MPP preamp is vastly improvable

[dbanner]

Brilliant. So much effort for perfection of front end. Nobody care about bumblebee tick tick sound at the other end.
The best improvement for MPP would be a smooth audio.

[green]

Yes. Simulation file in the attached zip.

thanks

[Teleno]

Are you charting TP3 reply#4? What did you use for coil inductance and capacitance?

Yes. Simulation file in the attached zip.

[green]

This is the modded MMP with the same coil on 1us and 0.5us targets:



Tried the autoswitch already, it doesn't get even close to seeing the targets.

Are you charting TP3 reply#4? What did you use for coil inductance and capacitance?

[Teleno]

We could name this version as "MPP Gold"

The timing logic will have to be modded to allow 5us dampling delays or even less.

[eclipse]

Ouch didn't expect that. Thanks for the feedback on this I was going to try it it on a real board.

[Teleno]

This is the modded MMP with the same coil on 1us and 0.5us targets:



Tried the autoswitch already, it doesn't get even close to seeing the targets.

[eclipse]

[Teleno]

Is it not time to also start removing the 1K input resistor (moodz auto blocking mosfet) or it will be too much improvements.

The 1K input resistor is absolutely necessary and is part of the damping resistor (in parallel with R1, to be determined by the user according to the coil).

You can try to make it work with a blocking MOSFET but I can tell you that biasing it requires control (variable with temp.) and the signal will be underdamped at the end of the transient. Plus it adds 800pF to 10nF "improvement" capacitance to the coil. I'm just trying to make the best of the MPP while keeping it simple.

[Teleno]

Great contribution Teleno, thank you.

What sort of image is hidden here (not visible for me):

It was the relevant section in the MPP which you can see in the post that followed. Somehow it got deleted by chance.

[eclipse]

Is it not time to also start removing the 1K input resistor (moodz auto blocking mosfet) or it will be too much improvements.

[WM6]

Great contribution Teleno, thank you.

What sort of image is hidden here (not visible for me):

[Teleno]

I made a mistake, U2b should be non-inverting.

[Teleno]

A modified preamp + integrator.

The EF is in fact an offset to the input, so instead of a differential integrator we can cancel the offset at the preamp (bye bye to matched components!). JFET op amps required for doing this (TLC081/082 recommended as U3a,b and U11).
U2a,b should be low noise, high slew rate and ample phase margin (unity gain stable). The LM4562 foots the bill. Do not use NE5532 because it's not stable enough at low gain.
The clamp diode D12 is necessary to achieve virtual ground as fast as possible.
C4 may even not be necessary, since offsets are cancelled by Q3 and the TLC08x parts have very low offset.




The relevant section in the MPP is the following:

[Teleno]

Proposed preamplifier:



The first stage quickly establishes the virtual ground, solving the problem.

R2 can be increased up to 3K, in which case R11 = 18K and R1 = 17K in order to achive a 1000 x gain. This way the bandwidth increases by 70% (from 200KHz to 350KHz).

Though TLC081 has been used in the sim, any unity-gain stable op amp with noise < 4nv,slew rate > 13V/us and BW >= 10MHz can be used instead, as long as it can operate with +-5V.