HV MOSFET Gyrator Filter

[GainFreak]

Hi,

I'm looking to replace an inductor in a project amp with a high voltage MOSFET resonant filter (gyrator) as found in Marshall JVM410.
The filter must be able to handle higher amplitude signals because it has a deeper FB 10k resistor. I assume it will need to handle at least 15V RMS to be on the safe side.
I was wondering how much signal this MOSFET gyrator can handle?

[vintagekiki]

About Gyrators

https://sound-au.com/articles/gyrator-filters.htm
Active Filters Using Gyrators - Characteristics, and Examples

http://www.muzique.com/lab/gyrator.htm
Bandpass EQ

https://forum.allaboutcircuits.com/threads/calculating-for-a-gyrator-notch-filter.154881/
Calculating for a Gyrator Notch Filter

http://tnt.etf.bg.ac.rs/~ms1aik/AIC-15-Active-Inductors.pdf
CMOS Active Inductors

https://www.diyaudio.com/forums/tubes-valves/158648-tube-gyrator-eq.html
how to make a tube gyrator eq?

https://www.diyaudio.com/forums/tubes-valves/191855-parametric-tube-eq-gyrators.html
Fully Parametric Tube EQ (with gyrators)

https://audiokarma.org/forums/index.php?threads/fully-parametric-tube-eq-with-gyrators.378808/
Fully Parametric Tube EQ (with gyrators)

[Helmholtz]

Why not breadboard the simple circuit and measure what you're interested in?

[GainFreak]

It will come to this sooner or later but I was wondering if one could tell from calculations or something.

[vintagekiki]

When make and measure that he has designed, let compare practice and theoretical calculations.

[GainFreak]

Since C11 is rated at 63VDC I assume no more than 50V at the gate (~100VDC at the drain) which should be sufficient for a ~15V signal.
If you omit C9 from the filter it looks to me like an FX loop Send source follower used in some designs.

[vintagekiki]

...#6...

How omit C9 when it doesn't exist on schematics.

Question
With the values shown in the schematics at what frequency the filter is working.

[GainFreak]

How omit C9 when it doesn't exist on schematics.

Sorry, I meant R9. Filter frequency is 130Hz which is in the ballpark of a 4x12 cab resonance but this can be adjusted according to one's particular cab.

[vintagekiki]

... #8 ...

Study a little how does a gyrator work.
Without R9 the circuit is not a gyrator. You only have a serial connection C10 and C11.
1)
In order for other members to understand your idea, try to be more complete in the future (more detailed)
For example ...

[GainFreak]

Without R9 the circuit is not a gyrator.

I never said I will remove R9. I meant without R9 it looks like a source follower.

[vintagekiki]

#10
I never said I will remove R9.

I probably misunderstood what you meant.

#6
If you omit C9 from the filter...

#8
Sorry, I meant R9

[Helmholtz]

The Marshall circuit essentially consists of a source follower, with a cap (C11) in series with a resistor (R9) between its output and input.

Do you know the DC voltages at the Mosfet terminals in the Marshall?

How did you arrive at the 15Vrms requirement?

What is your actual application?

[GainFreak]

Do you know the DC voltages at the Mosfet terminals in the Marshall?

No but since C11 is rated at 63VDC I assumed no more than 50V which considering R11/R12 voltage divider means ~100VDC at the drain.

How did you arrive at the 15Vrms requirement?

What is your actual application?

The actual amp is Bogner Uberschall. As seen from the schematic the FB resistor is 10k which makes a voltage divider with the 4k7 tail resistor. Assuming max output of 100Watts (40V RMS at the 16 Ohm tap) that makes 12.8V at the tail so 15V RMS is to be on the safe side.

[vintagekiki]

Filter frequency is 141.45 Hz
C4 and C5 have too large a value for presence (10uF)

[Helmholtz]

The actual amp is Bogner Uberschall. As seen from the schematic the FB resistor is 10k which makes a voltage divider with the 4k7 tail resistor. Assuming max output of 100Watts (40V RMS at the 16 Ohm tap) that makes 12.8V at the tail so 15V RMS is to be on the safe side.

Are you sure the Bogner uses the 16 Ohm tap for NFB? Looks like the 4 Ohm tap in the drawing.

Also the LDR resistance of the opto adds to the 10k.

[vintagekiki]

#13
The actual amp is Bogner Uberschall.

About Bogner Uberschall

https://ampgarage.com/forum/viewtopic.php?t=18291
Bogner Uberschall schematic

https://guitarplayer.ru/equipment-craft/sobiraem-bogner-uberschall/
Bogner Uberschall