[IpsilonSound]

I made my TDA1543-based DAC prototype last week and very happy with the results:
http://www.diyaudio.com/forums/showt...682&highlight=
http://www.diyaudio.com/forums/showt...threadid=35420

Powering it separately from another battery board or 12-24V adapter works like a charm with PPA as an amp. But connecting DAC to PPA power(I soldered it to C2 pins which were removed after installing diamond buffer) creates a problem, since DAC has common ground for power -V and line output ground. Shorting -V for PPA to its case may kill my amplifier which uses virtual ground with TLE rail splitter.

I tried using 2 2N5486 jfets between PPA -V +V supply and DAC power lines didn't work, I burned a few transistors already, they burn like nuts really if the pins is switched by mistake. But I used the right pins for sure, they worked fine when connected to the separate supply, still no luck when connected to PPA. I don't understand why it doesn't work, I checked later with AOS Ally DAC schema and it uses the same design as I did too.

What's the best solution to this problem? Maybe an isolation 1:1 transformer and DC to AC/AC to DC conversion for power will fix the problem? But the transformer will significantly reduce the battery life, right? 2N5486's were my choice because they consume little power and reduce ripple from the power source.

What transformer/brand I should be looking at for this portable setup?

Also anyone can suggest a small good quality audio transformer to put at the signal path to swith the phase? The passive i/v with Rikens resistors and BG Super-E caps flips the phase. And I would like using passive design to a descrete amp solution to reduce sound distortions and battery consumption.

Help pls.
Thanks a lot!

 

[IpsilonSound]

Would this one be suitable for power isolation task between DAC and PPA?

http://www.cdpoweronline.com/products/pdf/nmp_786_1.pdf

Hammond makes those as well:
http://www.hammondmfg.com/5cpwr.htm

 

[setmenu]

Hi IpsilonSound
Have you solved this yet?
Another point, are you still using the resistors to ground after the dac coupling caps?


Setmenu

 

[aos]

If your DAC uses V+ and ground, you obviously can't connect it to V+ and V- of the amplifier because your DAC ground will be the same as negative rail of the amp. You should be able to get it to work using a capacitor at the line output and obviously not connect the "ground" of the DAC to the amp. As you're feeding both from the same power source they're already related so you only need to connect one wire for each channel, from DAC line out to amp input, via capacitor as mentioned - you don't need (and can't) to connect the DAC's line output's ground to amp's line input ground. I think that should work.

 

[IpsilonSound]

TDA1543 DAC Grounding Schema

AOS, thanks a lot for your advice. I haven't tried this way yet, but have a feeling that it should fix the issue with the grounding. You're right that powering both units from the same supply makes them already related. I tried connecting without grounding before but only with separate power supplies. When powering separately and disconnecting output from the ground, the sound isn't good, too quiet and hissy. Connected to the same supply, I should sound normal then.

I attached my I/V schema to this post just to make sure I got it right what you recommended.

The Panasonic capacitor around 220uF or 470uF should be ok?

Also tried using 2 audio transformers last night to invert the phase and isolate line output. They work good, but the sound isn't great, lacking bass and more quiet. The proper audiophile transformers for this task would be prohibitevly costly and large for portable purposes.

 

[setmenu]

Hi IpsilonSound
You seem to have lost your dc path to ground with that layout.
Have you tried just removing the R9,10 and leaving the pot ground unconnected from dac ground?
This worked when I ran mine from a single battery supply.
I understand that all R9,10 do is provide a drain for the caps to prevent
pops when connecting the dac.
I presume your dac is being hardwired in a shared enclosure with the amp??


Cheers

Setmenu

 

[IpsilonSound]

Hi Setmenu,

I don't think so, if I get it right what you're saying... The DC V- is connected to the ground which is also a connecting point for the R9 and R10 (lineout)ground. Removing lineout from the ground affects the sound.

The TDA1543 chip power isn't affected by these changes and it's only the lineout that is connected to the ground and causes conflicts with V- from PPA.

It's not hardwired within the same case with the ppa yet, I'm testing it separately with a PPA and Battery board lying beside it, but the connectivity is the same as if they are sharing the same enclosure

 

[setmenu]

I mean you have now [according to the drawing] coupled your passive IV etc to ground with a cap.
Does it still function like that?

The thought the passive IV needed a dc ground connection?

Setmenu

 

[IpsilonSound]

My initial solution was isolating the DAC + and ground from the V+ and V- using isolated power rails with 2 2n5486 or PN4391 like this one, but it didn't work:

Any clue?

 

[IpsilonSound]

Quote:

Originally Posted by setmenu I mean you have now [according to the drawing] coupled your passive IV etc to ground with a cap. Does it still function like that? The thought the passive IV needed a dc ground connection? Setmenu

Hi Setmenu,

AOS suggested I use a cap and connect only L and R to the amp, but the IV needs to be connected to DC ground, you're right. I thought using a cap between the ground and IV was the recommended solution, but not sure whether connect the pot to the ground on the PPA linein, that's why the question mark. I am not at home now and cannot verify if this will work or not

EVerything's just a theory so far...

Could you show me on the schema pls what you think it should be? Just re-save the image and edit it with Paint

Thanks, Setmenu

 

[IpsilonSound]

Putting 2 film caps on each channel and avoid ground is what Aos was talking about?

 

[setmenu]

This is how I connected my units together.
No dac ground to pot ground connection.
No R9 and R10.
Only shared ground being battery V-

This worked but I preferred separate supplies ans the sound seemed a little
smoother.

Cheers

Setmenu

 

[aos]

Yes, I think that one should do it. Since your signal path from DAC to amp and back is now closed via power rail instead of ground, the sound could be negatively affected due to layout and component issues. E.g. your power supply decoupling capacitors between "amp ground" and V- are now going to be part of the amp input signal chain (more prominently than before).

Isolating FETs do not isolate one side from another in the manner you were thinking about. They reduce ripple or basically help reduce variations in the voltage, as they try to keep the current through them constant, but the voltage on the other side is still related to the voltage on the other side, as dictated by the formula that describes the function of FET (Id = Idss * e^Vg/Vgs, or something like that). The only way to transfer power yet keep voltages unrelated would be to use transformers, and there you need AC.

Problems like these is why I keep using virtual ground.

 

[IpsilonSound]

Thanks, Setmenu, that's how I imagined it too. What would happen if putting the R9 and R10 in place, just curious...
I noticed too that the DAC alone sounds different when connected to the separate power supply or a battery board connected to PPA. The latter is sounds more dynamic but smoother, less harsh, I think, but I'm not 100% sure.

Setmenu, did you try to use Super-E combination? I was comparing both single and Super-E for IV and cannot decide which one's better.

 

[setmenu]

I have not tried super E , not much space, and from Peters description would
not be to my tastes.
On the above I had pretty good faith in Peters findings based on the fact that He and I seem to have heard things in the same way regards the sonic
effect of passives..
Suggestion...who knows

Probably give it try [amoung other things] at a later date , I have built 3 of these dacs thus far , they are time consuming things to P2P together.

I did really WANT to run my little lot off one batt pack but could not bring
myself to do after listening tests.
Just means a little more weight and bulk to cart about.


Setmenu