Hi Vasile, On Jan 6, 2008 11:50 PM, Vasile Surducan wrote: > AFIK noise and impedance matching in audio are two different problems. > You may connect a 50 ohm signal source to a 10K input impedance amplifier easily > using either an operational amplifier (if you need bigger gain) either directly. > It's not RF, it's audio. > > Yes, that's true, but I think you missed the point. I have a signal source which has only a 50 ohm source impedance. If I could transform that up to something higher (it need not be exactly 10K), then I would have essentially "free" voltage gain. So, for example, if the audio noise level coming out of the mixer is 1uV, and the input noise level of the audio amp is 5uV, then directly connecting them will cause my signal to noise ratio to be almost 14dB worse than if I brought the impedances closer to matched. Yes, if my audio amp had a 1uV input noise, or if I inserted a preamp between them with a noise lower than the output noise of the mixer, then it would be just as good. In this case, that is probably what I will do. However, it just got me thinking about how this could be handled in situations where the noise levels were lower (for example, imagine that somehow you had a signal source with only 0.1uV noise - it is then challenging to design an audio amplifier which has a lower noise, especially at the low end of the spectrum. Sean -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist