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Sallen Key Low Pass Filter, bandpass filter

Harald Kapp

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I have a ryzen 5 5000 series with 48GB of ram
I count that as an already fast machine.
Ive been told that AMD is no good
That's imho crap. AMD would not have such a market share if they weren't good.
Btw: The 64 bit PC architecture as it exists today has been to a good part defined by AMD with Intel only being second.

because I wanted to play a tune and see the filters working with the music,
Then build the real thing.
 

Maglatron

Jul 12, 2023
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planning on building it soon, just waiting on a couple more bits and pieces, trying to cover absolutly everything that I can without actually building, the parts may arrive before the 20th but it's christmas so i'm expecting after christmas maybe early jan got the bar graph LED's the LM314's the TL074's, resistors, mic, pots. I am awaiting the film capacitors and some more proto-board otherwise I'm all set!
 

Maglatron

Jul 12, 2023
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Can I use the same model of the envelope detector, ie, the BAT43 and the 100nF cap and the 1Meg resistor, (just checked 7000Hz and it works like a dream, so I'm nearly done here and I shall build it;
just simulated the highest frequency and changed the variable resistor R23 to 1k also, I'm not sure about this, hence asking, the outoffilter signal is amplified from the B4filter and I thought that there was no gain in this design, whats with that? 1702486685606.png1702485926697.png
 

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Maglatron

Jul 12, 2023
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wait a minute if I'm not supposed to be changing the R23 resistor because its before the amp and I'm only making one of those but then when run with the 165k the 7000Hz tops out at 10.5V!1702488446323.png
 

bertus

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Nov 8, 2019
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Hello,

Do you still use the attenuator at the source?
The gain at higher frequencies can be caused by in series with R13, the 22 uF capacitor C14.
Also C15 and C17 of the amplifier are frequency dependend.
Try to adjust the 45 Hz version for max output by raising the value of C15 and C17.
Also have a look at the value of C14.

Bertus
 

Maglatron

Jul 12, 2023
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Hello,

Do you still use the attenuator at the source?
The gain at higher frequencies can be caused by in series with R13, the 22 uF capacitor C14.
Also C15 and C17 of the amplifier are frequency dependend.
Try to adjust the 45 Hz version for max output by raising the value of C15 and C17.
Also have a look at the value of C14.

Bertus
So I'm looking at it but not sure what I'm looking at I'll open the 45Hz version like you said and do I raise them in stages of 5 do these two caps C15 C17 have to be equal??
1702489242896.png
 

bertus

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Hello,

Yes, the values of C15 and C17 need to be the same to have the same effect on the frequency.
I see an other solution, Raise R20 to 100K and R21 to 500K and see the effect.
The capacitors would have less prone effect on the frequency in that case.

Bertus
 

Maglatron

Jul 12, 2023
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Hello,

Yes, the values of C15 and C17 need to be the same to have the same effect on the frequency.
I see an other solution, Raise R20 to 100K and R21 to 500K and see the effect.
The capacitors would have less prone effect on the frequency in that case.

Bertus
what and then run both the 45Hz and 7000Hz and look at them?
 

bertus

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Hello,

Yes, that way you can see the effect on low and high frequency.

Bertus
 

Maglatron

Jul 12, 2023
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actually much much better just need a tiny bit more, needs to come down about another half volt but on the other hand it is NOT clipping so this is goood, no I take that back that was before the filter after the filter there is still massive gain just to clarify this is the setup for all af the filters passband = centre / 4 stopband 2 x centre1702491489484.png
 

Maglatron

Jul 12, 2023
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so I have not tried changing the R13 or cap C14 yet any suggestions as to what I should set these at to change the outcome, I tried 1uf and 2200uf and there is no major difference to be honest
 
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Maglatron

Jul 12, 2023
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They both centre about 0volts the signals are from the signal generators and are in green!!1702494174069.png
 
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Maglatron

Jul 12, 2023
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the 45Hz one out of the sig gen is at the top 46millivolt the 7000Hz one out of it's sig gen it 76millivolt And I think this is the culprit
 

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Maglatron

Jul 12, 2023
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Hello,

Do you still use the attenuator at the source?
The gain at higher frequencies can be caused by in series with R13, the 22 uF capacitor C14.
Also C15 and C17 of the amplifier are frequency dependend.
Try to adjust the 45 Hz version for max output by raising the value of C15 and C17.
Also have a look at the value of C14.

Bertus
what do you mean by in series with (R13 and 22uF, C14)
 

bertus

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Nov 8, 2019
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Hello,

Now you have R13 at 4K7 and R23 at 165K.
Change that to R13 at 27K and R23 to 1Meg and see what happens with 45 Hz and 7000 Hz.
With those values C14 will have a factor of 6 less influence on the frequency dependend gain.

Bertus
 
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