On 21/10/2019 9:31 AM, Trevor Wilson wrote:
On 20/10/2019 1:07 pm, ~misfit~ wrote:
On 20/10/2019 1:03 AM, Mat Nieuwenhoven wrote:
On 13 Oct 2019 21:26:46 GMT, Trevor Wilson wrote:
snip
Â* Do they actually use FB?
**EVERY amplifier uses NFB. Every single one. Regardless of technology
or claims from manufacturers.
Â* If I look
at the spec sheet of the TDA7492Â* 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,
**Depends on what you are trying to achieve. For 4 Bucks, it represents very good value for money,
for an amplifier that can make some noise. It ain't 'proper' hi fi, but it will certainly
outperform many highly prized (and very expensive) valve amps. It cannot hope to perform as well as
any competently designed Class A/B solid state amp though. Still, it is FOUR BUCKS!
Thanks Trevor. Yeah US$4 + some postage, not a lot of money to spend to find out. I had zero
interest in this sort of thing until I saw the post I replied to then started to wonder it it might
be worth converting some of the less valuable speakers in my speaker collection (that I need to
part with soon) to powered speakers. The sort of thing a smart phone can be plugged into...
That might make them a bit more profitable to sell on the current market. The ones I'm thinking of
are old-ish but not classic. T'was just a passing thought. I see there are also Bluetooth enabled
versions of TDA7492-based power amps for sale for not a lot more than that one.
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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