How to Calc resistor for I/V stage

[Zero Cool]

well at some point we start getting into a trade off as far as noise is concerned i would think. I mean if we used a 10 ohm resistor, now the voltage level is so low that we need a lot of make up gain in the buffer stage to get to a reasonable 2vrms@0dbfs output and I would imagine there would be sonic trade off's one way or another if you had to use a buffer stage with that much gain! I mean at .0078mv we are in the phono cartridge range! that's pretty low.

So there has to be some point where resistor value vs dac output voltage vs gain makeup evens out.

Maybe I can talk the engineers at work into helping me setup the AP to do some distortion tests with various resistor values and see if we can find the sweet spot?

Zc

 

[SoNic_real_one]

If you looked into the link provided by me on the other page, engineers from ESS (Sabre DAC) made measurements with different OpAmps as I/V stage. They got THD in 114-116dB range and DNR in 120-128dB.

I really doubt you can get better that that with resistors and buffers...

To say that TI guys are bad analog designers is something. But to say that also the guys from Analog, Wolfson, ESS, Cirrus are bad too (because all use OpAmps) is a little excessive.

 

[Zero Cool]

Look, at a later date I will explore active I/V buffer stages. But right now that's not my focus.

 

[abraxalito]

I really doubt you can get better that that with resistors and buffers...

Me too if by 'better' you mean 'better numbers'. The purpose of going passive I/V is not to get better numbers, rather better sound.

To say that TI guys are bad analog designers is something. But to say that also the guys from Analog, Wolfson, ESS, Cirrus are bad too (because all use OpAmps) is a little excessive.

Its a good thing that's not what I'm saying. I'm saying they're bad designers for sound quality, an entirely different thing.

 

[Zero Cool]

I wonder what difference sonically the quality of resistor makes? I am currently using Vishays but used Carbon comp in a pinch during testing but did not get a chance to do any critical listening. But sounded good on the test system however.

I have access to the vishays 1% I am currently using, Vishay Metal foil ultra precision types, Caddock and Draloric types.

Also how about 1 resistor vs. several in parallel?

 

[abraxalito]

I haven't tried anything even slightly 'quality' in the resistor stakes myself. Bargain basement thick film SMT sounds pretty good, but that's not to say that better measurements in resistor wouldn't give rise to better sound.

 

[abraxalito]

Here's a newly released part which looks jolly interesting for adventurous passive I/Vers. A single one has max gain of 15.5dB though (differential mode).

ADL5565 | 6 GHz Ultrahigh Dynamic Range Differential Amplifier | Amplifiers | RF / IF ICs | Analog Devices