Side Project - Speaker Hack

Hi guys,

edited to fix images

This is more of a request for assistance in understanding IC datasheets and general circuitry than anythig else.

I wondered whether any of you audio / electronics wizards could help with a speaker hack I'm attempting as a side-project (am waiting for some HC-SR04's from China, so I have time!).

I scored some Harman Kardon soundsticks from Freecycle - listed as "power up and make a pop when USB cable is plugged in, but don't get recognised by computer"

I thought, sweet - the amplifier and power supply must be fine, digital USB interface / cable is goosed, but who needs that, I have lots of analog sound I can feed it. And so began the thoughts of simply wiring in an aux input to the analog side of the board (the USB digital signal is converted to an analog signal by a UAC3552A IC).

The only tutorial I found was in Japanese, and it confuses me for reasons I will elabourate on below:
Bad Google Translate Version

I added an AUX once before to an old stereo (way before the internet) and it worked fine, however things seem more complicated. The things that confuse me are:

(1) there seems to be a need to "bypass" some kind of mute function on the amp.
(2) the Japanse dude seems to add resistors into his analog feed, why is this done? I've never seen that before.

for (1) and (2) see picture below:

(3) I've located the datasheet for the UAC3552A and have seen it incorporates an AUX in function - diagrams below:

I'd like some help understanding the diagrams for AUXEN and AUXL / AUXR pins, I assume the triangle is the chip itself

In summary, I think hooking up the AUX in to a switch will do the trick, hopefully it enable AUX in, "un-mute" the amplifier and allow an analog signal through.

I propose to:

(a) Cut the pin / trace on Pin 33 (AUXEN) and them solder a jumper wire (possibly with a switch) directly between pin 33 (AUXEN) to pin 28 (VSS); and

(b) hook up an AUX lead with the L and R going to pins 36 and 37 (AUXL and AUXR), and the ground to a ground point somewhere (perhaps the one Japanese dude hilights in his diagram). Will I need 10k resistors in here somewhere to avoid damaging the chip?

As I got the speakers for free, I don't mind having a poke about, but would like to minimise chances of blowing up some salvageable speakers!

Any help hugely appreciated,


Looks like this thread never took off..

I've had a pair of the original sound sticks for nearly 10 years. They are sitting around gathering dust and I have just started a project that these would be perfect for if i could drive with analog instead of digital sound.

I haven't cracked 'em open yet to see what's inside but if my version has the same UAC3552A chip in there, it seems not only possible but a more elegant modification than I have seen elsewhere in my search (cut out traces between analog out on USB controller and amplifier.. Patch in analog). The data sheet makes it clear where and how to bring the AUX feed in.. iAsia88: Situs Slot Online, Bandar Bola SBO, Judi Online Resmi

The trick seems to be modifying the existing board that doesn't implement AUX in without screwing stuff up...

Has anyone has had success modifying original Harmon Kardon Sound Sticks to add connections for AUX input?


sorry to reply to a necro - but @clarkfarm I found the answer on another forum.

A French dude has acheived usb to jack conversion keeping the USB cable intact and removing the IC. I keot the IC and just replace the cable just 5 solder points and you are done