I've made a bass amp with an eBay sourced 100W+100W Class D module, and instrument input using a MOSFET preamp based on this circuit:
http://www.muzique.com/schem/mosfet.htm
(The preamp runs on a 12v regulated supply rail via LM317).
I run this from an 18v cordless drill battery, but would like to have an option for more power at some outdoor gigs. I'm going to upgrade the power amp module to a TDA7948E based one, which has 160+160W and, more importantly, a higher max supply rail of 45v (up to 39v recommended on the module). https://www.ebay.co.uk/itm/387627463746?_skw=TDA7498E
Ideally I want a simple way to use either one, or two batteries of the same kind. I currently have a 2.1mm barrel connector input going through a diode (for reverse polarity protection) and a smoothing cap.
My idea is to add a second 2.1mm power input like this:
That way, I can run off 18v or 36v. I might add more diodes in series on the top input, as fully charged batteries can give about 20.7v each.
As far as I can tell:
I should probably put internal fuses in line with the sockets too, for good measure.
Comments please.
http://www.muzique.com/schem/mosfet.htm
(The preamp runs on a 12v regulated supply rail via LM317).
I run this from an 18v cordless drill battery, but would like to have an option for more power at some outdoor gigs. I'm going to upgrade the power amp module to a TDA7948E based one, which has 160+160W and, more importantly, a higher max supply rail of 45v (up to 39v recommended on the module). https://www.ebay.co.uk/itm/387627463746?_skw=TDA7498E
Ideally I want a simple way to use either one, or two batteries of the same kind. I currently have a 2.1mm barrel connector input going through a diode (for reverse polarity protection) and a smoothing cap.
My idea is to add a second 2.1mm power input like this:
That way, I can run off 18v or 36v. I might add more diodes in series on the top input, as fully charged batteries can give about 20.7v each.
As far as I can tell:
- lower battery connected = 18v operation
- upper battery connected = non-operational (but safe)
- both batteries connected = 36v operation
I should probably put internal fuses in line with the sockets too, for good measure.
Comments please.
Last edited:
Hello!
I think it works.
The TDA7948E max voltage is 45V according to the datasheet so you're ok with 2 fully charged batteries (20.7+20.7).
Fuses right close to the battery positive connectors are a must, since in a circuit failure very high current from batteries can flow through the PCB.
160+160W = 320W. Considering 90% efficiency, it will be 355W. 355/36=9.8A.
15A fuse will be ok for non distorted signal.
TDA7948E overcurrent limits to a maximum of 14A, so fuse should not blow if TDA7948E is not faulty.
Depending on the circuit board that you buy, it may include decoupling capacitor(s) on PCB for the power supply rails - it will be easy to visually check.
If not, you can add it for decoupling if needed.
I think it works.
The TDA7948E max voltage is 45V according to the datasheet so you're ok with 2 fully charged batteries (20.7+20.7).
Fuses right close to the battery positive connectors are a must, since in a circuit failure very high current from batteries can flow through the PCB.
160+160W = 320W. Considering 90% efficiency, it will be 355W. 355/36=9.8A.
15A fuse will be ok for non distorted signal.
TDA7948E overcurrent limits to a maximum of 14A, so fuse should not blow if TDA7948E is not faulty.
Depending on the circuit board that you buy, it may include decoupling capacitor(s) on PCB for the power supply rails - it will be easy to visually check.
If not, you can add it for decoupling if needed.