STAX DAC Talent

So not sure where I'm going with this. Lets start with that.

Bought a STAX DAC Talent (despite my misgivings about SPDIF) and it is rather nice although old at this point

As is my S.O.P. with 30yr old gear, I've swapped out electrolytics. All THREE of them :D. In this case with "shiny" Nichicon ones. To be rewarded with a little red LED coming on in the power supply section (AKA I didn't notice it before) I assume this is good.

So case off, the chipset is mainly:
  • YM3623B
  • SM5803AP
  • V-12M288
  • PCM63P K :love:
  • AD845
Much opto-isolated glamour! with pictures

I have questions though... Not least of which is normal/direct !?! What does that even mean...

Information is hard to come by for this although I guess the money was spent on the digital rather than the analogue side :) it works well.

Can this (semi) sensibly be updated. I know there is an 'upgrade' for the SM5803 to DF1700 - worthwhile??

I also have already the ability to swap PCM63's to PCM1704's But it seems completely unnecessary.

Andy
 

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V-12M288 is not a chip. It is a dual VCXO for the PLL.
Yes sorry I'd looked that up already. Obviously not an expert but assume it helps the clock recovery somewhere along the line?
SM5803 to DF1700 would not be much of an upgrade. For that you would need the SM5842...
Food for thought, there is a drop in board available for the DF1700. I was half tempted but I'll leave that alone I think now,

Andy
 
More photo's for what it's worth
Swapped out the AD845 for Burson Audio 'glamour chips' Somewhat blindly as they were already in DIP adaptors

Two questions then should answers be forth coming:

Firstly: Direct / Normal. Currently assuming that skips an output cap Although this is where some confusion creeps in as the solder bridge for 'direct' is shown differently in the limited amount of information on line.

Secondly the POT next to the IV op amps...
 

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From what I remember, going back about two decades, the pots null the offset of the op-amps and the two sets of direct bridging pads insert a resistor to ground for passive i/v conversion and bypass the op-amp feedback resistor. Possibly why the op-amps were socketed. Not certain about the pots though. They may zero the output in direct mode.
 
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Really really not sure about the pots as the PCM63 has +2mA current output that can be added to audio current output to centre the output current swing around zero. Imagine it is a voltage offset correction setup of some sort but for normal, direct or both I have no idea.
 
@rfbrw Thanks. I couldn't see that direct mode for looking at it, never occurred to me that they'd skip the output entirely but duly traced out that's exactly what it does o_O

BPO is indeed connected to the Iout pin on the PCM 63 so no trickery there.

Only other oddity is the low value (?) of cap on the power supply 0.1uF at 250v

Andy
 

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Then I had thoughts...

Checking output offset - nothing even with different op-amps. OK fine that's how it should be (y)

Then it occurred that the potential divider VR02 (VR01) probably exists to minimise the 'work' that the silicon has to do, so I've now adjusted such that the voltage at the junction of the wiper of the pot(s) and associated resistors is zero.

Those pots are super sensitive. Multi-turn ones would be nicer as +/- 500mV is a fraction of a touch. Ergo: They're probably off to start with :) But they work.
 

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One more thing before I close this (as far as I'm concerned)

Final iteration - I've kept the (audiofool?) Burson op-amps after fairly limited listening. Limited as in it sounds good, 100% cannot guarantee that the original AD845's were same, similar or better ay this stage. (Never mind OP627 or AD797 etc)

Changed the felt feet for something nicer. 3D printed feet with o-rings. If only I had a lathe. This unit now sits 1-2mm higher but it's not too obvious. Can supply STL files for the feet but M3 holes need to be drilled

And that's it. Enjoying this DAC for a bit as it's rather musical

Andy