Planning my huge modular effect/synth board

[Taylor]

I have decided I need a big project.

I'm going to build a suitcase that will unfold to be a modular effects board, with some synthesis capabilities. I won't bore you yet with the details of which effects I am putting in it (but a hint: zero distortion/fuzz/od, but 4 ring modulators).

Besides audio effects, I want to have several control units, like an envelope follower, a Vanishing Point (hopefully with portamento - see here, and a few LFOs.

A few questions to start:

I want to make all, or at least many, of the parameters controllable by the controllers. How is this done? Is it as simple as connecting a jack in parallel with that parameter's pot?

I'm thinking that I may need to use some designs from modular synths, and I'm wondering if I should have a bipolar power supply for the synth modules in addition to the 9v supply, or if I would be best off not mixing 2 different forms of power. For example, will there be any issues with modulating parameters in 9v effects with a signal coming from +-15v modulation sources? Will this effect the scaling of the control signals?

How can I avoid ground loops?

The faceplate/front panel will likely be made of masonite with wood veneer over it, because I will be using a lot of slide pots and I'm unable to cut slots in metal. What's the best way to shield this? I'm thinking it would be best to shield each module separately, but I'm not sure the best way (ideally cheap and simple) to do this.

[MarcoMike]

I really like this idea... since I made the meatball I dream of a modular system, where you can use the envelope of this to drive that and a LFO to control the tone of a distortion... it would be great to have just one envelope detector, one really tweakable LFO, en expression pedal... and just patch cables to connect whatever you want... I have a synth (the one with keyboard ) where you can do that... it's just impressive how it can expand your horizons... even too much!!

the "interfacing different devices" thing is not as straightforward as we wished... for instance, 2 different voltage controlled devices may need a different voltage range in order to work properly (read meatball and ross paser  ). nothing that can't be solved... and if you design everything on purpose it should be easyer. vactrols are just great for the job, pity they are 5$ each...

about the +- supply...  there should be no problem... and I think you don't really need +15,-15, you can just use +9,0,-9 and the +9,0 half for single supply effects. but 2 me it seems +0- devices are much more versatile than single supply ones...

now about your suitcase... something I would really like to do, but probably won't because it would be just useless in my band  : first of all I'm a huge fan of John Frusciante and I suggest everyone to "get" the new album... or listen to it on youtube.. since last RHCP album he uses a lot reverb BEFORE dry signal (you would need a time machine to do that live, I'm not building this yet) or multiple delays on multiple reverbs and stuff like that... so I thought about making a pach-corded delay-reverb-tremolo device where you can choose where to send the signal to, where to take it from... like having the reverb only on the dry and not on the repeats, or viceversa. OR sending the dry signal to the reverb set on 100%wet and to the delay also at 100%wet, just 1 repeat at short time. and both out. so you play, hear the reverb in "phase" with your playing and then it comes the dry signal. it must be not that easy to follow the "tempo" (is this english?) of the song...
ok, I'm gonna do it!! 

[caress]

i would take a look at some synth module designs... there's a ton of useful information out there and it will probably be very beneficial to you in this project.
the simplest place to start (which also has loads of good links) is musicfromouterspace.com

the voltage control of all/most parameters is going to be the most difficult part, i think.

[Taylor]

i would take a look at some synth module designs... there's a ton of useful information out there and it will probably be very beneficial to you in this project.
the simplest place to start (which also has loads of good links) is musicfromouterspace.com

the voltage control of all/most parameters is going to be the most difficult part, i think.

Err... did you read my post...? It says that I intend to look at synth designs. The integration of these with 9v circuits is what I need help with.

[Taylor]

I really like this idea... since I made the meatball I dream of a modular system, where you can use the envelope of this to drive that and a LFO to control the tone of a distortion... it would be great to have just one envelope detector, one really tweakable LFO, en expression pedal... and just patch cables to connect whatever you want... I have a synth (the one with keyboard ) where you can do that... it's just impressive how it can expand your horizons... even too much!!

the "interfacing different devices" thing is not as straightforward as we wished... for instance, 2 different voltage controlled devices may need a different voltage range in order to work properly (read meatball and ross paser  ). nothing that can't be solved... and if you design everything on purpose it should be easyer. vactrols are just great for the job, pity they are 5$ each...

about the +- supply...  there should be no problem... and I think you don't really need +15,-15, you can just use +9,0,-9 and the +9,0 half for single supply effects. but 2 me it seems +0- devices are much more versatile than single supply ones...

now about your suitcase... something I would really like to do, but probably won't because it would be just useless in my band  : first of all I'm a huge fan of John Frusciante and I suggest everyone to "get" the new album... or listen to it on youtube.. since last RHCP album he uses a lot reverb BEFORE dry signal (you would need a time machine to do that live, I'm not building this yet) or multiple delays on multiple reverbs and stuff like that... so I thought about making a pach-corded delay-reverb-tremolo device where you can choose where to send the signal to, where to take it from... like having the reverb only on the dry and not on the repeats, or viceversa. OR sending the dry signal to the reverb set on 100%wet and to the delay also at 100%wet, just 1 repeat at short time. and both out. so you play, hear the reverb in "phase" with your playing and then it comes the dry signal. it must be not that easy to follow the "tempo" (is this english?) of the song...
ok, I'm gonna do it!! 

The backwards reverb thing is an interesting idea. I will actually have a spring reverb in my project, and a delay, and I do intend to have a splitter at the beginning and a mixer at the end so I can do parallel processing. I guess that mean I'll have everything necessary to do this. I'll record clips of that setup for you if I get going with my project before you do with yours, so you can see if you like enough to try it. I'm thinking it won't sound like Frusciante's, since his reverb signal is probably backwards, whereas the setup we're talking about would of course have a forwards reverb sound.

[Taylor]

I guess I'll explain all the modules I plan to have, so there won't be a need to suggest things I'm already doing. Stuff in red is aready built.

*Buffer/splitter - maybe 4 or 5 outputs
*Compressor
*Analog pitch shifter - this is my own design, based on the E&MM harmony generator. It will be rather huge itself, with volume sliders for 21 pitches, and highly patchable into itself. More on this later.
*Ring Stinger ring modulator (for dirty ring mod, also has lots of patchability, which will be cool for this project)
*2 passive diode ring modulators
*Frequency Analyzer ring mod (for clean ring mod)
*Analog sample rate reducer
*Heartthrob tremolo - was originally thinking the Tremulus Lune, but I had one already and found it to not be as versatile as its knobbage seemed to indicate. Listened to Hearthrob on John Lyons's site and I really like how smooth it is on slow speeds but nice and choppy on fast speeds.
*Phaser - don't know which one - any suggestions? I'd like something that sounds really thick at slow speeds, so Univibe for example doesn't work for me
*Vibrato - don't know which one. I want a true vibrato, ideally that can go really deep, like shifting an octave up and down. Don't know if such a project exists.
*2, maybe 3 Rebote delays with feedback loop send/return
*A digital delay of my own design
*A couple of feedback loops with limiters
*LFO
*Envelope follower
*Vanishing Point
*VCA/ADSR -this will be a synth design. The pitch shifter puts out a trigger signal, but I have no idea yet how usable it is. I realize that deriving a trigger and gate from a guitar (actually bass in my case) is going to be difficult.
*Spring reverb
*Mixer
*Possibly a Payback or 2 - I really want a looper with overdub capability but this doesn't seem doable in DIY

So, questions: Synth modules typically are working at higher levels than guitar signals and effects, right? So will the synth designs work with the quieter level that the stompbox circuits wil be outputting?

[Cliff Schecht]

I have decided I need a big project.

I'm going to build a suitcase that will unfold to be a modular effects board, with some synthesis capabilities. I won't bore you yet with the details of which effects I am putting in it (but a hint: zero distortion/fuzz/od, but 4 ring modulators).

Besides audio effects, I want to have several control units, like an envelope follower, a Vanishing Point (hopefully with portamento - see here, and a few LFOs.

A few questions to start:

I want to make all, or at least many, of the parameters controllable by the controllers. How is this done? Is it as simple as connecting a jack in parallel with that parameter's pot?

I'm thinking that I may need to use some designs from modular synths, and I'm wondering if I should have a bipolar power supply for the synth modules in addition to the 9v supply, or if I would be best off not mixing 2 different forms of power. For example, will there be any issues with modulating parameters in 9v effects with a signal coming from +-15v modulation sources? Will this effect the scaling of the control signals?

How can I avoid ground loops?

The faceplate/front panel will likely be made of masonite with wood veneer over it, because I will be using a lot of slide pots and I'm unable to cut slots in metal. What's the best way to shield this? I'm thinking it would be best to shield each module separately, but I'm not sure the best way (ideally cheap and simple) to do this.

For your first question, it depends on what the parameter is controlling. If the pot is just controlling a voltage that feeds the next stage, then yeah, you can easily place in a jack and use your own CV's. If the pot in question relies on resistance of the pot to control your parameter (i.e. the frequency pot of an LFO), you have to get a LOT more clever. Vactrols can work well here, but they are just too slow for anything past about 50 Hz (usually slower!!). This means that for your ringmod effects, you're forced into using super slow LFO's you get no variety. YUCK! Instead, there are circuits you can use that look like varying resistances, it's done by changing the current flowing into (or out of) a node by a proportional voltage. What device comes to mind here? An OTA circuit! OTA filters, for example, are just OTA's feeding a cap to ground. The OTA, in this instance, acts like a resistance that varies with the voltage/current seen at the Iabc pin.

Onto your power issue. The problem you're looking at running into with a lot of synths (including PAiA, Blacet, Doepfer, MOTM and other stuff) is that the control voltages like to be from 0 to 10 V. Even if you reduce this to 0 to 5 V (decreasing your dynamic range as well), you're going to run into problems with a single rail system. When you have one rail, what's the lowest voltage that any transistor-based device will usually recognize before clipping? About 0.7 V, or one diode drop to ground. Op amps are worse, they can't go past about 1.5 V from the rails. IMHO, you're better off sticking with the split supply just for the simple fact that going lower than +-10 V on just about any synth means extensive redesigning of the modules, especially CV processing sections. There are a few ways to go about powering your synth stuff that will make your life much easier. If you wait a month or so, the place I work for will be releasing a clean and quiet +-15 V and +45 V (phantom power) SMPS for use with synth equipment. There are even cheaper methods that work well for DIY'ers, however, which is rectifying 12 V AC in both positive and negative polarities, filtering and regulating using a 7815 and 7915.

Also, as far as ground loops are concerned, it's pretty easy to avoid them if you follow one rule: Know your grounding scheme. The best way to ground a synth system is to keep power and signal grounds separate up until one point (usually at the power supply). This not only helps prevents bad ground loops (assuming you are using tip-sleeve jacks with just the tips connected to do your patching), but it allows you to isolate any switching circuitry and oscillators from the system that can otherwise introduce themselves in ugly ways. Other than this, ground loops shouldn't be a problem, just plan carefully!

Maybe you could shield everything with aluminum roofers tape?

[Cliff Schecht]

I guess I'll explain all the modules I plan to have, so there won't be a need to suggest things I'm already doing. Stuff in red is aready built.

*Buffer/splitter - maybe 4 or 5 outputs
*Compressor
*Analog pitch shifter - this is my own design, based on the E&MM harmony generator. It will be rather huge itself, with volume sliders for 21 pitches, and highly patchable into itself. More on this later.
*Ring Stinger ring modulator (for dirty ring mod, also has lots of patchability, which will be cool for this project)
*2 passive diode ring modulators
*Frequency Analyzer ring mod (for clean ring mod)
*Analog sample rate reducer
*Heartthrob tremolo - was originally thinking the Tremulus Lune, but I had one already and found it to not be as versatile as its knobbage seemed to indicate. Listened to Hearthrob on John Lyons's site and I really like how smooth it is on slow speeds but nice and choppy on fast speeds.
*Phaser - don't know which one - any suggestions? I'd like something that sounds really thick at slow speeds, so Univibe for example doesn't work for me
*Vibrato - don't know which one. I want a true vibrato, ideally that can go really deep, like shifting an octave up and down. Don't know if such a project exists.
*2, maybe 3 Rebote delays with feedback loop send/return
*A digital delay of my own design
*A couple of feedback loops with limiters
*LFO
*Envelope follower
*Vanishing Point
*VCA/ADSR -this will be a synth design. The pitch shifter puts out a trigger signal, but I have no idea yet how usable it is. I realize that deriving a trigger and gate from a guitar (actually bass in my case) is going to be difficult.
*Spring reverb
*Mixer
*Possibly a Payback or 2 - I really want a looper with overdub capability but this doesn't seem doable in DIY

So, questions: Synth modules typically are working at higher levels than guitar signals and effects, right? So will the synth designs work with the quieter level that the stompbox circuits wil be outputting?

Deriving a trigger from a guitar (you can't get a gate on an instrument that doesn't have infinite sustain ) is actually very easy. Rectify and comparator will be your friends here.

As far as tremolo goes, maybe you should wait until I introduce the new mono/stereo trem I've been working on. It sounds fantastic on all settings and allows for a lot of different mono and stereo trem sounds. I'll try to get the design out before Spring Break lets out.

I would trust others over myself for recommendations on the other stuff, especially the phaser.

[frequencycentral]

*Vibrato - don't know which one. I want a true vibrato, ideally that can go really deep, like shifting an octave up and down. Don't know if such a project exists.

I don't think that's possible in the analogue domain, here's a good expanation of how vibrato works: http://www.geofex.com/Article_Folders/phasers/phase.html

[Taylor]

Deriving a trigger from a guitar (you can't get a gate on an instrument that doesn't have infinite sustain )

My bass actually does have infinite sustain! I have a Sustainiac pickup on it. This is an essential part of the equation, and I wouldn't even be bothering with stuff like ADSR if I didn't have infinite sustain.

Thanks for all your other comments, lots of info there to think about.

[Taylor]

I don't think that's possible in the analogue domain, here's a good expanation of how vibrato works: http://www.geofex.com/Article_Folders/phasers/phase.html

Right, I know how vibrato works. Why can't a big shift be done? It would just need more delay time, right?

[Cliff Schecht]

Deriving a trigger from a guitar (you can't get a gate on an instrument that doesn't have infinite sustain )

My bass actually does have infinite sustain! I have a Sustainiac pickup on it. This is an essential part of the equation, and I wouldn't even be bothering with stuff like ADSR if I didn't have infinite sustain.

Thanks for all your other comments, lots of info there to think about.

Ah..Very cool! Maybe a fundamental extractor to VCO will be in your near future?

[Taylor]

Actually, I'm doing something like that with my pitch-shifter. It's actually a PLL driving a VCO rather than a real pitch shifter. I'm using the fundamental extractor from the OC-2.

Maybe you can tell me this: does a fundamental extractor put out a sine wave? I assume it must, since the fundamental would theoreticaly have to be a sine wave, but things are rarely so simple in the analog world.

[Cliff Schecht]

Usually, a fundamental extractor puts out a square wave that is at the same frequency of your signals fundamental frequency. At least the one I've worked on does that.. I would assume you need some kind of processor to do a "real-time" FFT and then give you a sine wave output that's proportional to the input frequency. Of course now you're introducing a delay to your signal, but it wouldn't be noticeable with a good FFT algorithm (then you're only delayed a few samples).

[MikeH]

As far as tremolo goes, maybe you should wait until I introduce the new mono/stereo trem I've been working on. It sounds fantastic on all settings and allows for a lot of different mono and stereo trem sounds. I'll try to get the design out before Spring Break lets out.

Interesting... I am seriously about 8 hours away from starting Dean's Stereo version of the Anderton Trem.  Perhaps I'll see what your has to offer first... Keep me updated!

[Taylor]

Ok, so, an update on this. I will post some pictures soon. I have built as much as possible on the boards because I hate offboard wiring and it's even worse when you have 20+ circuits going on at once. So the knobs are mostly board-mounted, some jacks are, some aren't. The boards are mostly going to be mounted perpendicular to the faceplate, so I can cram them pretty close. The "module" size is 1.5" wide by 5" high. The modules are not on separate faceplates, so it isn't a true modular in that they can't be physically rearranged. But it is modular in every other way, since there is no normalization of connections, and as much as possible, the interesting parameters should be remotely controllable.

Some of the things I planned to build have morphed or been replaced. Stuff in red is aready built.

*Buffer/splitter - 4 outputs
*Compressor
*Analog pitch shifter. This is mostly done, but as it is huge, and I am figuring it out as I go along, I am chasing some weird little problems. Every time I stick a bandaid on some problem, a new one crops up.
*Ring Stinger ring modulator
*2 passive diode ring modulators
*Penfold Light Metal Effects ring mod - This one is a clean ring mod which tracks your input note and locks the carrier to it, so you get "harmonic ring mod". Haven't built it yet, seems no one has built it successfully.
*Analog sample rate reducer
*Heartthrob tremolo x2
*Huge phaser - I built a 12-stage Phase 90 (so Phase 270?) where all the stages are patchable into each other, so you can feedback stage 10 to stage 4, and stage 12 to stage 2 - haven't been able to fire it up yet, so it might be a huge failure, but I'm hopeful.
*Simple phaser
*Echo Base delay. Decided I don't need vibrato or chorus since I have this and the patchable phaser. I think I'll make a second Echo Base, too.
*A digital delay of my own design. Not done.
*A couple of feedback loops with limiters
*LFO
*Envelope follower
*Vanishing Point with slew control
*VCA/ADSR -this will be a synth design. The pitch shifter puts out a trigger signal, but I have no idea yet how usable it is. I realize that deriving a trigger and gate from a guitar (actually bass in my case) is going to be difficult.
*Spring reverb
*Mixer
*Possibly a Payback or 2 - I really want a looper with overdub capability but this doesn't seem doable in DIY

I hate reading huge posts, so see below for some questions.

[Taylor]

I am using 3.5mm mini-phono jacks. This was done for a few reasons. Chiefly, price. Costs add up when you buy 50 of something  , so even though there are good Neutrik 1/4" jacks for 70 cents, that would have been $35 just for jacks. Then there's the patch cables, which come out quite expensive in 1/4" even if you make your own. I found that 3.5mm is the way to go. I usually buy everything from Mouser, but All Electronics had great deals on jacks and patch cables. A second reason for mini-jacks is size. They are way smaller in every dimension. Due to a screw-up early on, I am using the sleeve of the jack to transmit signal instead of the tip. I can't foresee any reason why this would be a problem, but I do fear that that will somehow come back to bite me. I think as long as I am consistent throughout the whole system, I'll be ok, right?

As per Cliff's suggestion, I am not connecting ground through the signal jacks. Is star grounding the way to go for something like this?

How is feedback handled in modular synths? Would it make more sense to integrate multiple inputs to each module, or stick with the stompbox approach of having a dedicated feedback loop box?

[Mark Hammer]

A good place to start would be to look at the entire DEVICE series, and the fabled AMS-100 project that is posted at my site: http://hammer.ampage.org

[Taylor]

I have read most of that, very interesting stuff, but I haven't come across answers to my questions above. Is there a particular article you could point me to?

[Taylor]

Clockwise from bottom left: analog pitch shifter, Vanishing Point, Ring Stinger, modular phaser, Echo Base, 2 Hearthrob trems, compressor, fundamental extractor, sample rate reducer, input/buffer/splitter.