Will the real MS-20 filter please step forward

[Strategy]

Ultimately to do a group PCB order double sided is probably required, I don't think the Dorkbot submittals can be single sided. So PCB 'real estate' and size are a secondary consideration, I think, behind choice of best parts for the sound.

I'm not familiar with the TAPLFO, I know of it but haven't used it in a project yet. A couple of questions about it:
- Is it likely to have longevity or will this project age out relatively quickly if the relevant parts go away?
- Would it be possible to develop a bare bones version of the project without modulation and do the modulation as an optional daughter board? Seems crazy doesn't it but I like the idea of a project which is expandable/customizable based on desired configuration. So there would be a filter core PCB and then a modulation PCB.

Last question: Rick any interest in being the vision-quest-leader for the layout aspects of the project? As I've never done a layout, this could really take a VERY long time unless I rope others in to help

STRATEGY

[garcho]

(subscribe)

[frequencycentral]

TAPLFO2 is coding onto PIC16F684, so as long as PIC16F684 is available. The code is freely available:
http://www.electricdruid.net/index.php?page=projects.taplfo
...though I buy programmed PICs from Tom (support the designer!).

TAPLFO2 is used in a number of commercial devices:
http://steamsynth.com/e_ModulationOrgy.aspx
http://steamsynth.com/m_TTLFO.aspx
http://www.catalinbread.com/SemaphoreTremolo.html

It's the best LFO out there IMHO.

Being vision-quest-leader for the layout is tempting, but I don't lay out for double sided (yet). I've got a complete TAPLFO2 synth module project out there already though:
http://dl.dropbox.com/u/967492/ED%20VCLFO/Modulation%20Druid.pdf

Strikes me that this is actually a modular synth project anyway.  

[Jordan A.]

I'm not familiar with the TAPLFO, I know of it but haven't used it in a project yet. A couple of questions about it:
- Is it likely to have longevity or will this project age out relatively quickly if the relevant parts go away?
- Would it be possible to develop a bare bones version of the project without modulation and do the modulation as an optional daughter board? Seems crazy doesn't it but I like the idea of a project which is expandable/customizable based on desired configuration. So there would be a filter core PCB and then a modulation PCB.

STRATEGY

It sounds like the Tom Wiltshire PIC LFO, from here http://www.electricdruid.net/index.php?page=projects.taplfo

It uses a PIC 16F684, which will eventually go away, I'm not familiar enough with the PIC series of chips to know if whatever replaces it will likely drop right in, maybe with a teeny bit of tweaking.  For a project like this I would not worry about it too much.  It helps that Tom W. is active in the synth diy community, and even posts here sometimes I think.

One nice thing about that one is that with an investment of about $40 or less you can get a pic burner and burn as many as you like, for backups or future projects.  I can barely check my own email and I managed to successfully burn a bunch of PIC projects with a pickit 3, it's definitely a doable thing if you have the inclination.  Alternately, you can buy preburned PICs from a couple of sources, the TAP trem project from here uses exactly this chip.

The other cool thing about this LFO is that it is very easy to build it your way, you can add or leave off as many features as you desire.  It is definitely a lot of LFO for the square footage it takes up on a board, but to get the most out of it you need to add a bunch of extra switches and knobs.  I'm personally kind of divided, on the one hand it's really cool to have an ultra bitchin' LFO, but on the other hand it's kind of nice to have a simple and uncluttered layout and only use stuff you probably already have in the parts bin.

Let the discussion continue...

jordan

:edit, posted at the same time as FC:

yeah, what he said!

[Strategy]

Being vision-quest-leader for the layout is tempting, but I don't lay out for double sided (yet). I've got a complete TAPLFO2 synth module project out there already though:
http://dl.dropbox.com/u/967492/ED%20VCLFO/Modulation%20Druid.pdf

Strikes me that this is actually a modular synth project anyway.  
[/quote]

Well, for one thing I think developing the decided upon schem + PNP as a testing ground is probably a best first step before committing anythign to a board run. I have friends in the local Dorkbot unit who could probably help me with adaptation from there, and in fact that part is probably something I could endeavor to do on my own. I'm hesitant to really do the board run until there is a project with the known features in place and a few people have tried it and revisions made before going double sided

So if you'd be into helping develop vers. 1 that get's us very far into the process. Ponder it!

If we go with the bipolar power onboard, it could be optionally a modular synth or a "standalone" pedal project - I like ones that work that way, all of Juergen Haibles effects projects were developed as either one or the other.

[frequencycentral]

MS20 schematics:

http://dl.dropbox.com/u/967492/Korg%20MS20/MS20%2001.gif
http://dl.dropbox.com/u/967492/Korg%20MS20/MS20%2002.gif

[Strategy]

Ah yes with the 'Korg35' IC. I will see if I have the 13700 version on file later when I'm on my laptop!
Strategy

[frequencycentral]

MS50 schematics, VCF on page 11. I always found Korg schematics so hard work to read...

http://dl.dropbox.com/u/967492/Korg%20MS20/ms50schemos.pdf

[Strategy]

Yes - very hard work. It might be advantageous to crib from a modern remake that uses the desired chips.

For bipolar power I favor the Thomas Henry PSU configurations, will post if I can dig it up

Strategy

MS50 schematics, VCF on page 11. I always found Korg schematics so hard work to read...

http://dl.dropbox.com/u/967492/Korg%20MS20/ms50schemos.pdf

[Strategy]

I keep going back to the simplicity of the Rene Schmitz version but with LM13700 switched out for the multiple CA3080s...I see many have done this to his circuit but I can't find the modified schem actually drawn anywhere (yet)

strategy

Yes - very hard work. It might be advantageous to crib from a modern remake that uses the desired chips.

For bipolar power I favor the Thomas Henry PSU configurations, will post if I can dig it up

Strategy

MS50 schematics, VCF on page 11. I always found Korg schematics so hard work to read...

http://dl.dropbox.com/u/967492/Korg%20MS20/ms50schemos.pdf

[frequencycentral]

This is the 'Miss Ten' VCF/VCA from E.A.S's project on MW forum:

http://www.flickr.com/photos/23140551@N08/6051155716/lightbox/

[frequencycentral]

As far as the OTA version goes, Tim Stinchcombe's schematic seems the easiest to read (page 6):

http://www.timstinchcombe.co.uk/synth/MS20_study.pdf

[frequencycentral]

KLM-307 daughter board (2 x LM13600), from the MS-20 "Version 2":

http://machines.hyperreal.org/manufacturers/Korg/MS-synths/schematics/KLM-307.GIF

[frequencycentral]

René Schmitz's 3080 (LPF) version:

http://www.uni-bonn.de/~uzs159/rs20.png

[Strategy]

Still hunting for a version of the Schmitz with 13700's, otherwise I think we should go with the Stinchcombe page 6 version, sub the 13600s for 13700s and plug in the other aspects of the circuit...

Will post more tonite...

René Schmitz's 3080 (LPF) version:

http://www.uni-bonn.de/~uzs159/rs20.png

[Jordan A.]

Still hunting for a version of the Schmitz with 13700's, otherwise I think we should go with the Stinchcombe page 6 version, sub the 13600s for 13700s and plug in the other aspects of the circuit...

Will post more tonite...

René Schmitz's 3080 (LPF) version:

http://www.uni-bonn.de/~uzs159/rs20.png

You don't need to change anything as far as the OTAs go, just use one half of a 13700 in place of one CA3080, mapping the pinouts and ignoring the diode bias and darlington buffers.  I hinted at it earlier, but since the darlington buffers are not used, I'm not sure if anything needs to be done with them, I should probably just check the datasheet, but not tonight.

glad to see this project has some legs!

jordan

[Jordan A.]

...A little more time to think about this...

Here is how I would probably do it-

-Pick whichever version of the VCF itself suits the masses, they all sound cool.  Anyone curious could breadboard a couple of the variations and see if a consensus arises.

-Build up the two VCFs, with one hardwired as LP and the other with a switch for HP/LP.  I would build it with two inputs and three outputs, with switching jacks for series/parallel operation.  Input A for parallel, input B for series, output A, output B and sum output.  

   Each VCF gets a resonance and mix control, additionally there is a master frequency control and a "separation" control, which sweeps the frequency of VCF A up while sweeping VCF B down.

-Two simpleish LFOs.  LFO A switchable between triangle, slewed square and sample and hold, like Jurgen Haible shows in the Son of Storm Tide schematic, but no CV of frequency and built with opamps for lower parts count.  LFO B triangle only.  Each LFO gets a RATE and DEPTH control.

    A three position switch for LFO mode, with NORMAL (LFO A sweeps VCF A, LFO B sweeps VCF B) SYNC (LFO A sweeps both VCFs, LFO B disabled) and ADD (LFO A and LFO B are summed together and the summed control voltage sweeps both VCFs) modes.

    The CV input for VCF B has a switch to invert whatever is sweeping VCF B, for reverse sweeps in SYNC and ADD modes.

-An envelope follower with sensitivity and attack controls.  Two attenuverters send the envelope signal to VCF A and VCF B, for independent up and down sweep of each.

-An onboard wall wart power supply, using an AC wallwart + half wave rectifier + three terminal regulators for +/- 15 volts (or whatever, it will probably be happy with something lower as well).  This keeps people from messing with mains wiring and works well.  It does mean you end up with an AC wallwart which you need to be careful of/make sure you can't plug it into the wrong pedal.  

...anyways, that is an approximation of one way to go about it.  A setup like that offers a whole lot of control without getting bogged down too much by feature creep...

fun!

jordan

:edit: now that I think of it, I think you can get all of the output modes from just two output jacks with some clever switching jack use and an additional summer, I'll think about this some more if it is something people care about.  Stereo in-stereo out, mono in-stereo parallel out, mono in-mono out, mono in-series mono out, mono in-parallel mono out.

[Cliff Schecht]

Something I noticed recently about AC wall warts was the plugs on them are 2.5mm barrels instead of 2.1mm. This means that AC adapters (usually) won't apply to a standard Boss type power adapter, unless you insert it crooked or bend the male pin over a little to make contact. I think this (wall wart, rectifiers, regulators) is the best power option as of now just for the sheer simplicity of two regulators and a handful of caps and diodes.

[Strategy]

agree with the power option, will be simple and compact. Didn't get to find my favorite Thomas Henry super simple power schem yet.

@ Jordan A. that setup seems scaled nicely between features. still unsure of whether the simpler or more complex versions will have wider appeal on this forum (and others)

EDIT: I think I'd like to stay away from serial/parallel channels, it makes bypass switching a huge pain, is just not a typical direction for projects in the forum, would like to make this project do-able for "paint by numbers" builders (like myself! haha.) But I do like the syncable/invertable LFO's idea.

Strategy

[Strategy]

Another thought occurred to me: if we're running this circuit with a lot of headroom does that make some kind of boost stage up front necessary? for all the guitarists in the house? that part is certainly not hard

I was messing around with DIY layout creator and have a very long way to go without help!  hint hint layout experts

will have to re-scan the Thomas Henry super simple rectifiers/regulators +/-15V power supply. Used it in my DIY Maestro Ring Modulator, did it on perf and can't find the document I worked from (was my first ever DIY project - what was I thinking??!? what a hard project!)

Strategy