Would a Capacitor help me?

[tomzarbo]

Hey guys, on a recent visit to visit my wife’s family, I realized that two of my nieces don’t have decent (or any) tunes available. They both live in apartments in NYC and are just starting out. Rather than design/build something from scratch Eileen said why don’t you give them one of the small radios you’ve built? Smart wife, right?

So I got my MIND-65 radio all fixed up and ready to hand off, but the other one, I’ve reworked a bit so it will have battery power and not need to be taken apart to charge the batteries each time.



Here is a thread on that radio: https://techtalk.parts-express.com/f...etooth-speaker

It’s the light colored one. Anyway, I had three smaller batteries in there to get me my 12’ish volts, but wanted to rework it to be able to just charge the batteries in place, so I purchased a 2x18650 battery holder with a charger/over-under-protect circuit as well as a booster to 12v all in one. Pretty slick, and fairly inexpensive at Ali, since PE doesn’t carry this. Also, it's nice being able to charge this with 5v. (It pays to save any and all power supplies from any old electronic equipment)

It really works well and just fits perfect in the center of the radio, but I noticed that when pushing the volume to louder levels, it makes a weird ‘click’ type of sound when the bass hits usually. I suspect it's clipping I'm hearing -- It’s at a pretty loud level when this happens, and I can get to about (going from memory) about 90% of the undistorted volume available with this setup using the booster board – compared to using the batteries alone with the previous setup.

I believe this is happening due to the power booster circuit not being able to deliver the needed amperage to the amplifier on the power-hungry sections of music. I’m pretty sure 3RUTU5 has has similar issues with some of his ‘converter’ type of boards he’s used. To clarify, when I used three of the smaller Lion batteries I didn’t have this problem.

I’m happy with the sound and performance as-is, and I’m sure my niece will be as well, but it’s got me thinking to myself. Would a capacitor wired inline with the positive terminal to the amp add any benefit to stabilizing the voltage on the high-demand portions? And if so, what value?

Here is a pic of the booster board and amp (from PE)… I have an extra of both to goof around with to test this out if it’s feasible.



So what do you think, would a cap possibly help?

Thanks for any ideas…
TomZ

[DeZZar]

You could just try one and see?

[donradick]

Dang, that radio is purty!

[tomzarbo]

Dang, that radio is purty!

Thanks Don.

The DMA45's are pretty cool little drivers. There is even the hint of some bass in the output.

Dezzar, yeah, I probably will end up trying something out unless the braintrust here advises against... but I wanted to see if anyone has found this a workable solution to this issue or has any insight in the pros/cons. I know they sometimes use stiffening caps in car audio, but I have very little space to work with.

TomZ

[wogg]

Yeah... give it a try. I wouldn't go anywhere near a stiffening cap 1F level (not that you'd have room), perhaps try 10,000uF to see. The risk you run is the power on current surge to charge the cap killing your little power supply board. Does that thing have current limiting protection?

[DeZZar]

Yeah agree I don't think you'll need anything like the 1 farad caps we used to put in car audio installs. I don't know what value would suffice. I know for instance the power supply board you can add to the class d amp kits from sure is 12,000uf but that's for up to 100v and 20amps. I'd say you could likely get away with a lot less for this application.

[tomzarbo]

The battery board does have current limiting protection built in.

[Whitneyville1]

I tend to agree it's current sag causing the "clicks", but how much of a cap it will take to help it I dunno. You sure build a purty radio though! I thought I was clever when I took apart a CD/cassette/AM/FM radio boom box (with an IR remote) and repackaged it in a wooden box with better speakers in decent enclosures for my God-daughter years ago. Emma still has it and it's still going! Kinda sad how a mid '80's $79 SONY Boom-Box out-lasts lots of compact stereos that cost 6 or 8 times as much today, isn't it? And all lots of them do is amp "smart" phones and charge the phones...

[3rutu5]

Sounds like problems i have trying to be too small i've been getting some interesting results, but not that happy with. I know with mine, the AUKITS guy puts a 2200uf cap across the +/- terminals of the BT chip, i havent tried this yet and dont know why they do it, to be honest.

I'm wondering with my current issue of it sounding like i'm getting some cone breakup from mid/high frequencies that maybe my issue is from the combo 1s BMS charging/step up from 4-12v buck. Its a small circuit so i was excited about avoiding it. I definately know it isnt the speaker or enclosure as i tested it with the 12v 2x50 watt amp and it sounded sweet, just cant fit the amp into the build :( Maybe you are having a similar issue to me Tom, but you are getting more the clipping i've got prior which from memory was all around the budget step up and step down modules i was using at the time

[billfitzmaurice]

If the source of the click is the power supply I'd say additional batteries would work better than a cap. If it's the amp running out of headroom, which is what I suspect, you can't do anything about that. Test which it is by hooking it up to a 12v supply that has more capacity than the amp requires.

[devnull]

Tom.
in your post you said wired in series, it should be wired in parallel across the amp power terminals. I'm going to guess 50-100 uF should help.

[tomzarbo]

Just to clarify... This setup worked previously with the same amp running off of 12 volts from three Lion batteries outputting the same 12'ish volts with no clicking or any funny business, the amp seemed to be doing fine. I was able to overdrive the speakers before the signal got ugly.

Now with the booster board, it's clicking at high-ish volume on power-hungry bass hits. The booster/charger board can only deliver 450 mA I think I read, so that's a lot less than the other battery-direct setup of 1300 mA or so. I suspect that's the issue. The batteries are two 2100 mA 18650's so they by themselves have enough amperage to deal with these speaker/amp combo I would think. It's just that they are being 'boosted' to 12.1 volts instead of running direct.

So if I wanted to try a cap, it would be across the amp power terminals? I was thinking inline with the positive, but I've never really looked into it... well, whatta-you-know? Just learned something That would be a Non-Polarized cap then. I think I may have a few smaller-sized caps in that value range. I'm going to try it sometime this weekend if I get time.

Thank you all of you for your input, comments and thoughts on this. I know there are fewer of us on here the past few years, but you guys are really great and most helpful when trying to figure out stuff like this.
I really appreciate it.

TomZ

[billfitzmaurice]

This setup worked previously with the same amp running off of 12 volts from three Lion batteries outputting the same 12'ish volts with no clicking or any funny business, the amp seemed to be doing fine. I was able to overdrive the speakers before the signal got ugly.

In that case I'd say the power supply you're using isn't adequate, and I doubt that a cap will help. It can't increase the available current from the batteries.

[DeZZar]

So if I wanted to try a cap, it would be across the amp power terminals?

this is how it's done in car audio installs.

[3rutu5]

Looks similar to what this little Bose kit would do as well
something else I just noticed.....a separate charging board to the 1S BMS?