I only use mogami three wire lav cable and let me tell you I dont have theory I have tested it with my equipment and there is less distortion with this method I still use three wire cable. For the preamp I use pin 1 ground pin 2 signal pin 3 bias output is 3.5 mm stereo jack.
Chris Church
Replace that 27k with a 4.7 k resistor and watch what happens distortion goes way down levels are not reduced as much.
Chris Church
What's the theory behind that, Chris?
These electret FET circuits are pretty much auto-biasing to a given current, regardless of the source resistor. Reducing the source resistance should increase the distortion in a source follower circuit, not reduce it. It would also significantly reduce the overload levels, since the 4.7k would have less than 1V across it.
I'm not saying that you're wrong - I'd just like to understand your thinking
I'm not sure about this, Graeme, but Chris might be talking about running *2 wire* with a 5K source resistor (gain degeneration?) to limit gain/reduce distortion. I played with this a little bit using the Panasonic (WM60/61) mics. The idea was to use standard battery box wiring (and also use cheaper headphone cables) and but still reduce the distortion.
But if you're going to use three wires, you might as well use the circuit we have. My one change was to reduce the source resistor to 13.3k. This allows me to use the same battery box for both AKG CK91/93 and AT853 caps. This reduces the headroom for AT853 a bit, but not by much.
Anyway, Chris, can you please confirm the wiring of your *3-wire* box, both the plain box and the preamp version. I think you could sell the preamp version here. Several people asked me about mine, but I'm not building them for others...
Richard
Oh yeah, this just occured to me. Of course 5K is correct. The resistance depends on the current draw of the mics. If you put a voltmeter between the audio and ground pin (ie., across the 5k or whatever resistor), you should see approx. 4 to 5 volts, ie., half the battery voltage. The source resistor depends on the mics. 30K for AT853, 10-15K for AKG CK91/93, and perhaps 5K for your mics...
So, let me understand this:
- for your mics you use a 3.5mm plug *for each mic*, right?
- for your preamp/ battery box you use two mini XLRM panel mount jacks, right?
(Please forgive me if this is written down on your webpage or elsewhere.)
Anyway, good luck with the gear loan. Hopefully we'll hear some smokin' tapes out of this!
Richard