Hey JK - I've been wanting to measure the JB3s input impedance for a while but may need some help?
I've got an analog multimeter and lotsa resistors kicking around
I believe one approach was to drive a test tone to full scale and then determine what resistance value drops the signal in half (6 dB down) but that sounds like a pain since you can't monitor the JB3 live digitally (but now that I think about it I suppose I could monitor the analog out).
On the right track? thanks.
Hi there!
Very good idea!
Hmmm a drawing would have made this easier to discuss though (kuba makes nice ones ....
).
On the AC voltage source pick a frequency above the jb3's highpass filter (20 Hz?) but below the max frequency your analog meter handles (500 Hz?). Preferably one giving a steady secure reading. A good level is called for but keep it within the normal range of the jb3.
I suggest feeding the fixed-level AC through a 47 kOhms resistor and to the input of the jb3 (with the jb3 turned on). Then you have a nice 47k/Rin voltage divider right at the input. Now measure the divided voltage right at the INPUT terminal. It out to be V_source * Rin/(Rin + 47k). If the nomad input is 47k the voltage dropped to half. If it's something else it might be nice to redo the measurement with a drop resistor close in value to get maximum accuracy in the estimate of the value).
Possibly also check for dependencies in the measured voltage (ie. Rin) with the setting of the jb3 gain control (just in case there is such a dependency. Probably it's not but it's nice to know for sure).
I think this will do. Looking forward to your results!!
Jon