Saturday, 26 April 2014

Pedalboard Controller MK2

A few years ago I built an Arduino-based gadget with two CV outputs, a footswitch and an output for controlling an EHX Freeze pedal:


I wrote patches with oscillating or random CVs and used them to drive my Moogerfooger MF-101 Low Pass Filter. Now that I've got three 'foogers and a CV-controllable KOMA BD101 delay, it's time for an upgrade.

MK2 has a lot more features:
  • Eight 5V CV outputs for Moogerfoogers
  • Six 9V CV outputs for the KOMA delay
  • CV input from the KOMA sensor
  • Six opto-isolated outputs for the Freeze, tap-tempo and (maybe) looper control
  • MIDI support - for patch development and live control
  • Expression pedal input
  • CV input for Moogerfooger LPF envelope
  • Three footswitches with LEDs
  • Based on the much faster Arduino Due
There's not much free space on the pedalboard so it's all got to fit into a box the same size as the original. After several attempts, I settled on this design:


The Arduino is mounted vertically at the back of the box, with a shield PCB sitting on top of it. A ribbon cable connects the shield to another PCB that lies just below the upper surface, with a 4-digit, 7-segment display, up/down patch select switches and four RJ45 sockets at the front. Two more Veroboard PCBs with TRS connectors mount on the front panel and connect to the shield through PCB header/crimp connectors. The shield schematic looks like this:


The main elements are the CV DACs (5V SPI with level shifting for the Due), 9V gain stage, opto-isolators, 7-segment display drivers and an I2C EEPROM for non-volatile patch storage. The PCB:


The display/RJ45 board is mostly routing signals from the shield, so the schematic isn't very interesting. The PCB looks like this:

 
The PCBs were made on an LPKF C40:



I built the easy one first:


Then the shield:


Fitting the display PCB into the box:


I built the TRS Veroboards and fitted them into the box:

Wired the CV board to the PCB header that plugs into the shield:


The whole lot assembled:


One of the RJ45s brings out a 3.3V serial port from the Arduino. So I needed an external board to translate to MIDI:


The next phase of the project is to write the Arduino firmware and find or write an application to configure the patches from a laptop or iPad. It'll be a while before the original box is replaced on the pedalboard...

Wednesday, 31 July 2013

Moogerfooger/Looper Order Switcher

There's a new song in the works at Zaardvark Inc. that requires me to record a guitar loop with some Moogerfooger sounds applied and recorded with the loop. But the board is wired so that the looper is before the 'foogers, because sometimes I like to record a clean loop and bend it separately.

So what I need is a box that reverses the order of the set of Moog pedals and the looper - and possibly the Freeze - as a separate group.

This'll do it:


A IN/OUT (aka send/return) connect to the input of the first 'fooger (FreqBox) and the output of the last (Ring Mod.). B connects to the looper. IN is routed to OUT through the two pedal groups in the order selected by the 3PDT switch.

I made a space on the board:


Drilled some holes in a box:


Sockets + wires:

To avoid ground loops I just connected the grounds of the IN, OUT, A IN and B IN sockets. We'll see whether that's good enough.

I don't need to switch the order with my foot so it's just a manually-operated toggle switch:


No LED either - I can see the pedal order by the position of the switch.

Testing:

Velcro applied and in-situ:

The whole board:

In the end I decided to group the Freeze and looper together as group B. It means that the input and output for the whole board are the switch box IN and OUT, which is tidy.

The use of metal plugs could undermine the anti-ground loop strategy, but it doesn't seem to be a problem if they touch each other.

The plastic box isn't really robust enough so I might replace it with a diecast box if I can find one that fits the space available and has enough room for all the sockets.

The next project is to replace the black box to the right of the new one. It's an Arduino-based CV generator and Freeze controller. I'd like one with lots more outputs and a load of other features I haven't finalised yet.

Tuesday, 25 June 2013

Precision Analogue Multi-Effects

This:


Is one of these;


One of these;


 And one of these;



Or at least the gubbins from inside them, all mounted in an aluminium enclosure. The yellow panel is a decade box, which allows me to dial in any resistance value from 0 to 11110 ohms, in 1 ohm increments. This is currently connected in place of the Delay Time pot on the Arion DDM-1 PCM, which has also had its trimpots tweaked so that the minimum delay time is just about zero, and very short delay times become accessible in a precise way using the decade box. It also means that the delay time can be adjusted in steps whilst playing, where before it could only be swept with the pot. This makes for some pretty unique sounds. The clip below features the unit treating various percussion and a glockenspiel in a fairly random way.



At the moment only the delay has been modified for decade-box control but the flanger seems like a good candidate too. If the Rate pot is disconnected the unit no longer sweeps up and down driven by its LFO, but can be manually swept using the Manual control. If the decade box is substituted for the Manual pot, I should have a flanger that manually sweeps in steps. I'll post an update when that mod is done!

Monday, 24 June 2013

Casio SK5 External Drum-pads


A set of Kraftwerk-inspired drum pads that interface with a slightly modified Casio SK5, triggering the four samples assigned to the right-hand set of yellow pads. As per the Kraftwerk design, these work by having metal sticks which complete a circuit when brought in contact with the conductive surface of the pads. 

I traced the tracks on the SK5's PCB to find good solder points, and wired those to four RCA / Phono sockets to the left of the power switch. As you can see the pads are mounted on the top of an A4 box file, which has a lid that can be propped open at an angle using the internal sprung clip, and which also makes a handy carry case for the sticks and pedal, which isn't shown but is an old morse key, inspired this time by the Silver Apples.


The pads are squares of material cut from a neoprene mouse-mat covered with strips of aluminium tape. As you can see in the pix above this got badly pitted very quickly, so I brought some sheet brass and bolted it over the top to give a more durable playing surface. I guess I should really cut the top left corner off each of them to match the shape of the pads on the 5.

The original sticks were lengths of coat-hanger wire, but these have since been replaced by pieces of narrow (2mm) copper tube.


Sunday, 23 June 2013

Bass 6



Some time ago I stumbled across this thread on the TalkBass forum, one of a few on that site and others dedicated to the creation of Bass VI-type instruments from the parts of cheap short-scale 4-string basses such as the Fender Bronco. This was my inspiration to turn a tired old Gibson EB-3 copy into a rough approximation of one of these:


A stupidly rare 1962 Gibson EB-6 (see www.mygibsonbass.com for more pictures).

The Donor


My EB-3 copy was I believe made in the Ibanez factory in Japan at some point in the '70s, and would have been branded Avon, Kingfisher or Columbus. I found it in a very sad state in a shed on a dairy farm about 10 years ago, and fixed it up. The body had been half stripped of its original cherry finish and the electronics and hardware had been cannibalised, with the exception of the pickups, which were horrible microphonic single-coils hiding under humbucker-sized metal covers. I sanded off the remainder of the finish, found machineheads, made a bridge assembly and built the circuit. 



My then girlfriend (now wife) played it for a bit before moving on to a 1978 Fender Musicmaster. The EB copy languished in a wardrobe for several years before being dug out for the conversion project.

The Conversion


From the top:

The machine-heads are a set of 5 GuitarTechs I had left over from a repair I did to a friend's Epiphone Joe Pass a few years ago. The 6th tuner is the low E, left in place from the guitar's 4-string incarnation. One day I might treat it to a complete matching set.

The nut is a 6-string replacement bought from my local family-run music shop. I filed out the slots to accommodate the fatter strings.

The pickups are mini-humbuckers from Warman Guitars. The pickguard and pickup surrounds are oversize to cover all the existing routing and holes.

The circuit features 2 volumes, 2 tones and a 3-way switch in a Les Paul-type configuration, but with three additional microswitches. The two on the pickguard are coil tap and phase reversal for the neck humbucker, and the one next to the pickup selector is a strangle switch (bass cut).


The bridge is a tune-o-matic copy with a stop tailpiece. I had to dowel the holes from the old bridge assembly and drill new ones. Getting the locations of these right was more down to luck than judgement. The press-fittings for the bridge and tailpiece were squashed into undersized holes using a G-clamp to apply pressure. Being a laminate body I wasn't too concerned about this splitting the wood along the grain, which I might have been were it solid timber.

How it turned out

Surprisingly well. It's very playable, and I found that I adapted to the string spacing very quickly. Going back to a normal guitar or bass afterwards is very odd though. 
The pickups are quite widely spaced which means the neck pickup is considerably louder than the bridge as the string vibration has greater amplitude as you move toward the mid point. Consequently the bridge pickup is jacked right up and the neck backed off in order to achieve a close balance between the two. This means that some bassiness is sacrificed, but stops chordal playing from becoming too muddy. I've found that if I want to use it as a bass guitar rather than as a rhythm / lead instrument I need to use an EQ pedal to fatten the bottom end up.

The pickup selector, coil tap and phase switches give a lot if useful tonal variations, ranging from full-bodied and fat to something almost clavinet-like. Run it through chorus and delay and it does Cure-type noises high up, or through reverb and tremolo you're in Twin Peaks. I find myself playing the solo from "Wichita Lineman" a lot.


The strangle switch doesn't do anything useful currently, but I will experiment with some different capacitor values until it does, or think of something else to do with the switch.


It's not a work of luthiery by any stretch of the imagination, but it's a very usable instrument in spite of its low budget origins and many rough edges. It has also served as a very useful prototype for possible future projects. There are some good EB3 copies on the market that could form the basis of a mkII, and occasionally genuine EB3 bodies / necks come up on Ebay. I'd be particularly interested in creating a medium (32") or long scale (34") version of this type of instrument as I find that 30" scale basses always seem to suffer from floppiness of the low E string.
Watch this space...


Wednesday, 19 June 2013

Zaarduino MIDI Organ Pedals

What do you do with some grubby old bass pedals from a dead Logan organ? 




Build one of these, obviously:



It's a Korg Microsampler triggered through MIDI by the organ pedals, all mounted in a sturdy box that closes into a suitcase-sized unit. 

This post describes the journey, mostly in pictures...

Dave built the pedals into a wood and aluminium box and we got together to thrash out the requirements for the finished article:


The essential features are:
  • MIDI out - to the sampler
  • MIDI in - for future external triggering
  • Three octaves of notes with LEDs to show which octave is current
  • Control of analogue parameters with the swell pedal
  • Illumination for dark stages
  • A single mains inlet to remove the need for external power supplies
  • It folds into a neat unit that is quick and easy to setup on stage
For the brains I chose to use a 5V/16MHz Arduino Pro Mini. It's got just about enough pins and adequate processing power for this application. The original intention was to mount the Arduino on stripboard and hand-wire it. For this reason, I decided to allocate an input to each pedal switch rather than use a more conventional matrix that would require more components. This turned out to be a mistake. I'm pretty sure I ended up with at least as many components. In any case, the stripboard plan was dropped when I got access to a PCB prototyping machine. I also needed an excuse to learn Eagle, and this is the design I ended up with:



Manually routed, the PCB looks quite neat and only needs to be single-sided:



The end product:



Mounted into the box by screwing a piece of stripboard to the back and fitting stand-offs to it:


Wired to the pedal switches:



The mains socket is enclosed inside a plastic box for safety, and mounted on the rear panel:






The LEDs to show the selected octave, and the switch and swell pedal connections are going into a small box at the front. No PCB for this, just stripboard hacking:



The old optical swell pedal (also recovered from the Logan) had a filament bulb. Now it's a green LED:


The box is mounted and wired in:


Close-up of the swell pedal and indicator LEDs. The tab on the right-hand side of the pedal is a side-acting switch which toggles through the three banks / octaves.


With the MIDI in/out wiring, power to the illuminating LED units and a connection to the back panel for updating the firmware:



I was able to re-use a lot of the code written for the MIDI Trigger project. It just needed to handle more inputs + a few other tweaks:



Programming with a USB to serial converter:



The illumination in action in a dark rehearsal room:


High contrast colour scheme for the key-caps to enhance visibility on dark stages! 


The rear panel - On / Off, Serial, MIDI-In, AC In. Audio Out is via a flying lead connected direct to the Korg. The serial port allows us to squirt new code into the brain without having to unscrew the top of the cabinet. Note the effects of painting the unit in the dark!



All assembled with the sampler mounted into the lid using a combination of metal brackets and heavy-duty velcro. It's a neat package, but built heavy-duty to withstand life on the road:


With the lid closed - still awaiting handles, catches and corners for the cabinet.



A short video made during testing:


We gigged it for the first time last week, and it seemed to do all the things we wanted it to. It's a huge improvement over the old three-trigger pedal in terms of reliability, visibility and the time it takes to set up on stage. The downsides are its massive footprint on stage, and the bulk of it. The case is made from recycled / reclaimed timber so it weighs enough that I'm afraid to put it on my bathroom scales to find out how much it weighs. It probably would have been lighter if we'd had somebody make it from sheet steel. Consequently it's become the subject of a reverse custody battle among the three members of Zaardvark. Nobody wants to have to carry it home. It almost got left behind the other night. We remembered just in time and found it at the back of the club where a couple of guys were using it as a table.