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Old 20th April 2003, 10:03 AM   #1
PJR is offline PJR
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Default VRDS and I2S

I would like to know if there is an I2S signal somewhere in a Teac VRDS-type transport? It would be great to forgo the SPDIF link and use a buffered I2S link to connect the transport to the DAC or just build the DAC inside the transport.

I'm using a Teac P700 transport at the moment, but I'm looking for a VRDS-T1 that has a lot more room in the box for modifications.
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Old 20th April 2003, 12:49 PM   #2
GaryB is offline GaryB  United States
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Default inside a T1

I've got a T1 transport and I've got the schematic. I don't know enough about I2S to say if you can tap the needed signals, but for those with more expertise, here's a scan of part of the schematic where I think you should be able to pick up the signals. Can anyone else comment?
---Gary
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File Type: jpg t1_chip.jpg (91.2 KB, 1355 views)
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Old 21st April 2003, 06:33 AM   #3
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Default VRS and I2S

Hi PJR and Gary B,
I think that I help you in the model of GaryB I can see the eschematic of the pins U403 and I see the pins numbers
32 is LRCK, 34 is DATA, 35 SCLK all pins
connected with the resistor of 220 Ohms.
You can pick up next these resistors and you have the three singnals that we need for the I2S bus, I can help you more but I need the reference
of the U403, Type and manufacturer.

By carefully you don´t connetc before
the resistor becouse the square wave
is bettre next these resistors.


PJR if your Teac transpor use the same
chip the solution is the same.

Best Regards.

Jesús
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Old 21st April 2003, 10:33 AM   #4
GaryB is offline GaryB  United States
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Default chip id

The chip labelled as U403 is a CXD2500AQ.

---Gary
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Old 21st April 2003, 05:56 PM   #5
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Default CXD2500AQ

Hi gary,
I didn´t found the datasheet of the CXD2500AQ, I visited the web of sony semiconductors and I found that the CXD2500AQ is Discontinued Device
But you don´t worry becouse I´m sure that you pick up in the lines that I explained at you and it is Ok.
I´ll go to found the data sheet.

Jesús Puerto.
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Old 22nd April 2003, 03:13 AM   #6
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Quote:
By carefully you don´t connetc before the resistor becouse the square wave is bettre next these resistors.
really? the square wave looks nicer after the resistors? why would this be?

i connected them before the resistors because my digital decoder datasheet says these pins can only put out a maximum of 1ma. so if i could squeeze in an inch closer, i would do so.

http://diyparadise.com/rm20dac.html

DonJuan
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Old 22nd April 2003, 06:29 AM   #7
PJR is offline PJR
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GaryB and Jesús,

Thanks for the info! I'm glad to know it can be done and it's definately going to be my next project.

GaryB, do you have the full schematic scanned for the T1 transport? I would love to receive a copy since it's only a matter of time before I'll find one with my name on it...
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Old 22nd April 2003, 10:38 AM   #8
guido is offline guido  Netherlands
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Check out if the chip you are tapping the signals from is including the digital filter (decoder/dig filter in one).

If it is, the signals are useless...

Check the schematics, if the dac's are right behind this chip, the dig filter must be inside (or before). One other methode is checking the clockfreq..

GuidoB
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Old 22nd April 2003, 10:47 AM   #9
GaryB is offline GaryB  United States
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Default VRDS T1

Guido,
The T1 is just a transport, so I suspect the data will be valid. Just in case, the clock frequency is 16.9344Mhz. By the way, the stock VRDS T1 is just an OK transport. I've had it for a number of years (>5) and upgraded it with a low jitter clock and output driver from G+D transforms when they were still in business. The output driver uses some Motoroal ECL drivers and the combination is a big improvement over the stock unit.

Regarding a complete scan of the T1, no I don't have one. Why not just call up TEAC and have them send you a service manual. Thats what I did and it wasn't too expensive. Definitely less than $20.

---Gary
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Old 22nd April 2003, 11:08 AM   #10
guido is offline guido  Netherlands
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Gary,

You are right, if it is only a transport, there is no dig filter.
But it could be that the output is not i2s but some other format!!
Check were the signals are going (spdif transmitter i guess) and if it can handle
i2s and is setup to handle i2s. There are many serial formats..

Did not know it was a transport, don't have one. So i don't need the manual...


What i meant was the I2S clockline frequency, not the xtal freq !!

E.g. in an old philips player with 4 times oversampling:

samplefreq 44.1 kHz = 44100
32 bit data wordlength 44100 * 32 (16 bit unused)
left/right channel in one line 44100 * 32 * 2 = 2.8 MHz clock on I2S clockline

after the dig filter:
samplefreq 44100 * 4 (4 times oversampling)
16 bit data wordlength 44100 * 4 * 16
left/right channel in one line 44100 * 4 * 16 * 2 = 5.6 MHz clock on I2S clockline

So you can see if it is before or after a dig. filter when looking at the I2S clockline freq.
But it depends on the implementation and the wordlenght.

You need to know the freq and wordlenght if you want to connect something. I2S does not spec
wordlength or freq!!

Regards,
Guido
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