High pass filter with switchable slopes

I am thinking about a high pass filter with switchable slopes, for example 6 dB/oct and 12 dB/oct.
Of course with a minimal number of components...
My question: would a circuit as in the attachment be good enough for this, or are there better options?
(P1 and P2 are ganged.)

(re-)read the section on HPF by Steve Dove/Studio Sound, the basic topology seems to be optimal, but needs alittle gain for
best curve. You can also  get -18dB/oct and -24dB/oct out of that opamp!

EDIT: added schematic, sort out c18/c19 1pole, short out c3:2 pole switch open 3pole
I like the Shure Ksm141 hp, it´s 3pole with low cutoff and 1pole with higher cutof...

Interesting. But...where do I find that article?

Ok I guess it is most interesting if you want a freq pot and need equal component values, the article is in the front end chapter (12 I think)https://tinyurl.com/ya2u8mxj

This design made me think that is must be pretty simple; in this filter a single 5532 is used for both filter sections.

RuudNL said:

I am thinking about a high pass filter with switchable slopes, for example 6 dB/oct and 12 dB/oct.
Of course with a minimal number of components...
My question: would a circuit as in the attachment be good enough for this, or are there better options?
(P1 and P2 are ganged.)

Click to expand...

The circuit you provided does switch between 6dB and 12dB slope, however Q will vary with the pot setting, if you want a Butterworth response, the feedback resistance should be half the value of the resistance shunted to ground, if you use a ganged pot with the same values, this 0.5:1 ratio will not hold and Q will vary whilst sweeping the frequency, so you would need a ganged pot with different values, perhaps Im missing something on your circuit? how were you planning on keeping constant Q?

A better approach is using a circuit with gain rather than unity gain like yours, if you use gain, then Q is determined by the gain of the circuit by the following formula Q=1/(3-K) were K is the gain of the filter, this way you can set the gain to 1.59 (for Butterworth response) and have the same value resistors for the feedback and shunt arm, the gain will no longer be unity thou.

The biggest problem is to obtain a ganged pot with different values...
However: I see a lot of commercial filters with a standard dual pot.
Like the one in the picture, that uses unity gain.

I found that some pots are easy to disassemble and mix with other values tapers. maybe hard if you want to produce a lot of them but for one it could work.

Omeg have done custom dual-gang pots for me before, where each gang is a different value (47k and 4k7 revlog, in my case) - pretty reasonably priced for a custom part at less than £8 each inc VAT and shipping, so may be worth investigating if you want to go down that road. Minimum order is 10 pots I think.

https://www.omeg.co.uk

Andy

RuudNL said:

The biggest problem is to obtain a ganged pot with different values...
However: I see a lot of commercial filters with a standard dual pot.
Like the one in the picture, that uses unity gain.

Click to expand...

Using same value pots with the unity gain circuit will achieve a Q = 0.5, which is a bit shallow for my taste.  I still think that the Sallen-Key with gain is the way to go if you want a Butterworth response, why going through all the trouble of using different pots if you can add a couple of resistors and use a standard pot, plus we are talking about a gain of 1.59, thats 4dB if you are using a Butterworth response which does reduce headroom but has a sharper roll-off near the cutoff frequency.

Thank you. I think this is the best solution!

I use this one.
http://sim.okawa-denshi.jp/en/OPseikiHikeisan.htm

TwentyTrees said:

Omeg have done custom dual-gang pots for me before, where each gang is a different value (47k and 4k7 revlog, in my case) - pretty reasonably priced for a custom part at less than £8 each inc VAT and shipping, so may be worth investigating if you want to go down that road. Minimum order is 10 pots I think.

https://www.omeg.co.uk

Andy

Click to expand...

That is not that expensive actually! Thanks for the info.

On the other hand the LP/HP combo in the drawmer noise gate is as simple as it gets (equal component values, no gain), and I always find it really useful...(bottom of schematic)
http://photobucket.com/gallery/user/StephenGiles/media/bWVkaWFJZDo3NzU1MDExNQ==/?ref=

TwentyTrees said:

Omeg have done custom dual-gang pots for me before, where each gang is a different value (47k and 4k7 revlog, in my case) - pretty reasonably priced for a custom part at less than £8 each inc VAT and shipping, so may be worth investigating if you want to go down that road. Minimum order is 10 pots I think.

https://www.omeg.co.uk

Andy

Click to expand...

Do they also make plastic conductive or only carbon? And if so, has anyone tried them? How's the feel? Too smooth?

Tekay said:

I use this one.
http://sim.okawa-denshi.jp/en/OPseikiHikeisan.htm

Click to expand...

Thanks Thomas. (By the way: I am still very happy with your BC1-S!)

L´Andratté said:

On the other hand the LP/HP combo in the drawmer noise gate is as simple as it gets (equal component values, no gain), and I always find it really useful...(bottom of schematic)
http://photobucket.com/gallery/user/StephenGiles/media/bWVkaWFJZDo3NzU1MDExNQ==/?ref=

Click to expand...

Yes, if a Q of 0.5 is enough that filter will suffice, for more surgical stuff you really need higher Q and steeper roll-off for that matter. The interesting thing about the circuit schematic you posted is that there's a low-pass and a high-pass but both have different Q's, the low pass seems to be working as a Butterworth with Q=0.707 whilst the high-pass has Q = 0.5

I think they only do conductive plastic - the website should say, and they’re very helpful. The P16s I got feel okay to me, not light but not too stiff.

warpie said:

Do they also make plastic conductive or only carbon? And if so, has anyone tried them? How's the feel? Too smooth?

Click to expand...