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Old 16th January 2003, 05:54 AM   #21
Cobra2 is offline Cobra2  Norway
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Default Re: Pass D1 circuit

Will it work just as well in non-balanced config.? (trimming off the neg. half)?

Arne K
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Old 16th January 2003, 07:13 AM   #22
uli is offline uli  Austria
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I don't see why you wouldn't want to simply use the
I/V converter from the D1. Schematics at www.passlabs.com

Iīm afraid, basically itīs the same circuit

exept the using of MAT as matched cascode device.
the reason is that I got a few dozens of them by chance and
MAT03 too, so I play around with them.
Matching Mosfets can be frustrating sometimes, MATīs are
matched by design.
What I personally donīt like are caps in the signal path
therefore I decided to make the output nullable.
Since the MAT works as a cascode itīs influence on sound is a minor one.
U.
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Old 16th January 2003, 08:15 AM   #23
Lucas_G is offline Lucas_G  Netherlands
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Default Combine best designs

The idea of designing a firstclass DAC for DIY is very attractive!

I recently upgraded my Musical Fidelity 24bit 96 kHz DAC with Panasonic FC capacitors. This small step improved depth and spaciousness of the sound enormously, so I guess that when building one from scratch with topnotch components could really bring about a firstclass sound.

Maybe we should compare some presentday DIY designs floating around in the Internet, and pick out the best ideas for our balanced Pass-like design....?

Here are some links:

Lars Nielsen DAC, comments?

http://home.worldonline.dk/hifiside/ecdafsp.htm

http://www.dddac.de/

http://www.quadesl.com/dac.shtml

http://members.chello.nl/~m.heijlige...tml/dactop.htm

http://www.specmail.nl/zelfbouw/dac24/dac24.htm


Then there is this commercially available module form Hoerwege in Germany that, according to tests should sound very good indeed. It is built with highgrade components. Maybe we could learn something there (info only in German, but the pictures epak to themselves):

http://www.hoer-wege.de/dacup24192.html

There must be hundreds of other links as well...

Anyway, using 24 bit 192 kHz chips seems a must since these are no longer very expensive.

Regards,

Lucas.
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Old 16th January 2003, 10:50 AM   #24
uli is offline uli  Austria
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Thumbs up motivation

Quote:
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
Dear Nelson,
of course your circuit is in its simplicity AND performance
sensational (especially for one like me who heard a D1 working)
but I believe that motivation for DIYers is not only to copy good and proven designs but to play around a little bit with them and put in some (more or less good) own ideas.
Sometimes its like reinventing the 8 cornered wheel or
something like that, sometimes its an improvement.

Uli

PS: I donīt like caps in the signal path
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Old 16th January 2003, 11:34 AM   #25
Rookie is offline Rookie  Serbia
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Do the output capacitors in D1 really need to be that high? And what is the purpose of C43?

Thijs,
Which DAC did you use with passive I/V?
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Old 16th January 2003, 02:11 PM   #26
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Default D1 I/V converter

Here is my experience with the D-1 I/V at the output of Sony Current Pulse dacs.
I tried it the first time as you see it on the original schematic and found that at the sources of
Q2 and Q5 the voltage was too low to work (donít know why).
Then the use of constant current sources replacing R28 and R33 comes in help.
The CCS are with Jfets (2sk170) as seen on the Pass article DIYOPAMPS.
Once set the current at 10mA/halve , the voltage at the sources of Q2 and Q5 was around 4 volts.
This is not much because the current that drive the buffer is 4/1500=2mA : a bit low for a irf 610.
(especially remembering that the D-1 manual claims 14V at the sources of Q2 and Q5 for a current at near 10mA) .
Looking forward for this problem I set R27 and R34 (drain resistor for the cascode pair) down to 1000 ohm each. Now the buffers runs at about 6mA .
This electrically speaking.
From a performance standpoint I tried it on 2 different players: a CD and a CD/SACD .
In the first case every thing was quiet even without C15 and C16 (capacitors across drain resistors) .
In the second case (CD/SACD player) can say that the SACD is quieter than CD and a capacitor across the Drain seems necessary.
Regarding matching constant current sources (I used 2sk170) why not a pair of 2sk389dual Jfet Ö
Ah Ö the listening Ö a pleasure.
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Old 16th January 2003, 02:17 PM   #27
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Here the Pass article for constant current sources
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Old 16th January 2003, 09:53 PM   #28
OliverD is offline OliverD  Germany
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Tschrama, this is what I tried up to now during the trial&error design of my digital pre-amp:

- classic opamp I/V-converter

- Pass D1 output stage and
countless variations thereof
in simulation software and
real components

- Jocko Homo's "easy-to-build-
I/V-stage" and countless
variations thereof in real
components (Jocko's original
circuit wouldn't run in simulation,
only the real-world circuit
worked for me)

- LCAudio ZAPFilter mk II clone
with lots of modifications
(simulation only)

- passive (resistor only)
"I/V-stage"

I tried them with cheap DAC chips, I wouldn't want to use my pricey PCM1704's on test setups.

I haven't yet found something that I think would be a good solution for my DAC. The Pass D1 output stage sounds very good, but I don't like the rail voltages and I'm fiddling around with an additional stage that would give lower output impedance and enable me to remove the output caps (they get expensive if you don't want to hear them). The ZAPFilter clone could be promising, I'm trying to simplify the circuit without degrading its performance / functionality.

Requirements for me are:

- Best possible sound.

- Balanced operation with two DAC chips per channel. Balanced for me means making sure as much noise and distortion as possible appears common mode at the outputs to get canceled out at the input stage of the amplifier. This often requires more than just building two identical output stages and hooking them up to the same power supply.

- Low output impedance.

- "Normal" voltage rails, so the DAC and I/V-board can be used in existing CD / DVD players. "Normal" for me means something like +/-15 V.

- If possible, no caps in the signal path.

- Let the DAC work into an input it feels comfortable with: "virtual short to ground"

- Low noise. One of the few things you can measure and relate to what you hear.

- THD, TIM, whatever: Don't care. Can't measure it anyway. If my ears like the sound, I'm all happy.

I'm willing to drop any number of the above requirements if there are good reasons to do so - except the first. They represent what I'm aiming at if I didn't have to compromise.

I'm working on it and I'll post my results for you to comment on.

Lucas_G, good idea to compare what we have until now and take the best ideas from each design to make an ultimate I/V-stage! I think the Hoerwege DAC features a classic opamp I/V converter. If anyone needs a translation German -> English, let me know.

-----------------

Going off-topic now: I put together an airplane with some friends, and today we received an approval by the German FAA. If weather permits, we'll take it on its maiden flight tomorrow morning.
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Old 17th January 2003, 01:16 AM   #29
LBHajdu is offline LBHajdu  United States
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In my belief Uliís and Nelsonís I/V stages are the best. Lucasís links to I/V stages that use op-amps are all inferior, because of the feedback needed by the opamp and the large number of parts the opamp puts in the signal path. Say, you're not the same Lucas who designed the electrical system in my type-3 Jaguar . (Just kidding)

Uliís and Nelsonís I/V stages both very good well designed designs with only slight differences. Here are the tradeoffs the Nelson Pass D1 is known to work, we know this because Nelson has already built a few hundred. The Uli designed has as yet not been tested in real life. The Uli designed does not need DC blocking caps on the output the d-1 does. The Uli designed requires hard to find mat02. The d-1 uses parts that are all in digi-key. The Uli design may have lower noise then the d-1, however I think the difference is inaudible. Which one is better? I donít know.

I think if uli would be kind enough to add his DC nulling trick to the d-1 so we could remove the DC blocking caps we would have a winning combination.
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Old 17th January 2003, 07:44 AM   #30
Lucas_G is offline Lucas_G  Netherlands
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Quote:
Originally posted by LBHajdu
In my belief Uliís and Nelsonís I/V stages are the best. Lucasís links to I/V stages that use op-amps are all inferior, because of the feedback needed by the opamp and the large number of parts the opamp puts in the signal path. Say, you're not the same Lucas who designed the electrical system in my type-3 Jaguar . (Just kidding)
:


I wish I were... Then I would be rich enough to hire me the bodyguards to protect me from anguished Jaguar-drivers like you!

Quote:
Originally posted by LBHajdu
I think if uli would be kind enough to add his DC nulling trick to the d-1 so we could remove the DC blocking caps we would have a winning combination. [/B]
:

Indeed!
Could this lead to another 800 piece PCB order...?

I think few realize what an improvement this could be for the overall soundquality of their system...
Good commercial DACs would cost you many thousand dollars

Regards,

Lucas.
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