The product was really amazing. The option to choose between 5 through 12 volts is very good. I can hook up the Bluetooth board to car battery and connect it to the back of my radio. Since it powers on when my car turns on that allows for no waste of electricity and disconnects from my phone when car ignition is off. I use it to listen to music in my car with free access to my phone when I'm at home or out and about. So far it stays connected over 75+ feet without the external antenna. When u connect the external antenna it can reach about 200+ feet based on the car radio antenna.Update 2022For some reason, the components used on these boards deteriorate over a year of use and I get a lot of unpleasant noise in the audio output. It has nothing to do with the RF signal strength or the DC supply voltage. The noise appears to be coming from the internal charge pump driver and the capacitors that generate the negative supply to achieve the OCL headphone drive. I see the noise generated there, and increasing the capacitor in the charge pump did make difference but did not restore the original board performance when it was new. I would not use this product if you intend for a long-term use.Update Jul 2020If you compare reviews for this product and got confused, that's because the seller Drok changed the product, photo, specification and all, while keeping the old product ID. The old product did not have a relay and auxiliary input. The new one does.This bluetooth board has a significant DC offset, and drifting. So, when the relay changes (when the bluetooth connection is established), a loud pop will come out. That is no good. Also, there is no way to adjust the signal level difference to match the volume between the Bt and the AUX sources. Overall, good concept and lousy implementation.My original review:The Bluetooth chip is marked JL AS19AP10757-5C4 but I cannot find a spec sheet for it online. If anyone finds it, please post a link. So, I don't know the official rated supply voltage range for this chip. However, the power line is regulated by a SE8533, whose output voltage is 3.3V (minimum input requirement is 4.3V, but there are series diode for reverse polarity protection, so in total, you'll need 5V or higher). So, I suppose it is safe to remove and bypass the regulator and drive it with a single LiFePO4 cell, and possibly safe with a Li-ion cell. I've been using it that way with a Li-ion directly (the regulator and the reverse polarity protection diode bypassed). It's probably unsafe to drive at 5V, since they bothered to put the regulator with USB anyway. Proceed at your own risk.This board has no battery charging circuitry at all.The Bluetooth range is quite good. I cut this PCB antenna off and fabricated a full-wavelength loop antenna to extend the range a bit and improve the connection quality.The sound quality is ok. Good enough for casual listening. Typical of consumer electronics, it sounds a little rough and harsh. It's nothing like iPod 5G or any quality device that has a decent DAC and a headphone driver. The audio output has a very low level but high-frequency noise, clearly audible in pianissimo.Amazon shipped a completely unrelated product when I ordered it the first time. It's probably their fulfillment center error, but I read this kind of error is hard to rectify so I had to wait for months to reorder another. Finally, I got it.Got this BT board to install on my old car radio. Found all the right connections to do a perfect install inside the radio, used the CD left and right channels and all sounded perfect and connected well.Unfortunately! The unit drops connectionunexpectedly and does not show how to pair properly. It does not have a pairing button which means you have to turn the car off to reset it. One connection at a time only and spastically will reconnect. These issues maybe do to BT version or lack of antenna. Don’t know.Sounds good when it works, which is unfortunately sometimes. Currently looking for a BT 5.0 replacement and next time I will add an antennaPost installation update:I’ve added a 5v power supply transformer and also added an on/off switch to reset the Bluetooth connection while the vehicle was running. Where as I had it turn on with the head unit I literally had to turn the car off to reset the Bluetooth connection.After all this, the unit is functioning perfectly.I bought the module to install in my old BOSE Acoustimass system.I was able to tap the +15V power rail in the Bose system to power it.Connected the supplied connectors and cables to the Preamp input and closed up the unit.Set the tone controls neutral and the volume to about 3/4When the system is turned on the Bluetooth unit automatically goes into pair mode, making it easy to pair the unit to just about anything.When it pairs I hear a notification tone through the unit and then I'm ready to go.The reason for 1 star off is when the unit is not receiving any music or Audio, you can hear digital noise / buzzing in a silent room, coming from the speakers. So the Bluetooth communications are being picked up by the amp section. This may be avoided with better shielding between the BT module and the preamp section, which I may try later. You can't completely shield the BT module because the built in antenna is mounted on the board. However you can add an external antenna using the U-FL connector on the board. Relocating the Antenna to a different place may help with the noise.Other than the digital noise in complete silence, the unit is great and the overall sound quality is good.I'm happy with the unit.BTW adding a microphone to the Built in 3.5mm input jacks will make the BT module a handsfree phone system as well.Alexa seems to be picky about what bluetooth audio devices it will communicate with. It was able to find and play through this one. Audio output was okay with headphones, but on the low side for driving the line inputs on my audio amplifier.This little gem comes with TWO M-M audio cables and TWO F surface mount connectors - no guessing which connectors they used. If you're going the 1/8"/3.5mm stereo plug route, you'll need to purchase those separately.Power is connected via a stab-in connector.They say this can handle 5-24Vdc input. I highly doubt that. The fixed 5.0v linear voltage regulator is a GN726 and its datasheet claims a max of 16Vdc. Pushing 24V through the tiny regulator will get it nice and toasty, think marshmallows, before the magic smoke is let out.The audio output is lower than I expected and could use a 30% increase. It draws 51mA.Usé éste módulo para actualizar un amplificador Sony TA-A50 al hacer la interfase a una entrada que originalmente es destinada para un sintonizador de radio. Naturalmente la instalación requiere de soldadura y un vistazo al manual con los diagramas eléctricos para saber el lugar para instalar la conexión.Suena bien, cumple su función. Me agrada que el módulo tenga provisión para antena externa, pues instalar una ayudará a incrementar el rango de operación.Ampliamente recomendado.Esta en proceso de pruebas