Aurycle DIY Tube mic kit.

[DrNomis_44]

The pad on the mic would be between the capsule and the valve, to stop the valve going into mild overdrive if you're recording a loud source you want to keep clean, rather than let the valve drive a bit to add some valve 'character'.

The pad on the interface obviously reduces the signal level into the preamp stage to stop the A/D converter being overloaded, but can't prevent the mic from sending an overdriven signal.

These mics can be made to sound very good (they'll sound good anyway), but as they say, you'll need to swap out most of the provided components for more upmarket devices - especially the transformer and probably the capsule.

Capacitor C4 is the one that needs the most care in installing as it needs to be well insulated from ground. That's why it's provided with ceramic insulators for the leads, to keep the body away from the board.

Yep, C4 is the coupling capacitor between the capsule and pin 2 of the 12AX7 tube, it's job is to block the DC polarizing voltage but let through the AC signal, what's more is that C4 is located in a high-impedance circuit, so any leakage (either high or low impedance) path to ground will degrade the performance of the mic, hence the ceramic insulation.


And then there's R6, which is a 200M grid-leak resistor going to ground from pin 2 of the 12AX7.

The DC polarizing voltage is supplied through R10, which is a 1G, or one giga-ohm (that is if I've interpreted it correctly and I'm not mistaken) resistor, that means there's not much current being supplied to the capsule, so, any leakage path to ground is going to load the capsule's DC polarizing supply and cause it to drop quite a bit, a high-impedance leak will also cause noise too.


1 Giga Ohms equals 1,000 Mega Ohms.