The Conduit Amplifier r2

I made a major revision to my Conduit amp in order to free some internal space to ease cabling.IMG_8270

The original version used pin-headers on the mono TPA3110 amplifier modules to connect them to a perfboard motherboard. Connectors for power input and speaker output terminals were on the motherbnoard. The new version uses smaller screw terminals, and moves the speaker output terminals to the amp modules, which are held in place by sandoffs. Pin headers are still used for audio inputs to the modules, and power is still connected to the motherboard, and then supplied to screw terminals on the modules via 18 gauge silicone wire. I also managed a more compact layout for the volume control daughter board.


The new version also included improved fit-and-finish to the volume control. I used some aluminum rod and brass tubing to make an extension. This now passes through a drilled-out aluminum plug before being connected to the knob. I’d originally intended to fit a bearing in the plug to support the shaft, but I don’t have one in the proper size (even so, after adjustment shaft alignment is better than pictured).


I also fitted the thermal pad and copper shims to thermally couple the amp modules to the aluminum case.

Unfortunately, only one channel works. I checked for continuity and power before noticing that a small SMD cap near the PTA3110 chip on the amp board got knocked loose. I’ll have to figure out its specs and try to get and fit a replacement… though it would be easier to just replace the board for $2.50.

I think its a nice improvement. I still need to get wire and connectors I’m happy with the power, speaker, and audio pigtails. Someone suggested 4-pole speakon connectors for the speakers. There is an aluminum version that might be a good match for the case, except it costs about as much as all the other parts combined. There are cheaper plastic speakon connectors that I might try. I’d also like to find a decent pot with an integrated switch I can use to switch the power.

The Conduit: A portable, Class D TPA3110 Audio Amplifier

Update: I made a major revision to The Conduit Amp with some improvements and a bit better fit and finish.

A few months ago I was at the hardware store looking for cheap enclosures for electronics projects. Some aluminum junction boxes for electrical conduit caught my eye, so I bought a couple. In parallel, I was interested in building a small, portable amp that could operate off 12v, which led me to buy some little, mono, TPA3110 modules for a few bucks each.

Surveying my box of parts a couple weeks ago, I noticed that the TPA3110 modules would fit nicely in the smaller of the two junction boxes I purchased, and I started tinkering with ways to assemble them into a finished product.


The first idea was to join the boards together with standoffs and slip them inside. I ordered some small terminal blocks for the electrical connections. When they came, though, and I tried assembling things as I planned, I realized I’d need to cut the standoffs down in order to fit a board to hold a potentiometer. I was feeling lazy, and didn’t want to deal with metal filings, so I looked for another way.

I decided to use pin-headers to mate the amp modules with small motherboard made from perfboard. For added mechanical strength, I cut the headers with more pins than needed, soldered the pin positions with through-holes on the amp board, and then glued the rest and trimmed them to the same length as the active pins.

Routing the power input and speaker outputs was kind of a nightmare. Rather than trying to plan it all out, I ended up working a couple of connections at once, trying to leave room for the other connections. It took quite a while. I was concerned about some of the routing and figured I’d probably end up doing a second version, so I soldiered on soldering my prototype.

Once I was done, I used my multimeter to check to make sure that there weren’t any short circuits on the motherboard. Fortunately, everything checked out.

Next I had to finish up the input connections and passive volume control. Rather than routing the audio input on the protoboard, I decided to take advantage of the shielding on the input to help keep the signal clean while passing the high-current power and output connections, and the inductors on the amp board. I connected it to the board with the volume-control board at the far end of the case.

After assembling the components on the volume control board I checked everything with a multimeter. Again, I was fortunate that I hadn’t ended up with any shorts. The volume control board was connected to the the “motherboard” with an excess of soldered pin headers for mechanical stability.

I covered the solder pads on the backs of the amp boards with kapton tape to keep them from shorting on the case. Then I made up a power cable and some speaker cables, screwed them in to the terminals on the motherboard and fed them out of the opening of the case.

Maneuvering the amp board into the case with all the cables attached took a bit more force than I was hoping for, a situation not helped by the fact that the position I chose for for the audio input connector interfered with part of the case casting, depriving me of a few extra mm at the opposite side of the case, and putting the volume-pot a bit off center.


In the end though, I got it to fit.

My plan is to power it off a Quick Charge 2 USB power bank set for 12v output. I have the powerbank, but I still need to make something to negotiate the 12v output, so I powered it off a 12v power brick to test it out.

It works! Even better, it sounds good! So, a second version is a luxury, rather than a necessity. At full volume, the output level with my phone as the audio source is maybe a little lower than I’d like for something intended for use outdoors. I’m not sure yet if that’s a limitation of the 12v supply voltage, or if I need to bump up the gain of the amplifier.

Now that I know it works, I still need to finish it up. I need to fit an extension to the volume potentiometer shaft and pick out a knob that looks good. I also need to put some thermal pads on the bottom of the amp modules to transfer heat to the case. Also I’ll probably find some thinner gauge speaker cable.

Parts Used