Electronics > Projects, Designs, and Technical Stuff

Tuning Microphones with an Oscilloscope

<< < (3/3)

floobydust:
R7 sets the Q-point for the tube, you would choose the sweet spot or best linearity based on the curves for the tube you are using. A scope will not tell you much aside from clipping or cramped swing.

When the same mic capsule from going from triode to JFET gets abandoned, you have to wonder why. I haven't compared transconductance between the two parts, but know an output transformer is part of the recipe.

KungFuJosh:

--- Quote from: floobydust on June 14, 2019, 02:27:51 am ---R7 sets the Q-point for the tube, you would choose the sweet spot or best linearity based on the curves for the tube you are using. A scope will not tell you much aside from clipping or cramped swing.

When the same mic capsule from going from triode to JFET gets abandoned, you have to wonder why. I haven't compared transconductance between the two parts, but know an output transformer is part of the recipe.

--- End quote ---

The tube they used to use on that build became exceptionally rare, and too expensive. If you try to get a good one now, you can easily spend $1500 on an AC701K. That's why a lot of us use the 5840W converted to triode. The capsules used in that mic, were/are used in at least a few different models.

KK6IL:

Looks to me as if R3 is providing negative feedback, which probably sets the gain regardless of the plate current.

Are you driving the signal generator directly into the preamp? driving a speaker, and watching the microphone output might be more meaningful.

John

KungFuJosh:

--- Quote from: KK6IL on June 17, 2019, 05:51:22 am ---
Looks to me as if R3 is providing negative feedback, which probably sets the gain regardless of the plate current.

Are you driving the signal generator directly into the preamp? driving a speaker, and watching the microphone output might be more meaningful.

John

--- End quote ---

I've actually removed R3, and dropped C4 to 2pF. R3 contributes oscillations, and either needs to be raised or removed to get rid of them.

The signal is inserted where C4, R5, and the Capsule connect to the tube grid in the mic.

Josh

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod