Hi,
I bought a TPA3118 based bluetooth amplifier board with a view of putting it into a broken Bluetooth speaker. The board works fine, but i wanted a manual volume control/pot. This is the board:
https://www.amazon.co.uk/TPA3118-Amplifier-Channel-Bluetooth-Digital/dp/B07ST15KMJ
and the datasheet for the amplifier ic:
https://www.ti.com/lit/gpn/tpa3118d2
I lifted the pins 4 and 10 on the TPA3118 and wired them to a dual gang log pot, wiring pins 4 and 10 to the wipers of the pot.
What i discovered was that if both left and right channels are wired to the pot, the board goes crazy drawing lots of current, DC goes to the speakers squealing and I have to turn it off. I determined that if I remove the left channel from the pot then it works and i get volume control on the right channel. Digging into the datasheet found that there is a Mono Mode (PBTL) mode which activates if the left channel is grounded (INNL + INPL).
It seems to be that adding the pot onto the left channel might be causing the board to go into mono mode, and since the speakers are wired for stereo operation - the board shorts out?
I came across this forum and seems there's a lot of talk about these boards so thought id ask here. Has anyone wired up a volume pot before on this or similar and might be able to help as to what I'm doing wrong?
P.S. i tried just wiring up the left channel to the pot on its own but the board still does the same thing. Some means of disabling the mono mode would be great or tricking the TPA3118 into allowing volume control without tripping the mono mode.
Thanks,
James.
I bought a TPA3118 based bluetooth amplifier board with a view of putting it into a broken Bluetooth speaker. The board works fine, but i wanted a manual volume control/pot. This is the board:
https://www.amazon.co.uk/TPA3118-Amplifier-Channel-Bluetooth-Digital/dp/B07ST15KMJ
and the datasheet for the amplifier ic:
https://www.ti.com/lit/gpn/tpa3118d2
I lifted the pins 4 and 10 on the TPA3118 and wired them to a dual gang log pot, wiring pins 4 and 10 to the wipers of the pot.
What i discovered was that if both left and right channels are wired to the pot, the board goes crazy drawing lots of current, DC goes to the speakers squealing and I have to turn it off. I determined that if I remove the left channel from the pot then it works and i get volume control on the right channel. Digging into the datasheet found that there is a Mono Mode (PBTL) mode which activates if the left channel is grounded (INNL + INPL).
It seems to be that adding the pot onto the left channel might be causing the board to go into mono mode, and since the speakers are wired for stereo operation - the board shorts out?
I came across this forum and seems there's a lot of talk about these boards so thought id ask here. Has anyone wired up a volume pot before on this or similar and might be able to help as to what I'm doing wrong?
P.S. i tried just wiring up the left channel to the pot on its own but the board still does the same thing. Some means of disabling the mono mode would be great or tricking the TPA3118 into allowing volume control without tripping the mono mode.
Thanks,
James.
Your amp needs input caps.
By connecting pots directly to the inputs you connect the dc level of the chip directly to ground. That will cause problems.
You should include the pot before the input caps.
Edit: welcome to the forum, by the way!
Hi thank you, sorry i did forget to mention I had put 10uf non polar caps in series between the wipers on the pot and their relative pins on the TPA3118. There is probably arounds 2 inches of wire from the cap/wiper which is then connected to the TPA inputs. Should i have put the caps closer to the chip? I don't seem to get any issue with this wiring on the right channel, only the left channel causes the problem.
Just to confirm i seem to have resolved this now. If anyone has this trouble, i had to trace further back on the left channel of the board from the IC. there are two caps on the line. One seems to be a dc blocking cap but the other is some kind of bias cap that keeps the line at 3v. Since i had lifted the leg it had removed the bias that was helping to keep the device in stereo mode and so any fiddling on this line such as adding the volume made it go to mono. I put the leg back for the left channel and lifted the dc cap instead and soldered my volume output to that - this seems to have retained the bias and so far its working!