Limpkin's blog

I don't know about you, but for me this was one of these issues that would constantly annoy me as it progressively got worse.... there's so much an operating system's equalizer could do!
As customer support let me know that replacement parts weren't made anymore, I decided to sacrifice a Sunday afternoon to get to the bottom of things.
As you can imagine, the first step was to open the back of the left speaker, which contained all the electronics:


I was pleasantly surprised by the build quality: nearly all cables are surrounded by foam, all heat generating components are mounted to a big heatsink that is thermally connected to the speaker back-plate, and some kind of black silicon is used to make sure that no air can pass through the connectors holes (and dampen vibrations).
As the problem I was experiencing was a balance issue between the left and right channels, I started looking along the amplification chain for a place where I could probe both signals with my oscilloscope:


I then found this connector on what I called the 'input stage board', at the end of a cable connecting the latter to the 'amplification board'. Looking at the picture above you'll notice L/G/R markings, likely for Left / Ground / Right.
As to why there were 2 of them... I'm not fully sure but could guess it had something to do with the second input jack on the speaker (edit: they actually were mute & standby signals).


I then made the above contraption to feed a tone to the A5 input jack and checked for a volume imbalance at that connector's pins:



Success! I could definitely see different peak-to-peak amplitudes between the L and R marked pins.
I then disconnected the cable going to the amplification board and checked the resistance between each signal pin and ground:


47k for one pair, 15k for the other! The problem was on the amplification board... or so I thought.


Following the L/R signals to the amplification board I was happy to discover the utter left/right 47k resistors, connecting each L/R input to ground. I confirmed my 47k & 15k measurement across each resistor, then removed what I thought was the faulty 47k resistor.
I measured the resistances again.... and discovered in disbelief that my 15k reading had become a 22k reading, even though the other resistor connected to each L/R input was 740k. How come?
Well.... I'm not 100% sure but my best guess is that a small voltage was still present at each node, which would confuse my multimeter.


I then turned my attention to the closest IC next to the connector on the input stage board. A quick google search revealed that the N5532 was a low noise amplifier and its datasheet let me know what its output pins were.


I confirmed that each of its outputs was connected (through passives) to each L/R connector pin I had previously probed, switched on the amplifier with a tone fed to it, and found that a capacitor seemed to be blocking one output signal! That's unfortunately quite typical as electrolytic capacitors age this way. A quick Digikey order and a bad soldering job later, I was ready to confirm my diagnosis:


The capacitor replacement fixed the issue! But how to make sure it wasn't all in my head?


Well, why not check the transfer function between the jack input and the pads I was probing?


So it seems I definitely managed to repair my speakers! The gain difference between the left and right speaker is around .7dB, which isn't perfect but I'll live with it. You'll notice the large gain difference after 12kHz, but that didn't bother me too much as during testing I couldn't hear it (I'm getting old....).

An Even Better Conclusion

At the end of my debugging adventures I had a brain wave: if the manufacturer doesn't have the spare parts and doesn't sell this model anymore, why doesn't he release the source files?
I continued my support thread and got a nice surprise: Audioengine sent me the schematics!
You'll therefore find them below if you ever encounter an issue with Audioengine A5s...
a5_amplifier_board_schematics.pdf
a5_input_stage_board_schematics.pdf

Hats off to Audioengine!