Otari MX7800 ?

[rrs]

Hi
I have an Otari MX 7800 1' 8 track machine sitting in the studio gathering dust. Have had an offer to sell it but today I had a thought. :idea:
Back tracking a little recently I have been replacing caps and opamps in several pieces of gear quite successfully and was looking at my Control 24 console as weather to take a look at the mic pre's and see if I could make a difference.
I have noticed that my Otari MX7800 has two inputs on the back and two knobs on the front labeled Mic and Line.I am assuming that the mic input is an everyday mic preamp.
If anybody knows this machine well and if this is the case does it have the potential to be a very good mic pre / better than the one's on my Digidesign Control 24 console (Focusrite) mic pre's ?
Any help or advice would be appreciated.

 

[Bo Hansen]

Hi rrs,

I have work with this machine, but I have never use the microphone amp.

Anyway, it is a discrete three transistor microphone pre amp in "serial feedback" style (start with a PNP transistor, the second one is a FET and at last a NPN emitter follower)
The input is Hi-Z and unbalanced, and the amp have no active gain control, only a passive direct after the output.
(the mic. amp is very similar to the reproduce amp)

Then the microphone amp and the line input (also unbalanced, but transformer balanced as a option) share a old uA-748 op amp as a mix amp, but not in a usual way, it use the non inverted input for the microphone amp and the inverted input for the line input.
This mean that the two inputs not are in phase in non balanced original version.

Finally it have a power full transformer balanced line amp, but built around the old uA-748 op-amp with a "quasi complementary" buffer before the output transformer.

I don`t know if it is worth the bother, because you must add a microphone input transformer, add phantom power, add a active gain control, and change the op-amps to a better type.
But if you have time and if you like to work with electronics, why not, maybe you will like the sound.

--Bo

 

[rrs]

Thanks Bo
I will have to consider exactly how to do this if at all as I do have limited experience.