simple and compact ms20 filter

[andrea83]

Hi everyone,

I know there's another ms20 filter in the forum but this one is different, based on another schematic as the one on the effectlayouts site ( http://effectslayouts.blogspot.com/2016/08/korg-ms-20-filter.html ).
I needed it to be very compact so I left out the power filtering cap (I'm putting it with another effect).
The filter sounds nice and the layout is verified, but I got a problem with the switch, I got noisy pop sounds switching from HP to LP. Can someone help me to find the reason why?
Thanks and hope someone will find it useful!

[WeStartToDrift]

How is the volume on this? The one I built from the perf board layouts was barely above unity gain.

[andrea83]

Hi, I didn't put volume knob and yes it's barely above unity gain as yours.
Turning the lp down it also decreases a lot more till silence.

[GrooveChampion]

Guess it needs some kind of a buffer/gain stage like most pedals.

[andrea83]

For me the volume is not a problem 'cause I'm putting it after another effect, but I would like to know why it does pop a lot switching between HP and LP. maybe I could put some resistors somewhere? :)

[kragg]

Hi, I am planning to build this layout, but i am counting only 17 cuts while the text says "18 cuts" : am i missing something, or was the layout updated (while the cuts count wasn't) ?

[kragg]

Hello,
Verified !
I built it using the layout above (with 17 cuts -like on the picture-, not 18 as written).

The sound is a bit harsher than on a vintage MS20 (harder distorsion when feeding it bass frequencies), but it may be a matter of adding a buffer or another circuit prior to the core of the VCF.
I may also add a resistor in series with the cutoff and/or the resonance, in order to limit their range slightly.

[andrea83]

Hi! You're right, I looked for my file and I see there was an useless cut so it's ok 17

[andrea83]

thanks for verifying!

in the next days I would like to isolate the filter of the Evil Filter by DBA 'cause I find it very nice, more versatile than this one! take a look at it! the only problem is that it's more expensive than this. :(

[andrea83]

do you have the pop issue switching from lp to hp?

[kragg]

I didn't notice a pop, but after a couple switches, the DPDT failed and i need to use with a new one.
I will let you know how it works when i will have a new one wired.

What i noticed is that  limiting the pot range is required, as at the very beginning of the turn, the frequency pot start to "break" (sound getting fuzzy/gated before reaching silence), and the resonance pot seems a bit useless at the very end of the rotation (i mean : of course it goes into self-oscillation, as expected, but i find that after quickly reaching self oscillation, nothing more happens at the extreme right of the turn).

On question : is there any way to have the HPF be 1pole (6dB/oct) instead of 2 poles (12dB), like the original MS20 ?

I will look at the DBA Evil filter, thank you for the hint !
(And, if you want, you may give the WASP filter a try, it is a nice multimode filter with distorsion, it's very versatile).

[kragg]

I do not have any pop issue when switching from HP to LP.

Is there any simple DIY LFO circuit which would allow to modulate the frequency ?

[Pavlos]

not tried it myself yet (MS-20 and Wasp filters are still working their way towards the top of my to do list) but I think one of these might work?

http://guitar-fx-layouts.42897.x6.nabble.com/Mod-Boards-f24029.html


another nice modulation board is the one for the de profundis delay

http://tagboardeffects.blogspot.com/2014/04/grind-customs-fx-deprofundis-delay.html

[kragg]

Thank you, Pavlos.
I built the Mad Bean Modulaterator linked above, and it works with a PT2399 circuit, but i can 't manage to make it work with the MS20 (while sending some CV from a synth can modulate the frequency of the diy ms20 filter i have built).
So i guess that both boards (the MS20 filter and the Modulaterator ) aren't compatible ?

[Pavlos]

ok, that's worth knowing, but I guess it was worth a go though. I'm expect someone with far more knowlege than myself will be able to explain why?

Just had a quick scan through pseudo random and the psycho LFO threads and it looks like the pseudo random would work with the Wasp filter according to nocentelli's post towards the bottom.

And at the bottom of the MS-20 Filter thread there is an LFO layout, though I'm not sure if it's been verified?
http://guitar-fx-layouts.42897.x6.nabble.com/Korg-MS20-LP-HP-Filter-td31433.html

There's also the mod board for Freppo's arcadiator, which might be of interest
https://tagboardeffects.blogspot.com/2016/03/parasit-studio-arcadiator-20.html

[kragg]

Thank you, Pavlos.
- The layout made from the original MS20 layout is a bit overkill as a daughter board ;)
I'd rather just put a jack socket on the pedal, and feed it with external CV if the daughterboard is twice as big as the main board, eh eh.

- I will check the mod board for the Arcadiator. I see it works with vactrol, which is rather unusual for a LFO ?

[Pavlos]

vactrol or LED/LDR as part of an LFO are not uncommon, a few tremolo, vibe/vibrato and filter circuits have them as well as the previously mentioned mod boards. I guess it's probably just down to whichever method has the character the designer wanted?

Might be overkill but have you looked at the baby-8 and vanishing point at all?

[kragg]

Pavlos wrote

vactrol or LED/LDR as part of an LFO are not uncommon, a few tremolo, vibe/vibrato and filter circuits have them as well as the previously mentioned mod boards. I guess it's probably just down to whichever method has the character the designer wanted?

Ah ah, yes, you're right : i have built a couple tremolo and vibes featuring vactrols. :)
But so far i had never encountered any in LFO designs  i stumbled upon.

Pavlos wrote

Might be overkill but have you looked at the baby-8 and vanishing point at all?

Yes, I have a Baby-8 sequencer. I don't know the Vanishing point ?
I was not after a big thing, because i already have some CV/lfo modules (in Eurorack or other synths), so if the daughter board is too big or complicated, i'd rather put on the pedal a jack socket as cv input.
But if a simple LFO add-on is doable, it could be nice to have a "all in one", already wired, easy to use solution.

[Pavlos]

yep, was a long time until I realized that the the vactrol could be part of the LFO circuit, that was until I saw something about the de profundis mod board being based on the tremulus lune LFO, and various mentions in some of the other tremolo layouts that used transistors, opamps etc were being used for the LFO. If I remeber correctly, using vactrols or other kinds of optical sensors helps to de-couple any noise in the LFO circuitry from getting into the audio side?


Vanishing point
http://guitar-fx-layouts.42897.x6.nabble.com/Tone-God-Vanishing-Point-v1-0-with-filter-included-and-v-2x-without-filter-td26555.html

If you already have other CV/LFO modules you maybe wouldn't get any benifit there? Though I like the idea of an all in one with the filter and LFO..........hmm  makes me wonder..........wasp and MS20 filters with a baby 8 in a large-ish enclosure.......or is that just madness

[cjonesplay]

I have built this and I noticed that the LED's are off on the lowest settings of the Frequency range, then they turn on at about 10% They turn on at roughly ~3 volts. The delay causes a clip and so you don't get a smooth sweep from top to bottom. I used a 13700 so my only guess is that this chip has a different output current behavior in this circuit, so as soon as I got some 13600's I'll give them a go.

I always thought 13700's were interchangeable, even though they have the Darlington buffer in them, but perhaps in this application, maybe not?