COD - Current Output DAC

[schultzsch]

Ok...

Thanks!

[Zero Cool]

Hi, I just found out about Twisted Pair and boy have i got some questions!

I am interested in Buying the COD kit. or maybe 2. so the first question is, what is the difference in using one kit stereo, vs. 2x kits each configured for mono??

second. how do you choose the I/V stage resistor? I see that the kit uses 470 ohms while another high end DAC that uses the same PCM1794A chips uses 140 ohms resistors for the IV stage that feed a Jfet input stage.

The same company that makes the DAC also uses 140 ohms in the cd player they also make for their tube buffer stage.

What factors go into choosing the resistor value? I looked at the chips data sheet and couldn't find any info.

I pretty much want to duplicate the whole DAC stage as used in this CD player (using the COD DAC Kit) and add the (out of stock) S/PDIF 4:1 MUX/Receiver and USB Receiver/DAC all into one unit.


Zc

[Russ White]

Originally Posted by Zero Cool

Hi, I just found out about Twisted Pair and boy have i got some questions!

I am interested in Buying the COD kit. or maybe 2. so the first question is, 1)what is the difference in using one kit stereo, vs. 2x kits each configured for mono??

2) second. how do you choose the I/V stage resistor? I see that the kit uses 470 ohms while another high end DAC that uses the same PCM1794A chips uses 140 ohms resistors for the IV stage that feed a Jfet input stage.

3) The same company that makes the DAC also uses 140 ohms in the cd player they also make for their tube buffer stage.

What factors go into choosing the resistor value? I looked at the chips data sheet and couldn't find any info.

I pretty much want to duplicate the whole DAC stage as used in this CD player (using the COD DAC Kit) and add the (out of stock) S/PDIF 4:1 MUX/Receiver and USB Receiver/DAC all into one unit.


Zc

1) Dynamic range is increased when using the chip mono.

2) The most practical consideration is output swing. If you apply gain at the output stage then a lower output swing from the DAC is desirable.

3) That value is perfectly fine. I would strongly suggest however not using an I/V resistor at all and simply using a purpose built I/V stage like IVY-III or Legato 3.1.

Cheers!
Russ

[Zero Cool]

Originally Posted by Russ White

1) Dynamic range is increased when using the chip mono.

2) The most practical consideration is output swing. If you apply gain at the output stage then a lower output swing from the DAC is desirable.

3) That value is perfectly fine. I would strongly suggest however not using an I/V resistor at all and simply using a purpose built I/V stage like IVY-III or Legato 3.1.

Cheers!
Russ

1) is there a limit to this? any reason why a pair of DAC chips couldn't be paralleled per channel? would there be a marked advantage over a single mono chip per channel?

2) Is there a perceivable sonic difference between a high ohm I/V resistor and a Lower Ohm I/V resistor if you kept the final gain the same after the output buffer? One could surmise that it might sound a bit more open and relaxed with less current through the I/V resistor?

2a) How critical is the I/V resistor in terms of sonics? is this the place to spend a few extra bucks and drop a caddock or other "high end" type tweakie resistor in there?

3) I have a specific reason to want to use a I/V resistor stage to start off with. but playing with a legato might be in the works once i get the front end running.

[dirkwright]

Originally Posted by kstagger

can't offer much on the technical side, but I'm running a PCM1794 via the K&K RAKK DAC using a Lundahl transformer for the IV conversion / outputs. Sounds very good - would like to see your results since the line transformers raised the price of the RAKK considerably.

It's nice to see someone else using this chip with a transformer. That's my intention also.

[redback-mike]

Are the bare COD pcbs going to be available again soon?