Hi!
I have just finished dissecting a Thiele M4 tube mic. These mics have been discussed here before and are not very highly thought of, but the build quality is not at all bad and they have a certain deco charm.
The design is eccentric to say the least. I don't think a full schematic has been shown here, so I've traced it out.
The tube is ECC83. R1 value is high - > 40 Meg. The unmarked resistor between the two filter caps is 40K (sorry!)
A few observations:
The power supply is built into the mic.
Safety issues: The case is not connected to mains earth! +45V AC was measured on case relative to mains earth! No fuse! I grounded the case before I started working.
There are no output caps or transformer. The output cable is not twisted or screened! (I can't say for certain if this is the original cable or not).
AC heating. Hum is cancelled using two pots in base of mic (see the schematic). AC mains and heater cabling are not not twisted.
I'm going to get this up and running as best I can in original state and see how good the hum-cancelling pots can be in a tube mic. Then I'll make a decision on what to do with it.
Full schematic and notes:
http://www.xaudia.com/omnip/Mics/MicSchLib/ThieleM4.pdf
Previous Thiele thread:
http://www.groupdiy.com/index.php?topic=9780
:shock: :shock: :shock:
I have just finished dissecting a Thiele M4 tube mic. These mics have been discussed here before and are not very highly thought of, but the build quality is not at all bad and they have a certain deco charm.
The design is eccentric to say the least. I don't think a full schematic has been shown here, so I've traced it out.
The tube is ECC83. R1 value is high - > 40 Meg. The unmarked resistor between the two filter caps is 40K (sorry!)
A few observations:
The power supply is built into the mic.
Safety issues: The case is not connected to mains earth! +45V AC was measured on case relative to mains earth! No fuse! I grounded the case before I started working.
There are no output caps or transformer. The output cable is not twisted or screened! (I can't say for certain if this is the original cable or not).
AC heating. Hum is cancelled using two pots in base of mic (see the schematic). AC mains and heater cabling are not not twisted.
I'm going to get this up and running as best I can in original state and see how good the hum-cancelling pots can be in a tube mic. Then I'll make a decision on what to do with it.
Full schematic and notes:
http://www.xaudia.com/omnip/Mics/MicSchLib/ThieleM4.pdf
Previous Thiele thread:
http://www.groupdiy.com/index.php?topic=9780
:shock: :shock: :shock: