Multibit DAC core boards coupled with I2S-PCM driver board - Page 2 - diyAudio
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Old 26th September 2013, 09:26 PM   #11
noizas is offline noizas  Lithuania
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Quote:
Originally Posted by vzs View Post
I would like to have same position of input/output sockets for all boards.

The idea is to have all PSU and I/V external - so the board should have current output _without offset_. Core boards with DACs that have offset like TDA1541 will have to take care about this by using a current source to null out the offset. As far as the current output level is concerned it will be between +-1mA to +-2mA (AD1865, AD1862, PCM1702/4, PCM58, PCM63, TDA1541) - double that for dual mono.
OK, now we have clear requirements for sockets, output type and offset.

Quote:
Originally Posted by vzs View Post
Good you brought up this direct replacement (cold swaping) issue: up to now I didn't thought about directly replacing one board with another _without adjusting the power supplies_. I thought when replacing e.g. AD1865 with AD1862 the user will consciously take care that analog voltage should be +-12V and when switching back to AD1865 he/she will change it +-5V - indeed it's easy to shoot yourself in foot this way.
So there are two possibilities:
1. Have only 2x3pin connectors but switching will need attention - power supply adjustment/change is needed
2. Have as many power connectors as many different DAC needs...

I would certainly choose #1 for simplicity and let the gravity of switching boards to the user.
Actually, I had in my mind third possibility: power connector need to have dedicated pins for every voltage possibly needed for DAC chips and surrounding + GND, for example (-15;-12;-5;GND;+5;+12;+15).
Core board for TDA1541 would use 1,3,4 and 5 pins of power connector, PCM1704 would use 3,4 and 5 pin, etc. Indeed, this is long list of voltages, but it can be shortened if we are not going to make very universal "standard" for power supply here.

In that way if you really need cold swap for experiments, you simply need to have all necessary voltages for your experimental DAC type on power supply connector from your PSU side.
And no chance to make mistake during swap...

Thanks
Saulius
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Old 27th September 2013, 12:28 PM   #12
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I would also go for PCM 1704.
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Old 27th September 2013, 05:48 PM   #13
noizas is offline noizas  Lithuania
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Originally Posted by Tonyb View Post
I would also go for PCM 1704.
I also would buy core boards for TDA1541A, PCM1704, AD1865 - all of these DAC chips are very promising.

Thanks
Saulius
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Old 27th September 2013, 09:25 PM   #14
vzs is offline vzs  Europe
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Quote:
Originally Posted by noizas View Post
Actually, I had in my mind third possibility: power connector need to have dedicated pins for every voltage possibly needed for DAC chips and surrounding + GND, for example (-15;-12;-5;GND;+5;+12;+15).
Core board for TDA1541 would use 1,3,4 and 5 pins of power connector, PCM1704 would use 3,4 and 5 pin, etc. Indeed, this is long list of voltages, but it can be shortened if we are not going to make very universal "standard" for power supply here.
The simple approach has separate inputs for digital and analog voltages but without fixed voltages. On a second thought this separate analog/digital supply inputs would not be used when they are of same voltage.
Question: do we need separate supply inputs for digital and analog side of a DAC? PCM1704(2), PCM63, AD1864(5) all have +-5V analog and digital.
I personally would follow the recommendation of PCM63/1704: "No real advantage is gained by using separate analog and digital supplies. It is more important that both these supplies be as “clean” as possible to reduce coupling of supply noise to the output"

I like this idea with multiple voltages in one connector. I would use two 4pin connectors though (-15,-12,-5,0) (0,5,12,15).

Thanks,
Zsolt

Last edited by vzs; 27th September 2013 at 09:28 PM.
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Old 27th September 2013, 09:46 PM   #15
vzs is offline vzs  Europe
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Size matters

I made some sketches with DACs to see how they fit... Those DIP 28pin mono DACs are mammoths, they need double space in comparison with smaller ones. If we want same size boards it's a waste of space/money when used for small ones.

I suggest to keep the balanced/dual-mono idea for small DACs and make stereo core boards for large DACs. If dual-mono or balanced is wanted for those simply stack them and use U-FL connectors - see how dvb projekt did the same with his DACs used in parallel.

If we go this route the core board could be the size of I2S-PCM board.
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Old 28th September 2013, 03:03 PM   #16
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Waiting patiently for the AD1865 core board, save the trouble of making 1 myself. Thanks...

I see the inclusion of the THD+N Adjust Circuitry and also the negative supply for digital, possible to have some kind of a jumper to bypass these 2 ?

I don't think i will be using the THD+N Adjust Circuitry and the negative supply on the digital side.
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Old 28th September 2013, 03:53 PM   #17
vzs is offline vzs  Europe
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Quote:
I suggest to keep the balanced/dual-mono idea for small DACs and make stereo core boards for large DACs. If dual-mono or balanced is wanted for those simply stack them and use U-FL connectors - see how dvb projekt did the same with his DACs used in parallel.
Well, my former post is not too understandable

I was suggesting in order to keep the size(cost) of the core boards small allow balanced/dual-mono possibility, 4 DACs on one board, only for small packaged DACs, while for large mono DACs use 2 DACs per board.
If balanced configuration is wanted with these large mono DACs then use two DAC boards (stacked) and U-FL connectors to connect with I2S-PCM board.
For dual-mono configuration with these large mono DACs a small modification of the I2S-PCM board would be needed: image shows how dvb project customized it for his dual-mono two DAC board setup.
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Old 28th September 2013, 04:09 PM   #18
vzs is offline vzs  Europe
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Quote:
Originally Posted by flowerpot View Post
I see the inclusion of the THD+N Adjust Circuitry and also the negative supply for digital, possible to have some kind of a jumper to bypass these 2 ?

I don't think i will be using the THD+N Adjust Circuitry and the negative supply on the digital side.
THD+N circuitry will be optional, simply not solder the components if you don't need it.
Power supply connector will be standard for all DAC boards - will be explained how to use it when we decide which to use.

I prefer noizas suggestion more and more: [-15,-12,-5,GND][GND,5,12,15]
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Old 28th September 2013, 08:37 PM   #19
noizas is offline noizas  Lithuania
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Quote:
Originally Posted by vzs View Post
Well, my former post is not too understandable

I was suggesting in order to keep the size(cost) of the core boards small allow balanced/dual-mono possibility, 4 DACs on one board, only for small packaged DACs, while for large mono DACs use 2 DACs per board.
If balanced configuration is wanted with these large mono DACs then use two DAC boards (stacked) and U-FL connectors to connect with I2S-PCM board.
For dual-mono configuration with these large mono DACs a small modification of the I2S-PCM board would be needed: image shows how dvb project customized it for his dual-mono two DAC board setup.
Your idea is very clear and it is ok; as I wrote earlier - we need to be realistic with sizes.
I just hope two sets of TDA1541 will fit in 80x70mm board. Can you say which software you used for AD1865 core board schematic?
Possibly I would try to do the same for TDA1541.

Thanks
Saulius
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Old 29th September 2013, 10:19 AM   #20
Marek is offline Marek  Poland
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I think we shouldn't leave possibility to use separate analog and digital power supplies because of TI/BB recommendation.Most of DACs works with +/-5V and not every one is TI/BB and some may need separate power to achieve top performance. I think there is also reason why TI/BB use separate pins for analog and digital power.
I see some inconsistency in [-15,-12,-5,GND][GND,5,12,15]. The +15V is useless because TDA1541A use +5 -5 and -15V only.
If this is relly nessesary to minimize number of power pins (I think it is not) I suggest to use bonded -15 and -12V and use separate analog and digital pairs of +/-5V and +/-12V to allow most DACs be implemented in high end fasion.
I'm not sure if we need separate GNDs because as far as I remember it should be connected as close as possible to DAC chips.

So summing up I suggest [-12d, -12(-15)a, -5d, -5a] GND [5a, 5d, 12a, 12d]
or if we want even pin numbr [-12d, -12(-15)a, -5d, -5a] GNDa GNDd [5a, 5d, 12a, 12d]

BTW what kind of connector do you think about?
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