Experience with this DIY DAC ?

[gabanyayaya]

Originally Posted by McGyver

I found CS4397 better sounding than CS4398. And PCM1798 with proper analogue stage is best. So if you use this baby board - stay with it. And if you use bigger board with CS4398 on an adaptor - it's worth to change it to PCM1798 and to redo analogue stage.

does the PCM1798 works well with UTC A-20 traffo on the output stage?

[hafp]

Just an update on bypassing the opamp analog output stage and sending the signal to line transformers as posted.
Ended up using Altec 15356A's with the recommend filtering on the input and outputs.
Much thanks to Bill Fuss for all his help with this project; he as taken the time to post much of his findings, and also was nice enough to send me PM's with his recommendations on what filter values to use.
I have one of the early versions of this DAC, with the coax input transformer and without all those switches to change the sampling.
Have the transformers hooked up for only about 24 hours, but can say that it has much promise to be better than my tweaked out "small DAC" with Cinemag 15/15B transformers on the output.
IMO - the sound with the Altec transformers on my "big DAC" has more detail and transparancy, and should only get better with a few days burn in.
Cheers to all that have contributed to this thread.

[Bill Fuss]

Originally Posted by Farfe

Hello all,

New on this thread, I had many hours of reading and must say this subject is fantastic. I just ordered the DAC you are talking of, and I wish to switch the analog output stage to transformers.

I found these which are localy available :

Oxford Electrical Products | Transformateurs | Transformateurs | Transformateurs audio | Montage sur CI et châssis |A262A6E

Do you think they could do the job ? And also what is the value of resistors and caps needed ?

Btw has anyone noticed some sellers offer CS 43122 dac chip on a daughter board for this DAC ?

I,m afraid they are not large enough. They will saturate at lower freq . You need +15dbm or around 100mw at 30hz capable.

[Farfe]

Thanks a lot Bill,

I meanwhile found a provider for Neutrik NTL1 transformers which I understand are similar to the Studer used successfully by some experts here. Franz Gysi on first I think.

I remember a direct wiring from DAC chip and to outputs without any RC circuit. I'm going to check this on the thread.

[Bill Fuss]

Originally Posted by gabanyayaya

does the PCM1798 works well with UTC A-20 traffo on the output stage?

The 1798 is a current output chip, you will need step up trafos. They usually use 18-20/1 ratios.

Best, Bill

[McGyver]

Originally Posted by Bill Fuss

The 1798 is a current output chip, you will need step up trafos. They usually use 18-20/1 ratios.

Best, Bill

One can use also 1:1 trafo followed by for example tube stage with gain about 20x

[gabanyayaya]

Originally Posted by Bill Fuss

The 1798 is a current output chip, you will need step up trafos. They usually use 18-20/1 ratios.

Best, Bill

The A20 can be set at 600 : 50 ratio max (12 gain)...will that be enough..? or must it be at 18 to 20 gain...?

Originally Posted by McGyver

One can use also 1:1 trafo followed by for example tube stage with gain about 20x

can you kindly share some gain circuit McGyver?

[McGyver]

Originally Posted by gabanyayaya

The A20 can be set at 600 : 50 ratio max (12 gain)...will that be enough..? or must it be at 18 to 20 gain...?

I tried 1:10 trafo and it worked properly.

Originally Posted by gabanyayaya

can you kindly share some gain circuit McGyver?

Yes, I can, but not now. So many work to do and the hours are not made of rubber.

[Lucas_G]

Originally Posted by Bill Fuss

1nf is too large, try around 200pf. That should give you an f3 around 150khz.

Thanks Bill,

I tried this out, but the 1 nF had no impact in the visible audioband.

I asked David Carter. He told me that the 1k resistors after the Dac were responsible for the early frequency roll off.

He was right. I removed them and now I have a perfect frequency response!

The sound is extremely good, much better than before, but I do get a very hot signal now.

Maybe I should try the windings in paralell instead of in series...

[samoloko]

Lucas_G

where did you bought LL1674 and how much
what Is LL1690 price at that place
have you compare sound of Lundahl with other setups