Small mono bluetooth build, dayton KAB, wiring questions

[JoeWilsonEq]

Hi all, I'm working on a small single speaker bluetooth build and I have a few questions.

1. I bought the Dayton KAB-215 bluetooth amp board. I'm powering a single Wavecor 2 3/4" full-range driver. I didn't fully understand how mono wiring worked with a stereo amp before I bought it, but I need to sum the left and right channels. I've read that you shouldn't do this by simply twisting the L and R wires together and wiring them to the driver, though it's not entirely clear to me if this is due to safety or sound quality reasons. I have it hooked up like this right now and it seems fine, but I'm probably missing something.

I've read that to sum stereo to mono you should put a 1k resistor before connecting the L and R + wires. However, most of this advice seems to be for wiring before reaching the amp. My problem: my source and amp are the same thing since this is an amp board with integrated bluetooth. It looks like most 1k resistors are rated for low wattages, so I wasn't sure if that would work if I put them between the amp and the driver. So I bought a couple of 1k 10w resistors, and hooked them up as I've seen suggested. This seems to significantly reduce volume, and after a few seconds, the audio stops playing.

If I remove the resistors and sum both wires directly to the driver it seems fine. If I hook it up to a single amp channel it's fine as well, but I want the sound from both channels without converting to mono on my phone.

So, any idea what I did wrong with the resistors? Will lower wattage resistors work? Do I need a completely different type of resistor for this kind of wiring between an amp and a driver? Is there some sort of simple stereo to mono board I could fit in a small speaker?


2. I purchased a little USB-C charging board - ZY12PDN - and this seems to generally work well (when set to the auto voltage setting it registers as 18V and powers the amp and charges the batteries. However, there seems to be a quirk when using this with the KAB-215. When I turn the amp off, it continues to charge. But if I turn it back on, the USB-C board stops charging. If I unplug and replug the USB cable, it starts charging again.

There doesn't seem to be much I could have done wrong here so I wonder if this is just a problem with the USB-C board, and if anyone has recommendations for a USB-C board that can handle relatively high voltage (12-18V) and will continue to charge after cycling off and on. Or if anyone has experience with the KAB boards and can tell me if this is typical.

Thanks

[Dirttracker73]

The 1k resistors would be for summing the input +L and +R before the amp. But as you already stated, you really can't do that without dissecting the board. Typically, twisting the left and right + output wires together is not recommended. I think you are getting lucky that the amp board is low power and fault tolerant. A 4 ohm, 10 watt resistor at each + output lead would probably help to prevent amp failure. That would maintain 8 ohm minimum resistance between channels with minimal loss of output.

The charging board is kicking off when the amp powers on. It sees this as a sudden change in the battery's internal resistance and shuts off. This is probably to be expected and is programmed into the controller chip on the charging board. Also, the charge board doesn't compensate for the load of the amp and the amp's influence on the internal resistance of the battery, as measured / monitored by the charging board. The battery charging board should be used when the amp is off or at least allowed to finish the charging of the battery with amp off, to ensure the correct fully-charged voltage is reached and not exceeded.

[JoeWilsonEq]

The 1k resistors would be for summing the input +L and +R before the amp. But as you already stated, you really can't do that without dissecting the board. Typically, twisting the left and right + output wires together is not recommended. I think you are getting lucky that the amp board is low power and fault tolerant. A 4 ohm, 10 watt resistor at each + output lead would probably help to prevent amp failure. That would maintain 8 ohm minimum resistance between channels with minimal loss of output.

The charging board is kicking off when the amp powers on. It sees this as a sudden change in the battery's internal resistance and shuts off. This is probably to be expected and is programmed into the controller chip on the charging board. Also, the charge board doesn't compensate for the load of the amp and the amp's influence on the internal resistance of the battery, as measured / monitored by the charging board. The battery charging board should be used when the amp is off or at least allowed to finish the charging of the battery with amp off, to ensure the correct fully-charged voltage is reached and not exceeded.

Great, thank you so much for the detailed response that is very helpful. I ordered the resistors you recommended so I'll give that a go. I'm also playing around with a stereo configuration using two smaller drivers in roughly the same size enclosure and the 30w dayton DSP amp to try and boost up the low end a bit, so that may win out in the end.

Thinking about the battery charging more I don't think it will be a problem in normal use. Mostly likely I will turn it on, realize the battery is low, plug it in, listen to it for a while, and then turn it off. By the next time I turn it on the battery will likely be fully charged, so if it kicks off the charger at that point don't imagine it will be an issue.

[Chris Roemer]

How do you know that your Wavecor will work in the box size you'd like (which is WHAT)?

[3rutu5]

ok, ill get the dumb question out the way, instead of the 2x15 KAB, why not go the 1x60w version? i bought it to power my ND65 phantom inspired BT speaker and it worked great.

next is the charging, i always thought those things need 12v to power, so are you actually getting enough amps using a USB-C to charge? With my few builds i just forked out for the LBB board, plugged 3 batteries in and starting using/charging. I did stuff up on one build by not getting one that can charge on the amp its self, so the batteries ran out. Still trying to figure out how to open something thats been epoxied and 3d printed

[JoeWilsonEq]

How do you know that your Wavecor will work in the box size you'd like (which is WHAT)?

I've done some MDF enclosure tests with a few different sizes and going very small didn't seem to make much difference with this driver (FR070WA02). Of course, I'm not expecting to get bumping bass from a little ~3 driver in a tiny enclosure. Low end isn't really that important to me for this build since it will be mostly used for audiobooks, but I'm going to play with it and see if I can boost the bass to something reasonable with DSP.

I played around with a Peerless TC9FD18 since I have a few of those and like the sound of that a bit better, at least for music, but this is for my wife and she wants it to be as small as possible (otherwise she won't use it), and prefers less bass anyway for her audiobooks. She has a Bose Soundlink Revolve now which is relatively bad for audiobooks (with the exception of very poor quality recordings, which tend to sound better on the Bose). From quick tests here both the Wavecor and Peerless sound much better in any size enclosure, assuming the recording is halfway decent.

The current options are a single Peerless driver in a ~0.05cf enclosure or the Wavecors in a stereo config, with ~0.02cf of room for each of them.

[JoeWilsonEq]

ok, ill get the dumb question out the way, instead of the 2x15 KAB, why not go the 1x60w version? i bought it to power my ND65 phantom inspired BT speaker and it worked great.

next is the charging, i always thought those things need 12v to power, so are you actually getting enough amps using a USB-C to charge? With my few builds i just forked out for the LBB board, plugged 3 batteries in and starting using/charging. I did stuff up on one build by not getting one that can charge on the amp its self, so the batteries ran out. Still trying to figure out how to open something thats been epoxied and 3d printed

My driver is rated for 10/20w so I was concerned that anything significantly higher than that might damage it.

A mono amp was my first choice but when I looked there didn't seem to be many options for low-wattage mono amps, and for the ones I found it wasn't clear if it was genuinely mono or if I would only get the left or right channel. I had a look and don't see a 1x60w amp at PE, so I'm not sure which board you're referring to?

As to USB-C, I'm currently charging with a charger meant for a Macbook, and it pulls in 18V without issue and charges pretty fast. 12V works too. I should probably try with a couple of other chargers and see how it goes, but we have two of these Macbook style chargers so it shouldn't be an issue.

[3rutu5]

They might not do the 60 anymore, just hit me I built it a year ago..seems.to be some new ones there now