Sallen Key Low Pass Filter, bandpass filter

[bertus]

Hello,

Yes, insert the amplifier between the preamp and filter.
Use an other cap at the output of the amplifier.

Bertus

 

[Maglatron]

ok what are the numbers I should be looking at from the pre-amp just so you know the envelope detector works too

 

[Maglatron]

so for a gain of 5 what should the R1 and R2 be

 

[Maglatron]

Im just going to choose 1k for R1 and work it out I think,
R2 = 5k
is this good

 

[Maglatron]

so I have noticed that the envelope detector still envelops the smaller signal which I think is wrong red is output from the filter, green is after the pre-amp and before the amp and the dark blue is the envelope, surely it should be enveloping the red!!

the colour in the middle of the blue is actually green although it doesn't look it, it is the signal from the pre-amp the blue is after the amplifier are the numbers good? room for improvement?(bottom pic)

 

[Maglatron]

why is it enveloping the smaller signal??

 

[bertus]

Hello,

To much signal gets lost in the capacitors C15 and C17 at 45 Hz.
Increase the value to 10 uF and see the result.

Bertus

 

[Maglatron]

hmm, better! is this acceptable

 

[Maglatron]

so ok where do I connect the lm3914? its ok I've figured it, it peaks at 9v though so the lm3914 window is 2.4v what does this mean??

 

[bertus]

Hello,

The LM3914 circuit shows values between 6 and 8.4 Volts.

Bertus

 

[Maglatron]

Hello,

The LM3914 circuit shows values between 6 and 8.4 Volts.

Bertus

so I edit the amplifier?

 

[Maglatron]

the black box is not coming up when I press run

 

[bertus]

Hello,

Yes, You could change the amplifier to have a max output of 8.4 Volts.

Bertus

 

[Maglatron]

cool thats good I've run into a small problem my ltspice program is not showing the black box when I press run do you know how to fix?

 

[Maglatron]

so I've put it in the way the image was shown I put 1k for the Rx how do I get the black box back !!??

 

[bertus]

Hello,

What has changed since the last simulation?

Bertus

 

[Maglatron]

the black box won't appear but it's running in the bottom left corner without errors

 

[bertus]

Hello,

I seem not to have the LM3914 for the simulation.

Bertus

 

[Maglatron]

oh have you got the zzz collection?

 

[Maglatron]

For LTspice users. Libraries of models, examples, etc

For LTspice users. Libraries of models, examples, etc

bordodynov.ltwiki.org