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RE: The 4 ways to decode digital

Posted by Thorsten (M) on October 14, 2015 at 18:09:28

In Reply to: RE: The 4 ways to decode digital posted by J. Phelan on October 14, 2015 at 08:25:26:

Hi,

> Very interesting - however, a "famous co." swears they don't use an
> "off-the-shelf IC DAC-chip"

They do not. BUT, they DO use many "off the shelf" Logic and FPGA Chips as the core part of their DAC.

So they are 100% correct in their exact wording. As long as you do not read anything else beyond the exact wording into this, you will be fine.

> and have a transformer-coupled (passive) output.

So they do.

Back in the last millennium I wrote an article on using DAC Chip's for Ultra Fi (published among others in Valve if memory serves) and included a few mentions of this principle IIRC. Jensen's Bill Withlock wrote an application note each on replacing ADC and DAC input/output stages with transformers around that time, if memory serves (which it often does not).

Of course, that was for use with very generic Of The Shelf DAC Chip's and it was in the dark ages. Back then the best DAC Chips (AD1862 and PCM63) were great and the newlyfangled Delta Sigma stuff that had just come out was awful.

Of course, a DAC is a DAC, no matter if discrete, partially IC or monolithic chip, no matter delta sigma, hybrid or multi-bit, so in most cases transformer outputs can be applied very well.

It is just, good transformers (never mind great ones) are not cheap. They make very exotic Coupling caps start to look like a good

Not like (for example) a 5532 dual op-amp (like under 20 cent each in lost's of 1,000) which often measures better... So you do not see them that often.

My first experimental non-oversampling DAC (back in '98 - gosh, TEMPVS FUGIT) based on Kusonoki's CS8412/TDA1543 design used 600 Ohm studio line output transformers instead of coupling cap's.

The best sound I ever got out of an ESS DAC Chip used a 1:20 stepup transformer with I/U conversion resistance on the secondary followed by a modified Allen Wright "Super Linear Cathode Follower" with a 5687 Tube and an Audio Note Copper foil coupling caps. Of course, coupling Cap's and transformers together are almost a bag of sand by themselves.

Commercially this is perhaps not the best solution, unless you get to charge 50 bags of sand retail...

> But your designs have high regard - so I guess it's implementation !!

I don't know about high regards, I try to make them as good as time, budget and my rather limited skills allow. I think they are okay and give the kind of sound quality I am happy to listen to myself, even the really cheap stuff. Don't read too much into all of this. Just go and listen.

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

Edits: 10/14/15

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