Output Current from PCM56P K? - diyAudio
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Old 17th November 2008, 09:41 PM   #1
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Default Output Current from PCM56P K?

Can anyone explain how much output current there is available on pin 13 (I out) of the PCM56P and PCM61P as it states in the data sheet (Current: Output Range 30% 1 mA)????? What does that mean.

And I have 4x PCM56P K's per channel all pin 13 paralleled so what will mine be mA wise?
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Old 18th November 2008, 09:02 AM   #2
pilli is offline pilli  France
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...doesn't it just mean that the analog output (as a current) will be sinking 1mA when on the positive peaks, and sourcing 1mA on the negative peaks (or is sinking/sourcing the other way around?)

This is in the "typical" column for the output current,
then isn't the +/-30% just the tolerance, like it can be anything between the "smallest range" -0.7mA to +0.7mA
and the "largest range" -1.3mA to +1.3mA.

(sorry if this is a naive answer, maybe you're looking for something deeper... )

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Old 18th November 2008, 09:49 AM   #3
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Anything is good, as no one is giving anything else.
Is it safe to assume then because I have 4 x paralleled outputs from 4 dacs per channel I should get 4 times the mA ?
Remember these 4 dacs (PCM56P) per channel are not paralleled (stacked) up like other are doing with other dacs, only their outputs are paralleled.
Here is a link to the data sheet
http://www.datasheetcatalog.org/data...wn/mXutrrt.pdf
And a link to my dac
Wadia Digimaster X64.4 Help!
Cheers George
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Old 18th November 2008, 02:41 PM   #4
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n DACs have n mA.
There is +/-30% tolerance which can in worst case result in a few dB difference in output level between left and right .
You can match chips of course.

IIRC this DAC uses additional hardware os, the chips are not just parallel.
Like in the DAC of ECdesigns but with os filter-IC.
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Old 19th November 2008, 10:42 AM   #5
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Quote:
Originally posted by Bernhard

IIRC this DAC uses additional hardware os, the chips are not just parallel.
Like in the DAC of ECdesigns but with os filter-IC.
Charles Hansen Quote
Right Wadia used "64X 18-Bit Transversal Multiport DAC". The first thing you should know is that no audio DAC would operate at 64x in those days. So what they did was make a high frequency clock and take 4 DACs per channel in a "transversal" mode. The digital filter could only do 16x. Each DAC got a word clock signal that was staggered by 1/4 of the word clock rate. Then the output of the 4 DACs were recombined to make the final audio output. (I could be off by a factor of two here. Maybe the filter did 32x and there were only two "transversal" DACs.)

Over my head, can someone explain in laymans terms?
Cheers George
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Old 19th November 2008, 11:02 AM   #6
amc184 is offline amc184  New Zealand
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Quote:
Wadia used "64X 18-Bit Transversal Multiport DAC". The first thing you should know is that no audio DAC would operate at 64x in those days. So what they did was make a high frequency clock and take 4 DACs per channel in a "transversal" mode. The digital filter could only do 16x. Each DAC got a word clock signal that was staggered by 1/4 of the word clock rate. Then the output of the 4 DACs were recombined to make the final audio output.
AFAIK, it uses four DACs with each DAC getting every fourth sample only, such that:

Sample one to DAC A, sample two to DAC B, 3 to C, 4 to D, 5 to A, 6 to B and so on.

It means that each DAC is clocked at 1/4 of the frequency of the stream coming out of the digital filter, or whatever does the oversampling. To get 64X OS, each of the four DACs would be running as though OSed to 16X. I think the PCM56 is only good for 4X, so you wouldn't be able to get to more than 16X overall using this configuration with this chip.

Sounds like a good idea, and shouldn't be too hard to do with a CPLD.

Nice choice of chip though, the PCM56. I have heard that it is one of the best for NOS applications, I must try it sometime.

Anton
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Old 19th November 2008, 01:40 PM   #7
pilli is offline pilli  France
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Quote:
Originally posted by georgehifi

Over my head, can someone explain in laymans terms?
Above my knwoledge as well, but I have the feeling that it is related with some discussions on "multiple more-or-less-parallel DACs" for example here:
http://www.diyaudio.com/forums/showt...307#post980307


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Old 19th November 2008, 01:52 PM   #8
poynton is offline poynton  United Kingdom
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Old 19th November 2008, 10:32 PM   #9
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This is Wadia F. Moses take on it Anton, is it the same as you said? Also do you think it is safe to assume that the current output from the pin 13 I out will be 4 x as strong? as my Transimpedance Amp that I'll be using with it's output stage will have a gain of 2. and I would like to have 3v or more out.

Cheers George
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Old 19th November 2008, 11:03 PM   #10
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This is how I think to do this, I hope I get over 2v outs, the circuit has 2 x gain, will this circuit tax the 4 x PCM56p outputs too much as I was told it was less than 10ohm input impedance, all comments invited, I won't attack this, until I'm sure, as it it one expensive piece of gear.
Also I don't know if to bridge pin 4 for common grounding of both input and output?

Cheers George
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