Attenuator High Frequency schematic

[vmanj]

I welcome everyone.

This is the schematic diagram of my microphone.
What do I need to do to attenuate high frequencies with feedback?

I will be grateful for hints.

 

[Khron]

How about a capacitor in parallel with the drain resistor?

 

[gyraf]

Not easy in such a simple circuit - where we can't use the grid for feedback filter, as it's more or less a charge amp

In G7 I (sometimes) used a tertiary winding to feedback to cathode - here you could put in filtering

Perhaps inductor between cathode and gnd?

 

[Murdock]

What about a 150-600pF cap between plate and ground? Like in the M49?
Or how much attenuation are we talking about?

Edit: sorry, just saw you want feedback... Then the M49 Solution is probably not the right one for you.

 

[Khron]

I must wonder though, why necesarily feedback?

 

[gyraf]

Perhaps really a XY problem: The XY Problem

 

[abbey road d enfer]

NFB can't be used in a single stage circuit without a transformer with tertiary. Majot redesign.

 

[Khron]

NFB can't be used in a single stage circuit without a transformer with tertiary. Majot redesign.

I've got a hunch Ruud might disagree on that

https://groupdiy.com/threads/u67-ish-microphone.75162/
But that's maybe slightly more complicated that it really needs to be?

 

[vmanj]

Not easy in such a simple circuit - where we can't use the grid for feedback filter, as it's more or less a charge amp

In G7 I (sometimes) used a tertiary winding to feedback to cathode - here you could put in filtering

Perhaps inductor between cathode and gnd?

And how can you make feedback with the cathode if the cathode is connected to the ground ..?

 

[vmanj]

Perhaps really a XY problem: The XY Problem

To avoid "XY problem", you just need to buy a good microphone, but it's very expensive for me ..

 

[vmanj]

I tried the M49 option, it works, but on some tube it is unstable - a loud crackle ..

 

[Khron]

To avoid "XY problem", you just need to buy a good microphone, but it's very expensive for me ..

You slightly missed the point there - the idea was that there are other ways to attenuate the high frequencies, apart from ones that involve feedback. Like the one i suggested in my first reply here.

Your "Y" problem is feedback, while your "X" is (or should be) obtaining some attenuation of high frequencies, regardless of the method.

 

[vmanj]

You slightly missed the point there - the idea was that there are other ways to attenuate the high frequencies, apart from ones that involve feedback. Like the one i suggested in my first reply here.

Your "Y" problem is feedback, while your "X" is (or should be) obtaining some attenuation of high frequencies, regardless of the method.

OK.
Sorry, I guess I misunderstood your answer, maybe I didn't read it carefully..
This is true ?

 

[Khron]

Yup, that's pretty much it. You might need to experiment to find the right value (or just simulate the circuit in LTspice or something).

Alternately you could add a resistor in series with it, to have a high-shelf attenuation function, rather than a low-pass.

 

[vmanj]

Yup, that's pretty much it. You might need to experiment to find the right value (or just simulate the circuit in LTspice or something).

Alternately you could add a resistor in series with it, to have a high-shelf attenuation function, rather than a low-pass.

Thanks for the idea.
Are the images correct?

 

[abbey road d enfer]

I've got a hunch Ruud might disagree on that

And he'd be right! What I meant is voltage tovoltage NFB requires a xfmr or two stages.

 

[Khron]

Thanks for the idea.
Are the images correct?

They look ok to me

 

[vmanj]

Thank you all for your participation.

 

[oscarhuang]

This circuit is very similar to the c12. Can it attenuate high frequencies?

 

[oscarhuang]

How about this one？