Not quite shure how balanced out dacs work..

[Miniwatt]

Hello everyone,

after enjoying myself with a tube output stage for a TDA 1541 I want to take things a bit further and do the same with my good old Sony CDP X 555 ES.

First, the dac is balanced out. I thought I understood that, but when I look at the schematic that´s over.



I dotted the signal lines: Green is both fases coming from one dac chip, red the same for the other.
My question is: both fases are simply joined together Don´t they cancel each other out?

Thanks!

I´ve studied the player and dac datasheets thoroughly, I thought this dac was voltage out, but now I´m not so sure anymore. It´s a CXD 2552 Q.. Can anyone shed some light on this?

[dusfor99]

Hi Miniwatt,

Seems to me that they must be inverting the dac on one of the DAC's, or delaying it. If they are inverting it, then it would be a summation going on at the opamp. If they are delaying it, they would effectively be making a notch FIR filter at some frequency abouve the audio band that is related to the amount of delay from 1 DAC to the other.

Hope this helps..

Dustin

[stephensank]

Actually, it is evident that all Sony is doing there is running two balanced out stereo pulse dac chips in parallel, directly summed at each +/- input of each output stage.
Interestingly, the output stages & GIC filter are identical in configuration to the Denon DVD5900(a player I am not fond of). Too many stages for my taste, and I've yet to hear a GIC filter in a dac setup that sounded really great.

[Miniwatt]

That helped!
I'll get back to this later, thanks so far.

[Miniwatt]

At the risk of sounding silly..

I did a little bit of testing today. Played some music, and hooked up my DMM to the different outputs. I was trying to figure out if the different phases also gave opposite measurements So + would give say 1 volt, and - would give -1 volt ( i could be terribly wrong here..)
Anyway, none of that happened, I got similar results every way.

Time I get myself a serious scope..

[homemade]

Originally Posted by Miniwatt

Hello everyone,

after enjoying myself with a tube output stage for a TDA 1541 I want to take things a bit further and do the same with my good old Sony CDP X 555 ES.

First, the dac is balanced out. I thought I understood that, but when I look at the schematic that´s over.



I dotted the signal lines: Green is both fases coming from one dac chip, red the same for the other.
My question is: both fases are simply joined together Don´t they cancel each other out?

Thanks!

I´ve studied the player and dac datasheets thoroughly, I thought this dac was voltage out, but now I´m not so sure anymore. It´s a CXD 2552 Q.. Can anyone shed some light on this?

This is very interesting . I, too, have been enjoying my TDA1541 player(s) , after converting to resistor i/v and tube gain stage. I also have a Sony , an X333, that I was looking to do the same thing too. Not to get off topic ,but i would also like to know if this SONY dac is suitable for using a resistor for the i/v conversion. Like Stephen , I believe the dacs to be in parallel , and by the way they connect to the op amps, indicates the dac output goes to virtual ground. If these dacs are balanced(+-) , I suppose you could use just the postive signal when doing resistor i/v. Just my take

[Miniwatt]

Oh, that's cool!

I haven't done much to the player lately, connected wires to the outputs of one dac, and fiddled around with them a bit. I hooked the + and - out up to an old Denon (ss) amp. Sounded okay, but there was a lot of hiss. The hiss is a direct result of the way these dacs work. There is a low pass filter in the schematic, which I want to avoid because of all the opamps.
But there's also some filtering right after the output with a series resistor and next a small cap connecting both phases. Took the output from one leg of that cap, and the hiss is gone. I've only done this for one channel, so I can't really say much about it, but it was encouraging enough to take the player to the living room tube system and hook it up. It sounds okay, as far as I recognize the music with one channel missing..

My system is not balanced, so I tried connecting both phases to a rca plug. It worked, but gave hum. Then I replaced one output with the player's ground, and that solved the hum -and halved the volume

I got discouraged by the complexity of this all at one point, but now I'm starting to get somewhere, so the tube output stage might not be that far away..

All of this was done without I/V-conversion, so I'm pretty sure the dacs are V out. Which makes it a bit easier afaic.
The service manual is very clear about this, there's notes about all the IC's functions, de-emphasis, mix amp, low pass filter etc.

[Huntingdon 361]

As you already know, this player uses two stereo DACs. The two DAC chips receive the same input data stream, but are configured to give opposite output polarity. That is, DAC IC401 is configured for inverted polarity (POL input is H), while DAC IC501 is configured for normal polarity (POL input is L). Thus, for example, output L(-) on IC401 is in phase with output L(+) on IC501. Likewise output L(+) on IC401 is in phase with output L(-) on IC501. Output L(-) from IC401 is then summed with output L(+) from IC501 on the virtual-earth input of one half of IC406, and likewise L(+) from IC401 is summed with L(-) from IC501 on the other half of IC406. And similarly for the four right-channel DAC output signals, which are summed on IC506.

I hope this will at least help your understanding of how this DAC functions. Because there are in fact eight signals all together which need to be combined to provide the two output channels, I think you have given yourself a mountain to climb if you wish to modify the output circuitry. However, I wish you good luck.