Author Topic: Modify Harman / Kardon Soundstick USB speakers to add AUX input (IC has AUX IN)  (Read 1997 times)

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Offline gotoid

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Hello all,

I want to modify the Harman / Kardon Soundstick speakers that currently only have digital input through USB, to also receive input form an AUX source - without canceling the USB input.

I have found this french site (Google Translated)
which lists the steps to make this modification by bypassing the DAC and using the USB cable wires to convert to a 3.5mm jack plug.

What I would like to do is keep the digital in from the USB, but also add an AUX IN.

From the french site I have found the data sheet for the UAC 3552A IC which handles the USB connectivity and DAC:

Reading though the data sheet, it appears that the IC has an option to receive AUX.

My question is how to go about adding the AUX IN using the functionality provided by the IC. I am having some difficulty in figuring out what the circuit would look like.

The plan is to add a 3.5mm jack socket to the woofer so I can use a standard 3.5mm jack to jack cable to connect the speakers to devices.

Would I need to add a switch to select between USB and AUX, or is there some way to wire the socket so that the IC switches to AUX when a jack is plugged in? In the data sheet it states that "AUXEN (33) Aux enable. This pin must be connected to VSS if an analog source is connected to the AUX input. Otherwise connect to VDD".

The data sheet also states that the input signals for AUXL AND AUXR should be connected by capacitive coupling: "AUXL (36) AUXR (37) The AUX pins provide two analog stereo inputs. Auxiliary  input  signals,  e.g.  the  output  of  a  conventional receiver circuit or the output of a tape recorder can be connected with these inputs. The input signals have to be connected by capacitive coupling.". If I am reading the "4.2. Typical Application" correctly, I would need to add one 470nf capacitor on each AUXL and AUXR. The diagram states "470n" which I guess means 470nf?

Basically I am a bit in over my head regarding the information I am reading in the data sheet, and I need some help to decipher the "4.2. Typical Application" diagram witch I guess provides all the information I need, but I just don't understand everything.

P.S. there is also a note on Page 8 "Table 2–1: AUXEN pin" that I don't really understand and don't know if I should be concerned about, because I don't know if BassBoost is even enabled when connected through USB: "The  AUXEN  pin  also  keeps  the  UAC 3552A  from entering  the  low-power  mode  when  an  analog  source is  connected.  Please  note  that  in  this  mode,  the UAC 3552A  is  not  USB compliant.  If  the  USB  is  not connected  the  GPIO  pins  work  as  an  USB-independent volume control (see Table 2–2). BassBoost is not supported in this mode."

Thank you for taking the time to read this. Hopefully someone can help me with the circuit for this mod. Please let me know I can provide any additional info.

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