A NOS 192/24 DAC with the PCM1794 (and WaveIO USB input)

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#5,001
Technical stuff

Now the technical stuff:

as you can see the trimmers are at the edge of the board. So even when stacked you can trim every DAC chip to get 0,4mA

The trick is simple. Just added a 100Ohm resistor. now you can measure at the test point for 40mV. If you do this at all points things are fine even for multiple boards.

I have tested this of course and the 40mV is in the middle of the trimmer, allowing for spread in other FET batches.

It is also very stable. after 24 hours I had a 1mV difference which is NO problem at all. The dac works fine even plus minus 10%

Just to mention, both 6k resistor AND the current source can be installed. So you can experiment and try yourself

DDDAC PBT proto 2.JPG

DDDAC PBT proto 3.JPG

DDDAC PBT proto CC pin 20.JPG
 
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#5,006
dwjames said:
Also, not sure if it's decided already or open for suggestion, but it would be nice to include 2 of these pps caps per deck to use in the local decoupling of the digital supply for each dac chip in place of the Wima film caps.
SMR5683J100J03L4BULK Kemet | Mouser
It seems a few people have found that a nice pps decoupling cap on the digital supply can give more magic than a fancy regulator for a much cheaper cost 🙂
Click to expand...

PTH device, far to much lead inductance wont do anything, need SMD small packages for decoupling with caps of this value.
 
#5,007
dddac said:
Yes it will. It is hard to make a smooth transition, so we wil have some dead time.
I am finishing the prototype as we speak and will do listening tests hopefully this week. than order boards and SMD soldering in March. April should be target month. The embedded Tent shunt is for the 8Volt only. The 3,3V stays LF33, with option to mount a shunt replacement (for those who really want to do this. My tests showed that the 8V does the most. I truly hear no real difference with or without shunt on the digital side) It also includes a current source for pin 20. And of course totally back wards compatible with mainboards and old dacs (you could even use them mixed if you want)
Click to expand...

The ultimate DDDAC board is finally in the making, super!
Do you still remember my tweaks or shall I refreshen your memory with some pictures 😀
 
#5,008
dddac said:
Now the technical stuff:

as you can see the trimmers are at the edge of the board. So even when stacked you can trim every DAC chip to get 0,4mA

The trick is simple. Just added a 100Ohm resistor. now you can measure at the test point for 40mV. If you do this at all points things are fine even for multiple boards.

I have tested this of course and the 40mV is in the middle of the trimmer, allowing for spread in other FET batches.

It is also very stable. after 24 hours I had a 1mV difference which is NO problem at all. The dac works fine even plus minus 10%

Just to mention, both 6k resistor AND the current source can be installed. So you can experiment and try yourself

View attachment 531551

View attachment 531552

View attachment 531553
Click to expand...

I have my current sources in a year now without any re-adjusting, still working fine. Last time I checked; no drifting.
 
#5,011
DDDAC PSU Question

I'm thinking about beefing up my standard 12V DDDAC PSU so it's comfortable with feeding a 4 stack DDDAC fully kitted out with Tent shunts (so that's 16 shunts and the mainboard to feed). From other posts here it seems extra heatsinking on the TIP122 is advised. My idea is to fit a taller heatsink on the TIP122 so that it touches the top of my case - the whole of the aluminium case top then can assist. The old TIP122 heatsink will go on the diodes (may as well).

Also, is there any merit in increasing the big 4700uF caps (C1 and C3) to 10000uF? Can I do that alone or would I have to change other components to bring it back into balance?
 
#5,012
SimonJ said:
Doede how will the shunts be supplied, in the kit and also optional if we already have the shunts?
Click to expand...
The 8 volt Tent shunt is embedded in the design and the parts are on the pcb board and smd parts are pre assembled. This is a special agreement with guido tent. Powered by Tent so to speak.... For the 3.3 volt there is a normal LF3.3 and space on the pcb for those who want to do more DIY ...
 
#5,014
A question for juancho perhaps, or anyone else in the know.
I am wanting to add a PSU for the digital side of the dac boards and obviously isolate the analogue from the digital on the dac boards. My question is do I need shunt regs on the digital side to run a separate PSU to the digital side? And can you recommend a good PSU for the digital side of the dddac?
Thanks
 
#5,016
Sovereign1 said:
A question for juancho perhaps, or anyone else in the know.
I am wanting to add a PSU for the digital side of the dac boards and obviously isolate the analogue from the digital on the dac boards. My question is do I need shunt regs on the digital side to run a separate PSU to the digital side? And can you recommend a good PSU for the digital side of the dddac?
Thanks
Click to expand...


Shunts are not needed and you can use a separate PSU on the digital just fine with the regs on the boards.
 
#5,017
PSU for the digital side of the dddac

can you recommend a good PSU for the digital side of the dddac?
Click to expand...

I have a separate power supply on the digital side of my DDDAC.
I use a 4amp 6.3VAC filament transformer which provides about 7.5VDC unregulated power after rectifiers and caps into a load. I also feed the WaveIO 5VDC Belleson Vreg from this PS.

I assume that there Vregs on the main board and DAC board and not using the PSU to provide the final voltage. A digital voltage regulator should be as close as possible to the digital use point.

IMO the TentLabs is an excellent analog Vreg, but that there may be better Vregs for the digital side. I have heard sq improvements from using the Belleson and the excellent ADM7150 using a small PCB of my own design.
 
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#5,018
carlsor said:
I have a separate power supply on the digital side of my DDDAC.
I use a 4amp 6.3VAC filament transformer which provides about 7.5VDC unregulated power after rectifiers and caps into a load. I also feed the WaveIO 5VDC Belleson Vreg from this PS.

I assume that there Vregs on the main board and DAC board and not using the PSU to provide the final voltage. A digital voltage regulator should be as close as possible to the digital use point.

IMO the TentLabs is an excellent analog Vreg, but that there may be better Vregs for the digital side. I have heard sq improvements from using the Belleson and the excellent ADM7150 using a small PCB of my own design.
Click to expand...

Thanks for your post Ross.
Just to clarify, I don't have any regulators on the digital side, only tent regs on the analogue side. Do I need regs on the digital side in order to have a dedicated PSU for the digital side of the dac boards?
I would be very interested in your design and recommendations.
 
#5,020
Sovereign1 said:
Thanks for your post Ross.
Just to clarify, I don't have any regulators on the digital side, only tent regs on the analogue side. Do I need regs on the digital side in order to have a dedicated PSU for the digital side of the dac boards?
I would be very interested in your design and recommendations.
Click to expand...

You will need the standard regs that came with the kit and were soldered there when supplied
 
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