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CD7000 - possible to tap into the DAC?

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Killyp
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Killyp posted on Tue, Aug 25 2020 10:20 AM

Hey All,

Long time with no posting here but still enjoying my 7000 system.

This is my second system and wondering if it's possible to make a modification to the (still fantastic sounding) CD7000 enabling me to use the internal DAC with an external S/PDIF source? My limited electronic experience is holding me back. Looking through the service manual it seems as though there are a few connections between IC7 and IC9 labelled 'E Flag' 'Data' 'Clock' and 'WS' (36, 37, 38 + 39).

I know the TDA1541 is an unusual config. Should I be looking between IC9 and IC10 instead?

Interested to know if this is feasible before I approach an electronic engineer I use for work related stuff to look into actually doing any modifications of course (I wouldn't even think of doing something like this myself).

 

Thanks!
Alex 

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Dillen
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Dillen replied on Tue, Aug 25 2020 11:35 AM

I seem to remember the audio signal is muted, until the decoder starts delivering valid audio data.
This to avoid "playing" TOC data, track search restults etc.
Not sure if it's done by muting the audio circuits or disabling the DAC, though.

But why would you want to use the DAC for an external source?

Martin

Killyp
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Killyp replied on Tue, Aug 25 2020 2:02 PM

I see two mutes, both from IC6 to IC9.

One is 'ATSB' on pin 22 which attenuates IC9 by 12 dB. The manual reads:

"When 'low', the signal is lowered with 12dB'

 

The other is 'MUSB' on pin 23 which is a soft mute between the sample impolators and the upsampling filters, also in IC9. The manual states:

"MUSB is 'low' when jumping from one track to another.

*Will be 'high' when using search in service position 4'"

 

Can these be disregarded?

 

The 'E Flag' seems to be an error indicator which mutes the input stage of IC9 when the transport is searching.

 

It's hard to know if IC9 will do it's thing with an incoming PCM stream and clock signal (assuming these are at the correct voltages) and pass this signal on to the DAC chip (IC10). There seems to be an oscillator which feeds back into the decoder (IC7, which is where the signal feed for IC9 comes from).

Killyp
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Killyp replied on Tue, Aug 25 2020 2:05 PM

As to why I want to use the DAC - it's part of the system I have already and I'd rather try and utilise what's there.

 

Also, it sounds great, even comparing it to other modern digital sources. I'm quite fond of the sound of this unit...

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