PCM1804 bal/unbal adc

meta · 15th May 2004, 03:56 PM

Hi...

Could a digi head with more know-how then a newb tryin to wing it (which would be me ;p) please run they're eyes over this PDF schem for an adc:

Bal/UnBal PCM1804 ADC

Any feedback appreciated

Ta

kiwi_abroad · 16th May 2004, 03:41 AM

It seems a bit wasteful. The input takes a balanced signal which is then converted to unbalanced (IC3a IC3b), it is attenuated and then two more op-amps are used to convert it back to a balanced signal to feed into the ADC.
Why not use a PCM1802, which is the same ADC chip which accepts a single-ended input, thus elimintaing the need for two op-amps in the signal path?

Adrian

meta · 16th May 2004, 10:46 AM

Because I wanted the option to take both bal and un bal inputs - not just unbalanced only. The 1804 also seems to have better specs then the 1802. Electronically, does everything look okay to yas tho?

Cheers

meta · 24th May 2004, 01:49 AM

Okay, howzabout this then version then? It uses the OPA1632 (I pretty much followed the application schem in the opa datasheet and filled in the blanks by way of the PCM1804 eval brd schems...

Schematic PDF

PCB Layout PDF

Cheers.

NOTE: The unbal header is for a switch - which when pressed flips the inverting input to gnd for single ended input.

Nisbeth · 5th July 2004, 08:37 PM

Sorry to dig out this old thread, but did you (meta) or anyone else ever try this ADC?

/U.

meta · 8th July 2004, 09:50 AM

Hey Nisbeth...

Nope, never tried this circuit in the realworld yet - gettin some DACs done 1st is a higher priority atm

Best.

Nisbeth · 8th July 2004, 10:41 AM

I am considering giving it a go. Will you share you pcb layout and parts list (if you have it)?

TIA!

/U.

meta · 8th July 2004, 10:58 AM

do u want the layout as a pdf or open eagle files u can edit/print urself?

Nisbeth · 8th July 2004, 11:14 AM

A pdf please

You can post it here or email it to uffe(at)nisbeth.dk

Thanks!

/U.

EDIT: But someone else might like the eagle files...?

meta · 8th July 2004, 11:33 AM

HERE is a zip containing the top overlay (showing the 3 bridges too), bottom and schem (use that for a parts guide?). I've added the LED overflow circuit too (based on the layout on the ti 1804 eval brd)...

Keep u posted

15th May 2004, 03:56 PM	#1
meta diyAudio Member Join Date: Nov 2002 Location: London	PCM1804 bal/unbal adc Hi... Could a digi head with more know-how then a newb tryin to wing it (which would be me ;p) please run they're eyes over this PDF schem for an adc: Bal/UnBal PCM1804 ADC Any feedback appreciated Ta

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16th May 2004, 03:41 AM	#2
kiwi_abroad diyAudio Member Join Date: Sep 2001 Location: Wellington, New Zealand	It seems a bit wasteful. The input takes a balanced signal which is then converted to unbalanced (IC3a IC3b), it is attenuated and then two more op-amps are used to convert it back to a balanced signal to feed into the ADC. Why not use a PCM1802, which is the same ADC chip which accepts a single-ended input, thus elimintaing the need for two op-amps in the signal path? Adrian

16th May 2004, 10:46 AM	#3
meta diyAudio Member Join Date: Nov 2002 Location: London	Because I wanted the option to take both bal and un bal inputs - not just unbalanced only. The 1804 also seems to have better specs then the 1802. Electronically, does everything look okay to yas tho? Cheers

24th May 2004, 01:49 AM	#4
meta diyAudio Member Join Date: Nov 2002 Location: London	Okay, howzabout this then version then? It uses the OPA1632 (I pretty much followed the application schem in the opa datasheet and filled in the blanks by way of the PCM1804 eval brd schems... Schematic PDF PCB Layout PDF Cheers. NOTE: The unbal header is for a switch - which when pressed flips the inverting input to gnd for single ended input.

5th July 2004, 08:37 PM	#5
Nisbeth diyAudio Member Join Date: Jan 2001 Location: Denmark	Sorry to dig out this old thread, but did you (meta) or anyone else ever try this ADC? /U.

8th July 2004, 09:50 AM	#6
meta diyAudio Member Join Date: Nov 2002 Location: London	Hey Nisbeth... Nope, never tried this circuit in the realworld yet - gettin some DACs done 1st is a higher priority atm Best.

8th July 2004, 10:41 AM	#7
Nisbeth diyAudio Member Join Date: Jan 2001 Location: Denmark	I am considering giving it a go. Will you share you pcb layout and parts list (if you have it)? TIA! /U.

8th July 2004, 10:58 AM	#8
meta diyAudio Member Join Date: Nov 2002 Location: London	do u want the layout as a pdf or open eagle files u can edit/print urself?

8th July 2004, 11:14 AM	#9
Nisbeth diyAudio Member Join Date: Jan 2001 Location: Denmark	A pdf please You can post it here or email it to uffe(at)nisbeth.dk Thanks! /U. EDIT: But someone else might like the eagle files...?

8th July 2004, 11:33 AM	#10
meta diyAudio Member Join Date: Nov 2002 Location: London	HERE is a zip containing the top overlay (showing the 3 bridges too), bottom and schem (use that for a parts guide?). I've added the LED overflow circuit too (based on the layout on the ti 1804 eval brd)... Keep u posted

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