I recently picked up a Sears SR-2100 series box at a garage sale for $2. Looks real good, sounds real bad. Intolerable distortion kicks in at about 1/2 volume and that is just not loud enough. I'm really not interested in the historical value of this thing, just looking for a nice sounding box with vintage aesthetics, and even a wi-fi Raspberry Pi thrown in to act as a pseudo-Squeezebox player. I'm thinking of replacing the 4" speakers with some better full-range units, bypassing the very poor tweeters all together, and even bypassing the built in amp with something like a class-T 15-watt amp board.

I understand the issues with mounting the speakers, like looking out for proper depth and mounting hole diameter. Replacing the amp will free up options with power-handling and impedance (currently 3.2 ohm, 5-watt max Sanyo drivers).

I'm also confident I can get the power supply situation sorted, with 12v going to the amp, and 5v to the Raspberry Pi.

I'm not so clear on how to go about adding the amp. Do most boomboxes have a point in the circuit where one clean line-level signal (after any input selection, pre-amp, tone control, balance, etc) is sent into the stock amp and then cleanly sent out to the speakers? If so, this would simplify things considerably as I could just bypass the stock amp, possibly replace the stock volume pot, and theoretically retain all other functions normally? If not, it would mean more work and probably more headaches than I'm looking for.

Any tips on doing this mod, such as finding the input & output side of the amp on the circuit board, good full-range speakers for this application from part-express, or any other things I'm not considering?

Thanks!

I did locate the amp chip on the board, a Toshiba TA7232P, with a whopping 2w/channel!

http://www.electronica.ro/audio/TA7232P.shtml

Unfortunately, this unit has a removable front panel but not the back, so seeing the traces on the board will require a complete disassembly...

You can try tapping out from the Volume control Pots?

From the amount of work you want to do to this box, sounds like you have the wrong unit.

By the time you have replaced the drive units, amps etc you would have a new machine.

Save yourself time and money and just buy what does what you need, unless you just like the project.

Yes, I just like the project! I've been wanting to do this for a long time but never had the time, money, or suitable box.

I am also working on a design for a custom plywood boombox with ultimate sound quality in mind but it will lack that great 80's aesthetic and authenticity.

Looking at drivers, this is going to be tricky to pull off. I can't find many suitable candidates in 4". Many more exist in 5".

If you are doing a custom job, you will need to look at Class D amps as they are very efficient and high powered. If you do your research I am sure you will find good 4” drivers, but will not be cheap. To make them sound good in a boombox will be tough.  

Try Dynaudio, I think they make some nice small drive units. The 4.5” drivers in the Totem Arro’s are made by Dynaudio I think.

Why don't you take the front panel of a 80's box and build the rest of it to your design?

Look for a box with all controls on front side. 

Thanks for the tip on the Dynaudio, I'll check them out. I've got the amp narrowed down, probably a Tripath TA2020/TA2024 for high efficiency.

Yeah, it's a great idea. Would definitely sound better than anything I could retrofit. I've even considered having a custom front panel 3d printed or something. That is a little further away in the design process!