S.houBed DAC 132db Dual MONO pcm1794 - diyAudio
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Old 26th October 2012, 12:31 PM   #1
xslavic is offline xslavic  Moldova
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Default S.houBed DAC 132db Dual MONO pcm1794

anyone interested ? pcbs only
14x8cm

dual mono pcm1794A 132db

Upscaller 32 bit cs8421 - can be bypassed
receiver wm8805 - 24bit 192khz --- 50ps jitter

Output XLR and singl ended ,opamps + gain stage for XLR

XLR standart 3.16v using Toshiba sc1815

Center tapped transformer input
12-0-12 to 22-0-22
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Old 26th October 2012, 12:36 PM   #2
xslavic is offline xslavic  Moldova
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It has the resistor-cap to dump the high freq noise to ground(many of the builders omit that)
so it will be clean,its like using a transistor for supply noise filtering in analog circuitry
and LPF before preamp,usefull thing
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Old 6th November 2012, 02:54 PM   #3
xslavic is offline xslavic  Moldova
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Default S.houbed DAC revise 1.1

Hi
have some new ideas
-replace in IV the 4 caps that are in line with 2.2nF
-add a low pass filter before i/v if you want to use opamps like the Opa2277
with 0.8 slew rate LC low pass recommended
-also you can add 680pf + 2ohm in series from opamp neg input to GND

Last edited by xslavic; 6th November 2012 at 02:56 PM.
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Old 8th November 2012, 11:28 PM   #4
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interested. how much and how to order?
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Old 9th November 2012, 10:22 AM   #5
Aiace is offline Aiace  Italy
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Quote:
Originally Posted by xslavic View Post
It has the resistor-cap to dump the high freq noise to ground(many of the builders omit that)
so it will be clean,its like using a transistor for supply noise filtering in analog circuitry
and LPF before preamp,usefull thing
It's no cleare where you put them. Could you be more precise ?
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Old 9th November 2012, 10:57 AM   #6
qusp is offline qusp  Australia
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being a diy site and being a diyer, it really would be better if you didnt just pull the 132db performance spec directly from the pcm1794A datasheet and print it on the PCB; presumably deciding to print it on the PCB before youve even built it.... its bad enough when companies marketing departments do this.

the design is OK, but I doubt youve met the datasheet spec, thats usually a pretty hard task that involves a tighter SMD layout and several iterations. how about some real performance measurements?

Last edited by qusp; 9th November 2012 at 11:13 AM.
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Old 9th November 2012, 01:33 PM   #7
Aiace is offline Aiace  Italy
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Quote:
Originally Posted by qusp View Post
being a diy site and being a diyer, it really would be better if you didnt just pull the 132db performance spec directly from the pcm1794A datasheet and print it on the PCB; presumably deciding to print it on the PCB before youve even built it.... its bad enough when companies marketing departments do this.

the design is OK, but I doubt youve met the datasheet spec, thats usually a pretty hard task that involves a tighter SMD layout and several iterations. how about some real performance measurements?
I agree with you, and , if you want say all the truth, even the data sheets have fake performance printed on.
I.E., the following link is a discussion where you can find out that the PCM1792 (almost the same of the 1794) has performance issues....

PCM1792 performance issues. - Audio Converters Forum - Audio Converters - TI E2E Community

Last edited by Aiace; 9th November 2012 at 01:35 PM.
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Old 9th November 2012, 10:21 PM   #8
xslavic is offline xslavic  Moldova
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you meassure yourself,i choosed the best in it and will try to improve it,i dont tend to get rich from this.
here some tweaks
add capacitor between i- and i+ will act as a LPF
Coupling Capacitor Calculator by V-Cap
and the cap parallel to 195 ohm should be :
Rf is the 195 ohm resistor can be increased up to 400ohm to increase voltage if you want more from XLR,but it will limit The Q factor of the opamp gain stage
Voltage bigger --needs higher slew rate
with <5v you can go with 0.8v/us up to 25khz
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Last edited by xslavic; 9th November 2012 at 10:24 PM.
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Old 10th November 2012, 07:22 PM   #9
Aiace is offline Aiace  Italy
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Quote:
Originally Posted by xslavic View Post
add capacitor between i- and i+ will act as a LPF
Thank you for your prompt answer.
I've also noticed some high frequence noise floor on the output of the PCM so in the layout of my PCB I put the place for a small polyester SMD capacitor between the i+ and i-. But actually it's a 20Mhz noise of few mV so i decided to not mount them.
Do you think this kind of noise can be a problem for the next stages ? Have you experience that the capacitor make any difference at listening test?

Last edited by Aiace; 10th November 2012 at 07:24 PM.
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Old 11th November 2012, 04:54 AM   #10
qusp is offline qusp  Australia
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Quote:
Originally Posted by xslavic View Post
you meassure yourself,i choosed the best in it and will try to improve it,i dont tend to get rich from this.
here some tweaks
add capacitor between i- and i+ will act as a LPF
Coupling Capacitor Calculator by V-Cap
and the cap parallel to 195 ohm should be :
Rf is the 195 ohm resistor can be increased up to 400ohm to increase voltage if you want more from XLR,but it will limit The Q factor of the opamp gain stage
Voltage bigger --needs higher slew rate
with <5v you can go with 0.8v/us up to 25khz
all good, I just think its unnecessary. not suggesting you will get rich from this, just that it would be better if you didnt print false specifications on the PCB and on the thread title when you obviously dont know its actual performance.
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