Variable HPF Kit

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SamS
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Joined: Wed Feb 15, 2023 7:10 pm

Variable HPF Kit

Post by SamS »

Just looking to confirm the component changes to for the 1meg input impedance and the 22hz-220hz frequency range.

Is it just R4 - 1meg and both C1,C2 - 100nf?

Any other build details available?

Thanks

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Joe Malone
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Re: Variable HPF Kit

Post by Joe Malone »

SamS wrote:
Wed Mar 29, 2023 9:25 am
Just looking to confirm the component changes to for the 1meg input impedance and the 22hz-220hz frequency range.

Is it just R4 - 1meg and both C1,C2 - 100nf?

Any other build details available?

Thanks
For 1Meg in yes change R4 to 1Meg and use fet input opamp type like TLO72 etc

For 22-220hz use 220nF for C1 & C2. Make these caps larger to move the frequency range down.

Depends on the -dB point used as the roll-off reference point for the frequency.

Some users like the 220nF in parellel with 100nF or 330nF for C1 & C2

Feel free to ask any questions you have here
Joe :-)
JLM Audio
Capturing Audio without Injury

SamS
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Joined: Wed Feb 15, 2023 7:10 pm

Re: Variable HPF Kit

Post by SamS »

Thanks for clarifying that, I think maybe the cap values in the product information on web store are around the other way.

ofoot
Posts: 3
Joined: Thu Jun 01, 2023 4:21 am

Re: Variable HPF Kit

Post by ofoot »

So I'm a bit of a newbie to this so I apologize if I sound way out of my depth here.

I would love to make a stereo HPF and was wondering a few things before buying a few:

1) Is the 0V connection for the Sleeve of a T/S wire? I assume I'd connect both sleeves of the Input and Output wires?

2) Because this a TL072, could I just use the V+/V- of a standard 9V power supply found on guitar pedals, or would I need the full listed 18/36V difference? I've done other projects with the chip and standard 9V power worked fine.

3) is the potentiometer a 3-pin or 6-pin?

Thank you so much and thank you for making this amazing package!

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Joe Malone
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Re: Variable HPF Kit

Post by Joe Malone »

ofoot wrote:
Thu Jun 01, 2023 11:39 am
So I'm a bit of a newbie to this so I apologize if I sound way out of my depth here.

I would love to make a stereo HPF and was wondering a few things before buying a few:

1) Is the 0V connection for the Sleeve of a T/S wire? I assume I'd connect both sleeves of the Input and Output wires?
Yes both sleeves should be connected to 0v power supply common
2) Because this a TL072, could I just use the V+/V- of a standard 9V power supply found on guitar pedals, or would I need the full listed 18/36V difference? I've done other projects with the chip and standard 9V power worked fine.
9v is a bit low for a TL072 opamp but some will run on that but you need to make a rail splitter with 2 x 4.7v zeners to make +/-4.5v as this kit need 2 voltage rails + and -. This low voltage will limit headroom a lot. Ideally, you could use 2 x 9v batteries to make +/-9v rails which would run on fine.

3) is the potentiometer a 3-pin or 6-pin?
6 pin dual 20k reverse log pot
Thank you so much and thank you for making this amazing package!
8) :lol:
Joe :-)
JLM Audio
Capturing Audio without Injury

ofoot
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Re: Variable HPF Kit

Post by ofoot »

Would this DC/DC converter fit the bill? Seems to fit the voltage spec of the OP-amp and avoid the need to reinvent the wheel(also Im terrified of working on power). I think this would help a lot of other people. Thanks!

https://www.ebay.com/itm/172751512784?h ... R9SawMuOYg

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Joe Malone
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Re: Variable HPF Kit

Post by Joe Malone »

ofoot wrote:
Fri Jun 02, 2023 6:20 am
Would this DC/DC converter fit the bill? Seems to fit the voltage spec of the OP-amp and avoid the need to reinvent the wheel(also Im terrified of working on power). I think this would help a lot of other people. Thanks!
While it would power it. It is also way overkill and likely to inject lots of noise in the audio spectrum making the HPF useless. It is a symmetrical design so Opamp may cancel most of the noise but impossible to say without trying one.
Joe :-)
JLM Audio
Capturing Audio without Injury

ofoot
Posts: 3
Joined: Thu Jun 01, 2023 4:21 am

Re: Variable HPF Kit

Post by ofoot »

So I found a more appropriate PSU that converts 2-pin 12V to +12/0/-12V(massive ebay link below) and the filter works! It sounds great!

However I was wondering if you have the P/N of the older smaller caps on the previous BOM as I would like to have a higher cutoff.

I'll also experiment with a smaller pot value like 10k or something if I can find the right ones.

For anyone reading this, I am going to try to use the dedicated pin-outs at the very edge of this eurorack power supply as that is where +12/0/-12 are most common in synths: https://www.thonk.co.uk/shop/fc-power-kit/

This power supply worked with a 12V DC power wallwart, but gave me only +/-10V because I routed the power to the remote start as well. https://www.ebay.com/itm/172751512784?_ ... %7Ciid%3A1

Thank you all and I'll compile a github link or something to put everything in one place with pictures such.

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