MING MC300 PRE

[spippolone]

Someone have a schematic diagram of Ming preamplifier MC 300 PRE ??

I have a continuos 100 HZ Noise. Thank you

 

[steve...]

 

[spippolone]

wonderful Steve !!

A big thank you !

 

[theppd]

Someone have a schematic diagram of Ming preamplifier MC 300 PRE ??

I have a continuos 100 HZ Noise. Thank you

Hello, I have the same preamp and the same 100hz hum issue. Is there a solution you have come up with?

* BTW I have very different values from those on the schematics above.

 

[Lavane]

Is the noise in both channels? If so, look at the power supply. The filter caps may be getting flaky. Also look to see if the top of the caps are bulging, fluid coming out of the bottom of the caps, etc. And lift a leg and test them if you can. The values may have drifted too far out of spec.

 

[gadget73]

yeah, double the mains frequency in both channels is pretty much always power supply.

Also 100uF off a 274b is a huge capacitor, entirely possible its killing the rectifier. Not sure what the supply impedance is but I'd probably knock that down to something like a 22uF at the most.


this is really sort of a baffling unit. Its almost a power amp, except using a 300b as a cathode follower which is really kind of a waste. Wouldn't take very much to turn this into a single ended 300B power amp. An output transformer and a little power supply re-configuration to bump the plate voltage to the 300B.

 

[Lavane]

I agree, that is a huge value cap right after the 274B rectifier. It should be lower as gadget suggested.
I just read that the first filter cap should be 4uf, and 22uf in a CRC supply?
That 100uf first cap must be pretty hard on that 274B rectifier.

 

[gadget73]

Depending on the supply impedance you can get away with a larger cap, but its generally not a great idea to push it too far. PSUD can calculate the inrush current if supplied with the proper data.