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Looking for a Low-Pass Filter with a Q or Peak control (State-Variable Filter)

600 Ohms

600 Ohms

Supporting Member
Jan 4, 2012
2,059
3,273
#1
What I want is basically an envelope filter where you can turn off the sweep.

The Alembic Superfilter rack mount preamp does this, as does Alembic's Series I and II electronics. I want a pedal that reproduces this effect.

I've been using a 3Leaf Proton in a funny way, by turning the PEAK control all the way off and the DECAY knob all the way up, then I set the frequency where I want the high end of the bass to cut off. This has the effect of acting like a hard roll-off but with a hard shoulder and a slight peak at the cutoff frequency. In this way, it sweeps but not very much. I'd love a pedal that let's you set this and it doesn't move.

The difference between what I'm after and turning the tone knob down on the bass is the curve of the roll-off. A passive Tone is way too gentle a slope. I'm looking for the hard, brutal slope you get in an envelope filter, plus the narrow Q.

I suppose a Source Audio EQ could do this, and that might be an idea, but I'd like to find an analog way to do this.
 
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#4
davelowell2 said:
Broughton State Variable Filter
or
Resonant Filter Equalizer
or
Musikding Pro Filter kit
or
Audiofab Frequency Distiller
Click to expand...
Wow, check you out.

Screenshot 2025-07-31 at 13.32.36.jpg
 
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#5
You can build just about any onboard “filter preamp” (JTEX, Underhill, Lusithand, ACG/East, etc.) into a pedal enclosure pretty easily if you are reasonably DIY capable. I have an open source non commercial solution on GitHub too, but it requires hand soldering surface mount components and is a lot more work.
 
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#6
Passinwind said:
You can build just about any onboard “filter preamp” (JTEX, Underhill, Lusithand, ACG/East, etc.) into a pedal enclosure pretty easily if you are reasonably DIY capable. I have an open non commercial solution on GitHub too, but it requires hand soldering surface mount components and is a lot more work.
Click to expand...
I can solder; this might be a good option.
 
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#7
As @Passinwind suggests, I have successfully put a handful of onboard filter pres into pedal boxes over the years. I currently have a Lusithand NFP filter in a box and it's a great one knob option (love the push/pull Q boost). The JTex filter is also great, with an external switch rather than the push-pull for three Q-boost levels and I briefly had one in a box as well as an ACG EQ-02 and a Boogieman Alembic clone. I also have a Broughton RFE which is a great all-around option (for whatever reason I prefer the tone of the Lusithand for just basic LPF, it seems a bit more aggressive- which may be a headroom "issue" that works out in my benefit! It can be run at 18V though if you want the added clean headroom).

If you want maximum versatility, the recently-released Audiofab Frequency Distiller looks like a killer dual-channel pedal-sized Alembic SF-alike.
 
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#10
600 Ohms said:
What I want is basically an envelope filter where you can turn off the sweep.

The Alembic Superfilter rack mount preamp does this, as does Alembic's Series I and II electronics. I want a pedal that reproduces this effect.

I've been using a 3Leaf Proton in a funny way, by turning the PEAK control all the way off and the DECAY knob all the way up, then I set the frequency where I want the high end of the bass to cut off. This has the effect of acting like a hard roll-off but with a hard shoulder and a slight peak at the cutoff frequency. In this way, it sweeps but not very much. I'd love a pedal that let's you set this and it doesn't move.

The difference between what I'm after and turning the tone knob down on the bass is the curve of the roll-off. A passive Tone is way too gentle a slope. I'm looking for the hard, brutal slope you get in an envelope filter, plus the narrow Q.

I suppose a Source Audio EQ could do this, and that might be an idea, but I'd like to find an analog way to do this.
Click to expand...
Not to derail this thread, but that’s a cool way to use the Proton. I wound up selling mine from a fairly recent batch, but have been regretting it and plan on getting another on the next release. I’ll have to give this a try!
 
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#12
jmattis said:
Not to derail this thread, but that’s a cool way to use the Proton. I wound up selling mine from a fairly recent batch, but have been regretting it and plan on getting another on the next release. I’ll have to give this a try!
Click to expand...
Starts with the straight sound of my active J bass then changes every 4 bars. The freq knob is around 11:30 to noon, but it sounds great across the range. This is what led me here. It’s really nice to limit the extended high end in this way.

 
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#13
Passinwind said:
You can build just about any onboard “filter preamp” (JTEX, Underhill, Lusithand, ACG/East, etc.) into a pedal enclosure pretty easily if you are reasonably DIY capable. I have an open source non commercial solution on GitHub too, but it requires hand soldering surface mount components and is a lot more work.
Click to expand...
I thought Lusithand already offered it in pedal format?
 
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#15
Passinwind said:
You can build just about any onboard “filter preamp” (JTEX, Underhill, Lusithand, ACG/East, etc.) into a pedal enclosure pretty easily if you are reasonably DIY capable
Click to expand...

sunbeast said:
As @Passinwind suggests, I have successfully put a handful of onboard filter pres into pedal boxes over the years
Click to expand...
Not to derail this thread, but do you have any docs or instructions on doing this? I have two brand new Jtex filters that I don't have a home for, and was thinking about either putting them in a stand alone box or adding them to a distortion or fuzz circuit. Anything helps!
 
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#16
moon-bass said:
Not to derail this thread, but do you have any docs or instructions on doing this? I have two brand new Jtex filters that I don't have a home for, and was thinking about either putting them in a stand alone box or adding them to a distortion or fuzz circuit. Anything helps!
Click to expand...
It wouldn't derail it, it would be genuinely helpful. I'd love to know for example how to connect a 9V plug to avoid battery use into a Hammond enclosure. If you took a simple circuit, like a Distiller, I'm imagining:

1. TS jack input (but how to wire to the card? There are too many wires)
2. Need two holes, one for frequency and the other for the switch
3. Standard 9V socket
4. TS jack output

But I've never done this before. It's within my capabilities, just need the instructions.
 
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#17
600 Ohms said:
It's within my capabilities, just need the instructions.
Click to expand...
Me, too…. I guess I could find out with a breadboard but I don’t have a Jtex preamp.

Edit—- actually, it shows on the board where everything goes. I’ll give it a shot @moon-bass if you want to send one to me and you trust me…
 
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#18
600 Ohms said:
It wouldn't derail it, it would be genuinely helpful. I'd love to know for example how to connect a 9V plug to avoid battery use into a Hammond enclosure. If you took a simple circuit, like a Distiller, I'm imagining:

1. TS jack input (but how to wire to the card? There are too many wires)
2. Need two holes, one for frequency and the other for the switch
3. Standard 9V socket
4. TS jack output

But I've never done this before. It's within my capabilities, just need the instructions.
Click to expand...
@Jerry Catanescu
 
#20
moon-bass said:
Not to derail this thread, but do you have any docs or instructions on doing this? I have two brand new Jtex filters that I don't have a home for, and was thinking about either putting them in a stand alone box or adding them to a distortion or fuzz circuit. Anything helps!
Click to expand...
It's super simple- just replace the input connections with an input jack's connections and the output connections with an output jack's connections. You can hook all the grounds together (just make sure you have a ground attached to the preamp). If you want to use pedalboard 9V power instead of a battery, just make sure you get the + and - connections right to the preamp (standard pedal power is center-negative). Depending on the power supply though, know that you will potentially experience a higher noise floor than when powered with a battery (battery power will always be the cleanest, though a nice isolated power supply should be fine). If you want a battery, then use a TRS jack for the input and wire it the same way you'd wire the output jack on an active bass (so that the battery - goes to the ring connection of the TRS jack and is only sent to ground and completing the circuit with a jack plugged into the input). If you want a battery AND 9V pedal power options then use the typical switching pedal power jack wired to bypass the battery when there is a jack plugged into the 9V input. If you want a bypass stomp footswitch and LED then it gets a bit more complicated to describe, personally I have done both and don't really use the footswitch. there are countless diagrams on the net on how to wire a basic bypass footswitch and LED. If you want a volume control, then I'd recommend adding a 10-25K ohm audio taper one between the output of the pre and the output jack.
 
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