Hi, I've bought two TDA8932 modules, and their gain is very high, so I would like to ask what is the current state of the art for the feedback to be applied to class D modules.
I read some TI files that suggest to apply a second order filter including the output chokes into the nfb loop, and other files suggesting not to include output chokes.
This is in particular for TDA8932 modules, but also to other modules (I have some IRS2092S modules as well).
I can dramatically reduce gain because I would like to add a simple preamp with triodish sound before them.
Thanks for suggestions.
Roberto
I read some TI files that suggest to apply a second order filter including the output chokes into the nfb loop, and other files suggesting not to include output chokes.
This is in particular for TDA8932 modules, but also to other modules (I have some IRS2092S modules as well).
I can dramatically reduce gain because I would like to add a simple preamp with triodish sound before them.
Thanks for suggestions.
Roberto
Since reducing the closed-loop gain increases the open-loop gain, I would not recommend changing the control structure unless you really know what you're doing. The high gain could be compensated for rather easily by adding attenuation on the input side. The state of the art is post-filter feedback from the point-of-load (POL).
That you might. However, in case of self-oscillating amps like UcD, it maybe possible to reduce gain as stability is no longer a concern.
Thanks, I will do some tests with/without feedback, with/without attenuation.
The good thing is that I can change preamp gain and “triodeness” quite easily to adapt it.
Any other specific suggestion?
The good thing is that I can change preamp gain and “triodeness” quite easily to adapt it.
Any other specific suggestion?
Why not just follow the datasheet suggestion for reducing the gain (pages 25-26) and see how you like it?
https://www.nxp.com/docs/en/data-sheet/TDA8932B.pdf
Yes, this is what we were talking in previous posts, with the downside of increasing S/N. Thanks anyway!
You're right that using a resistive divider as in the DS worsens the S/N. I use an input transformer to reduce the gain. A commercial one is available on Aliexpress : https://www.aliexpress.com/item/32990269364.html
Have you measured the frequency resposne of those? I have a project that would be much easier to get done with transformers vs active components, but I don't really want to sacrifice response, especially low end.
I have done a FR check yes, but I was mainly interested in what they were doing at the top end (leakage inductance). I didn't notice any problems at the bottom end, they seem to have sufficient inductance. Are you worried they'll saturate?
I don't really have any experience using audio transformers. I always (wrongly?) assumed that transformers with good FR cost big $$$.
Besides saturation at low frequencies even in the midrage at decent levels transformer induced THD will degrade your average amp. I did the tests with mu-metal shielded studio xformers made by German manufacturer Pikatron.
I rather suspect TDA8932 doesn't quite make muster as 'average' as its THD at frequencies above 1kHz is higher than 0.01%.
For me it is still ok to have 0.01% THD as I will add a fet preamp in a triode-like configuration to add harmonics to it.
Being the switching frequency 320 kHz, is it ok to have a low pass in the feedback loop at 400 kHz with 1 kOhm and 390 pF, then the resistor to the input?
Being the switching frequency 320 kHz, is it ok to have a low pass in the feedback loop at 400 kHz with 1 kOhm and 390 pF, then the resistor to the input?