Phono Analog to Digital Conversion for DSP

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wgh52

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Joined 2011
#1
Hi folks,

not having found an affordable DSP alternative which is functionally comparable to my failing DEQX PDC2.6p, I am on the verge of deciding for a miniDSP Flex Eight because I'm driving digital 3/4way active DIY Speakers.

Drawback is that the Flex Eight does not have an ADC, so playing my LP records is a significant issue. To mend this I have just found this "Analog Digital Converter PCM1804 RCA to SPDIF 24bit" board at Audiophonics.fr, but am unable to judge if this board would be appropriate for decent Phono AD conversion.

SPDIF or Toslink Output are OK (as an initial solution) as my digital sources are selected with a digital source selection box (CAS2.V3SE) anyway. Putting the ADC board into a box and provide a good, stable and low noise power are no problems, but I think the optimum would be a board integration into the DSP system by I²S connection (maybe as a second step solution).

As the PCM1804 is really an old chip, I am unsure if the 40€ ADC board linked above would really be a viable solution. for Phono

I'm greateful for any advice or pointings to better alternatives.

Thanks and regards,
Winfried
 
#2
It looks quite decent to me. I've seen cheap Chinese ADC boards where the complete input application circuit was left out to reduce costs, but as far as I can tell from the pictures, this board has the op-amps and class 1 capacitors required to drive the ADC inputs properly. I gather you use an analogue phono amplifier for preamplification and RIAA correction.
 
#5
Hi Marcel,

thanks a lot for your evaluation, this helps! Actually, there are I²S Solderpoints on the back side of the PCB. May these be usable if I can find the counterpart connections in the Flex Eight, so to potentially integrate the small board as a slave circuit?

@gberchin
Yes, a Benz ACEH drives a Lehmann Black Cube SE II with improved PWX Power Supply.

@frbrw
I did buy this board several years ago, but it turns out too bulky to potentially integrate into the Flex Eight and use its internal I²S/clock.

It would be nice to understand the advantages of your suggestion over others.

Thanks a lot and regards,
Winfried
 
#7
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#8
wgh52 said:
@frbrw
I did buy this board several years ago, but it turns out too bulky to potentially integrate into the Flex Eight and use its internal I²S/clock.
It would be nice to understand the advantages of your suggestion over others.
Click to expand...
I'm not sure there is any particular advantage over any other option and it size is clearly a disadvantage to you. I was simply offering up a possible option.
 
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#9
Hello Rob and Mark,

I had looked into the Cosmos E1DA and due to its USB only Output it is not suitable for me. The RIAA Firmware is not really needed as my PhonoPre does this for me and so far I did not see a reason or plan to yank it 😉

Thanks for the suggestions anayway!
Winfried
 
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#11
wgh52 said:
Actually, there are I²S Solderpoints on the back side of the PCB. May these be usable if I can find the counterpart connections in the Flex Eight, so to potentially integrate the small board as a slave circuit?
Click to expand...

I don't know which board is large and which is small, but I would expect the ADC board to be an I2S master, just like the output of an S/PDIF receiver with I2S output.
 
#15
wgh52 said:
Actually, there are I²S Solderpoints on the back side of the PCB. May these be usable if I can find the counterpart connections in the Flex Eight, so to potentially integrate the small board as a slave circuit?
Click to expand...
It might be a good idea to find out as much as you can on the Flex Eight first. There is no reason for it to have any exposed serial audio input connections beyond the IDP ports on the chip itself.
 
#16
@rfbrw
I'm not certain what IDP means, but e.g. the Flex Eight has a Toslink and a bluetooth input which I'd happily sacrifice for the ADC output connection to I²S. Not sure how to do this yet, but that seems a possibility to me... and fall back is SPDIF or Toslink.

So, anyway Folks,

I have decided for the PCM1804 board, costing an affordable 48€ incl. Tax & shipping from France to Germany and offering sufficiently many relevant options: I²S, external clocking, SPDIF, Toslink, external power supply, all paired with compact size and seemingly good input OpAmp input circuitry. Seems good enough for an acceptable financial risk experiment 😉 😊

Thanks to all of you!
Winfried
 
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#18
wgh52 said:
@rfbrw
I'm not certain what IDP means, but e.g. the Flex Eight has a Toslink and a bluetooth input which I'd happily sacrifice for the ADC output connection to I²S. Not sure how to do this yet, but that seems a possibility to me... and fall back is SPDIF or Toslink.
Click to expand...
The ADSP-21489 has onboard SPDIF I/O so it doesn't need a receiver which leaves the Bluetooth module as your only option. And there is the issue of two clock domains.
IDP = Input Data Port.
 
#19
Thanks! Your answer is interesting! I was not aware of the ADSP-21489 being used in the Flex Eight and about its features, so that's good info!

In terms of clock domains: The ADC board can be jumpered as clock slave device, so clocking/synchronising/running the ADC board with the Flex's internal 24.576MHz clock (instead of the on-board oscillator) seems feasible. Would connecting the ADC board's S/PDIF output to the S/PDIF input (internaly to the Flex Eight, e.g. sacrificing the Toslink Receiver) not work? This way I²S would not be used, but the signaling quality feels like it should be better than going "external". No internal function would be affected, the Flex Eight would just be fed with an SPDIF signal he handles like the one coming from the Toslink input...
Please share your thinking about this. 🙂

Greetings,
Winfried
 
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