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Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 KHz

If you end up feeding separate +/-15V to the opamps then there is very little reason to not go straight +/-5V for the dam, then bypass bridge rectifier and both onboard 7x05 regulators. A general observations over the years is that there is more bass to be had the more you tank up the vref rails be it with caps and/or super regulator. The super reg was a time before the current production vref with low output impedance however it is known to improve things so long as you dump the 7x05 regulators upstream.

On my own setup I can still see the vref dip at higher volumes on the uV scale even with the super regulator and straight 5V so to see more caps improving the response on a stock dam1021 v4/5 isn't so surprising.

Also note the onboard mute circuit is locked muted at 5V inputs and there isn't a known way to make it work other than by using a muting relay which I better prefer anyway as it's not an active device the signal chain.

Thanks! I'm going to build a multichannel unit (16-32) for studio mixing purposes soon. In this scenario local regulation is probably preferable to one high performance PSU feeding all the boards (through isolating resistors). I might end up powering all the buffer op amps from a separate PSU though.

I don't need the mute circuit and the output volume circuit and currently haven't connected anything there.
 
modding and distortion

After the successful modding of adding 12 polymer caps, I continued with the extra 4 caps of 2200uF by attaching them to the 4 SMD caps; and also swapped the 2 filtering caps with blue color caps (560uF). I believe the polarity is correct.

It failed. There was a horrible distortion/some popping coming out of the speakers. I tried both SE and buffered balanced output-same problem.

Now I reversed back to the previous state by removing all 4 caps and putting the 2 original filtering caps back in near the clock.
I know I ripped one of the 4 SMD caps so I desoldered it and turned it to other side when re-soldered it. The dac worked as normal with fantastic SQ for a couple of seconds and then severe distortion came back again.


How do I troubleshoot this? Is the board dead forever?
Can I just replace the 4 SMD capacitors? what value are they?
or should I replace the whole Vref section there?

Thank you for your help! Sad weekend.
 

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I have found a strange noise coming from the DAC like white noise. Im using Bib 1.1 regs for regulation. I thought its coming from the regulators but when I have used two 12V batteries i still get this noise. Im thinking that the firmware might have got corrupted. The signal is getting locked and synchronized but im getting this additional noise from the new boards. I have used ver1 and 2 but I never got any issue with them but now Im getting this strange noise i have tried all version from unbuffered to buffered outputs as well. Do i need to use new firmware for this? or just install new firmware?
 
@Soren

I have a firmware issue with a dual-mono DAM1021

Filter set to Mixed, when playing DSD quality is very poor with lots of noise.

Happens with loading 4K filters after upgrading firmware to 1.19 full. Same result with fpga 1.20

Firmware was 1.06 full (fpga 1.05)
Downgraded and good again.

Is it a problem with the 4k filters?
 
@Soren

I have a firmware issue with a dual-mono DAM1021

Filter set to Mixed, when playing DSD quality is very poor with lots of noise.

Happens with loading 4K filters after upgrading firmware to 1.19 full. Same result with fpga 1.20

Firmware was 1.06 full (fpga 1.05)
Downgraded and good again.

Is it a problem with the 4k filters?

Let me check, I actually didn't do much testing DSD with new 4K filters as there was no changes to the DSD parts.
 
Soren,

what are the correct resistor values to change the S/PDIF input circuit to professional level - AES/EBU?

Also, I have ordered 16 DAM1021 modules to build a 32 channel studio converter - I'd like to stack the PCBs side by side in a 19" enclosure. How close can they be to each other without causing noticeable interference?

Would it be a problem to have one high quality discrete external +/- 7 VDC PSU to feed all 16 boards? Would it be adviseable then to add series resistors and/or decoupling caps before/at each modules DC inputs?

Thanks!
 
So I went through lot's of filters and finally installed the latest firmware and the 4K filters (but removed the DC offset filter).

The new linear filter is easily the best. Dynamics are all there, bass has weight, high end sounds clear and without artificial sparkle (no audible noise modulation or aliasing), midrange detailed and focused. Good recordings pass the NS10 (studio monitors) test.

Great DAC! Thank you Soeren.
 
So I went through lot's of filters and finally installed the latest firmware and the 4K filters (but removed the DC offset filter).

The new linear filter is easily the best. Dynamics are all there, bass has weight, high end sounds clear and without artificial sparkle (no audible noise modulation or aliasing), midrange detailed and focused. Good recordings pass the NS10 (studio monitors) test.

Great DAC! Thank you Soeren.
hi pal can you send the links of the firmware and also the filters that you are recommending.
 
hi pal can you send the links of the firmware and also the filters that you are recommending.


Latest firmware:

http://soekris.dk/download/dam1021/1021full_119.skr

Source file for latest filters:

http://soekris.dk/download/dam1021/1021filt_120.txt

If you are sure you've got DC blocking covered somewhere in your playback chain you can delete the following part:


dam1021,352800,8,29,5,1
29 DC Blocking IIR, 352.8 Ksps, 2 Hz HP 1st order

1.00
-1.00
0.00
0.99996438167
-0.00

dam1021,384000,8,29,5,1
29 DC Blocking IIR, 384 Ksps, 2 Hz HP 1st order

1.00
-1.00
0.00
0.99996727561
-0.00


Use Mkrom to create an skr file
http://soekris.dk/download/dam1021/MKROM.EXE

the filter text file needs to be named 1021filt.txt and be located in the same directory as mkrom.exe
 
Soren,

what are the correct resistor values to change the S/PDIF input circuit to professional level - AES/EBU?

Also, I have ordered 16 DAM1021 modules to build a 32 channel studio converter - I'd like to stack the PCBs side by side in a 19" enclosure. How close can they be to each other without causing noticeable interference?

Would it be a problem to have one high quality discrete external +/- 7 VDC PSU to feed all 16 boards? Would it be advisable then to add series resistors and/or decoupling caps before/at each modules DC inputs?

Thanks!

My two are about 12mm distance stacked and no interference. Single +/-7V rail driving all boards would not be an issue, directly connect them. The boards themselves have enough decoupling caps you don't need to worry about that.
 
My two are about 12mm distance stacked and no interference. Single +/-7V rail driving all boards would not be an issue, directly connect them. The boards themselves have enough decoupling caps you don't need to worry about that.

Thanks!

I had a look at the images of your DAM. Do you think the modifications WRT to power reply/decoupling are worth it?

Did you remove the ceramics providing a lowpass at the output?
 
Yes have removed those since I last updated the pictures, haven't had anything negative to say about it.

Did it make an audible difference?

After a few days with the new linear phase filter I found the DAC to sound a little too bright and tried minimum phase again. This one actually sounds more natural.

Now the only thing I find the DAM to be a little lacking is in low end weight. The bass is very tight and controlled though.