PCM1704 Diy dac+ discrete i/v+ valve buffer

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abebernis

abebernis

Member
Joined 2014
Dac pcb v2

3b184e22901f616bcb0b6a0a416faa6f.jpg


Dac pcb v1 was :

3b079a2c593ee6deb4a6c1d2c3bef17e.jpg
 
abebernis

abebernis

Member
Joined 2014
starbender said:
Why TI stopped production of this fine dac ic?
Is internal structure influenced from pcm69 from BB or is it equivalent?

Nice project btw! Keep up the good work.
Click to expand...
Thank you,
Really i am wondering too, why this chip's manufacture is stopped. Mostly old schooll hi end cd players had pcm1704. Maybe marketing strategy?
Maybe modern player's formats mismatches? But i really like its sound.

I think pcm63 is equivalent.
http://www.diyaudio.com/forums/digital-source/85468-replace-pcm63-pcm1704-dac-chip.html
 
O

OlegSh

Member
Joined 2010
I am about to start my own DAC design using the PCM1794. Looking at your PCB design I have a question, why ceramic capacitors are further away from the DAC pins then the electrolytics? The only benefit of using SMD ceramic caps is their low parasitic inductance (small size/leadless) which is important for supply pins bypass, but if they are connected to the IC pins with a long trace (high parasitic inductance) the single benefit they have is gone, IMO. Or maybe I'm missing something...?

Regards,
Oleg
 
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OlegSh

Member
Joined 2010
mp3dragon said:
Hi oleg,
Normally, datasheet and other applications use only electrolitic capacitors. We use aluminyum organic polymer nichicon caps. These seramic caps only just to help. Possible, even if we don't use
Click to expand...

Understood. Thanks!
I just had a look at the PCM1704 datasheet and it shows the most misleading "typical application circuit" (Fig.5) that I've seen before. If you look carefully they indicate 0.1u caps in parallel to the 100u electrolytics on each supply pin. While 100u can be anywhere on the board (typically within 1"~2" from the DAC IC) the small 0.1u ceramic bypass caps should be as close to the supply pins as possible. This is indirectly stated on page 8. If you read other datasheets/app notes on high frequency circuits design then it will be clear why it should be done this way. Using polymer caps helps a bit but they are still inferior to ceramic caps at high (MHz range) frequencies. So if you plan another PCB revision you can position ceramic caps closer to the IC pins. Voltage reference pins do not need ceramic bypass since there should not be high frequency noise there. Also put 0.1u ceramic caps at each supply pin (to GND) of all op-amps. Fig.5 shows only one set but I guess it is meant for a skilled designer to fit the remaining parts. Adding a bunch of SMD capacitors pads in the right locations is easy. They can be left empty if not needed but can be very handy if you really need to fit a bypass capacitor there.

mp3dragon said:
Your PCM1794 design's dual mono, single chip stereo or non oversampling mode?
Click to expand...

I'll try a single chip stereo first and then see if I am satisfied with it or not before going further.

Regards,
Oleg
 
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