Discrete I/V converter board
Apr 15, 2008 at 1:59 AM Thread Starter Post #1 of 6

cetoole

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I wont have time to get this in one of my DACs for at least a week, and probably more like two, but I thought I would share this with you guys now. I just received a small box in the mail from PCBNet today, with the following inside.

discreteIVtop.jpg

discreteIVbottom.jpg


They are prototype PCBs for the discrete I/V converter board I designed, to be used with current output DACs, especially of the multibit variety (PCM63, PCM1702, PCM1704, AD1862, TDA1541, ect). I currently own two DACs, an Audio Alchemy DDE v3.0 (PMD100 digital filter, dual AD1862N-J DACs) and an Adcom GDA-600 (DF1700 digital filter, dual PCM63 DACs). Both of these will be receiving one of these boards, replacing the entire analog output stage up to the output jacks. Each board is a SE stereo board, with onboard +/- discrete shunt regulators. Board measures 4"*3".

Board layout files and schematic below:
TooleIV.png

TooleIVsch.png
 
Apr 15, 2008 at 2:32 AM Post #2 of 6

Pars

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Colin,

Looks good, nice layout. A couple of comments (from my trials of one of your previous efforts):

1) Buffers: when I used this buffer arrangement, the stereo crosstalk dropped to 6dB in RMAA, mainly because of the shared PSU between channels. Ohming R and L out to each other, the resistance was pretty low. The only thing I could wind up doing to fix this was to pull the 2SK389s that I was using and jumper from in to out on them. I noted that Pedja Rogic uses a nearly identical buffer on his TDA1541a DACs, but feeds each channels buffer stage with their own +/- TO92 VREGs (to isolate the rails?).

2) Adjustment for 0V in I have found works best at R4 with a large (10K or so) pot in series with R4.

3) Adjustment for output DC offset might work better with a pot in parallel with R7 than where you currently have it, although the current method should work.

Did you build a prototype of this yet or is that what these are for? What do you calculate for input impedance?

Chris
 
Apr 15, 2008 at 1:53 PM Post #5 of 6

regal

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The DIY community needs more high end DAC oriented stuff like this.

There is are lot of budget DIY DAC's and a lot of highish end amps, but a big hole when it comes to higher end DAC stuff.
 
Apr 15, 2008 at 2:23 PM Post #6 of 6

tomb

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Quote:

Originally Posted by regal /img/forum/go_quote.gif
The DIY community needs more high end DAC oriented stuff like this.

There is are lot of budget DIY DAC's and a lot of highish end amps, but a big hole when it comes to higher end DAC stuff.



x2, regal!

Nice looking boards, Colin!
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