DSP Bi-amping and FEIXIANG TDA7492 Modifications

Hi all,

I am about to get to the crossover phase in a bi-amped DSP active speaker build.

The build consists of an SB Acoustics SB12PFC25-4 in an MLTL cabinet and a Peerless TC9FD18-8 in a 1 litre sealed cabinet crossing over somewhere around 700hz using a Sure ADAU1701 board. To power these drivers I have ordered two TDA7492 amp boards. For £4.60 a board (delivered) and generally favorable reviews I took the shallow plunge and ordered two. This is a budget build.



The boards have a rating of 50wpc but after researching and seeing YT videos the likely output I will achieve with my 20v/3.5a PSU is most likely somewhere between 20-25wpc. Many places have noted that this board has distortion issues at higher levels but there are no conclusive measurements or solutions.



I am hoping that having a board per speaker and channel per driver will limit the use of very high level driving and therefore less chance of distortion. However, I would like to see if there are any modifications to this amp available. I appreciated it is a 5 year old amp but I can't find much on it on here or elsewhere.

Are there core components on this board that if swapped for higher grade components would yield a better performance?

If you have any suggestions of mods or improvements for this amp or even different boards I should try, please let me know!

I will follow with some information I have collected re this board.

Cheers,

G.

This page (in mangled google translate) details how to lower the noise floor and adjust gain:

TDA7492使用D級アンプ基板 : とっしーの徒然工作記

To reduce gain remove R28 - "It seems to be set to 33.6 dB, so it can be lowered to 27.6 dB by taking R28."



To lower noise floor drill through C46 through-hole and supplying power from the 3.3V regulator. - It seems that there is a modification to reduce the white noise at the time of silence when you are fishing the net. I decided to try it. By cutting the through hole at C46 and supplying power from the 3.3V regulator, it is a modification that reduces noise.

This guy talks about the mods in post #2 and more that go way over my head. It may, in fact, be where the information for post #2 came from:

萬屋オタクの戯言:格安TDA7492デジアン基板の解析と改造！

XRK971 adds capacitors to what I think is the power input line:

TDA7492 Amp

"a pair of Panasonic OSCON 330uF 25V SEPF caps and a Panasonic 560uF 35V FM cap to the single stock 2200uF 25V cap" However, only 3 caps show on the board.

What does this do?

And... snubbers? "added 330pF and 10R snubbers at the inputs of the inductors"

Again, I'm clueless here but he claims it makes an improvement. Is this measurable?

chermann said:

hi Graham

i found that:...just to warm up with class D 😉
YouTube

2 threads which you should read...and learn... alot of information to learn how the expert handle some topics...i did this...😉

https://www.diyaudio.com/forums/class-d/317519-sound-tda7492p-amp-2.html#post5326673
How to prevent popping sound on power on on TDA7492P Amp?


the Caps which you refer in XRK971 post are for decoupling = some reserve storage in the caps if a hugh "request" of power is happend. to use 3 diffrent caps is not bad...its an improvement to the Hf noise because normaly at the chinese amp boards you get older long storaged caps with bad ESR values. in class D its recommended to use about 1500-4700µf with (very) low ESR

the snubber filter... sorry i don not have an idea what they will do at the inductance...

my recommandation if you us this amp at home...
set the gain as low as possible = GAin0 + Gain1 settings. 21db or max 27db. because every amp is more "noisy" at higher gain.


chris

Click to expand...

Thanks for your input man!

Yes, that YT video is what made me realise that the distortion most people talk of is the stage at which 10% THD kicks in, think.

I'll be setting the gain low, for sure.

So, at least you'd recommend replacing that big capacitor with a same value one but new? Or should I replace with a higher value?