I’m looking to find a good High Pass filter, a portable, versatile one like the MF101, only High pass instead of Low pass.
I’m sure the easiest way to get a high pass response filter would be to invest in a modular synth with a dedicated HP or variable state filter, but just for the sake of argument:
Is there any way to convert a Low Pass, like the MF101, into a High Pass?
Are there any components or component values that could be substituted in this Moog ladder filter that might change it’s response to that of a High pass filter?
Even if this is possible somehow, I’d imagine that changing certain components would easily throw off the linear response of any given filter… but if one wanted to start down this path, does anyone have any suggestions of where to start?
I have schematics for the Moog Modular High Pass module and some others, but I thought I’d also ask here if any of the more tech saavy forum members have any idea of if and how a conversion as described above might be possible?
You could invert the output of the lowpass and mix it with the ingoing signal of that filter in a simple mixer. This should cancel certain frequencies depending on their filter caused phase shift. Thus resulting in a highpass filter.
Or just buy a single modular module and ad a simple power supply. Build it all in a single bock and you are done.
Till’s suggestion is interesting - I’ll have to try that.
You might consider buying a filter instead of building one. AFAIK, the only stand-alone filter that’s still being made is the Sherman Filterbank. The Filterbank is like the back-end of a synth, with two gangable multimode resonant filters, EG’s and VCAs and CV/gate control options. It’s not cheap, but of you’ve got the bucks to spare it’s a cool and very capable addition to the Voyager.
There are some other stand-alone filters no longer made that you might find second hand. Electrix made a multimode resonant unit called the Filter Factory that offered two pole stereo or four pole mono operation, and independent CV control of the filter cutoff. Alesis had a smallish multimode filter box called the Philtre that was part of their ModFX line. You might find either of these boxes for cheap at your local music store (music stores in my area blew out the Alesis boxes for $30 each last year - a steal!)
Thanks for all the replies. I’d like to try this inversion patch, Till, it sounds pretty interesting.
I’ve used alot of these standalone filters, but most of them I don’t like so much. The Electrix and Alesis I don’t even think are real analog filters, despite what they may claim. The Akai MFC is a pretty good, if somewhat ordinary, multimode, but it doesn’t have any voltage control, just MIDI.
The Sherman filter seems pretty great, reminds me of a Korg MS20 filter, which I like alot, but it’s a little expensive and for the price I think it might make more sense for me to just start building a small modular set-up. This way I can add more modules if I decide I want to.
Which is probably what I’ll eventually do, but I was just wondering about the possibility of moding an MF101. Seemed like, if it was possible, it might be a fun and interesting project.
I like the look and price of the Dot Com modules, but their filter selection is a little lean compared to some other companies.
Does anyone have an opinion of the Dot Com Variable State Filter? Does it self-oscillate in Band and High Pass modes?
I had forgotten about that one. Thanks for reminding me!
Eric,
The Sherman Filter is kinda pricy, but keep in mind that amongst the many features it also offers EG and LFO CV outputs (on 1/4" jacks) which you can use straight-away with the Voyager. I have the rack mount version, which has all of the I/O jacks on the front (handy!). The Filterbank definately has a character all it’s own, and the Korg MS20 is probably the closest reference point.
i think the filtered coffee module would be seriously awesome in a fooger setup. all you would need to do is dedicate a cp-251 to attentuate (±12v for inputs and outputs on it) voltage requirements to suit the rest of the fooger line, and it’d fit in marvelously.
Check out the Electrix Filter Facotry - a 2-unit rack analog filter. It takes MIDI, control voltage, and is stereo 2-pole or mono 4-pole. It operates as a lowpass, highpass, bandpass, and notch, with extremely high, self oscillating resonance.
It also has an analog, solid-state distorion setting to beef up signals, various LFO shapes as well as a solid envelope follower, single-shot LFO triggering (for ADSR-type behavior) and wet/dry mix.
It’s built like a tank, it’s a cool green, with great feeling chunky metal knobs and springloaded switches. Can be racked or used on a desktop. Company is semi-out of business, but units are inexpensive on the second-hand market (like ebay) and sounds fantastic.( There was a mini-version of it called the Filter Queen.)
Only one drawback - the filter, though analog, is digitally controlled, (DCF?) so high-resonanace settings, and slow knobtweaks (and slow LFO settings) will reveal little steps in the pitch. Absolutely does not matter for most situations. Inaudible at normal and medium resonance settings. Only audible “in the lab.” or if you are “playing” the self-osc like a therimin very slowly.
If the filter cutoff was control-voltage smooth, I’m convinced the Electrix Filter Factory would be one of the hottest pieces of gear ever. Much more musical than the very cool but strange Sherman filterbank.
The .com does self oscillates in all modes but the Notch mode. Since I have multiple Envelope generators, I find it more versitale than my two MF101s, though my 101s have the “moog” sound that I gravitate to more. on it, you have 2 inputs to control the cutoff, [one being the 1 volt per octave for precise tuning] a attenuator for reso control, 2 inputs, and the use of 4 outputs at once.
I wish the MF 101 had the full function and control that this or some of the other brand filters do, but hey- I am not really complaining just dreaming
IF you really want to take the plunge, and want warmth.. don’t get sherman, get the mutronics mutator ebay has them going for $700s every month or so. but it is in european voltage. so you will have to find a way to power it.
I would add that the Filter Factory’s CV control is limited to just the Filter Cutoff (1V/oct), but each filter has it’s own CV input, allowing for some interesting stereo possibilities.
But THE Moog filter is a lowpass ladder filter as seen on the Minimoog. Not a state variable filter. A state variable filter requires a completely different design and is not the classic Moog filter.
You can still buy the modules brand new from the original Moog Custom Engineering company, which has been called ‘Modusonics’, since B.Moog bought back the rights to the name "Moog Music’. The modules are apparently made to spec and look exactly the same as their vintage counterparts, right down to the Moog logo.
They’re not exactly inexpensive ($1185 for an oscillator module, $785 for the LPF), but it would be pretty amazing to start building a “real” Moog Modular.
I’ve never played the Modusonics Mutator, but I’ve read alot of reviews that make me think it’s not right for me. I already have an MF101 and some other synths that have a very even-tempered, natural, typically “Moog” sound, so I’d like to find something different.
For instance, the MS20 filter is one of my favorite sounding filters because it makes alot of sounds that are quite different than a typical Moogy ladder filter.
I also like the Sherman filter because of it’s unique, somewhat MS20-like character, and tone color. I think Sherman tends to over-advertise the grimmy distorted sounds it’s capable of (these are the only type of samples that appear on their web-site); maybe because these are popular sounds right now. But, I’ve found that it can also do a wide variety of non-distorted filtering (but still full of color).
The frostwave or filtered coffee would probably suit me as well, but I’m leaning much more toward starting a modular synth now. So I’m wondering if the dot com Variable State filter module is capable of this sort of degree of tone color. It’s probably not made to do this type of thing.
Eric, I can post or email some sound clips of the .com if you want. email me matt at nickelcreek dot info, i will be happy to try to build a patch that showcases the sounds you are looking for, The Q107 does it for me at least.. YMMV I use it for some toen coloring, not so extreme filtering- I have been working on a sequenced square wave pattern fed into it’s self the last couple of days that is a good example of how I use it for tone… I dont’ personally like the shermann demo sounds you guys mentioned that pop up on their site, however I would like to expirement with one to see if i would want to get one..
Yes, I know “the moog” filter is different than the rest. It is why I own 2 of them with my .com Though I thought that the HP and LP w/ white noise was the moog ladder. I Guess I am wrong. In a perfect world, it would be nice to have the ability to have 2 modules [101, Multiband] “controlled” by the same parameters/ pots etc, combined into one boxed module [though the different charactisic of the filters would be But I am dreaming more than anything if that one I posted earlier is not so.
I just want my cake and to eat it too [interfacing 1 volt per octave modules with 3 volt moogs gives less than accurate CV pitch tracking, etc. between them]
just dreaming