I currently have a small audio amplifier in a custom case I built. In order for it to look cooler, I decided to find an old analog gauge to add to the case. Well, my local surplus store had a REALLY cool looking gauge that I HAD to have. The gauge is a 0 - 1mA analog gauge, 130ohm internal resistance. It is a bit small in range. What I would like for the gauge to do of course is move in step with the audio input to the amp. I did not want to hook it to anything on the amplification portion of the amp, as it might reduce/change some audio quality. Someone suggested a great idea that I split out the input signal (Note: only 1 channel would be needed) and "use an op-amp to drive a dummy load with the gauge inline". The source of the audio is a computer audio out jack.
This sounded like a great idea, so I started researching op-amps and their use in circuits. I have learned quite a bit, but I am by no means an electrical engineer, so I am turning to you for help. Here are my current stumbling blocks.
- What circuit to use? Voltage gain, Voltage to Current...??? (Note I built a simple Voltage to current amp last night, The gauge went to about .8mA and stayed there. There was no fluctuation that I could see based on the audio input)
- I gather that I am using the op-amp mainly to act as a high impedance buffer only, I do not think I need any gain that I can think of. Does this sound correct?
- I would prefer using a single power supply (24V off of the amp power supply). If I do this I would need to add a DC offset to the signal. I would like to avoid this, as I do not want to get any DC sent back to the main amp. I guess I could use a capacitor if need be, but I would like to avoid it, so was going to use resistors to split the 24V into +12V, and -12V to feed the op-amp so that it can handle +/- swings. Perhaps add the DC offset after the op-amp?
- I currently am testing this with a lm741 op-amp. Is the 741 bandwidth good enough for this (It only goes to 1kHz)? Should I be using a different op-amp?
Any help or even a good "Right path" would reeally help me out. I am having quite a bit of fun learning this, but a nudge in the right direction could help.
Thanks, Tom