I have built a powered speaker to go on my moped . When adjusting the volume of the preamp up or down the speaker cones move like a dc current is being fed to them for a spit second ...., this of course is accompanied by a reduction in sound for that short time frame . The preamp is a XH-A901 .
It would not surprise me if that is illegal while driving (if not they may make it illegal if you ask me) and the times I was confronted with idiots passing by with a lot of terrible sounding and loud noise I was shocked. Probably power on pulse (no muting) and not enough current by the vehicle battery and maybe even oscillation so better remove all the stuff and drive safely because you hear what happens in traffic.
For bluetooth/smart phone use while not driving many rechargeable BT boomboxes exist like those by JBL.
For bluetooth/smart phone use while not driving many rechargeable BT boomboxes exist like those by JBL.
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There is plenty of current there, as the system cranks out plenty of volume. The issue concerns volume adjustment . P.S. your opinion about whether this system should be on my bike is neither here nor there .... but thank you for sharing .
I have a bluetooth module feeding a 20k pot that in turn feeds two preamp modules . . One preamp has tone controls and feeds a class d amplifier for the full range speakers , the other is a subwoofer preamp and feeds another class d amplifier for low end duties . With the bluetooth module on , if I adjust the 20k pot or the tone control preamp volume , both sub and full range speakers move in ( or out depending on direction of rotation ) . Sub preamp volume adjustment doesn't exhibit this phenomenon . Also bluetooth module is fed by a buck converter .
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You may have a large DC component on the output of the bluetooth module. With the bluetooth and preamp both powered up but not connected to the volume knob and with no signals present, measure the DC level at the bluetooth output and the preamp input and see if they are both zero. If not, you have a DC offset that needs to be removed with a coupling cap. No DC should be placed onto a volume control, as it will cause offset problems and usually cause a scratchy sound when the control is operated. If the bluetooth has the DC offset, put a cap in series with the output before the volume knob. If the preamp has an offset too, place a cap between the volume knob wiper and the preamp. Yes, you may need two coupling caps if there's DC on each module. This should not happen with "normal circuitry", but then again, you have a problem that sounds exactly like DC where it should not be - each module seems to have been designed thinking DC would be solved somewhere else.
Install a capacitor between the pot and the input to block DC. Your bluetooth module probably uses cheap electro caps on the output and they tend to leak a small current.
any suggestions as to what kind and value of capacitor I might use , I do appreciate the help ...
That SCREAMS of DC on the pot and/or leaky preamp input .
Suggest you measure and even better scope (DC coupled input) both Volume Pot "Hot" and wiper terminals and adjust it to various levels, DC should be visible and/or shown on meter, set to 2Vdc or 20Vdc scales to begin with, but even 100-200mV DC present are too much.
IF present, take note of polarity, so you don´t really need a bipolar cap (somewhat harder to source) but a regular one, which you may already have, then just orient it the proper way.
Suggest 1uF in series with pot, another from wiper to amp input which I assume to be 10-20k (very popular values).
No larger value needed, this already has 8-16Hz turnover frequency, more than adequate.
Doubly so because we are trying to olve a SUB-sonic problem. .
Start with whatever small film cap you have as proof of concept. 10µF is a good guess. Go film if you can. All electros leak to some degree.
I use these in my tube amps and they haven't disappointed. Or you can get something from Cornell for 10x the money.
https://lcsc.com/product-detail/Pol...ors-CBB_KYET-MKP20106J2EAC461625_C521055.html