Balanced mono output with single TDA1543, possible ?

[Bidule]

Hello,

For GiBi, a very small mono portable battery powered audio product I'm working on, I was considering trying to use a single TDA1543 in balanced mode.

The setup :
Anker Pro Battery 5Vx3 and 12V
Raspberry Pi2
Sound server : Squeezebox Server
Sound Player : Jackd + Jconvolver + Squeezelite
I2s Out -> TDA1543
Amplifier : TDA7391
Speaker : Monacor SPH30X4 in 1.8L DBR (55-18K +/- 1 dB)

Here is what I have tried to suppress the Amplifier input capacitors

Send I2s MONO DATA -> as Left channel DATA
Send I2s INVERTED MONO DATA -> as Right channel DATA

TDA1543 L out -> Pin2 + In TDA7391
TDA1543 R out -> Pin1 - In TDA7391

An externally hosted image should be here but it was not working when we last tested it.

Here is my asound.conf file
/# Send alsa API to jconvolver
pcm.rawjack {
type jack
playback_ports {
0 jconvolver:in.L
1 jconvolver:in.R
}
capture_ports {
0 system:Output_L
1 system:Output_R
}
}
# jackplug
pcm.jack {
type plug
slave { pcm "rawjack" }
hint {
description "JACK Audio Connection Kit"
}
}
# use following peripherical by defaut with alsa:
pcm.!default {
type plug
slave { pcm "rawjack" }
slave.channels 2
ttable.0.0 0.6
ttable.1.0 0.6
ttable.0.1 -0.6
ttable.1.1 -0.6
}

RESULT :
1/DC offset is still there, so I can't suppress the amplifier input coupling capacitors.
2/Sound is not good, some kind of echo

Any idea to make it working ?

Best Regards
Jean

 

[ahiukka]

Hi Jean.

Please do attach your (what-ever-it-might-be-as-I-can't-see-it) image...
This forum has a very well implemented file attachment system, so why not use it?

http://www.diyaudio.com/forums/everything-else/183084-pictures-why-not-attach-them.html


Best Regards,
A.Kiuas

 

[poynton]

The Image

..

 

[ahiukka]

Thanks Andy!


Jean,

I could be mistaken, but I recall TDA1543 has a current output?
In that case I think you should have some sort of I/V conversion in between the DAC and the amplifier..

-A.Kiuas

 

[Bidule]

Hello,

Thank you for taking care.

Yes TDA1543 is current output DAC, I use passive I/V as most of the people here.

I don't connect Vref and use a voltage reference as virtual ground.

Here is the full schematic, I still have to finish the RPi power managment and to add the Gestic Microchip.

Any way, the part of interest, here is in the lower left corner.


Thanks to asound.conf it is supposed to be Mono channel on both Left and Right Output and accordingly to be a mono symetrical single TDA1543 output.
I should then be able to suppress the two signal coupling capacitors.

However, I beleive that there is a slight delay between "L" and "R" that prevent this trick to work.

Any idea ?

Thx,
Jean