CrossOver Filter

Carl Hungus · Post by **Carl Hungus** » Sat Sep 26, 2015 10:56 am

Hey Tom

Starting to wish I grabbed this instead of a PEQ, ha. When's the next batch?

Cheers!

BugBrand · Post by **BugBrand** » Sat Sep 26, 2015 1:22 pm

I've got plenty more boards and, in fact, 3 done up just needing cases & final testing, so I could whip one out very easily next week - I just haven't done more of these up because they've been such a slow burner..
So, yeah, ping me an email and I can sort easy!

soup · Post by **soup** » Mon Nov 16, 2015 5:48 pm

What started as an ongoing desire to modulate cutoff and use the internal bandpass modulation has led to ... a desktop cofilter expander

drwiener · Post by **drwiener** » Mon Nov 16, 2015 5:51 pm

soup wrote:What started as an ongoing desire to modulate cutoff and use the internal bandpass modulation has led to ... a desktop cofilter expander

BugBrand · Post by **BugBrand** » Tue Nov 17, 2015 4:08 am

Nice! So, using the extra CV inputs on the front bananas & taking the direct filter outs from the jacks, right?

soup · Post by **soup** » Tue Nov 17, 2015 1:01 pm

BugBrand wrote:Nice! So, using the extra CV inputs on the front bananas & taking the direct filter outs from the jacks, right?

Exactly, with the switches toggling which filter response is sent to the outs. Thanks for making it so easy!

harlequin · Post by **harlequin** » Wed Dec 02, 2015 5:25 am

So... someone has got to be using one of these as a phaser?? Flip polarity on one or two bands and modulate the cutoff?

Haven't got one but after reading - seemed an obvious application for a neat unit!

BugBrand · Post by **BugBrand** » Wed Dec 02, 2015 5:47 am

Kind of -- I've not been playing with the phase switches much still, but asimple application I've been using is to keep all three bands turned up about the same, then modulate cutoffs and have a bit of resonance. It isn't really phasing as such, but gives lovely resonant swirly additions!

I've only just got the studio re-jig roughly to a point to play - I should now get on with taking the different band outputs and feeding them to different post-processors - daresay phase switches could be extra useful there.

Post by **Paranormal Patroler** » Mon Mar 13, 2017 6:50 am

So after an email exchange with Tom and some fair time studying the schematic is seems that in order to use the extra inputs of the COF you'd need extra preamps to match the required modular levels. In addition to that the BP outputs from the original design (not the expansion part) don't seem to be leading anywhere, so I'm curious, what is exactly output at the BP? Obviously it's a band at the Cutoff frequency of each filter, but is it's size controlled by the Q ? If not, what are their purpose in either Serial or Parallel use?

As per the schematic they're never used (I might be reading this the wrong way) and since there is one frequency knob per filter I'd like to know how the BP band is determined.

Also, does the internal normalization (LP > BP > HP) apply for the expanders as well?

Obviously I'm looking to get on COF and use it in stereo, using the parallel functionality, but it seems one is forced to buy two COF for that purpose.

soup · Post by **soup** » Mon Mar 13, 2017 12:58 pm

Paranormal Patroler wrote:So after an email exchange with Tom and some fair time studying the schematic is seems that in order to use the extra inputs of the COF you'd need extra preamps to match the required modular levels. In addition to that the BP outputs from the original design (not the expansion part) don't seem to be leading anywhere, so I'm curious, what is exactly output at the BP? Obviously it's a band at the Cutoff frequency of each filter, but is it's size controlled by the Q ? If not, what are their purpose in either Serial or Parallel use?

As per the schematic they're never used (I might be reading this the wrong way) and since there is one frequency knob per filter I'd like to know how the BP band is determined.

Also, does the internal normalization (LP > BP > HP) apply for the expanders as well?

Obviously I'm looking to get on COF and use it in stereo, using the parallel functionality, but it seems one is forced to buy two COF for that purpose.

I don't have an official expander but theoretically mine should work the same ...

The COFilter expansion ins/outs work fine at line level. The BP output is exactly what you would think and the Q knob changes the Q. Without an expander the BP output is only available a mod source. There is no normalization with an expander it's just allows you to use the 2 filters inside the COFilter as 2 independent filters.

I'd love a stereo COFilter and have mentioned it here but think running 2 in quasi stereo would be a soup sandwich.

BugBrand · Post by **BugBrand** » Mon Mar 13, 2017 2:36 pm

There are two 12dB State Variable filters - standard fair in my work - always with Low/Band/High outputs possible.

As soup notes, the BP is fed to self-modulate the Cutoff.

I termed the unit sections Low/Mid/High to differentiate from the State Variable terminology (Low/Band/High-pass).

In serial mode, first filter gives Low-pass output and passes on to 2nd filter.
2nd filter gives Mid band (highpass in first filter, lowpass in 2nd) and High band.

In parallel mode, first filter again gives Lowpass. 2nd filter gives LowPass (instead of Mid) and HighPass.

The unit has a simple/standard preamp to bring external signals up to typical modular levels (+/-5V). The expander offers a direct input to the filter stages, along with direct outputs and an extra CV input per filter. You should generally then switch the mode to Parallel (so the filters are completely independent)

Post by **Paranormal Patroler** » Mon Mar 13, 2017 3:14 pm

Thank you Tom and soup. I understand how the Mid band is created in Series. I'm just not sure how the BP is defined when the two filters work in parallel, since each one has only one cutoff control. Does that specific value define the band and thus each BP is of a fixed width? I mean, there's no way to change the size of the BP when the filters work in parallel, right?

I would personally love to have the band outputs and be able to cut a stereo signal in three distinct sections and have them fed to other devices. I tried my best to see if this version of the COF would do this but it seems having stereo requirements is trying to make the design into something that it isn't. I will add my voice to the choir, I'd love to see a stereo version of this with common control. Maybe something to look forward to after the stereo PEQ ?

soup · Post by **soup** » Sun May 21, 2017 7:11 pm

soup wrote:I'd love a stereo COFilter and have mentioned it here but think running 2 in quasi stereo would be a soup sandwich.

nevermind or rather ... one in stereo is mos definitely my kind of sandwich!

BugBrand · Post by **BugBrand** » Mon May 22, 2017 3:44 am

Oh, that's neat!
Like the switching (On/On/On, right?) & the extra jack outputs.
The jack inputs is neat too - though you'd maybe have to watch resonance levels if the input signal isn't up around +/-5V amplitudes.

soup · Post by **soup** » Thu May 25, 2017 11:04 am

BugBrand wrote:Oh, that's neat!
Like the switching (On/On/On, right?) & the extra jack outputs.
The jack inputs is neat too - though you'd maybe have to watch resonance levels if the input signal isn't up around +/-5V amplitudes.

The switches are on/on/on. The jacks are intended as an octatrack interface so there's not much intentional self resonating but I've used a lot of modular filters with line level devices and yeah, it's pretty easy to blow your head.

jimmie · Post by **jimmie** » Thu Jul 27, 2017 7:40 am

Just fascinated by the sound of newly acquired COFilter

just had to hit the rec button of the phone. I need no fcking tube

[video][/video]
Sorry for phone mic recording. But, this sounds so vintage! Volca keys plays a simple chord progression seq (backing pattern). Volca is fed into Bugbrand Crossover filter then PTDelay. Filter 1 of COFilter is self-oscillated (sine wave generated) and sequenced a melody by SQ1 (top melody). Played on the Roland mobile cube. Volca's filter is wide open and no delay added, roland is flat as well. PTDelay sounds so vintage at some setting, boosted by COFilter.. Even though mobile cube is a small amp, with this setup it's so vintage sounding. oh you only have to listen it over here...

BugBrand · Post by **BugBrand** » Fri Jul 28, 2017 2:54 pm

Aye - lovely sounds there!

chrisdermo · Post by **chrisdermo** » Fri Oct 06, 2017 5:16 am

I picked one of these up yesterday - what a stunning sound!

The sine tones from self oscillation are particularly beautiful - so creamy and smooth, looking forward to playing them with a keyboard. I've had great fun this morning using a repeater electronics horndog and double knot to modulate both cutoff CVs with lowpass panned left, bandpass centred and highpass panned right, playing with the phase switches and parallel/series

. This thing is seriously powerful and I've barely even got to sending an audio signal to it's input yet

jimmie · Post by **jimmie** » Mon Nov 13, 2017 10:31 pm

https://soundcloud.com/hajimmie/dream-of-cachalots

COFilter - PTDelay chain. I got pretty nice overdrive on the sidrax.

/\/\/\/ · Post by **/\/\/\/** » Wed Nov 15, 2017 9:10 am

Tom posted a nice ping demo when this was released - I was wondering how exactly this is accomplished. Is the expander needed to send the gate signals in? Or could a gate signal go right into the audio 1/4" jack?

chrisdermo · Post by **chrisdermo** » Wed Nov 15, 2017 9:17 am

/\/\/\/ wrote:Tom posted a nice ping demo when this was released - I was wondering how exactly this is accomplished. Is the expander needed to send the gate signals in? Or could a gate signal go right into the audio 1/4" jack?

No need for the expander - just shoot your gate straight into the input jack and adjust the gain as necessary for more or less of a 'tick'

chrisdermo · Post by **chrisdermo** » Tue Nov 28, 2017 4:24 am

Been getting froggy testing the new setup.... cof, tetrax, voltage memory, horndog. Double knot has to go for repair but will be getting involved soon

Many many many many many Huge thankses to Tom for helping me achieve my dream filter system

jimmie · Post by **jimmie** » Wed Nov 29, 2017 7:04 pm

That's looking so awesome! I want the expander for the filter (if it's obtainable) but am not sure how to prepare the casing then...

BugBrand · Post by **BugBrand** » Thu Nov 30, 2017 4:50 am

I'm not looking to open the floodgates making such custom setups, unfortunately - it was a one-off for Chris, partly helping me take a step along prototyping a new Dual Preamp.
The Expander (which is fully passive, just sockets on a panel) is available from me, though I don't push it - figuring how to mount it is really the issue as I don't have 4FW cases.

jimmie · Post by **jimmie** » Thu Nov 30, 2017 11:43 am

Thank you Tom, yeah, with the expander I'd have problem for space even with an 11FW case so I'm holding the idea till you might someday come up with some other option - something 4FW perhaps (like LFOs for PTdelay/COfilter, then fit with 11FW

(but I want the expander before

)

MUFF WIGGLER

MUFF WIGGLER

CrossOver Filter

ffffazzzze

re: pings

Re: re: pings