Ever see one of these?

[pucho812]

Anyone have any info or schematics?

 

[mrclunk]

Nope but looks very cool.
Outside broadcast mixer.
Germanium transistors?

I picked up a similar box recently.
Marconi OB mixer.

 

[user 130681]

The EMI runs on 12 x D cells or mains in the studion.
Early Plessey silicon transistors with 2N3054 complimentary output pais for headphone output.
Circa 1965, Australia.
No schematics anywhere but not complicated to work on.

 

[pucho812]

The EMI runs on 12 x D cells or mains in the studion.
Early Plessey silicon transistors with 2N3054 complimentary output pais for headphone output.
Circa 1965, Australia.
No schematics anywhere but not complicated to work on.

a client picked one up. he thinks it's wired to run 50Ω mics and needs it for 150Ω mics. I haven't had it on the bench yet so can't say what is what. thanks for the info.

 

[user 130681]

a client picked one up. he thinks it's wired to run 50Ω mics and needs it for 150Ω mics. I haven't had it on the bench yet so can't say what is what. thanks for the info.

They have input transformers and the usual impedance back in the day was 50 Ohms. I can't remember if there is a tapping for 150 Ohms or not. If not, replacement transformers are avaolable but mostly set at 600 Ohms.
Running them as they are should work but may alter the responses. Worth a try before spending a small fortune on it.

 

[pucho812]

They have input transformers and the usual impedance back in the day was 50 Ohms. I can't remember if there is a tapping for 150 Ohms or not. If not, replacement transformers are avaolable but mostly set at 600 Ohms.
Running them as they are should work but may alter the responses. Worth a try before spending a small fortune on it.

that's what I was thinking but I won't see this unit until the end of the week so I won't know for sure.

 

[pucho812]

So the unit is in my possession, it has been modified for direct output.
The big complaint is that it sounds good but gain is off the charts. so even at the lowest setting(far counter clockwise) it's still too loud...
lets see what we can come up with.

 

[pucho812]

Initial testing,
Sadly the input transformer does not have a 150ohm tap. Test signal of -20dBu sinewave. Direct outputs are at +9dBu with gain at lowest setting. The output measurement is direct out. At +9 it’s a pretty flat sweep from 20 - 20k, noting drastic. The noise specs and distortion is pretty bad. At full gain direct out is + 12dBu and way bad. However if I have +4dBu at the direct outs, noise floor is a decent -60dBu and .09% thd + noise. Unit still maxes at about +12dBu at the direct outs. it’s primary use will be for drums or other loud instruments so I might get away with just padding the front end.