I am the proud new papa of an Altec M20 system, as well as a 195a mic with a 29b capsule. I understand from Electrical Audio that the 165a can be made to work with the cardioid capsule with the use of one resistor:

http://electrical.com/item.php?page=135 ... es/135.jpg

Can anyone fill me in on the details of doing this? I would like to take on this project, and perhaps take it a step further by installing said resistor on a "switch" , allowing me to choose between the 21b and the 29b capsules.

Thanks for any help,

Lou

Congratulations,
The resistor is located in the connector housing of the mic (which connects to the PSU). I imagine this is so the power supply does not have to care which mic plugs into it.
If you were to add a switch, I would put it as close to the connector (psu side) as possible. It might cause a problem, but it might be worth it to see.
Look at the M-30 and M-20 schematic to see where it is. I am in-session now and can't. Maybe later.

Ah - looks like there's a 22K resistor between 6 and 4 pin (?)

Does this have to be on the mic connector side? Could it be on the p/s side to make the switch easier to implement?

Or even easier - Could the 21b capsule be used with the resistor in place?

bump?

bump again - greg, steve, or anyone that could weigh in on this?
thanks,

I actually got this sorted out. Kinda busy at the moment, though so pm me for details.

LouD. wrote:Ah - looks like there's a 22K resistor between 6 and 4 pin (?)

Does this have to be on the mic connector side? Could it be on the p/s side to make the switch easier to implement?

Or even easier - Could the 21b capsule be used with the resistor in place?

I have never made a switchable PSU. I'd be afraid of stray noise if I did.
I think there is a compromise in level with the 21b capsule there.

I know this thread is old and got sorted, but for what it's worth, the "new" manual for the M-30 actually has info on this. third page.http://www.audiogearguide.com/upload/33/bTMwbmV3.pdf