Question for Alan Hyatt ( Harvey too)

[tubedude]

This seems kind of weird, its from the VTB-1 info page...

Input Impedance:
Mic Input (Rear switch in 200 ohm position): 2000 ohms
Mic Input (Rear switch in 50 ohm position): 300 ohms
Line Input (Front panel TRS jack): 1.5 meg ohms

How come its 2000 ohms in the 200 ohm position, and 300 ohms in the 50 ohm position? Seems weird, but then electronics never make sense to me.
Lets say I have a microphone, like a Beta57a.. rated impedance is 150 ohm (290 ohm actual). What does that mean in relation to input impedance? would a 150 ohm mic be better served by a 150 ohm preamp, or does the math get all weirded out? And according to the spec on that particular mic, it has two different one, 150 and 290? Which on is which? How would it be affected by the VTB-1's impedance switch? Is it a close match? What would be the outcome if it was set to 50 ohms for a mic with 150 ohm (or 290, whichever it REALLY is)?
What would be the perfect mic impedance to match the VTB-1 in the 200 ohm position? 200 ohm? 2000? Something weird and unexpected?
Lotsa questions, sorry... very curious.
Peace!

 

[Harvey Gerst]

The mics are basically voltage devices, not current sources. You're interested in best loading for a voltage transfer, so the typical preamp input impedance is usually about 5 to 10 times the source impedance.

 

[alanhyatt]

Harvey is correct, so no need for me to expand on this. Even on vacation I can't get away fromn these BBS's...

Alan Hyatt

 

[Buck62]

And how is it there in beautiful Gary, Indiana?

 

[alanhyatt]

And how is it there in beautiful Gary, Indiana?

Gary was wonderful. We visited the house where Michael Jackson grew up, and stayed at the new $6.00 a night Roach House. We had a great time.....

Actually, we are staying with friends at Maui, Hawaii. Got a bunch of scuba diving in and lots of Mai Tai's!... So now I can get back and finish the SP-828 prototype, and begin the VTB-2. Being well rested is a good thing...