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Old 15th June 2008, 10:51 PM   #1
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Default JFET D1 I/V stage for ESS Sabre DAC

To go with the Twisted Pear Buffalo DAC I will be constructing the simplest and/or best sounding incarnation of the D1 with JFETs. I have been reading for days and can find quite a few different versions. However, if I am going to build the D1 JFET I/V stage I would find it much easier decide which version by asking the man. Mr. Pass, do you have a schematic and pretty pictures of your favorite D1 I/V? I have searched and read for quite some time and have found many schematics. Second, as I am not an EE, do PCBs sound better or are they just easier to build with? Finally, are there any PCBs available for the D1 JFET I/V(not entire DAC) stage or would others be interested in getting some made? I am good with my hands and soldering(I hope good enough) but I lack the experience in electronic design. If boards were to be made, would it make sense to do the I/V stage seperate from the balanced to SE conversion so that one could actually go balanced for less money for once and if SE is required, an additional board could be made for that? Or would it make sense to do it all on one board and just populate only what you need?

Nelson, have you played with or heard the ESS Sabre DAC yet?
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Old 16th June 2008, 01:31 AM   #2
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Default Re: JFET D1 I/V stage for ESS Sabre DAC

Quote:
Originally posted by khundude
Mr. Pass, do you have a schematic and pretty pictures of your favorite D1 I/V?

Second, as I am not an EE, do PCBs sound better or are they just easier to build with?

Finally, are there any PCBs available for the D1 JFET I/V(not entire DAC) stage or would others be interested in getting some made?

If boards were to be made, would it make sense to do the I/V stage seperate from the balanced to SE conversion so that one could actually go balanced for less money for once and if SE is required, an additional board could be made for that?

Or would it make sense to do it all on one board and just populate only what you need?

Nelson, have you played with or heard the ESS Sabre DAC yet?
So many questions.

1) My favorite is the production version, which used Mosfets. This
should not dissuade you from building the JFET version.

2) PCB's are easier and much more consistent

3) I don't know.

4) No, I don't think so.

5) Populate all of it, you'll eventually need it.

6) No.

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Old 16th June 2008, 02:54 AM   #3
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Thanks Nelson,

I have to thank you for all of the support you give us. I am a decent guy with a small bank account and have one vice, music! I am living a Zen lifestyle with only my music left in my possesion and your Zen approach appeals to me greatly! What do you prefer about the MOSFET version over the JFET and what are the key sonic traits? Do you prefer the sound from the SE or balanced D1? If the SE sounds near as good as balanced I would prefer to go SE as it would cut cost everywhere else.

Thanks again.
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Old 16th June 2008, 07:50 AM   #4
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I'd also be interested in Mr. Pass's views on the Mosfet D1.

I'm currently running Spencer's implementation of a D1 style JFET I/V on a D1V3 and I get the sense that the JFET versions lose some of the "zen" simplicity of the mosfet version. The D1V3 uses 12 jfets per channel, compared with 4 Mosfets per channel for the D1, and I'm not quite sure how much benefit the extra complexity actually brings. From NP's comments elsewhere the advantage seems to be a slightly lower noise floor using JFETs. I'm not sure what else is gained.

I assume the only way to know is build both, so to that end I've ordered a pile of IRF610's to match.
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Old 16th June 2008, 02:45 PM   #5
Goffe is offline Goffe  Sweden
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Can this be the one your guys are looking for I/V Output Amp
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Old 16th June 2008, 08:18 PM   #6
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The only advantage the Mosfet has over the JFET in this
application is a lower impedance at the Source pin, being that
the Mosfet has a much higher transconductance. This results
in lower voltage seen at the output of the DAC. If the DAC is
not sensitive to this, then there is no advantage.
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Old 16th June 2008, 08:56 PM   #7
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Quote:
Originally posted by Goffe
Can this be the one your guys are looking for I/V Output Amp
Perhaps the other guy? I have a couple of Ralph's ono boards - nicely laid out and very well constructed.

Quote:
This results in lower voltage seen at the output of the DAC. If the DAC is
not sensitive to this, then there is no advantage.
Mr. Pass, could you explain how the voltage sensitivity manifests itself in the DAC's performance?


cheers
Paul
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Old 17th June 2008, 08:38 PM   #8
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Quote:
Originally posted by spzzzzkt
Mr. Pass, could you explain how the voltage sensitivity manifests itself in the DAC's performance?
We are talking about DACs whose output is a current source,
designed with the presumption that they will be driving a
virtual ground. Any impedance that they see for an output
load will result in voltage at the output of the DAC chip, which
may (or may not) have an effect of their performance.
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