Hi Richard,
I had a reply from Cinemag about other input transformer models that are not listed on their website.
Could you help reply to the following;
What is the peak signal level that will drive your Class-D amplifier? What is the source impedance range for the input signal? The input impedance of the TDA8932 is pretty high, so you can load the transformer with an appropriate resistance.
Hope all is well
I had a reply from Cinemag about other input transformer models that are not listed on their website.
Could you help reply to the following;
What is the peak signal level that will drive your Class-D amplifier? What is the source impedance range for the input signal? The input impedance of the TDA8932 is pretty high, so you can load the transformer with an appropriate resistance.
Hope all is well
Yes, that's correct.
The Aliexpress trafo has the same inter-pin spacing but is about 0.1inch narrower so you'll need some wires to bridge pads to pins. Unless you're gung-ho enough to bend the trafo pins outwards....
The peak signal level is the peak output divided by the gain. Assuming we want a trafo which can fully drive the chip under all power supply regimes, the max output is 35V peak and the gain is 36dB. Which gives a peak input voltage of 550mV. Source impedance isn't too critical, let's say sub-100ohm. Input impedance of TDA8932 in BTL mode is 25kohm on each phase (50k between phases).
Thanks for the heads up Richard. Many moons ago I followed the long 8932 thread on here and I bought some 22uh inductors to modify the Chinese blue boards...inwas intending adding these higher amperage coils along with some film caps....never happened..... so I'll see if these can be shoehorned on too!
Thanks for the detailed reply Richard, excellent stuff, I have passed it on : )
I've been working on the MonoAmp boards that I parked a few months ago when I encountered problems.
I started by powering them up again and, curiously, had a different situation to the one I described back along - both of the amps powered up with a solid yellow LED lit and no flashing red LEDs. There was a slight difference though, one board powered up more slowly (Yellow LED took longer to reach full brightness and ended up a little less bright than the other channel). I hooked up a source and plugged in a speaker but there's no output from either board.
I noticed that after a couple of minutes powered up the board with the less bright yellow LED occasionslly had the red LED flash on for an instant a few times.
Any thoughts Richard?
The problems manifested themselves after I powered the MonoAmp boards with the SMPS brick that proved to be faulty - I'm wondering if that incident has damaged the MonoAmps - it seems too much of a coincidence that both boards now have no output when they both previously worked? Perhaps I'll need to buy two more kits.
I started by powering them up again and, curiously, had a different situation to the one I described back along - both of the amps powered up with a solid yellow LED lit and no flashing red LEDs. There was a slight difference though, one board powered up more slowly (Yellow LED took longer to reach full brightness and ended up a little less bright than the other channel). I hooked up a source and plugged in a speaker but there's no output from either board.
I noticed that after a couple of minutes powered up the board with the less bright yellow LED occasionslly had the red LED flash on for an instant a few times.
Any thoughts Richard?
The problems manifested themselves after I powered the MonoAmp boards with the SMPS brick that proved to be faulty - I'm wondering if that incident has damaged the MonoAmps - it seems too much of a coincidence that both boards now have no output when they both previously worked? Perhaps I'll need to buy two more kits.
My memory's a bit poor Ray but I have a vague recollection that your R17 (2R2 1206 size) might have been suspect? It couldn't be completely open-circuit though or the yellow LED wouldn't light at all. But that can't be causing the lack of output, the red LED goes off so that indicates the chip's self-check passed OK. A dodgy R17 (overheating normally raises the value well above its marked number) could be the reason for a slow rise of brightness in the yellow LED.
When I have a suspect board I'll check the DC level on both output pins, it should be just under 11V on both. That's the voltage relative to 0V.
When I have a suspect board I'll check the DC level on both output pins, it should be just under 11V on both. That's the voltage relative to 0V.
Sorry, just wanted to make sure Richard.
So on the channel with the brigher yello LED I'm seeing around 500mV on each output, relative to ground. It's pretty steady.
On the other channel it is all over the place, constantly changin. Low is circa 150mV, high around 1.9V. I didn't see the red LRD flash but I'm assuming that it will if the voltage goes a little lower.
So on the channel with the brigher yello LED I'm seeing around 500mV on each output, relative to ground. It's pretty steady.
On the other channel it is all over the place, constantly changin. Low is circa 150mV, high around 1.9V. I didn't see the red LRD flash but I'm assuming that it will if the voltage goes a little lower.
That sounds like you have a dead TDA8932 chip then. When its working fine the DC on both pins (relative to 0V) should be mid-rail. As the supply voltage out of the regulators is just above 21V the 'offset' on each should be 10.5-11V. With such low voltages it would seem there's no PWM output - likely no oscillation. You could confirm that if you have a 'scope by looking at the input side of the 22uH inductors - those are the pins nearest R13 and R16.
As a final sanity check, measure the voltages on either side of D6 relative to 0V.
As a final sanity check, measure the voltages on either side of D6 relative to 0V.
Thanks Richard. I'll reconnect and perform the 'final sanity check'.
On the bright side, I'm listening to my unmolested STA333BW board as I type this - considering it's just temporarily hooked up with croc leads and the speaker is a naked 4in unit that is my test/sacrificial unit, it actually sounds OK!
On the bright side, I'm listening to my unmolested STA333BW board as I type this - considering it's just temporarily hooked up with croc leads and the speaker is a naked 4in unit that is my test/sacrificial unit, it actually sounds OK!
Looks like something's wrong with the regulators then, all those voltages should be about 21.5V. So your second board looks more promising with one voltage correct. Do measure the resistance of R17 on both boards, check it with the probes both ways around as there may be residual charge in the caps affecting the measurement.
It might still be the TDA8932 haven't blown up.
It might still be the TDA8932 haven't blown up.