Using digital out from Discman

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I am thinking about dismantling (actually already did it ) an old Sony Discman (D-E441) so as to put it in a nice micro enclosure similar to my micro amp (Amp 6 from 41Hz see also: http://www.diyaudio.com/forums/showthread.php?s=&threadid=93198&highlight=)
Now I would like to try an optical out for a future, similarly enclosed, external DAC. Even found the correct pin out on the board. However since this player works at 2.5 to 3 volt (2 AA batteries) will it be able to correctly drive an external DAC?
The internal DAC is the TC 9348FN see also this link (especially page 15) http://www.datasheetcatalog.com/datasheets_pdf/T/C/9/4/TC9438FN.shtml

So the question is: do DACs normally require TTL voltage levels or can they function with less. If not, how can you 'boost' the digital signal to the required output?
 
Hi,

Which line were you intending to get the SPDIF data from? If there is another chip upstream of the TC9348FN that outputs a SPDIF signal, fine. However, if you were intending on tapping pin 22 on the TC9348FN, I have bad news. This pin receives I2S format data, not SPDIF.

If you intend to make a DAC yourself, this is not to bad, as I2S format is superior to SPDIF, and it is easy to make a DAC that accept I2S. If your are going to buy one, the you have a problem, as they mostly take SPDIF, very few (very expensive) models take I2S.

Anton
 
Hi AMC184,

Thanks for the useful info. Pin 22 indeed. I did not immediately learn from the schematics that pin 22 from the DAC is receiving I2S data. Further upstream is a BA6386K processor which receives signal from the optical pick up and in between sits a RAM controller SM5902BF which function is probably just (mechanical) shock protection. Have you have any experience with DIY I2S receiving DACS?
 
Neither of the ICs you mentioned in your last post is the decoder/controller. The SM5902 is a RAM controller, the BA6386 runs the servos. What other chips are there on the board? The decoder/controller may have a SPDIF out pin. Otherwise you have two options:
- Add an I2S to SPDIF transmitter, such as the CS8406.
- Transmit the I2S directly, using something like a MAX234.

Anton
 
Hi Anton,

You are right about the BA6386 being only the servo controller. I meant the BU 9326. It's description says servo/digital signal processor. The only other chip on the board that could apply is the MC6BHC05L15 (what a code name) which is, IMO, a more general controller of the Discman performing functions like mute/resume/battery-status and driving the LCD display.
So does the BU9326 have a SPDIF out?
 
I do not have the datasheet myself but the pic is a snapshot from the Discman service manual.
 

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I just had a look at the datasheet for the very similar BU9321B, and unfortunately it is just as I thought, (43) DOUT is the serial data line for the microcontroller interface. So if you want to make the transport compatible with other consumer gear, you're going to have to use a SPDIF transmitter, such as a CS8406.

So, the DAC you want to use, will it be DIY or store bought?

Anton
 
Thats not so bad then. It's pointless to bother with SPDIF in a situation like this, as you'd end up with:

I2S ---> SPDIF ---> (cable) ---> SPDIF ---> I2S

besides, SPDIF is inferior to I2S anyway. There are still a couple of issues though:
- This walkman looks like it will make a poor quality transport.
- I don't think the type of I2S that the RAM controller is transmitting is standard, but I have to have a careful look.

Anyway, if you want to proceed, you're best to get a quad RS232 transmitter, such as a MAX234. You'll have to build a 5V regulated supply for it, 3V is too low. Transmit the 3 I2S lines (DATA, LRCLK, SCLK) over 50 or 75ohm with BNC connectors. You'll have to check that the type of I2S that RAM controller outputs is compatible with whatever DAC you chose.

Anton
 
First of all, the Discman is cheap and easy to obtain! With some proper damping/suspension it may be a compact stable transport. Why do you think it is a poor choice?
Second, can't I just bypass the RAM controller? I do not need the skip-protection, that is it's function right?

Third, it is fun to try isn't it?
 
Oh, yes, definitely. I am not trying to discourage you!

It's just that it is a bit trickier than some of the other things you could chose to mod. But I guess you'll need to use a walkman to get it into a tiny case like the ones in your other post.

There is only one problem with bypassing the RAM controller (which I do think is a good idea, by the way), is that without a datasheet, who knows what kind of data to expect from the BU9326. I had a look at the BU9321B datasheet, that suggests that the I2S from the BU9326 is probably OK though.
 
Yes, looks good. The output of the BU9326 looks compatible with the input of the TDA1543. If I were you, I would look at using paralleled TDA1543s, rather than just a single one. This doesn't make the design any more complex, makes it sound miles better, and I think you can get away without any active I/V conversion.

If you construct the DAC and transport in the same case, you can wire them directly to each other through 20R resistors. If you are using two different cases, I would look at using something like RS232 for the link.
 
I would say if there is not a big choice in affordable DIY DACs that accept I2S data then there's no reason to go for an external DAC. It may be better to find a good quality I2S->DAC for internal use. I know about the parallel TDA1543 trick but feel this is a kind of silly compromise. Is it better at all than the standard Discman DAC? Has time stood still since the development of the TDA1543 (1991 right?) and sonically superior chips not been developed in the last decade? And what exactly is the reason behind using RS232 in case of two housings? Timing problems or other? More questions the deeper we go into this topic. Thanks in advance,
 
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