somorastik
Well-known member
- Joined
- Dec 12, 2008
- Messages
- 47
Hello,
I built CMV5/B according to this schematic
http://elektroakustika.cz/cmv5b.html
And I am having some problems.
Both the Anode and heater supply are regulated by a linear regulator from a transformer.
I am using a capsule from a cheap single sided chinese microphone. The output cap is 500nF (Tesla box 250V), the tube is measured and 100% (Tesla EF12). Transformerr 1:10 I guess, it is something very interesting one guy suggested to me. It is a transformer from old microphone adapter(sometimes even build into a body of a dynamic mic) that was used to adapat the dynamic to a Hi-Z input aka an input for Piezo mic, typical tube preamplifier.
You can find them really cheap, hidden in these things.
The microphone has some hum and low sensitivity. I think the problem is connected to the fact that it should use a negative heater supply. I have possitive. I read that just now here on the forums that this circuit uses heater voltage to bias the EF12.
Is there a way to use a positive heater supply?
Thanks
Raz
P.S.: If anyone is interested in the supply I used I can post it here. It is a simple mosfet regulator for the 100V (set by trimmer), and an LM317 for the heater.
I built CMV5/B according to this schematic
http://elektroakustika.cz/cmv5b.html
And I am having some problems.
Both the Anode and heater supply are regulated by a linear regulator from a transformer.
I am using a capsule from a cheap single sided chinese microphone. The output cap is 500nF (Tesla box 250V), the tube is measured and 100% (Tesla EF12). Transformerr 1:10 I guess, it is something very interesting one guy suggested to me. It is a transformer from old microphone adapter(sometimes even build into a body of a dynamic mic) that was used to adapat the dynamic to a Hi-Z input aka an input for Piezo mic, typical tube preamplifier.
You can find them really cheap, hidden in these things.
The microphone has some hum and low sensitivity. I think the problem is connected to the fact that it should use a negative heater supply. I have possitive. I read that just now here on the forums that this circuit uses heater voltage to bias the EF12.
Is there a way to use a positive heater supply?
Thanks
Raz
P.S.: If anyone is interested in the supply I used I can post it here. It is a simple mosfet regulator for the 100V (set by trimmer), and an LM317 for the heater.