General Question: Modular Circuits.

[Thecomedian]

I've been kind of a big fan of the idea of being able to build modular circuits, such as a treble or bass boost/cut tone stack, That you can just click into place like you would an IC into a socket. Is there any flaw with this design method? I was thinking that I could make Passive circuits that click into place, and use a transistor with feedback loops (or an op-amp) to Gain the signal back up to near equal to the input.

Are there any issues with this to be aware of?

( Beginner projects forum is dead right now)

[R.G.]

See
http://geofex.com/Article_Folders/fxbus/fxbus.htm
http://geofex.com/FX_images/Modlr_phase.pdf
also
http://geofex.com/Article_Folders/wrapper/wrapper.htm is heavily modularity based.

Modularity is a good idea. The problems with modular systems are:
- People have no familiarity with them.
- Adding controls and displays in a modular fashion is tough; see the comments in the Fxbus about controls.
- It's tough to do sidechains and loops modularly.
- Packaging is an issue for anything except garage versions where hanging-garden wiring is OK. There's always the issue of what goes in the open spaces and how big the backplane is. See http://geofex.com/Article_Folders/FXRack/fxrack.pdf

[amptramp]

When you couple circuits together, you have to ensure the output impedance of the driving circuit is sufficient to drive the input impedance of the next circuit.  If you want to add a tone stack to a pedal chain, you have to have a high-impedance input buffer and a low-impedance output buffer to isolate the controls from whatever other circuitry it will connect to.  Controls should always be buffered.

It is difficult to come up with a design that permits modules to have the various number of controls that they may have.  Ultimately, you have to waste part of a standard connector pinout accommodating circuits that are possible but will not be used.  You have to have a mechanical package that will fit the largest design and use that size in all locations unless you can have a pedal take up multiple units.

[earthtonesaudio]

Pedals are modular units.  If you break the signal chain up into smaller bits, you will run into issues, but that could be part of the fun.

[Thecomedian]

When you couple circuits together, you have to ensure the output impedance of the driving circuit is sufficient to drive the input impedance of the next circuit.  If you want to add a tone stack to a pedal chain, you have to have a high-impedance input buffer and a low-impedance output buffer to isolate the controls from whatever other circuitry it will connect to.  Controls should always be buffered.

It is difficult to come up with a design that permits modules to have the various number of controls that they may have.  Ultimately, you have to waste part of a standard connector pinout accommodating circuits that are possible but will not be used.  You have to have a mechanical package that will fit the largest design and use that size in all locations unless you can have a pedal take up multiple units.

okay, that's what I heard from a friend of mine about the impedance issue.  iscthere some shorthand general estimatimation rule to calculate total circuit impedance and how much is required to drive the next? I suppose the same thing would be, like the other poster said, just having another pedal.

[gritz]

When you couple circuits together, you have to ensure the output impedance of the driving circuit is sufficient to drive the input impedance of the next circuit.  If you want to add a tone stack to a pedal chain, you have to have a high-impedance input buffer and a low-impedance output buffer to isolate the controls from whatever other circuitry it will connect to.  Controls should always be buffered.

It is difficult to come up with a design that permits modules to have the various number of controls that they may have.  Ultimately, you have to waste part of a standard connector pinout accommodating circuits that are possible but will not be used.  You have to have a mechanical package that will fit the largest design and use that size in all locations unless you can have a pedal take up multiple units.

okay, that's what I heard from a friend of mine about the impedance issue.  iscthere some shorthand general estimatimation rule to calculate total circuit impedance and how much is required to drive the next? I suppose the same thing would be, like the other poster said, just having another pedal.

An engineer might say that if your input impedance was equal to, or greater than ten times the output impedance of the preceding module then you're golden. A mojo fanatic might differ. He / she might even say that impedance loading was a good thing...

I've always thought that the modular thing had merit, but was always at a loss as to how to implement it. A pedal carcass, with i/o jacks, power input + battery and signal switching that could accept interchangeable audio processing units (i.e. a little plug-in block with teh knobs on) might be cool, but would take a fair amount of engineering - and miniaturisation - for the home hacker.

I guess that the pedal array or board is a modular thing anyway - and hammond enclosures, jack sockets and the like are cheap enough that we can put all of our creations into seperate boxes and plug them in and out at will. I'd still like an amp with swappable tone stacks though.

[pinkjimiphoton]

Pedals are modular units.  If you break the signal chain up into smaller bits, you will run into issues, but that could be part of the fun.

+1

[PRR]

I don't know how much of this made it to the interwebs. But the _first_ generation os Moog and ARP synthesizers were totally modular.

I know the ARP better. Module had a 2"x4"(?) face, which looked bare with one headphone amp and was mighty crowded with a 4x10 array of sequencer knobs. The card was 6"(?) deep. The rack was 48" wide and would take 18 or 20 modules. All I/O was on the module back-connector routed to matrix switches on the front (unique to ARP; others used jackbays).

Electrically the specification was 1K output impedance and 100K input on everything (except pitch VCO interface). Not too hard to do with the then-new chip opamps. With this spec you could mix any outputs directly together, and you could put multiple inputs on any output.

Maximum signal was 10V peak (+/-15V rails). For best S/N you'd work modules near clipping then pad-down before monitor and tape-recorder, but we usually just trimmed the patch for ~~1V signals. Since noise was not a prime design consideration, sticking guitar straight in usually got you well toward the hiss, we'd rig an external preamp for weak sources.

You could re-aim for 1V signals and single 12V rail; the +/-15V was mostly about coupling very-slow/DC control signals.

Everything the big ARP could do *musically* could be done a little smaller and much cheaper on later generations of non-modular synths. Yes, I could rig some full-mod patches the little synths couldn't do, but I wouldn't listen to them again.

Generally, the small amps are the cheapest part of a music creation rig. Next the pots and jacks. Next the enclosure. Then any non-common connectors. So enclosing MANY modules separately, then connecting ALL them together (without R.G.'s wire-garden) is more expensive than building extra amps and knobs in ONE enclosure. So if you may want a T/B control, but don't know where, put one EVERYwhere (with bypass). More knobs is cheaper than more enclosures and connectors.

Anyway more knobs is always cool. Excellent bang/buck for impressing other electric musicians and geeky fans. Not as good as LEDs, meters, or oscilloscopes, but you can add those also.

[garcho]

Anyway more knobs is always cool. Excellent bang/buck for impressing other electric musicians and geeky fans. Not as good as LEDs, meters, or oscilloscopes, but you can add those also.

+1


Put a bantam jack bay on a big enclosure and make a faux modular pedal.

[skjaldborg]

Been a bit of a lurker around these parts and gained a heck of a lot of great info (thanks for that everyone) - thought it was high time I started posting!

To me, the piece I would like to make more modular in my diy world isn't the core effect per-se but the control of it  - have more, standard expression pedal type inputs for basic controls and then be able to vary parameters more dynamically using various control circuits separate from the box - We don't throw away the essence of the individual stomp box but we do get more scope for linking the little blighters together in interesting ways.

I have built a small modular guitar synth loosely based on Ray Wilson Subcommander type guitar voice + various other modules. In the end I added a VCO and basically have an analog synth with the option of plugging a guitar in. Became a bit of a beast (certainly lived upto the "more knobs is always cool" philosophy) - I loved the challenge and have got some interesting sounds out of it - whether it is worth it musically is another issue entirely..........



Paul