On 20/10/2019 1:03 AM, Mat Nieuwenhoven wrote:
On 13 Oct 2019 21:26:46 GMT, Trevor Wilson wrote:
snip
Do they actually use FB?
**EVERY amplifier uses NFB. Every single one. Regardless of technology
or claims from manufacturers.
If I look
at the spec sheet of the TDA7492 it doesn't look like it. Do they
sound worse than a good analog amp?
**I see a loop feedback mechanism in the block diagram. I see some
audibly significant problems with the amplifier. Max THD is cited aas
0.4% and the frequency response is poor, compared to even modest Class
A/B amplifiers. The low switching frequency ensures that low impedance
(4 Ohms) loads are not well catered for.
The TDA7492 has a switching frequency of typically 310 kHz. How is
this related to bad handling of a 4 ohm load, and why is that
dependent on the load resistance? And this IC is specified for 4 ohm
or more.
The low frequency fall off is deliberate (page 24 of the ST spec),
easily fixed by increasing the input size capacitor. The
THD-versus-frequency plot is indeed not impressive, THD rises in
spots to 0.2 %. You don't happen to have a link to a similar plot
from a good quality analog amp? Also, a link for a similar FFT plot ?
I am curious.
The IC is also dirt cheap, on a board for less than 10 $. For that
price, it is superb value for money.
There is indeed a feedback path from the OUTx pins to the second amp
inside.
snip
For a professional product, see e.g.
https://icepower.dk/products/other/a-series/ . Its datasheet is at
https://icepower.dk/download/2414/ . It supports loads down to 2.7
ohm loads. Again I wonder what the switching frequency has to do with
load.
I wonder if the phase plot can be matched by any analog amp, or even
the output resistance of 50 mOhm .
Mat Nieuwenhoven
So would it be worth my while to buy one or two of these and play with them?
https://www.aliexpress.com/item/32796154933.html I have a few ~100w laptop power bricks around
that I could use to feed power to them (that I could supplement with a large local capacitor...).
I realise it's in a different class to the links you provided but I don't have a big budget. That
said I don't have money to waste either...
Cheers,
--
Shaun.
"Humans will have advanced a long, long way when religious belief has a cozy little classification
in the DSM"
David Melville
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