I am still somewhat new at electronics but I could use some help.
I have a video capture box that for some reason has very poor gain on the audio input. I want to add a pre-amp to increase the gain.
I purchased a Velleman Super Stereo Ear kit MK136 (http://www.vellemanusa.com/us/enu/product/view/?id=351278) and did a simple modification of changing the two microphones into a 1/8" stereo input jack. I have tested the circuit and it works fine for what I need.
Since I will only be using this with my capture box, I would like to power it by the USB port instead of batteries that I'll have to keep replacing.
The circuit is measuring at 4.8 V which I figured would be close enough to the 5V that USB provides that it should be fine. I wired it up to a usb port and it worked but I got horrible line noise.
Just to see if the voltage did make a difference, I hooked it up to a 4.5 V power supply at 500mA and still got line noise.
I plugged my multimeter into the circuit and it seems to be drawing just under 10 mA. My understanding is that USB gives about 500mA so my conclusion is that the amps are too high.
Does this sound right?
I could add a resister to lower the amps but won't that effect the volts as well? I know that V=IR but I have never been really clear on how that relationship works when V and I are dynamic (which seems to be the case).
any assistance would be appreciated.
Wesley
I have a video capture box that for some reason has very poor gain on the audio input. I want to add a pre-amp to increase the gain.
I purchased a Velleman Super Stereo Ear kit MK136 (http://www.vellemanusa.com/us/enu/product/view/?id=351278) and did a simple modification of changing the two microphones into a 1/8" stereo input jack. I have tested the circuit and it works fine for what I need.
Since I will only be using this with my capture box, I would like to power it by the USB port instead of batteries that I'll have to keep replacing.
The circuit is measuring at 4.8 V which I figured would be close enough to the 5V that USB provides that it should be fine. I wired it up to a usb port and it worked but I got horrible line noise.
Just to see if the voltage did make a difference, I hooked it up to a 4.5 V power supply at 500mA and still got line noise.
I plugged my multimeter into the circuit and it seems to be drawing just under 10 mA. My understanding is that USB gives about 500mA so my conclusion is that the amps are too high.
Does this sound right?
I could add a resister to lower the amps but won't that effect the volts as well? I know that V=IR but I have never been really clear on how that relationship works when V and I are dynamic (which seems to be the case).
any assistance would be appreciated.
Wesley