Reverse engineering Bose SoundDock 2 volume control

Thread Starter

SailCS33

Joined Mar 18, 2021
40
I have an old Bose SoundDock 2 speaker. It works but the housing is damaged. I was thinking of making my own enclosure and making it a "diy" style speaker. The problem is that everytime it is powered off/on the volume defaults to very low and must be raised by pressing the microswitch (+). The goal was to preset this to a specific volume before putting all the parts in a newly made speaker box. I wont need to adjust volume since I would be able to do it from the source player like the phone.
Im trying to find a way to bypass these volume microswitches and have it go to say 1/2 or 3/4 volume when it is turned on. Would anyone have any thoughts on how this could be done?
 

panic mode

Joined Oct 10, 2011
2,110
speaker housing condition is unrelated to question asked.

you can use circuit that produces several pulses on powerup and corrects this. if the circuit is powered from the device itself, this can be automatic on every powerup. several options exist, analog, digital, MCU...

what are you comfortable with? what voltage is available? what is the exact type of the button and more importantly are the button contacts accessible? how long delay is needed before pulses are sent? how long or short pulses can be? how many?
 

MisterBill2

Joined Jan 23, 2018
11,556
My experience with Bose is that they do their very bast to hide all the details of their products. I have a Bose surround sound system and it is only controlled by the remote that I do not have. And no circuit information is available.
 

MisterBill2

Joined Jan 23, 2018
11,556
OK, the fix is to find the point just past the volume control and adapt that as the new input, picking up the signal at a point just before the volume control, which may be one of those electronic volume control IC devices. I have not yet opened the Bose amplifier that I just got, my intention is to see if there is an easy way to use just the two channels and not the bass channel. Big Bass has no part of what I watch for entertainment. And I do fault the Bose company for not putting any of the specifications even in the owner's manual. Nor are those circuits available on line.
 

Thread Starter

SailCS33

Joined Mar 18, 2021
40

Thread Starter

SailCS33

Joined Mar 18, 2021
40
One possibility is to wire your input directly (or through a manual volume control) directly to the amp chip inputs. According to this teardown, that chip is the TDA8922BTH. https://www.nxp.com/docs/en/data-sheet/TDA8922B.pdf Bypassing the processing may also remove some useful equalization and/or limiting, so it could have weak bass or be more prone to overloading.
Thank you. I looked at the PDF you linked. I am lost how I could wire the input directly. Any recommendations would be very helpful. Thanks you.
 

MisterBill2

Joined Jan 23, 2018
11,556
Thank you. I looked at the PDF you linked. I am lost how I could wire the input directly. Any recommendations would be very helpful. Thanks you.
Wiring directly will require following the signal path through the amp, not a little effort there. And without a circuit schematic a real effort at best. I did find one Bose schematic on the "schematic for free" site, probably not the same one. But that one was a challenge to follow. And of course no board layout to help find one's way.
 
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