Ebay TPA3116 50+50 / 100W amp modules - good and the bad features, plus a warning.

[rjenkinsgb]

Hi all,
I'm gradually rebuilding my home automation setup and part of that is updating the audio system, to stereo and a bit more power capability.

I've bought a few TPA3116-based amp boards from ebay, costing around £4 to £5 each. I liked the look of the amp IC from the Texas data sheet as they are both very efficient and have a differential input, which is ideal for the audio mixers I will be feeding them from (XAP800's), it avoids any possibility of ground loops.

[Edit - for info for anyone interested, the rebuilt audio setup is based on this, reconfigured for full stereo: **broken link removed**
The original was based on a setup by Jim Lipsit that was to work with HAL2000 software].


I only need possibly 10W or so at most for voice interaction and background music, so hopefully they will run quite cool and with reasonable quality

These are the two types I've bought:




The top ones are configured for stereo, the lower ones are mono - it's a configurable option with the IC, to parallel the two channels for higher power.
Data here for anyone interested: https://www.ti.com/lit/ds/symlink/tpa3116d2.pdf


Good points: They appear to have genuine Texas Instruments TPA3116 ICs and the power components look decent quality - in comparison to some other TPA3116 or similar boards on ebay that have nothing but tiny surface mount components.

Dubious points: Both have one of the inputs grounded (via a cap) within the circuit board, ignoring the data sheet info that it should go to the source audio ground not the local ground.

The stereo one has ceramic caps for input coupling. I don't know what these specific ones are like but my past experience of those in Chinese audio gear has not been good - they tend to be microphonic and cause distortion in coupling applications as the dielectric has piezoelectric properties!
They will be replaced with small electrolytics.

Bad points: And, the main reason for this post, in case anyone else gets any modules such as these!
The heatsinks were in at varied angles and one was not even anywhere near flat down to the board - and that bounced around as the board was moved.

It was stuck on with a blob of silicon rubber.

All the heatsinks on both styles of board would move slightly under pressure and they all pulled off quite easily. Every one of both types was just bodged on with silicon rubber. It does not seem to be any special type, it's not like any heat sink bonder I have ever seen.

If you get any Chinese audio modules I'd suggest seeing of the heat sink is "elastic mounted" and if so remove it and re-fit with a proper thermal adhesive!

Heatsinks removed & silicone blobs revealed; the top one is from a stereo module, the bottom from a mono one:




The old silicone rubber does clean off very easily, you can just scrape the parts with a fingernail and they clean up well.

Re. the balanced input or source ground, the ICs have coupling caps connected to both inputs, with one directly grounded. Removing the caps allows direct connection to the IC input pins so they can be used in other configurations just by lifting caps or using alternate ones.

The volume control pots are also redundant then as they have a direct ground. I've removed all the spare bits from the input side of the stereo ones, though I've not quite figured out if I am going to fit connectors or hardwire a couple of twisted pair tails to those.

I'll figure that out over the weekend, hopefully, and get some powered up for audio testing.

 

[shortbus=]

Heatsinks removed & silicone blobs revealed

Could that be the "new" thermal adhesive people are talking about?
https://en.wikipedia.org/wiki/Thermal_adhesive

GENNEL 10gram Thermal Conductive Glue , Silicone Thermal Plaster Viscous Adhesive Compound For LED GPU MOSFET Chipset Heatsink Cooling: Amazon.com: Industrial & Scientific

GENNEL 10gram Thermal Conductive Glue , Silicone Thermal Plaster Viscous Adhesive Compound For LED GPU MOSFET Chipset Heatsink Cooling: Amazon.com: Industrial & Scientific

www.amazon.com

 

[audioguru]

Could that be the "new" thermal adhesive people are talking about?

ebay junk is made as cheap as is possible. No-name-brand parts and products, ceramic coupling capacitors instead of film, overloaded tiny resistors and bathtub caulking instead of thermal adhesive.

 

[rjenkinsgb]

Could that be the "new" thermal adhesive people are talking about?

I don't think so - one of the comments from the Amazon link:
"Yes, when fully set, it becomes solid and adheres strongly to the pieces you might try to join. If you need it to be rubbery, like caulk, thermal glue isn't the best choice. "

The stuff on those amp chips was rubber that tore off easily!

 

[audioguru]

There are a few manufacturers of bathtub caulking. I have some called, "DAP Kitchen & Bath Adhesive Caulk" and it dries soft and rubbery.

 

[dr pepper]

I tried to save a little cash recently by buying a cheap chassis smps, it too has the silicone poo, and trannies that were not fastened down square.
I wasnt as lucky, expecting the supply just to work I loaded it up and it went kapow.
When I get around to it I'm thinking of building a powered bluetooth speaker for the mrs, and might go for a class d amp.

 

[rjenkinsgb]

Just an update on the functionality of these little boards.

I started fitting replacement input caps and adding cable to the boards last night, ready to fix them in the rack chassis i stripped the original amps out of.

After a few false starts trying to figure out how to solidly anchor the cable so it could not pull any components (or pads/tracks!) from the PCB, I thought I had come up with a neat way of arranging things.

I finished the first one and took a couple of photos for future reference - and when taking a photo from directly above, realised I'd used half the space the heatsink fitted in....



I decided to try running it and seeing just how hot it got like that, to see how badly I've messed up.

For testing, it's connected to a pair of cheap "100W"?? wall mount speakers from a bulk batch I got on ebay a few years ago and a 24V PSU, with input lashed up to one of the volume controls I stripped from these and a hacked up PC audio cable to give a 3.5mm connection.

Using my phone headphone socket as an audio source.

Turned on - power light on the amp, no click, pops or any signs of anything untowards. Started to turn the volume up and got pretty good audio; gradually going up to full volume on the external pot with my finger on to of the ic - and it's still stone cold!

The volume on the phone itself wasn't that high; taking that to around half scale gives a good "background music" audio level and the IC barely perceptible warm after a couple of minutes.

Full volume on the phone; 85 - 90 dBA at a metre from a speaker so annoyingly loud for background audio. That warmed it up, to the point it's obviously not cold but I'd say less than body heat...

Turning it down to normal background it's still around the same temperature 15 mins on, but with board flat on a notepad as an insulator and no real airflow.

I'm impressed!

I think the component arrangement may stay as it is with the heatsinks remounted vertically on copper L brackets - it should have better airflow if the fin channels are vertical as well.

A metal block stuck under the IC may help as well, the PCB has a grid of vias there for heat transfer to the ground plane.

Hmm... >dig in parts archive - aka junk boxes<
I knew this would come in useful one day..

 

[JimB]

parts archive

I like that expression, I will borrow it for use in the future.

JimB

 

[audioguru]

Of course the max output power of an audio amplifier depends on the power supply voltage, speaker impedance and how much clipping distortion you can survive.
The datasheet for the TPA3116 shows 30W max per channel at clipping into 8 ohms with a 24V supply. Its efficiency is >90% so at this output level the heating is <5.4W and it takes time for the heatsink to heatup.

 

[rjenkinsgb]

The datasheet for the TPA3116 shows 30W max per channel at clipping into 8 ohms with a 24V supply

I'm probably running it at something like 5W to possibly 10W total output, so the dissipation is quite low. I've no interest in high power levels with these, it's strictly background audio & a separate audio feed & amp module for each room.
(I have a surround system rated many hundreds of watts RMS plus a couple of big guitar / bass amps when I want high power audio).

I've found it is quite easy to add a "Z" bend copper strip, soldered to the via grid on the underside, to give a tab that will contact the metal chassis. The copper strip I have is only 0.4mm but it's enough to provide a decent heat flow.

I have not found any heatsink bonder yet to add copper angles on top. Must be in another archive..

The amp feed come from a couple of these; XAP800 12 input, 12 output fully real-time controllable matrix mixers with mic threshold detection, DSP echo cancellation and many other facilities. Although mine are stacked, they can be linked over 50m or so just using cat 5 cable to pass anything up to 12 channels in or out between units.
Amazing gadgets and you can pick them up easily on ebay, sometimes for as little as £20..