Tube or R-2R DAC for Tube System

there seems to be some confusion with terminology.  Multibit = R2R.  They can be discrete resistors soldered onto a PCB or thin or thick film hybrids on a IC; but they are both ladders, and both take in PCM and spit out PAM.

Bitstream is a different animal, based on pulse density modulation.


Arguments can be made for and against chips based R2R but the real reason for the proliferation of discrete DAC is that R2Rs vanished from the market place long ago.  AD has re-introduced one that is used by several, including Schiit, but it is not designed for audio and glitches.

Whether you place a tube I/V and filter after it or the same deal with transistors is an independent question.  tubes of course help get glowing reviews (ducks for cover after bad pun).

@itsjustme,
Do you have any particular opinion regarding I/V conversion method, i.e. passive (resistor) versus active. Transistor vs transformer vs OP-amps?
Charles

Learning now!  Entirely passive seems like a tough proposition since the output will have a variable impedance and a high one at that.  For a home/hobby project where you can control the next stage maybe its feasible - but in commercial proactive that sounds, to me, like suicide.

Transformers are a natural for the task, but are typically big and expensive ( and most that are not , are not very good) . I have not experimented with any custom ones.  I plan to use discrete circuitry, combining FETs and BJTs where each as an advantage - and keeping it pretty simple. (what was it that Einstein said? "as simple as possible, but no simpler" :-)

The output characteristics of bitstream DACs vary quite a bit too- some only give a voltage output - meaning an onboard opamp i presume. The real world gets messy.   But again, still learning. All my DACish work so far has been on the other end of the chain - input, isolation, clocking etc. 

@itsjustme, 
 Some DAC designers prefer the sound and simplicity of a passive resistor and want to avoid the use of OP-amps due to what they consider to introduce sonic degrading NFB. I do recognize that another approach is active I/V conversion via a discrete circuit again avoiding OP-amps.

 I know that Audio Note utilizes transformers for I/V conversion duty. Given their reputation for very good sounding DACs I have to assume that the chosen transformers are of excellent quality. 
Charles 

@charles1dadsI
I must be missing your point,since i addressed why one of those options is commonplace and sub optimal, and the other has serious issues.  Could you clarify what you are pointing out, or want to know?
G