Borbely ALL-FET DAC I/V stage

[hollowman]

I'm new to this forum so the answer to this query may be in its archives. Apologies in advance for any redundancy in this message.

In these articles (<http://www.borbelyaudio.com/adobe/borb502.pdf>, <http://www.borbelyaudio.com/pics/305borbely-new.pdf>), Borbely describes an ALL-JFET line stage, provides schematics and part values.

I'm interested in building the ALL-FET Dac audio board <http://www.borbelyaudio.com/allfetdac.asp>. Some schematics are provided on this page, but no part values are given. Can anyone hypothesize what the values may be? (Even the Starter Kit version of Borbely I/V may work for me: <http://www.borbelyaudio.com/eb604417.asp>, but again, no component values are given.)

In any case, is/are there an equivalent or better I/V design(s) in the diyaudio.com archives that may work like (or better than) the ones at borbelyaudio.com?

Please note my criteria for DAC I/V:

- No vacuum-tube-based projects, as I prefer smaller, more-portable solutions.
- Should work for a variety of DAC chips (e.g. TDA1541, TDA1543, TDA1545; and PCM1704, PCM1794)

Thx in advance for any help you can provide.

[spencer]

This is a balance version Jfet IV modified from NP D1.

R9/10 adjust output stage gate/source at 10V.

R11/12 adjust input offset at 0V or desire value.

Adjust R3/4 for different DAC out current. 1.5k is good for PCM63 and TDA1541.

Use half will be Single ended verrsion.

I have good result with that.

Spencer

[hollowman]

Originally posted by spencer
This is a balance version Jfet IV modified from NP D1.

R9/10 adjust output stage gate/source at 10V.

R11/12 adjust input offset at 0V or desire value.

Adjust R3/4 for different DAC out current. 1.5k is good for PCM63 and TDA1541.

Use half will be Single ended verrsion.

I have good result with that.

Thx for posting that.

Do you have a standard (unbalanced) schematic?

[spencer]

Use left half for left channel, use right half for right channel.

Spencer

[mark_titano]

Hi hollowman,

I'd like to build a similar I/V stage for my Philips cd723 (tda1545a).
I've found an interesting article on Borbely's site, look:

http://www.borbelyaudio.com/adobe/xover.pdf

Regarding this page:

http://www.borbelyaudio.com/eb604417.asp

the input discrete opamp is the same that he describes here (604/410)

http://www.borbelyaudio.com/pics/305borbely-new.pdf

I don't know what kind of fet and values he used in filter buffer, sorry.
I'm not referring to the filter values but to the cascade buffer.
Probably 2sk/2sj series are a really good choice.

I hope someone knows and share it here ;-)

Mark

[spencer]

This is my estimation:
Q9 = 2SK246BL
Q10=2SK170BL
Q11=2SJ74BL
Q12=2SJ103BL

It must be the jfet that he is selling in his website!

Also take not on the below stated by Borbeley:
The 3rd order Bessel filter is built around a complementary JFET follower Q10-Q11. These are cascoded with Q9-Q10 to reduce input capacitance and distortion caused by capacitance modulation at high source impedance. Q10-Q11 is selected for Idss=8-10mA. Idss of Q9-Q12 has to be higher than that of Q10/Q11 to avoid forward biasing.

[hollowman]

Originally posted by spencer
This is a balance version Jfet IV modified from NP D1.

Was the orig. Nelson Pass D1 a single-ended class-A preamp (not sure if your schematic is SE class-A...sorry, I'm a novice, here)? How feasable (accurate-sounding) are solid-state single-ended class-A I/V's for DAC's? I can't recall having encountered any in the past, so I'm not sure if the lack-of-popularity is based on over-technicality-of-design, availability of needed components, etc.

[spencer]

Study this thread.

D1 I/V Stage Finished.

[rfbrw]

Originally posted by hollowman


Was the orig. Nelson Pass D1 a single-ended class-A preamp (not sure if your schematic is SE class-A...sorry, I'm a novice, here)? How feasable (accurate-sounding) are solid-state single-ended class-A I/V's for DAC's? I can't recall having encountered any in the past, so I'm not sure if the lack-of-popularity is based on over-technicality-of-design, availability of needed components, etc.

You can't throw a stone in this place without hitting a ss/se i/v of some sort from the 2 mosfet original Pass D1 through Jocko's simple i/v and its variants, rbroer's i/v, Elso Kwak's i/v to Pedja's AD844 based i/v , an OP660 based i/v, the Hawksford i/v and the Wadsworth/Wadia/PA630 i/v and on and on.......

[hollowman]

Originally posted by spencer
Study this thread.

D1 I/V Stage Finished.

Thx. It looks like a very do'able project but rfbrw mentions a bunch of other "ss/se i/v's" so I'm tossed as to which one to build first.

Originally posted by rfbrw


You can't throw a stone in this place without hitting a ss/se i/v of some sort from the 2 mosfet original Pass D1 through Jocko's simple i/v and its variants, rbroer's i/v, Elso Kwak's i/v to Pedja's AD844 based i/v , an OP660 based i/v, the Hawksford i/v and the Wadsworth/Wadia/PA630 i/v and on and on.......

As I said in the last thread: "sorry, I'm a novice, here".

IAC, I appreciate the keywords you provided above. They will help me use diyaudio.com's search engine to find topical threads.

BTW, is there a "consensus" amongst DIYers as to which is the better design to build -- SE or Diff (both SS) -- if $/effort are equal but sound quality was the ultimate deciding factor?

Thx again!