Analog filters used with digital sampling/signal acquisition.

[Analog_Fan]

Nowadays, a web tool like Analog Devices Analog Filter Wizard or Texas Instruments Filter Design Tool, are the typical way to go if a quick solution is needed.

Used the Analog devices one.

set it up as low pass to 20Khz, would require unconventional resistors and capacitors values, i don't have at home, a lot more stages (but that's no problem).

9.7kΩ 0.1% (Vishay) https://nl.mouser.com/ProductDetail/Vishay-Dale/TNPW12069K70BEBD?qs=%2B4TWai3HcVp%2BXbmImfxA9Q==
(currently not available).

43.6kΩ (doesn't exist.)
8.36kΩ (doesn't exist.)

113kΩ 0.1% (Vishay) https://nl.mouser.com/ProductDetail...=sGAEpiMZZMtlubZbdhIBIGVQ/zJadjsEmCK2a/GSSN4=

5.56kΩ 0.1% (Vishay) https://nl.mouser.com/ProductDetail...GAEpiMZZMtlubZbdhIBICB2h%2BaJmJs0EsVZDyOHMgU=

169kΩ 0.1% (Bourns) https://nl.mouser.com/ProductDetail...=sGAEpiMZZMtlubZbdhIBICVtsFvKVwjkKF3TtUhPhck=

capacitor 40.6pF <--- doesn't exist.

: )

that's gonna be kinda complex
parallel resistor and capacitor to match the analog Devices Schematic?

 

[user 37518]

Used the Analog devices one.

set it up as low pass to 20Khz, would require unconventional resistors and capacitors values, i don't have at home, a lot more stages (but that's no problem).

9.7kΩ 0.1% (Vishay) https://nl.mouser.com/ProductDetail/Vishay-Dale/TNPW12069K70BEBD?qs=%2B4TWai3HcVp%2BXbmImfxA9Q==
(currently not available).

43.6kΩ (doesn't exist.)
8.36kΩ (doesn't exist.)

113kΩ 0.1% (Vishay) https://nl.mouser.com/ProductDetail/Vishay-Dale/TNPW0805113KBEEN?qs=sGAEpiMZZMtlubZbdhIBIGVQ/zJadjsEmCK2a/GSSN4=

5.56kΩ 0.1% (Vishay) https://nl.mouser.com/ProductDetail/Vishay-Dale/TNPW04025K56BEED?qs=sGAEpiMZZMtlubZbdhIBICB2h%2BaJmJs0EsVZDyOHMgU=

169kΩ 0.1% (Bourns) https://nl.mouser.com/ProductDetail/Bourns/CRT0805-BY-1693ELF?qs=sGAEpiMZZMtlubZbdhIBICVtsFvKVwjkKF3TtUhPhck=

capacitor 40.6pF <--- doesn't exist.

: )

that's gonna be kinda complex
parallel resistor and capacitor to match the analog Devices Schematic?

You can select in the tab "Tolerances" the component tolerance values, and the E series, you can select something like E12 for the capacitors and E24 for the resistors, 5% capacitors and 1% resistors will do fine. Don't select 0.1% resistors, you are not doing any precision work here, it is absolutely unnecessary.

 

[Analog_Fan]

You can select in the tab "Tolerances" the component tolerance values, and the E series, you can select something like E12 for the capacitors and E24 for the resistors, 5% capacitors and 1% resistors will do fine. Don't select 0.1% resistors, you are not doing any precision work here, it is absolutely unnecessary.

Indeed, Thanks.

accept for the 5K6, 120K, 180K resistor, i got all accept the capacitors.

Awesome.

(i didn't select 0.1% in mouser, that's what showed up.)

 

[user 37518]

accept for the 5K6, 120K, 180K resistor, i got all accept the capacitors.

I accept your offer

 

[ccaudle]

that's gonna be kinda complex

Then just start out with a 2nd order filter, one op-amp, two capacitors, two resistors.

Once you have the hardware in place, some of the techniques used for direct digital synthesis could be used in the software.
DDS whitepaper at Digi-Key
DDS web page at Analog Devices
Fundamentals of DDS whitepaper at Analog Devices

 

[Analog_Fan]

Then just start out with a 2nd order filter, one op-amp, two capacitors, two resistors.

Once you have the hardware in place, some of the techniques used for direct digital synthesis could be used in the software.
DDS whitepaper at Digi-Key
DDS web page at Analog Devices
Fundamentals of DDS whitepaper at Analog Devices

I have to make an order at mouser anyway for the 74HC574.
i got quite a gap to reach 50€ for free shipping.

no the question is, the audio output.

normally i deal with eurorack modules and bi-polar voltages, the audio is pretty much automatically centered.

now i wanna feed the audio in the desktop (for recording) or pc speakers.
Now, uni polar supply and i got no way to center it.

Any advice on that?

 

[user 37518]

I have to make an order at mouser anyway for the 74HC574.
i got quite a gap to reach 50€ for free shipping.

no the question is, the audio output.

normally i deal with eurorack modules and bi-polar voltages, the audio is pretty much automatically centered.

now i wanna feed the audio in the desktop (for recording) or pc speakers.
Now, uni polar supply and i got no way to center it.

Any advice on that?

Voltage divider and capacitor at the input?

 

[user 37518]

Indeed, Thanks.

accept for the 5K6, 120K, 180K resistor, i got all accept the capacitors.

Awesome.

(i didn't select 0.1% in mouser, that's what showed up.)

Do you really need a 7th order filter? In any case, go all the way to 8th order, it will use the same amount of op-amps, just add an extra capacitor and a couple extra resistors.

 

[ccaudle]

normally i deal with eurorack modules and bi-polar voltages, the audio is pretty much automatically centered.

now i wanna feed the audio in the desktop (for recording) or pc speakers.
Now, uni polar supply and i got no way to center it.

IC7A in that drawing has no DC path to the non-inverting input, so cannot operate properly. With bipolar supplies to the op-amps you would just need to add a resistor to ground between the series capacitor and the op-amp non-inverting input (between C1 and R6). That will reference the input to ground with bipolar supplies, so is all you need.
If you wanted to use only a single voltage for the op-amps as well you would need to use two resistors, one from power supply to op-amp input, and one from op-amp input to ground, to form a voltage divider providing a voltage at half the power supply voltage. That will reference the input to half of the supply voltage, so will need a capacitor on the output in order to prevent sending DC voltage to the next device.

 

[Analog_Fan]

Voltage divider and capacitor at the input?

the dac will swing between 0.1x or so and not quite 5 volt.
the opamp is a standard TL074 (i could opt for MCP6004, rail-to-rail input and output, i got at hand), uni-polar powered and doesn't reach 5V, the 5 volts will be coming from the USB cable powering the Microchip Fubarino, it has a tapping point to get the 5 Volt.
I might need to throttle it a bit.

the capacitor at input, is something i always do in my modules when regarding audio.

 

[Analog_Fan]

Do you really need a 7th order filter? In any case, go all the way to 8th order, it will use the same amount of op-amps, just add an extra capacitor and a couple extra resistors.

Thank you, did not considered that, just looked at the slope of the "suggested" Butterworth filter and some of the previous version as the fastest version.
The slopes of the previous version showed some ripples, the 7th order a smooth line overall and slope.

will use the 8th order.

 

[Analog_Fan]

If you wanted to use only a single voltage for the op-amps as well you would need to use two resistors, one from power supply to op-amp input, and one from op-amp input to ground, to form a voltage divider providing a voltage at half the power supply voltage. That will reference the input to half of the supply voltage, so will need a capacitor on the output in order to prevent sending DC voltage to the next device.

Yeah, that's how i started when updating the schematic for the new filter, with a voltage divider, like they did in guitar pedals, but moved it out of view in the previous screenshot.
Will be sourcing the 5 volt from the USB cable from the micro controller I'm using, provides a tapping point.
Adding it to my modular will a pcb version 2.

Will this solve the "center point" issue for the pc onboard sound card or pc speakers?

 

[ccaudle]

Will this solve the "center point" issue for the pc onboard sound card or pc speakers?

Yes, that the usual way to do it. The total input impedance seen by the next stage is the parallel value of the two resistors, so with two 5K resistors that will be 2.5K. Using two 10k or 20k resistors would be more common in order to reduce the load which the previous stage much drive.

 

[Analog_Fan]

Yes, that the usual way to do it. The total input impedance seen by the next stage is the parallel value of the two resistors, so with two 5K resistors that will be 2.5K. Using two 10k or 20k resistors would be more common in order to reduce the load which the previous stage much drive.

ok, will increase them.
I got 10k, 12K, 15K, 22K.

Thank you.

 

[user 37518]

With Sallen-Key filters it is not wise to use high valued resistors, because of common mode distortion. But I think you are using MFB filters, so it should be ok.

 

[Analog_Fan]

With Sallen-Key filters it is not wise to use high valued resistors, because of common mode distortion. But I think you are using MFB filters, so it should be ok.

the resistor for the voltage rail divider to center the input.
Not the suggested resistors by Analog Devices.

i found this very interesting IC to create a 15V bipolar voltage source from 5V.
lm2577

https://www.ti.com/lit/ds/symlink/lm2577.pdf
But the suggested transformers in the datasheet.

Pulse PE-65300
Impuls transformator THT Flyback Xfmr 100uH .45Ohms
https://nl.mouser.com/ProductDetail/Pulse-Electronics/PE-65300?qs=dK9pu4bAtj1p1YAIExfgAw==Pulse PE-65302
Impuls transformator THT Flyback Xfmr 400uH .26Ohms
https://nl.mouser.com/ProductDetail/Pulse-Electronics/PE-65302?qs=dK9pu4bAtj0JGF7tEQpOxw==
Are "End of Life" and no more available.

both are indicated as:
Producttype: Audio & Signal Transformers

Because there is a Ocean of transformers at mouser, not sure what the correct type would be.
Would like to give it a try.