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A nice dac to complement the Aleph-X.
A nice dac to complement the Aleph-X.
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Old 15th January 2003, 08:50 PM   #11
Elso Kwak is offline Elso Kwak  Philippines
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Default Jocko

Originally posted by tschrama
Where is Jocko Homo?!!!!!!!!!

Hi Thijs,
Jocko announced to be two months off the board, making $$$$$ and was not sure if he would come back.
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Old 15th January 2003, 09:10 PM   #12
uli is offline uli  Austria
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Default voltage source

those transistors are voltage sources which define the voltage
on top of the 1k65 resistors, in this case about 20V +-0,2V
which means about 3.5V at the gate -> zero at the source.
Adjust for zero output (DC). you only need to select the led for 1,65V at 2mA. Even tight matching of the fets isn´t necessary,
but select them for about 3,6V G-S at 10mA.If you have Fets with 3,8-4,0V swap 47k with 51k. Intrinsic matching is done by using
MAT´s and 0,1% Emitter resistors.With the 2 1k2 resistors both
halves of the MAT see the same collector-current(->same BE voltage)


PS: As the DF1704 will be replaced by DF1706 (192kHz 8times
oversampling 24bit) I´m looking forward to make a new DAC
with 4 PCM 1704´s per channel instead of 2, but thats a bit

'Jazz is not dead, it just smells funny' F.Zappa
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Old 15th January 2003, 09:18 PM   #13
Nelson Pass is offline Nelson Pass  United States
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A nice dac to complement the Aleph-X.
I don't see why you wouldn't want to simply use the
I/V converter from the D1. Schematics at www.passlabs.com
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Old 15th January 2003, 09:48 PM   #14
OliverD is offline OliverD  Germany
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Two suggestions why people might be afraid to build it:

1.) output capacitors
2.) high rail voltages

Try it, though. It's simple, it's beautiful, and last not least it sounds good. Well, at least better than all the other designs I've stolen until now
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Old 15th January 2003, 10:19 PM   #15
Rookie is offline Rookie  Serbia
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How about using passive I/V conversion with resistor and then amplify the voltage across this resistor with Balanced Zen Line Stage? This would be the simplest possible approach but I hope good sounding too.
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Old 15th January 2003, 10:23 PM   #16
grataku is offline grataku  United States
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Originally posted by Nelson Pass
I don't see why you wouldn't want to simply use the
I/V converter from the D1. Schematics at www.passlabs.com
Because you said that "IT IS NOT INTENDED AS A PROJECT" and we are all very respectful.
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Old 15th January 2003, 10:46 PM   #17
tschrama is offline tschrama  Netherlands
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Jocko is gone... so now what I'm gonna do .. I guess this is a bad time to anouce a new, simple, not seen before, (non-original) idea to drastic improve the I/V stage.. I've got a feeling that I've got Jocko's trick now on my computer screen... too bad I can't share it with him... even more bad I can't measure the real performance.. and maybe it is original ... Wel .. if Jocko is alowed to not publish: so am I...

Your spot on about the Pass D1 circuit. My ideal I/V stage works of -/+ 5 volt, high PSSR, low THD, low parts-count, no caps.. I/m allmost there.. would you all believe that? Me ? who couldn't even understand the inverting gainclone gain-figure?

I think the D1 I/V stage works very well, but the high Voltage rails make and low PSSR make it more suiteble as an add-on for the BOSOZ...good idea? But I still don't understand why he is addicted to MOSFETs.

AMT-freak: how many I/V-stages have you tried .. I've published 5 or 6 of them .. most of them non-original, but some have a nice feature .. tried any?

As for passive I/V stage: I didn't liked it as much as my simplest active stage? don't now why, may be due to the DAC-chip charateristics..

hmmmmmmm too much beer .. too late... goodnight,

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Old 16th January 2003, 12:59 AM   #18
Mark A. Gulbrandsen is offline Mark A. Gulbrandsen
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I agree with Nelson on that one. Have you all taken a look see at the D-1 schematic. Its quite unique!!
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Old 16th January 2003, 03:03 AM   #19
LBHajdu is offline LBHajdu  United States
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Maybe I was a bit hasty about dismissing this I/V stage. I’m shore Nelson doesn’t care about us building it he just doesn’t want any questions on it e-mailed to him, although he would probably answer them anyway on this site. It certainly looks to be a good design otherwise pass labs would not be selling it and if price is any indicator it was selling for something like $5,000. I didn’t see as many reviews as would I have like to. The reviewer all generally like it, however there was a consensus that the high-end was rolled off. This is most likely because of c40, c33, and c43. I think Nelson put these in there to get rid of HF noise from the dac. I think a diyer may be able to get away without putting these in (feel free to chime in any time here Mr. Pass). Most of this noise is filtered out by the other equipment and the cable in the audio chain, this is 44.1 KHz and 96 KHz noise so to here it you’ll need tweeters that go all the way up.

One fear I do have about using this stage is, the PCM63 outputs 2ma of current, however most other Burr Brown dacs only do 1.2ma. Does some change have to be made to accommodate this, and would this drop the i/v stages voltage swing.

One funny thing about this i/v struck me when I was going threw the Zen balanced line stage article. Mr. Pass notes that distortion is lower with the Zens rails a 60volt’s as compared to 30v. As voltage goes up distortion goes down. So why didn’t he connect R32 to the negative rail that way there will be at least 30v there. Why did he stop at ground?

I put this design out there on the “Easy-to-build I/V stage” thread and even redrew it to get all that other stuff out of the way. I only got one reply to it:

Originally posted by Ric Schultz
Yes, I am not only aware of the Pass I-V stage but have tried it. I am concerned by the possiblility of high distortion with the mosfet circuit and also highish noise from the mosfets. That is why I want to try the lower impedance, lower noise and possibly lower distortion bipolar route(soundwise, I really like FETS). The only way to know which circuit sounds best is to try different ones. And tweek them, of course.

So, any suggestions on using the bipolar circuit with a PCM 1738?

Ric Schultz
I can post this pic as a PDF if anyone wants it .

Attached Images
File Type: jpg pass-iv.jpg (35.5 KB, 4731 views)
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Old 16th January 2003, 05:11 AM   #20
Nelson Pass is offline Nelson Pass  United States
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A nice dac to complement the Aleph-X.
What is interesting about the D1 I/V (besides it being the
only part of the circuit I participated in) is that it simply
cascodes the output of the DAC, the output being a current
source looking for a virtual ground. Thus, it contributes
almost no noise or distortion, and is unbelievably immune
to high frequency (RF) modulation and has no feedback
(just for sex appeal).

Why didn't anybody think of this before? Hell if I know.
It is an obvious thing in retrospect, but nobody seems to
have picked up on it. I blame the educational system for
cranking out "digital only" design engineers.

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