Originally Posted by Matt Finley
Since we’re getting more into specifics, let me explain why I use one. Two reasons: first, I use a ribbon mic from Royer to record my horns and the gain from them is normally lower. Second, I have quite a long cable run between the room where I record and room with my DAW.
Both good reasons and thanks for explaining.
Edit: Not that you needed to explain, but I was curious.

Yes, ribbon mics are another issue altogether. Some preamps for them use multiple amplifiers in parallel to reduce the input resistance and thence the noise, and also to do a trick with the summing. All wanted signals are in phase, but noise from each amplifier is random, giving around a 3dB signal to noise improvement every time one doubles the number of amplifiers.

With long cables, the 'other' noise issue of 50Hz/60Hz also comes into play. It may no longer be just the hiss.

JOM ... the JFETs I found with my quick look were 1.2nV per root Hertz, matching your numbers closely. That's "typical" of course. BJTs can be slightly lower, but there's now next to nothing in it. I'm not so sure from memory how well the fA per root Hertz figure affects things in real circuits.

Around 40 years ago I built a preamp with a JFET input and just about everyone told me I was silly to do so because BJTs were quieter. I replied then that my main noise issue was being about 1 mile line-of-sight from a 10MW TV transmitter. His wasn't the problem, the frame-rate signal was. BJTs rectified the signal and injected the hum. JFETs didn't.

Last edited by Gordon Scott; 12/19/23 10:13 AM.
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