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microphone for H120

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perik:
Hi!

I know some but not very much regarding electronics ... do u think u could give me some more detailed description on how to build these two preamps?

Here comes a couple of (maybe stupid  ??? ) questions:

1) where do u connect the ground, and why have u been writing 2 grounds? any special reason?

2) what component is i where it says 1M?

3) what component is it where it says BC 549c ?

4) what is the thing in the lower end between the two grounds, the thing that looks like a T upside down. what does that stand for?

5) how do I build it for balanced inputs?

6) it doesnt need any powersupply?? how can that be?

7) and theres no noise?

something I should think of?

thanks

P

Datman:
1) The grounds are connected together.

2) 1M??? There is a capacitor "1u" at the input. It's 1uF, one microFarad. "u" is the greek "mu". The simplest way to write the symbol with a computer is using the letter "u"...

3) BC549C is a transistor, "NPN" type.

4) It's a simplified Ground symbol.

5) Being the circuit connected directly on the mic connector (cable lenght=0, nothing), a balanced connection has no sense. A balanced input configuration will only give more hiss. There are no hum problems.

If you are talking about other applications, to send the signal to a balanced input, you need a different circuit.

6) Power supply is the same used by an electret capsule connected to the H120 input: H120 gives the 3V power to the preamp. H120 internal resistor series to the supply is the transistor collector load.

7) Minimal components, low value resistors (390KOhm resistor is shunted by the input transistor resistance and the mic impedance) = minimal noise.

I think you will have to ask someone to help you in the work.

Gianluca

Datman:
5a) Connect XLR pins 1 & 3 to ground; pin 2 to the preamp input.

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