Direct i2s connection from soundcard to Panasonic XR55

[pawelp]

I have searched the archive and know that some people have made it to feed the i2s lines in Panasonic XR. It seems though it was done for older models and there are no report from anyone who did it for the famous XR55. I have this amp and I'm very determined to connect i2s lines from my M-Audio 410 bus lines to the appropriate Panny lines. For a test run I do not plan any communication circuits as I can place them less than 0,5 m apart. The biggest problem currently is to work out the Panny circuits to identify the places to attach to. Surprisingly, the local Polish Panasonic has firmly refused to sell or make the service manual anyhow available. In local service points they even treat as a commercial spy. A prolonged search in the Internet was also fruitless. Is this service manual available in other countries, especially US ? I am sure I have seen in some other thread someone saying it is. Can you tell me how to get it or maybe someone has the most critical schematics in PDF ? I do not think it is an industry espionage while it is sold in some countries...

[pawelp]

I have done some research, have a general idea of the XR internals and looks like I am quite close to the identification of the right tap-at place in XR55. The key question that I am not sure about while it is very important is where is the volume control in XR55 performed ? Is it the DSP/decoder chip, which is Yamaha YSS944 or directly at the PWM amplifier TAS5076 (with help of M16C microcomputer). It is so important since I would like to have my i2s signal from the soundcard amplified with the standard Panas's volume control circuits. What do you think ?

[pawelp]

It looks like I am talking to myself in this thread... Never mind, perseverance should be rewarded.
After a bit of study the for-now-conclusion is I should connect my i2s lines after the decoder Yamaha YSS944 chip. There is a 26-pin connector which carries the i2s signals. However it looks like there are three clock-related lined which I am not sure how to map onto the corresponding Envy (soundcard) lines (see attached) - ideas ? Panasonic lines:

[pawelp]

And the Envy lines:

[kims]

HI Pawelp

M-audio 410 -> XR55

PMCLK -> SDOMCK
PBCLK -> SDOBCK
PSYNK -> SDOWCK
PSDOUT[3:0] -> SDO[3:0]

verify that you have the right frequencies in the M-audio box before you actually connect.

kim

[pawelp]

Thanks, kims.
One problem is solved, now the plain practical aspects worry me most. There are two potential places I can put my i2s soundcard lines:
1. After codecs (A/D) before the Yamaha decoder/DSP
In this case I will 100% have the full stamdard volume control (if it is partially performed digitally in Yamaha DSP) but I am not sure if I should not somehow switch off (e.g. by physical desoldering) the codecs to whose output I would connect my i2s ? Can it get damaged ?
2. Between the Yamaha decoder/DSP and TAS 5076 PWM processor.
- not certain about the volume,
+ there is a separate, convenient 26-pin connector where i2s lines cen be plugged. The question is, though, can I just feed the i2s lines and leave the other (different level of power, control lines for the Yamaha decoder and the AK4114 digital receiver, interrupts and status lines set by Yamaha decoder and the AK4114, directed to the main control processor) floated
+ shortest signal path
What would you recommend ?

[pawelp]

OK, I get it it is an unexplored territory. So I'm gonna be the first brave experimentor. Hopefully the Panasonic warranty will cover it...
Just maybe a few control questions, just i2s:
- do you think there is risk of a physical damage to the Panny if the clock frequencies and/or i2s format or bit-length will be out of sync (between the Panny and my soundcard) ?
Do you think it may get damaged if the TAS5076 does not all the control signals it needs (for example if I only feed the i2s portion, leaving some control signals from the DSP and digital transceiver floated) ?

[pawelp]

I can happily report that a direct connection between Envy-based PC soundcards and Panasonic SA-XR 55 WORKS ! I plugged the soundcard after Yamaha DSP board. It sounds good but doing it after Yamaha has the following consequences that I do not the reasons for:
- volume adjustment is skewed - it is rather loud just one step after mute and it goes up only to -30dB then the displayed volume changes but the actual perceived loudness not,
- front channel is boosted +10dB which unfortunately gives audible distortions at higher levels (that is why I use surround and surround back).
Does anyone have an idea what can cause such behaviour ?

[lucpes]

Originally posted by pawelp
I can happily report that a direct connection between Envy-based PC soundcards and Panasonic SA-XR 55 WORKS ! I plugged the soundcard after Yamaha DSP board. It sounds good but doing it after Yamaha has the following consequences that I do not the reasons for:
- volume adjustment is skewed - it is rather loud just one step after mute and it goes up only to -30dB then the displayed volume changes but the actual perceived loudness not,
- front channel is boosted +10dB which unfortunately gives audible distortions at higher levels (that is why I use surround and surround back).
Does anyone have an idea what can cause such behaviour ?

Could you please post a picture of the i2s connection at the soundcard end? What about perceived sound quality compared to the card's internal DACs? How long are the wires you use for I2s? Shielded or not?

[pawelp]

Originally posted by lucpes


Could you please post a picture of the i2s connection at the soundcard end?

In a few days

What about perceived sound quality compared to the card's internal DACs?

Difficult to compare as apart from the DACs it also no ADC conversion on the Panny side. The most prominent difference is greatly reduced harshness compared to analog. To this extent that on the first listening I thought the sound was too dull. It seems that our ears are very used to listening to distorted sound in the highs... How can it be explained differently ?

How long are the wires you use for I2s?

Surprisingly, 0,5m is not a problem at all.

Shielded or not?

I used (mostly) UTP5 cable.
[/B][/QUOTE]