Amek M2000 maintainance and possible upgrade

[wizedo]

Hi everybody, this is my first post.
My knowledge in electronics is limited to basic schematics reading and understanding, soldering and simple multimeter and oscilloscope usage.

I' ve recently acuqired an Amek M2000 (2016 modules) console in good working order, recapped (electrolitycs and radial tantalums, the axial ones are still the original) and rechipped as well.
The only issue is a quite audible, and measurable, hiss from the master buss.

I' ve already contacted Jensenmann and he kindly pointed out possible problems with the master module chips.
Digging into it i found out that all the original ICs were motorolas 741s and 458s (mc1741scp1, mc1458sp1) which have been replaced, where actually replaced, with ne5534ap (also 5532  where still a single amp is specified?) and LF353 respectively.
Now, the 353 is a fet chip and i think the 458 is a bjt one, wouldn't this bring problems?
Should I rechip all the old ones?

Thank you
Ed.

 

[bluespills]

Hey, I have the same mixer.  Can you post a picture of the module?  My modules are a bit different than the schematics and it sounds like you have the same.

 

[radardoug]

When you say it has noise, what level is it at below operating level? If its more than 60 dB you are good to go. You dont say who did the chip changes, if it works then leave it alone.

 

[wizedo]

Hi everybody and thanks for the replies, which i promptly missed. My bad.

Anyway, the origin of the noise, which gotten worse showing a 100hz hum, was in the failing power supply capacitors. After i replaced them the desk is all good and dandy.

I didn't say who changed the chips because i don't know.

@bluespills
Indeed, the desk is rev B, so the q29/q30 section in the mic amplifier has been redesigned with a dual opamp instead and the 3 diodes are not there anymore. Plus, the buss drivers are the same as the master section (gl80c) while in the schematics a slightly different circuit is shown (gl80b).