I am waiting to see what other improvements they bring with the new DAC. There are some additional features which would make the newer DAC more desirable i think.

Volumite is for volume control on the DAC..I won't be using one for the DAC.

THe Joshua tree attenuator is a ladder type R-2R config with relays doing the switching..geared towards pre amplifiers and amplifiers.

Amp_Nut
Inventar

#20 erstellt: 25. Jan 2009, 08:32

Oh, OK. I did not know that you were using a Pre-Power.

I thought you were a Computer Audio guy, dedicated to 'cans'

Savyasaachi
Inventar

#21 erstellt: 25. Jan 2009, 08:47

Amp_Nut schrieb:

Oh, OK. I did not know that you were using a Pre-Power.

I thought you were a Computer Audio guy, dedicated to 'cans'

:prost

I love 'cans'

BUt i still prefer speakers. Given current situation though I am relegated to cans to do my serious listening.

For my speaker setup, I am using an integrated amplifier , SAnsui Au-217 with a pair of Wwarfedale EVO-10 speakers and a Onkyo DVD player.

THe Joshua tree attenuator would be used for a new amplifer that I would be building, Class A for headphones mainly.

However, I may forgo a ladder type attenuator in lieu for the ubiquitous Alps Blue Velvet pot.
Have bought the transformers for the amplifier already. The components are in India though. Hopefully my friend will be able to haul them for me soon.