Isetta Boombox

[Quiller]

I recently built a Paul Carmody Isetta for kicks, and because it's fun to have a bluetooth box to take along. Speaker is powered by the Parts Express TPS3116D2 2.1 bluetooth amplifier-board.
This is really a pretty simple build. Except for fitting the amp board and sealing it up, all was pretty straight forward per the designer's instructions at https://sites.google.com/site/undefinition/isetta

So, the great part is that this is a very easy speaker to listen to. Even with crappy Apple Music, playing through bluetooth, the box is very musical and sounds great! This past weekend, we had a fire on the patio with friends, and as the liquor started flowing, folks just kept turning the volume up, and up. We gave it a thorough thrashing for about 4 hours, and I can only say, wow! Capable of some pretty high volume levels, while more than holding its own. The tang band W5-1138SMF is a super little sub and punches out some serious bass. Very impressive overall for what it is.

[bullittstang]

Nice build! I need to find time to build one of these.

[andykriech]

Great looking, any pictures of the guts?
Andy.

[Quiller]

Here’s the “guts”.

There is not much real estate in this enclosure when it comes to bolting in the sub behind the port tube, mounting a handle with nuts inside the small full range enclosures, etc. I mounted the amp board upside down to try and get as much space as possible between it and the sub magnet. Not sure if that is important though.

Another challenge was sealing the amp board. Air leakage around the controls made a very loud vibration sound from air being forced through small spaces. I was able to get a good seal by “painting” calk around the edges of the seal and on the inside surface of the metal plate, effectively making a gasket for the pots to press into when screwed down.
This turned into a bit of a science project for me, being a complete beginner.

• I had to use a 1.5” sch 40 pvc pipe, so since the diameter is 1.6”, with a little help, determined that the length of the port tube had to be 11.75” to compensate. I initially cut the tube short so that I could hear things at 10” and 11.5”. Note: if you use 1.5” pvc, move the placement of the port 1/8” to the rear so there is clearance for the sub..

• Initially, I was running the amp with a 12v power supply and that was producing distortion from the sub. This setup really needs a 19 or 24 volt power supply to run at higher volumes without clipping on the sub channel. You can see my “test” setup for an amp and sub amp I was pretty sure would provide plenty of clean power for comparison purposes.

• I wanted to hear the speaker with and without the filter, with and without the high pass filter, etc. So, the soldering ended up a bit wanky looking from all those changes, but I think electronically its okay.

This was a fun project for me.I think I learned a lot from the process of toying around with configurations and ending up with a final product that I’m happy with.

[joeybutts]

Great looking project! Other than shining off a high voltage, any other pros/cons you could give regarding that amp? And any plans for battery power or nah?

Thanks and great work!

[Quiller]

Regarding the amp question:

Pros: - The functionality of the board is pretty much flawless.
- Dead silent
- Connects to bluetooth instantly, good range, no dropouts. I like the way it powers down automatically.
- For a 2.1 - the price is good
- PE seems to have done a great job sourcing this product. I went through a number of ebay "crap" boards that were worthless - noisy, non functional, etc.

Really, the only con is that the "novice", ie. my daughter, who has decided that her room is the best place to store the Isetta, can't make heads or tails of all of the knobs and what they do. Hence the two large knobs - one for volume and one for bass. I actually like the controls though, so not a con to me.

No way around the power consumption issue. DIY is a challenge in terms of a heavy MDF cabinet running a larger speaker with higher voltage. It would be easy to compensate for the internal volume of a 24v battery pack, place it internally, and just deal with the added weight. I don't have much use for that level of portability so it's not worth it to me. I would probably opt for putting together a free standing battery module if I really needed it.

And maybe it's just me, but I sort of consider Li-on battery packs to be bombs waiting to go off anyway after a bad laptop experience. The last thing I want is a DIY thermal device.

[joeybutts]

Thank you sir!