I'm just putting the finishing touches on my first Class-D DIY amplifier. It's nothing fancy, just an ESP32-WROVER board (to be running Squeezelite-esp32) connected to a PCM5102 board for DAC via I2S with this wired to a rather inexpensive TDA8932 BTL Mono Amplifier Board while I'll be using to power a single bookshelf speaker. The amp is advertised as working best at around 24V. I've been digging through my box of discarded AC adapters hoping to find a match and the best I can find is an old Lenovo Laptop AC Adapter which runs at 20V and can provide up to 90W (which on my math is around 4.5A). My understanding of electricity is that amperage provided will be a matter of what the device pulls in, so I can use an overpowered amp without fear as the board will draw however much it wants in a given moment and that 4.5A is just the ceiling for what it can provide.
To sharpen this information towards a couple questions:
(1) Am I right in thinking this will work as a PSU for that little amp? Happy to hear tales of success or woe on other similar builds using Laptop AC PSU
(2) I'm considering splitting the PSU into 2 power channels with 5V for the ESP32 and the rest for AMP. Anyone want to advise against this? I can just use a separate USB power adapter, but seems a bit silly to use two cords.
To sharpen this information towards a couple questions:
(1) Am I right in thinking this will work as a PSU for that little amp? Happy to hear tales of success or woe on other similar builds using Laptop AC PSU
(2) I'm considering splitting the PSU into 2 power channels with 5V for the ESP32 and the rest for AMP. Anyone want to advise against this? I can just use a separate USB power adapter, but seems a bit silly to use two cords.
It will work.
Use a drop resistor, to 9V or so, then 7805, or a LM317 to get 5V.
And add 100 pf + 1000 pf or so filters on the rails to reduce noise from the adapter.
An adapter with earthing will give better results, so if that is a better choice , if you have one around.
And try to earth the housing, wire mesh or cage will work.
Use a drop resistor, to 9V or so, then 7805, or a LM317 to get 5V.
And add 100 pf + 1000 pf or so filters on the rails to reduce noise from the adapter.
An adapter with earthing will give better results, so if that is a better choice , if you have one around.
And try to earth the housing, wire mesh or cage will work.
Thanks @NareshBrd that's really helpful. I'm assuming you mean to put in drop resistor after I've split off a line for the TDA8932 board, is that right? Is there any particular way to wire this, or can I just bridge off two sets of wires and run the second set to the resistors, regulator and EMI filters before going into the ESP32 via 5V rail?
Do you think that 7805 / LM317 have too high a cost in terms of voltage drop and might be worth swapping in some kind of low dropout regulator? Also for the 100/1000 pF EMI Filters can you advise how / where to wire these.
Good idea re: earthing. I'll make sure I've got a 3-prong adapter, and will see if I've got some mesh lying around. I've noticed a few other posts on the forum detailing this approach.
Do you think that 7805 / LM317 have too high a cost in terms of voltage drop and might be worth swapping in some kind of low dropout regulator? Also for the 100/1000 pF EMI Filters can you advise how / where to wire these.
Good idea re: earthing. I'll make sure I've got a 3-prong adapter, and will see if I've got some mesh lying around. I've noticed a few other posts on the forum detailing this approach.
The 5 volt unit draws very low current, so dont worry about regulator loss.
The regulator will harder if it has to drop the input too much, so drop it to 9 volts or so at regulator input. Resistor is for that, use Ohms Law to calculate value.
The negative rail is common to 5v and 20v.
Have fun...
The caps are in parallel at the unit input, different values to cover a larger range of frequencies.
The regulator will harder if it has to drop the input too much, so drop it to 9 volts or so at regulator input. Resistor is for that, use Ohms Law to calculate value.
The negative rail is common to 5v and 20v.
Have fun...
The caps are in parallel at the unit input, different values to cover a larger range of frequencies.
Besides a blanket statement, can you suggest a value for such resistor?
You are dropping from 20V to 5V ."low dropout" isn´t even a factor here.
Have you read the datasheet?
Can you suggest how to do it?
Care to suggest a definite value?
Not a generic/blanket statement .... any number?
Reason being:
Hint: I find it hard to drop voltage to a fixed value (say 9V) when current can vary from 80mA to 500mA, a 6:1 ratio.
Yes, I was wondering about this too. So power is coming in from the adapter at 20V / 4.5A, the ESP32 will draw 3.3V at around 50-100ma and the Amp prefers someting like 24V at 2A (or a touch more). Would be glad to hear about specific values others have used for this kind of setup.
I believe the PCM5102 outputs SE, whereas the TDA8932 has differential inputs. How do you plan on connecting the two?
TBH I hadn't thought of that yet. I was planning on going off the PCM5102 3.5mm jack using a mono plug with wires soldered to the amplifier board. Will this be problematic?
That seems dangerous to me as you will be shorting the left and right outputs of the stereo jack together.
I believe the later versions of LMS allow you to combine the left and right signals and send that combined signal to either the left or right output. You could then wire that to the amp. However, the positive input of the amp will get the signal, and the negative side will get zero volts as opposed to the inverted signal. Even if that doesn't cause a problem on the amp, the output voltage will be half of what you are expecting.
I believe the later versions of LMS allow you to combine the left and right signals and send that combined signal to either the left or right output. You could then wire that to the amp. However, the positive input of the amp will get the signal, and the negative side will get zero volts as opposed to the inverted signal. Even if that doesn't cause a problem on the amp, the output voltage will be half of what you are expecting.
I would just use a USB charger for the 5V. A extra cord is much less complex than a bunch of electronics.
Or use something like this: https://www.mouser.be/ProductDetail...tfZmXiUnRRWZIj0J6UIc344tYlxrfXjGTO%2BTNa3JA== with a couple of capacitors.
Jan
Ok, that's really helpful. Is there a way to take audio off the DAC board pins rather than the 3.5mm? I wasn't able to ascertain if there's audio out going anywhere besides that jack. Assuing that's not possible, it sounds like its better to combine and redirect to a single channel via software (LMS) and then use a stereo 3.5mm 3-pole connector from the DAC so I can draw out as a 2 channel signal (I think these three pole plugs using a shared negative?) and simply leave the third pole unwired.
If you have something like this, then yes.
https://www.amazon.com/HiLetgo-Lossless-Digital-Converter-Raspberry/dp/B07Q9K5MT8
The G R G L vias allow direct wiring.
For 100 mA and 8V drop, the resistor is 80 E
For 12V and 500 mA, the resistor is 24 E.
Put a 47E, 2 to 5W, and be done with it.
OR:
Like suggested above, use a parallel 5V supply, old cell phone chargers are perfect.
Here our FM radios use a 12V supply for the 6283 chip amp, and it is dropped to 5V for the FM module with a 7805 regulator.
It is a reliable arrangement.
As for the connections being balanced or not, let the more experienced members guide you.
For 12V and 500 mA, the resistor is 24 E.
Put a 47E, 2 to 5W, and be done with it.
OR:
Like suggested above, use a parallel 5V supply, old cell phone chargers are perfect.
Here our FM radios use a 12V supply for the 6283 chip amp, and it is dropped to 5V for the FM module with a 7805 regulator.
It is a reliable arrangement.
As for the connections being balanced or not, let the more experienced members guide you.
🤦♂️ Yep, that makes sense when you put it that way. And I do indeed have that board.