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Dr.EM said:Hi. I dont know too much about impedance, but I was basically wondering, what are the implications of using say a 3kohm device with perhaps a 600ohm input. Other than degraded sound quality, are there any more serious issues involved with this?
Dr.EM said:Yep, this is probably the signal transfer type, and yes, its for mics.
I am already using it, and I think it sounds ok. Basically, the mic input on my mixer reccomends 600ohms, but is actually 3k. The mic I made and am using with it is 2.2k, so I suppose its ok to use. But, say, if the input were ACTUALLY only 600ohms, or less? You say that would attenuate the signal, which I guess would result in more noise, but will it damage anything? The mixer, or mic?
Dr.EM said:Thanks for that
The mic I have made is an electret condeser type, and yep, its the resistors value that is 2.2k.
http://www.uneeda-audio.com/pzm/pzm-ch.htm
^first circuit on there, minus the 10k, powered by 3v.
I also wondered, when you switch it on, it makes a fairly loud pop. Would that "surge" be able to damage anything? It goes through that capacitor, so I assume it cannot be DC, and thus it is safe, but just want to be sure
Dr.EM said:Ok, thanks for your help
I don't have a multimeter :shock: , I suppose I should really get one...
audioguru said:Hi Nigel,
I have always thought that the drain of a junction FET is a high-impedance current sink, eg a constant-current diode. Therefore the output impedance of the mic with a 2.2K drain resistor is very close to 2.2K.
Hi Nigel,Nigel Goodwin said:The output impedance of the mic isn't the value of that resistor - it's probably considerably lower than that
audioguru said:2) I fed 100mV, 1KHz through 10K in series with 1uF into the mic's output (the junction of the FET's drain and the 10K drain resistor):
Supply..Measurement..Calculated Mic's Impedance
..open...50,0mV..........10K (check)
..2V......8.9mV............1087 ohms
..4V......19.5mV..........2422 ohms
..8V......23.8mV..........3123 ohms.
I thought of doing it that way, but couldn't find any Crazy Glue to make a fixed distance. Clamps and screws? No thanks. As it was, I had the mic in a blanket to stop it from hearing me swearing at it when it was warming up. Hey, it's winter and freezing outside. I should try...... nah.Nigel Goodwin said:I would have fed a speaker with a 1KHz tone and monitored the output of the mic with a scope
My spare pots are all intermittent cheap Chinese ones. My good ones are all installed in projects. Besides, my old slide-rule still works pretty well for calculations.Or, same method but with a variable resistor as a load - adjust the variable resistor for half the signal, then take it out and measure it's resistance