HOMEBREW
MICAMP - 3
My first QSO with my new Crystal mic. Amp.
ASTATIC D104 microphone.
| My two first microphone amplifier was designed for
Lo-Z balanced dynamic or condenser microphones with 48
volt phantom power. Crystal microphones have Hi-Z output
impedance and can not be used on my amplifier. I have designed a new low noise amplifier for crystal microphones. |
| I have started with the work. Box from IKEA. Power with two transformers. My ECC83 amplifier card. |
| Here is the power supply. I use DC power for tube heating. This prevent 50 or 100 Hz hum. The power have 12 VDC for heating. LM7812. + and – 15 VDC for opamp. LM7915 and LM7815. 230 VDC for anode voltage. I use my anti hum regulator here. |
I use the ECC83 / 12AX7 for the balanced gain amplifier.
The input impedance is more than 800 kohm. More info later.....
Amplifier and power are mounted in the box.
| The microphone element in D104 has a balanced output
signal. The problem is that the negative signal is grounded in the connector. I have here mounted new balanced wires for my balanced amplifier. Red – positive signal, pin2. Blue – negative signal, pin 3. Black – GND, pin 1. |
Balanced and shielded cable for audio.
Shielded cable for keying.
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