TDA1543 resistor i/v

[till]

experiment

sounds realy bad:

 

[till]

sound better :

 

[Bricolo]

you have to put something between vref and gnd

http://jwg.student.utwente.nl/fedde/images/nonoz3.gif

 

[jean-paul]

Hereby a pdf of what's been discussed to death. It was explained excellent by Rbroer:

 

[till]

"you have to put something between vref and gnd"

my datasheet say " R bias - optional " what should mean i don´t need it it the shown config.

 

[Bricolo]

I think it's optionnal with an opamp IV, not with a passive IV

 

[carlosfm]

till, with passive I/V, it's very critical the value you use between Ref and ground.
You have to use a resistor there.
I always use a 2.2k trimmer and it's so critical that you can tune it by ear.
Sound goes away, hiss, comes back distorted and finally clear (in both directions this happens).
There's a sweet spot thats not wide.
In the end you can measure the trimmer and put a resistor of that value there.
Unfortunately, the position where it sounds best is not the one with lower DC.

 

[Bricolo]

but there's no advantage in having a low DC, since you have a cap at the output

 

[carlosfm]

Of course.
Better with no cap, but not here.

 

[till]

I did the trimmer at Vref some time ago, and i ended up with very low resistance there.

The reason for this attempt was i wanted without the resistor, and i´m sure it will work without. (datasheet)

Following the information in posting above and the datasheet i would need to set the voltage with the divider to about 2,3V, and use 650R/760R resistors.

 

[till]

thanks to jean-pauls advice in #4:

 

[carlosfm]

When you do this, check DC on the output.
You may have to change those 33k resistors to ground by something lower...
I'd say 10k.

 

[till]

carlos, please tell me, from what miracolous source the DC should appear at output? i can´t see any ???

 

[carlosfm]

Forget it.
Try it and measure it.
You have huge DC before the caps, don't you?

 

[till]

You have huge DC before the caps, don't you?

Yes, 2.8V

and because i fear DC i use those caps. As my caps are real caps i do not belive in any DC coming throug them.

But it may be worth to try without caps in balanced configuration.

 

[carlosfm]

Those caps without the 33k resistors may do anything to remove DC.
The caps WITH the 33k resistors form a high-pass filter.
If you have high DC on the output, lower the value of the caps or lower the value of the resistors.
This is what I was talking about.

Don't remove the caps!

 

[till]

This should be a highpass with Fg = 1Hz, so no DC should be visible at output. The only way DC could show up would be with crappy caps like elektrolytics or so. I can not measure now as the device is at a friend who will listen to it for some time now.

Also i can´t see a problem with removing the caps when used for driving a balanced preamp. As we ad 2,8V at both sides to the signal this 2,8V would be removed by the balanced stage. Only you should not connect DC coupled and non balanced amp to this, else...