Class d pedalboard amp project

[Miyagi_83]

It should make no difference whether the fan is set to suck or blow.  Air flow should be equal either way.

Thanks, g1. Another question. Should I cool the chip or the heatsinking PCB plane on a class D amp?

[g1]

Cooling is never a bad thing.  Capacitor failure is a way higher percentage of faults in the modern era, and it is mostly caused by heat.

[Miyagi_83]

Cooling is never a bad thing.  Capacitor failure is a way higher percentage of faults in the modern era, and it is mostly caused by heat.

Ok, cool
I'm asking because I read over at diyaudio that in a class AB amp it may be a bad idea to blow air at the transistors because the temperature sensing device might not operate correctly, so it was suggested to fan-cool the heatsink. I wasn't sure how it's done with class D.
Thanks.

[Loudthud]

Ok, cool
I'm asking because I read over at diyaudio that in a class AB amp it may be a bad idea to blow air at the transistors because the temperature sensing device might not operate correctly, so it was suggested to fan-cool the heatsink. I wasn't sure how it's done with class D.
Thanks.

Biasing is not an issue in a class D power amp, the transistors are either on or off.

[Miyagi_83]

Biasing is not an issue in a class D power amp, the transistors are either on or off.

All right,thank you. There's still so much to learn 

[Tassieviking]

I cam across this today looking for something else so I took a picture.
I remember now that there were a trimpot on the input of the amp module so I removed it and put a pot on the front of the box

[Miyagi_83]

I cam across this today looking for something else so I took a picture.

Thanks, Tassieviking 
Looks really tight inside but, from what I understand, you had no issues with that, right?

Sadly, I didn't have a chance to do anything with mine last weekend   but I'm not in a rush.

[Tassieviking]

I have not had any problems with it, I just havent used it since I blew up the last laptop power supply, I think the amp is still fine.
If you want to see an even smaller one there is a company selling tiny 30 watt poweramps that are 25mm x 25mm x 100mm.
Even their 50 watt pedal is nice with a VU meter on it.
https://svisound.com/index.php/products/amps-cabs

[Miyagi_83]

If you want to see an even smaller one there is a company selling tiny 30 watt poweramps that are 25mm x 25mm x 100mm.
Even their 50 watt pedal is nice with a VU meter on it.
https://svisound.com/index.php/products/amps-cabs

Nice!

[Miyagi_83]

I wanted to test the amp today using an oscilloscope, so I connected a dummy load resistor and hooked up the probe and ground across it, but the waveform didn't even budge even when I applied a test signal to the input.

Later I remembered that the output on this module is bridged, hence such reading on the scope. I started wondering, what are the odds that I blew the amp? I shorted one of the outputs to ground, after all. When I connected a speaker and a guitar, it worked, but I don't know how to tell if it's working correctly.

[Loudthud]

Use the scope to see if there is signal on each side to ground.

[Miyagi_83]

Use the scope to see if there is signal on each side to ground.

Thank you for the suggestion. I'll do that tomorrow (it's 11 pm in this part of the world) and report back.
M.

[Miyagi_83]

Use the scope to see if there is signal on each side to ground.

Perhaps it's important to mention first, my oscilloscope is nothing fancy. It's a 1 MHz, single-channel digital unit by FNIRSI (DSO-153) with a built in signal generator. I wanted something cheap for starters in case I were to mess it up.

I tried the following just now. I used the built-in signal generator, plugged it into a Tube Screamer clone to be able to change the signal amplitude more easily. I tested this setup with my scope and it worked ok.

Next, I plugged it into the amp module, turned it on and tried testing it following your suggestion. A sine wave appeared on the screen when the volume knob was at minimum, but nothing happened to its shape when I turned the volume knob up. It just started floating up and down. The same was true for both outputs.

EDIT: Attached is the sine wave with the Screamer's volume knob at 0.

[Loudthud]

Next, I plugged it into the amp module, turned it on and tried testing it following your suggestion. A sine wave appeared on the screen when the volume knob was at minimum, but nothing happened to its shape when I turned the volume knob up. It just started floating up and down. The same was true for both outputs.

See on the screen where it says the frequency is 284.09 kHz ? That is the class D modulation being filtered by the output filters on the class D amp. The floating up and down, that is the signal from the generator. Set the frequency of the generator to 500 Hz and set the scope to 10mS (Ten millisecond) per division. Set the Volts per division to 5 to 10 Volts per division, whatever it takes so the trace doesn't go off the screen vertically. The scope trace will look really thick or out of focus because the 284 kHz will still be there.

[Miyagi_83]

Thanks, Loudthud. I'll do that as soon as I get some time on my hands.