Ultraanalog D20400 app. note ?

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#5
I realise it was a long time ago but did you ever test their linearity Bernard?

Manley and Stax used the D20400 with valve stages and were considered top reference dacs of the time so shouldn't put people off.. The hardcore can always scrape away the resin and bypass the AD844 (or AD825) opamps used for I/V.
 
#7
Has anyone here attempted a NOS D20400 dac?

I have a Manley/Langevin studio DAC (same as Manley Junior) which uses the D20400 in a basic form (simple power, simple output stages, simple Yamaha/NPC reciever/filter). Sounds good - nice and natural sound, good dynamics but terrible transformer buzz on my mains as its a 220V unit on what is probably 245v in my block of flats.

I'd like to both improve it AND allow the chip to handle HD material, say 24/192 (384KHz even but obviously a cut-off at 20 bit !) by running it in a NOS mode. It runs at true 20 bit and up to 400KHz.

Is there any reason it shouldn't be possible? Is there a simple solution in replacing the filter/receiver chips with direct drop-ins?

I had read too that Manley/VTL used custom units that ommited the an OP somewhere at the end of the internal chain so that it was better used with a valve output stage and had a 0.5V output rather than 5V - this could be incorrect (as I think was in a Stereophile review) but does anyone know?

I'm hoping that this project will be my 2013 project (I'm a newbe to DIY although been reading a fair while) so hopefully I'll start a thread for help soon enough..

Somewhere I have downloaded the schematics for the VTL and Stax valve output D20400 dacs (from a russian forum).
 
#8
I'm in the NOS crowd, though not valve so as tritosine points out, I'd not be interested in D20400 because of the internal opamp which will probably compromise the linearity. I shall be interested in following your thread though 🙂
 
#9
Well, some interest is hopefully the presure I need to get around to it. I should warn though that I am a complete novice and would be my first project (other than straightforward replacement repairs).

I wouldn't be too put off by the op amp as there have been at least 4 great valve output DACs using the chip:

Stax X1t :

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Sonic Frontier SFD2 (or is it 3?):

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Manley Reference 20:

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VTL Reference:

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Just a shame I don't have two chips to play with...
 
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#10
Just because others say a piece of kit is 'great' that doesn't nullify the technical arguments for why opamps sound bad 🙂 No amount of post processing by valves can undo the damage done to SQ by a single opamp and this is demonstrable with measurements (which I haven't devised yet 😀). Incidentally I use the same argument basis for when people try to tell me how 'great' SACD players sound.
 
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