Can I power my 9v amplifier using usb?

I made a small amplifier in a design class once and it requires a 9v battery to run. I want to use it to make some LED's flash in time with music and so I would like to run the amp off usb. I thought about using a transformer or dc converter but I'm not sure whether it will give enough current to run. Could I just run it straight off usb or will the 5v not be able to powere it? I have a multimeter so if needed I could possibly use it to find out the rquired voltage and current? Please reply if you can help me with what to do. Thanks

gmxx8 years ago
I would not. USB is only rated to give 5v at 100ma when data does not flow, and 5v at 500ma when the connection has data and th device asks for it. You might be able to use two usb ports hooked up in series, but it would probably not be good for the computer. firewire might work... depending on coputer you would get 9v to 25v and up to 7-8 watts. at 9v you would get about 800 ma. at 25 volts, you would get about 300ma. Honestly the easiest thing to do would be to find a 9v or 12v wall wart. It would be the safest option.
BluTiger7 years ago
There's a lot of recycle centers that I purchase walwarts  from for as little as 50 cents (US).  If I need a dedicated pwrsupply that's what I use. Look on the label and see how how many volts/amps they are. If its a little high a diode (silicon diodes, 0.7 volts, germanium diodes 0.3 volts) will drop some voltage...
Try running it off 5V and see what happens. It will reduce the power output of course, but it might still work well enough. You can only draw 100mA from a USB port without active handshaking with the supplying hub, which I believe can supply upto 1Amp if it can.