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New Zen I/V proposed from Nelson Pass

post #1 of 23
Thread Starter 

In case anyone missed it : http://www.diyaudio.com/forums/diyaudio-com-articles/172983-zen-i-v-converter.html

 

 

This is significant in that the D1 stage has been highly regarded as one of the best DAC analog stage to use for over 15 years.  There have been a lot of complex ideas floating around in the DIY community the past decade but none I have found sound as good as the D1.

 

For Nelson to endorse this it is definately worth a look.   I may try this out on my 1862 DAC.

post #2 of 23

I've been looking for an output stage for my PCM1794 DAC, I may try this too!

post #3 of 23

i'm pretty happy with the modified D1 i'm running already on my sabre (OPC's latest schematic), we have found that performance increases a great deal along with the amount of transconductance and this generally gets higher with mosfets at higher voltage. i'm running +/-45v rails. all the same i'll probably give this a go with some nice modern sic jfets just for kicks. I saw the post on DIYA yesterday. 

 

it does sound excellent I might add

post #4 of 23
Quote:
Originally Posted by regal View Post

In case anyone missed it : http://www.diyaudio.com/forums/diyaudio-com-articles/172983-zen-i-v-converter.html

 

 

This is significant in that the D1 stage has been highly regarded as one of the best DAC analog stage to use for over 15 years.  There have been a lot of complex ideas floating around in the DIY community the past decade but none I have found sound as good as the D1.

 

For Nelson to endorse this it is definately worth a look.   I may try this out on my 1862 DAC.

Curious as to what you have tried and listened to? The D1 (and this one) have the drawback of requiring coupling caps, unless you can add cascodes/DC servo to this to allow DC coupling.
 

post #5 of 23

Well, that coupling cap is only there as a high-frequency filter, it's technically optional.

post #6 of 23

<deleted>


Edited by Pars - 9/12/10 at 12:12am
post #7 of 23
Quote:
Originally Posted by NP (diyaudio)

R1, R2, C1 and C2 are simply passive filters.

 

If you think your 30V supplies are noise free then you can modify or delete the filters. C3 and C4 capacitively couple the output so that we don't have DC arguments. R5 is simply a resistive load, which you can modify or delete if you like. C5 is the high frequency filter, which you can also modify or delete. There is no feedback. The Jfets were selected for matched Idss at 10mA, and present a DC offset voltage at the Source about 1 mV, which is plenty low. If you have unmatched Jfets, then I suggest you use a low impedance resistive voltage divider to offset the DC Gate voltage by the required amount. By low impedance, I suggest that the resistor to ground be on the order of 10 ohms or so.

Note that at 10 mA bias, the Fets will end up with about 15 volts Drain-Source. With other Idss bias figures you may adjust the values of R3 and R4 up or down to get this figure. If you want more gain (and I bet some of you do) then you can increase R3 and R4 to 2.2 Kohm each for twice as much, but you then need to add about 10 more volts to each supply rail to arrive at the +/-15 Volt Drain voltages on the Jfets. The input impedance is the inverse of the transconductance of the two Jfets in parallel, which at 30 mS each comes out to around 15 ohms. The output impedance is roughly the values of R3 and R4 in parallel, and for the example shown that is around 500 ohms.

post #8 of 23
Thread Starter 



I've tried most of whats been up at diyhifi and diyaudio,  none I find as good as a simple D1.   I agree the coupling cap is an issue,  but this new zen should easily be servoed by monitoring the output with an opamp outputing to the gates I believe.  

Quote:
Originally Posted by Pars View Post



Curious as to what you have tried and listened to? The D1 (and this one) have the drawback of requiring coupling caps, unless you can add cascodes/DC servo to this to allow DC coupling.
 

post #9 of 23


any other mosfet output I/V? I bet that is what your preference is. Nothing particularly spectacular about this circuit.

Quote:
Originally Posted by regal View Post



I've tried most of whats been up at diyhifi and diyaudio,  none I find as good as a simple D1.   I agree the coupling cap is an issue,  but this new zen should easily be servoed by monitoring the output with an opamp outputing to the gates I believe.  


 
post #10 of 23

Whoops, mind must have slipped when I was reading that article.  Those caps looked more like decoupling but I missed the resistor there.

post #11 of 23
Quote:
Originally Posted by regal View Post



I've tried most of whats been up at diyhifi and diyaudio,  none I find as good as a simple D1.   I agree the coupling cap is an issue,  but this new zen should easily be servoed by monitoring the output with an opamp outputing to the gates I believe.  


 

How about some specific examples of what you tried as there are a lot of I/V stages (mostly incomplete examples) at diyaudio alone? I know of no complete examples at diyhifi. Also, I haven't seen a servo that can deal with 15V of offset, which is what it appears there is present on the Zen stage...
 

post #12 of 23
Thread Starter 
Quote:
Originally Posted by Pars View Post



How about some specific examples of what you tried as there are a lot of I/V stages (mostly incomplete examples) at diyaudio alone? I know of no complete examples at diyhifi. Also, I haven't seen a servo that can deal with 15V of offset, which is what it appears there is present on the Zen stage...
 



Pedja's (dihifi, its complete), Rudolf's(DIY Audio). the "improved" Jocko stage (DIYAUDIO),  Cetooles transistor surplus stage PCB ,  there were a few on a thread we had here, you name it I've tried it,  always come back to AUDIOGD or PASS D1, or tube (passive IV + anode follwer). 

 

I agree and dont think there is a means to servo this without adding transitors the more I look at it.  But I think Nelson Pass designs are normally top notch.  Are you implying this gift isn't worth building 'cause of a couple capacitors in lieu of complexity? 


Edited by regal - 9/15/10 at 6:25am
post #13 of 23

I'm sure it is worth building, but I prefer DC coupled if possible. I've never listened to the D1 stage, so don't have an opinion. I have used rbroer's and cetoole's I/V stages, and have built Pedja's NOS DAC with the AD844 I/V. I assume you like MOSFET sound (since you seem to like tubes). I do really like my Pass preamp, so I would be interested in hearing the I/V.

post #14 of 23


Let me ask this another way. How many of NP's "free designs" in the source/preamp/crossover category use coupling capacitors and how many of his commercial designs in this same category use coupling capacitors?

Quote:

But I think Nelson Pass designs are normally top notch.  Are you implying this gift isn't worth building 'cause of a couple capacitors in lieu of complexity? 

post #15 of 23
Thread Starter 
Quote:
Originally Posted by luvdunhill View Post


Let me ask this another way. How many of NP's "free designs" in the source/preamp/crossover category use coupling capacitors and how many of his commercial designs in this same category use coupling capacitors?


 


Good point but how about this,  for the price one can build the NP "free designs" how many commercial products are any where near the same league?  
 

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