So you're not revelaing your secret?....another lucky surplus store find
The 47 uF is probably best left out between the 1512 and the 1646. Which drawing shows that?
So you're not revelaing your secret?....another lucky surplus store find
Yeah. Where do you keep the coffee filters?Good call....have you been snooping around my lab ???
Hi Chris. Thanks for joining us and posting here. A very good question.Using the T-bias scheme, what impedance will a mic see? I'm concerned about loading dynamic and ribbon mics. I have built a preamp around the 1510 using two 3.3k resistors to ground using the rule of thumb that the input impedance should be 10x the mic impedance (I do have a 600-ohm mic, AT804, and built the preamp to have a 6.6k input impedance). Rane builds a preamp around the 1512 with two 10k resistors to ground. What value should the resistors in this network be for a higher input impedance, say around 6k? Am I correct in saying that the circuit as drawn will present a 3k impedance to the mic?
In your situation try using ~3k bias resistors for a 6k load. I don't think you'll have a problem but you may notice a slightly higher open-circuit noise, not due to T-bias, but simply larger bias resistors. With the source connected there may not be any discernible difference.Item #2 (loading of the mic’s output stage by multiple input stages and cable capacitance) can be quite significant, especially with poorly designed condenser mics whose output stages are current starved. Ray Rayburn observes, “Take the example of a three way split where each console has a 1500 ohm input impedance (1,000 – 2,000 ohms is typical). The resulting resistive load is 500 ohms which will drive these mics into distortion. One popular podium mic loses 15 dB of headroom as the resistive load goes from 1000 ohms to 700 ohms.” For a three way split, each console would need an input impedance of 3000 ohms or higher to work with that microphone. David Josephson (Josephson mics, and chair of the AES Standards Committee Working Group on microphones) makes it his business to know what is going on with his competitors. He says that his mics and the better pro mics of his major competitors are designed with considerably more robust output stages. One clue that a mic can’t drive multiple consoles is its phantom current - in that it doesn't’t draw much phantom current.
Yes, to make my rather long story short that should work fine.So I'll be OK using the two 3.3k resistors and 22k for the center resistor?