pasarski
Well-known member
- Joined
- Jan 29, 2010
- Messages
- 416
Once again out of my depth on the subject, but here we go! I built a simple JFET microphone that uses a K47 capsule and U47 -style body. I made it a "vibe mic". Single fet, a transformer and no feedback. I think it sounds really nice, on male vocals at least. And biased for symmetrical clipping it has enough headroom for vocal use. THD is quite high - unacceptable some could say - but that's what I aimed for.
I compared it to an other K47 mic (a tube mic and my main vocal mic) which sounded quite similar, but had little less mud and little more treble. So for the heck of it I tried if I can match my mic to sound more like it. I messed around in LTspice and came out with this little feedback loop (R2, R3, C3). It's kind of like the U87 de-emphasis but does the opposite thing so I guess it's an emphasis circuit then
Fr after adding the filter:
For my surprise it works and the mic really sounds closer to the reference mic now. But there's one down side (you guessed it) - noise. The mic got quite a lot noisier after the mod. It was really quiet before. I didn't try to measure the noise at any point, but it was the quietest fet mic I've built this far. Now the mic has something like 7db more noise. I was kind of expecting the noise to increase, but didn't expect that big of a difference.
Being out of depth on the subject and the "design process" being "messing around with a simulator" I'm not quite sure how to reduce the noise without messing up the fr? I guess the circuit cancels out the advantage gained with the 5gig resistor(s)? I also guess the capsule is part of the filter?
If someone has an idea how to make it quieter it'd be fab! If not, there's a noisy microphone emphasis feedback circuit for your pleasure, be my guest
I compared it to an other K47 mic (a tube mic and my main vocal mic) which sounded quite similar, but had little less mud and little more treble. So for the heck of it I tried if I can match my mic to sound more like it. I messed around in LTspice and came out with this little feedback loop (R2, R3, C3). It's kind of like the U87 de-emphasis but does the opposite thing so I guess it's an emphasis circuit then
Fr after adding the filter:
For my surprise it works and the mic really sounds closer to the reference mic now. But there's one down side (you guessed it) - noise. The mic got quite a lot noisier after the mod. It was really quiet before. I didn't try to measure the noise at any point, but it was the quietest fet mic I've built this far. Now the mic has something like 7db more noise. I was kind of expecting the noise to increase, but didn't expect that big of a difference.
Being out of depth on the subject and the "design process" being "messing around with a simulator" I'm not quite sure how to reduce the noise without messing up the fr? I guess the circuit cancels out the advantage gained with the 5gig resistor(s)? I also guess the capsule is part of the filter?
If someone has an idea how to make it quieter it'd be fab! If not, there's a noisy microphone emphasis feedback circuit for your pleasure, be my guest