The output impedance used to be 200r, but I have no clue what it is now that I've moded them. I'm guessing it's whatever the output Z of the tranny is in conjunction with that 1.2k res.
here's what I'm dealing with as far as the mics go...
Is this the schematic of which you speak??
Two questions;
How do I determine the value of R4??
It's a bit hard to tell from the drawing which wires are connected and which jump over other wires, can you elaborate on that??
Is this version correct, as far as the above question?
Hi Scooter,
I have had some discussion on this with Chuck last month. In order to find out the correct value for R4, you need to measure to output impedance of the circuit inside the Nakamichis. I have measured two of my Nakamichis following this:
http://www.jensen-transformers.com/as/as048.pdf I used a CD-player as a signal generator (just mulitply the readout by that value, 2 Volt is common). My Nakamichis measured 475 and 556 Ohms. If you are running a balanced connection, the impedances must match in order to achieve a good noise cancellation at the mic preamp input. R1 and R2 should be within 0.4% of each other too. "Balanced" = the impedancies must be balanced. If not, most of the point in having a balanced connection is lost. I think R3 can be deleted.
At the micbuilder forum, we had a discussion on the subject too.
Here are some ways of how to power the Nakamichis. Rather high output impedancies, not suitable for running long cables. C and D are not first choices. Some more components can be added for noise better noise rejection.
This one would be better suited for running long cables. This is for an internal 12V battery (four CR1632 lithium cells). You can place the 2k2-3k9 resistors and the battery elsewhere but you need to add some capactiors then. If you like to use 48V of phantom supply, you need to add a few compontens and increase the voltage rating of the 0.1uF capacitors. For sure, that will take up more space!
I am right in the process of modifying a couple of my Nakamichi CM-300. The microphone bodies have been cut-down. I intend to use them with a internal battery and make the output impedance balanced. I can also power them from my Nakamichi MX-100 mic preamp but then no balanced connection is possible.
Roger