1/8/2024 0 Comments Sk transistor cross reference![]() ![]() Thus the 50-Ohm setting of the microphone's output transformer might help with the input overload problem, while causing a frequency response problem at the same time. In addition, the input transformers of some of those preamps were used in a circuit configuration which would cause audible errors in frequency response, and sometimes even parasitic oscillation, if the microphone's source (driving) impedance wasn't in the range of 150-200 Ohms. The output levels of professional condenser microphones were as much as 10 to 20 dB higher than the preamps in those consoles had been designed to handle. market in the 1950s and 60s, when many broadcast and recording consoles were still in use which had been designed for dynamic microphones, including ribbons. Permeke, the "p" version of the output circuit was designed primarily to solve certain problems of the U.S. You can't use a normal 'analog' voltmeter as it will upset the circuit too much. If you are using this voltmeter method, make sure you measure the voltage using either a digital or a vacuum-tube voltmeter or an oscilloscope. If you stop at the first (rough) part of this test (just setting the voltage), you might find that the mic will cut out occasionally on plosives or even loud passages. Obviously his is better and more accurate, but I've done this in a pinch. This is a very crude way of doing what Klaus' method is doing. ![]() If the voltage drifts around a lot, then adjust the pot a bit one way or the other to try to keep it from doing that. Then, speak very loudly, very close, but without popping air at the capsule, into the mic while measuring the drain voltage on a DC voltmeter. If you are in a pinch or in a hurry, and don't mind a compromise, you can use the same trimpot method except measure the voltage at the drain of the mic and get it to about 10 to 11 volts - that'll be in the general ballpark. ![]() If others have found another or better way to bias source-biased FETs in condenser mics, please post them! But please be conscious of the forum's rules: keep the explanations simple! I then copy the ideal value I found with the trim pot and choose a fixed source resistor of the same value for final installation. If you don't want to do it aurally, you can use an oscilloscope. All of this is best done at very low listening levels over headphones in a quiet environment. The trick is to feed enough 1k into the gate that at this ideal bias point the distortion is indeed barely audible or gone altogether, and clearly audible to each side of the ideal bias point. This will be a pretty precisely defined point right after the highest output of the mic, right after the first heavy distortion audible when the FET turns on, and right before the more gradual onset of the distortion as the FET's output decreases again. I set these FETs up the following way: I feed a 1K sine wave signal to the gate and slowly increase the source resistance from 0-10k Ohm with a temporary trim pot (10k) until I reach the lowest distortion of the FET. As FETs vary, it needs to be done for each individual FET in each individual mic. Biasing of single FETs in mic applications is done to minimize distortion and maximize output. Neither is the SK 107, despite its letters. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |