Multi Effects Controller

[tthoen]

Hello all,

I am a newbie to DIYStompboxes, but have built my own effects and designed circuits for quite a while.  I'm wondering if anyone is interested in following a project that can control a number of DIY effects with Arduino or PIC?  The idea is to allow users to use their own custom modded effects circuits and allow programmability to turn on and off sets of effects.

Thanks!

Tom

[nickbungus]

Hi Tom

Is it the programming you need help with?  I'm a software developer by trade and have dabbled with PICs before. 

This is actually something I've thought about before.  Is the plan to get a big enclosure, stick x number of effects in the box, replace all the pots and switches with digital ones and control them with a microprocessor with a screen and keypad?

I built a cricket bowling machine and used a pic and digital pots to control the speeds.  It was quite straightforward but I'm not sure about the practicality of this project.

[Tightpants]

Hi Tom, I've had a dabble (still dabbling) with this sort of thing. If you just want to turn on/off effects there are some good and cheap programmable loop switchers out there. If you want to be able to save and recall effects settings then it's more difficult but not as hard to do as you might think. As the man says, just replace all the pots and switches with digital ones and control it all with a microprocessor. In my experience there are just a couple of potential areas where you could run into problems. Firstly the digipot voltage; as far as I know you are pretty much limited to 5V rail to rail unless you can do smd. Obviously this will limit your dynamic range. Also both sides of the pot need to be biased to the midpoint of supply and ground to work properly. Some useful information here: http://www.eetkorea.com/ARTICLES/2002DEC/2002DEC20_AMD_MSD_AN02.PDF
http://www.maximintegrated.com/en/app-notes/index.mvp/id/4262
Provided you set them up properly they sound pretty good to me (I can't really hear much zipper noise and no pops/clicks). However the low voltage probably limits you to op amp-based distortion circuits. I'm not sure if any of the nice mu amp distortion circuits will work well at 5V (more knowledgable people will probably chime in here).
The other thing is that current is limited to a couple of milliamps with most digipots. This can be a problem if you are controlling leds, vactrols and the like.   
Good luck with it!

[tthoen]

Thanks for the replies!

My main goal is to create an open source system that the DIY community here can take advantage of and hopefully save some money.  I don't want to reinvent the wheel if it's already been done on this forum.  My main gripes with commercial effects are the high costs and complexity of putting a decent pedalboard together.  To give a few more specifics these are my goals:

1.  Control only effect loop switching (at least for now!) with relays. 
2.  Allow manual control if desired.
3.  Provide 9V to each effect.
4.  Use a laser-cut wood enclosure to save cost and allow flexibility for others to modify.   
5.  Allow users to use their own tag-board or PCB designs so it's individualized.
6.  All of this is on one PCB.

Some questions for the community:

1.  What's a realistic # of effects?  I'm thinking of starting with six but want to make it "cascade-able" to add more groups.
2.  Are people interested in this type of project?  I want to do it for my own pedalboard but am interested to see if others are too!

Thanks!

Tom

[tthoen]

One comment on digital pots - have you tried log type VCA's?  I ran into the same issue on voltage limitations with the digital pots - plus they are typically linear.  I've successfully used THAT corporation's 2180 series with D/A converters.  They are overkill as far as spec's are concerned, and not super cheap, but can handle a wide range of signal levels.  They wouldn't work in all applications but have a wide voltage swing.   Here's a link to an app. note if interested:

http://www.thatcorp.com/datashts/dn02.pdf

~Tom

[Hatredman]

If I understood correctly, you want a switching device with 6 loops.

There are already some projects of the kind if you Google it, both modular (Bradshaw-esque) or off-the-shelf (like the Martin Octa Switch).

[Hatredman]

I've seen something similar in this very forum, but I could not find them right now.

[R.G.]

There are quite a number of articles on effects loop switching and loop controllers at http://www.geofex.com.

Been there for some years now.

[tthoen]

Hi R.G.

Thanks for the response!

I looked at the GeoFX website and found the post on "Remote Footswitch Bypass with Relays and CMOS" and  "A programmable FX switching system" - are these the one's you're referring to?  These look similar in concept to my project idea; however the effects would reside inside the enclosure so the signals being switched don't need to go outside the box.

Tom

[tthoen]

Hi Hatredman - please let me know if you find the link - from what I've seen these controllers are pricey (although reasonable from a manufacturer's standpoint).  My goal is to make this accessible to the DIY group.

[Tightpants]

Hi Tom, have you seen this:http://www.donnerdeal.com/joyo-pxl-plx8-multi-effects-pedal-programable-looper-control-station-switcher-system-truebypass-black.html?acc=98f13708210194c475687be6106a3b84&gclid=CPqt3-rXxMcCFRQTGwodR3YGDQ
Seems like a good price to me, I don't think you could DIY this any cheaper. By the time you have bought all the switches, jacks and relays etc you will be in for a fair bit.
Edit: just noticed that they are out of stock! Oh well, not in the spirit of DIY anyway....

One comment on digital pots - have you tried log type VCA's? 

Not tried the VCA approach but a good way to do log taper with digital pots is simply to get your input from a log pot (into 8 bit ADC on the micro to generate the steps for the digipot). Works quite well for me.

[tthoen]

WHOA!  $129?  Amazing!  You're right - almost impossible to beat that price. 

However, the difference with my approach is you don't need to "box" all the pedals, wire all the adapters, and buy all the short pedal cables. 

Update:  You can buy these for ~$180 on eBay.

[Tightpants]

However, the difference with my approach is you don't need to "box" all the pedals, wire all the adapters, and buy all the short pedal cables. 

Yes quite right, I forgot about that Also I'm not sure that they use relays, maybe electronic switches (not that there is anything wrong with them). Do you have a reliable (noise-free) method of switching with relays? If so I would be quite interested in having a look at it. Have you decided which micro to use? If you are still looking around the Picaxe is well worth a look for this sort of thing: http://www.picaxe.com/

[tthoen]

The best way I know of for "noise-free" switching is by muting the audio output for enough milliseconds to bypass the noise of the relay.  I've seen a lot of amplifier manufacturers that use that trick - on the order of 10 - 20m.s. so you can't hear anything. 

R.G. also uses a 0.1uF capacitor between the base and collector of the transistor that drives the relay to limit noise - I haven't tried it but it makes sense to me!

Update:  Here's a link to an example of muting if interested:  http://stompville.co.uk/?p=423
He uses a TLDP222 opto-mosfet, which may be overkill - I think a simple fet that grounds the signal would work too.

[Tightpants]

Thanks for the link and the idea Tom, I will investigate further.
Cheers,
Pat