Hey guys, how're you doing?
I'm here to ask for some help and advice from you on improving a tda7492p chinese board. Mine is one of the red pcb 7492+csr8635 like the sanwu ones.
First, it has the classic problem of chinese cheap class D boards, a high pitch noise and trebble a little too prominent.
I've saw some of you doing some mods to it, add a snubber, change some of the crappy x7r caps, bypass the input buffer.
First I tried to add the snubber, and was at that time that I knew, I ****** up.
Cause of a horrendous mistake, picking 330nF caps instead of 330pF, when I powered it up, my speaker clipped, I heard something popping, imediatly disconected it from power.
After analising it, my 10R resistors burned a bit (it happened quite fast, <3 seconds), caps seen intact (polyester film caps, rated 63V). The chip and other components seem intact.
Now All I get from the left channel is a high pitch single tone sound, almost like a buzzer, but pretty low intensity.
Do you imagine what could've happened?
My first thoughts are that it bypassed too much power, but I'm not sure if it would kill the output stage. I think that the cap/inductor associant formed a tank and rised a ripple that killed the filter caps, since the manufacturer probably used a tolerancy as tight as he could for the components. I don't have a setup for measuring, but I can do some simple ones. Buying another board is out of question, but replacing the chip and some components is possible. Where do you segest to start looking for the problem?
I'm here to ask for some help and advice from you on improving a tda7492p chinese board. Mine is one of the red pcb 7492+csr8635 like the sanwu ones.
First, it has the classic problem of chinese cheap class D boards, a high pitch noise and trebble a little too prominent.
I've saw some of you doing some mods to it, add a snubber, change some of the crappy x7r caps, bypass the input buffer.
First I tried to add the snubber, and was at that time that I knew, I ****** up.
Cause of a horrendous mistake, picking 330nF caps instead of 330pF, when I powered it up, my speaker clipped, I heard something popping, imediatly disconected it from power.
After analising it, my 10R resistors burned a bit (it happened quite fast, <3 seconds), caps seen intact (polyester film caps, rated 63V). The chip and other components seem intact.
Now All I get from the left channel is a high pitch single tone sound, almost like a buzzer, but pretty low intensity.
Do you imagine what could've happened?
My first thoughts are that it bypassed too much power, but I'm not sure if it would kill the output stage. I think that the cap/inductor associant formed a tank and rised a ripple that killed the filter caps, since the manufacturer probably used a tolerancy as tight as he could for the components. I don't have a setup for measuring, but I can do some simple ones. Buying another board is out of question, but replacing the chip and some components is possible. Where do you segest to start looking for the problem?
I've not compared the datasheets, but I've seen some guys that apply 22 or 10 ohm with 330pf as a standard snubber on these cheapo class D filters, since under 100w per ch there's no much change in topology and internal construction of the ICs, they're quite standard. Some of them even used it with the 7492p and had no problem for as long as it has been done, the problem here was to mistake a cap with one 1000 times bigger.
While I wait the new chip to arrive( probably will order 2 and some trinkets to play with) I'll design a simple psu, and think of way of using better the bluetooth module capabilies (aux in and some sinalizing, audio prompts, and little details), change the on/off to the digital circuitry off the bt module, and so on, since I'm much better with digital stuff than power/analog.
While the time goes by I'll also make a enclosure for my setup, I wish to make a stereo bt module to play some music and watch movies, since a decent home theater is away too overkill and pricier for me, this one will do the job, but would be really better if I had acces to the dsp inside the csr chip, so I could make a "tuned" setup.
Btw, do you have any suggestions of design for the psu and enclosure?
Since it got a pretty decent psu noise rejection (datasheet claims >50db), I think it doesn't need regulation, just a hugged transformer(at least 3 amps) with good filtering will do. I'll probably use a 15 v transformer, since they're quite standard, this will give me around 20V rectified, put on some delay circuits for inrush protection and voila, a good enough psu.
While the time goes by I'll also make a enclosure for my setup, I wish to make a stereo bt module to play some music and watch movies, since a decent home theater is away too overkill and pricier for me, this one will do the job, but would be really better if I had acces to the dsp inside the csr chip, so I could make a "tuned" setup.
Btw, do you have any suggestions of design for the psu and enclosure?
Since it got a pretty decent psu noise rejection (datasheet claims >50db), I think it doesn't need regulation, just a hugged transformer(at least 3 amps) with good filtering will do. I'll probably use a 15 v transformer, since they're quite standard, this will give me around 20V rectified, put on some delay circuits for inrush protection and voila, a good enough psu.
Got a new chip, swaped them, guess what
It continues to output a single channel, with weird signal on the other.
Swap caps for good ones: notthing
Swap inductors: nothing
Disconect input and put a little high impedance speaker on the line: CSR8635's DAC is gonne for god
It's supposed to go trhoug decoupler/buffer/decoupler and then amp in(with all that "supposed" protection and high impedance input, so, maybe these chinesium chips are prone to fail with failure mode: short circuit, and that passed a surge to the DAC that's meant for maybe a couple watts, or my mistake caused some horrendous transient that ripped of every bit of protection between the output and my DAC
So, watch carefully before powering up a modded board, it can fry not only your amp, but your bluetooth soc too
I'll try to make it into a mono bass channel, using the aux in of the 8635 and the DSP inside of it
It continues to output a single channel, with weird signal on the other.
Swap caps for good ones: notthing
Swap inductors: nothing
Disconect input and put a little high impedance speaker on the line: CSR8635's DAC is gonne for god
It's supposed to go trhoug decoupler/buffer/decoupler and then amp in(with all that "supposed" protection and high impedance input, so, maybe these chinesium chips are prone to fail with failure mode: short circuit, and that passed a surge to the DAC that's meant for maybe a couple watts, or my mistake caused some horrendous transient that ripped of every bit of protection between the output and my DAC
So, watch carefully before powering up a modded board, it can fry not only your amp, but your bluetooth soc too
I'll try to make it into a mono bass channel, using the aux in of the 8635 and the DSP inside of it
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.