The Mystery Mic Preamp

[Consul]

So I'm going through all my crap trying to figure out what's what and what to use it for when I stumble across two of these boards:

http://dl.dropbox.com/u/7330808/Photos/Mystery%20Preamp%20Top.jpg
http://dl.dropbox.com/u/7330808/Photos/Mystery%20Preamp%20Bottom.jpg

I'm pretty sure the etched logo on the bottom says MCI. I remember getting them from someone here and he told me they're mic pres. Other than that, I know nothing about these, other than it has three NE5534 op amps on it. Can anyone out there point me to some information? Thank you!

 

[ggoerss]

looks like a LM394 supermatched pair feeding a 5534 a pretty standard topology for a transformerless mic pre of the day

 

[signalflow]

Pretty sure those are MCI 600 series mic pre's.  Schematic below.

-Casey

 

[Consul]

Wow! Yep, that's the one alright. The part number on that schematic matches a number I found on the boards. Thank you very much! Looks like it won't be much work to get it going, either.

 

[wolfgang]

Yes it is a MCI 600 Micpreamp.
Just power it with +/- PSU . Maybe you want add a balancing stage!
The only thing a little hard to get is the rev.log Poti for gain. if i remember right you ned a 5k pot!

wolfgang

 

[signalflow]

Here's one.

http://www.smallbearelec.com/Detail.bok?no=116

good price too.

-Casey

 

[Consul]

Thanks a lot, guys! It should be pretty easy to get these up and running.

 

[noisywill]

Darren,

Any luck with these?  Just racking a few of these myself, and having problems with oscillation when the gain is turned up to maximum. 

Did you just use the 5k rev audio pot across the connector for the gain circuit...or something a little more elegant?

Thanks,

Will

 

[mylesgm]

I've racked a few of these and haven't had any problems with oscillation.  When the gain is at maximum they are noisy but only at maximum the rest of the gain settings sound clean.  Have you wired the gain pot correctly?  If I remember correctly you need to add a small value resistor feeding the pot so that there is always some resistance between pin 1 and 3 on the gain terminals.  Check the full channel schematic to see how the preamp sits in the surrounding circuitry.  As to balancing I used the channel out transformer from the MCI console and it works very well (of course).