Because of a lack of new content I’ve resorted to posting old projects. This is one of the first builds I completed somewhere around 1995, a PAIA Theremax Theremin. PAIA has been around since 1959 and has been making DIY kits for musicians for decades. In addition to several analog modular synthesizers, Reverbs, EQs, a vocoder they also have their twist on the Theremin, the Theremax.

From PAIA’s website:

…In addition to the traditional mellow sine-like tone, Theremax’s Timbre control can mix in a harmonic rich square wave to produce a signal that’s ideal for use with external filters and processors. And to control outboard units, there are Pitch and Volume Control Voltage outputs.

But the features that really set Tmax apart as a gestural controller are it’s Velocity Control Voltage (proportional to how fast you increase the Volume) and Gate/Trigger outputs. A convenient foot switch input allows muting the internal tone source without disabling the CVs…

Panel controls:

• Pitch & Volume Trim – these control provide a vernier null of the reference and variable heterodyneing oscillators in the Pitch and Volume control circuitry.
• Pitch CV – controls the range of control voltage produced in response to hand proximity to the vertical pitch antenna on the right side of the instrument. Clockwise rotation increases range up to a maximum of 6 Volts. This control does not effect the sensitivity of the internal pitch circuitry.
• Timbre – controls the brightness of the internal tone generator. At full counter-clockwise rotation the output is pure sine wave. At full clockwise rotation the output is a square wave. Intermediate settings produce a mix of the two.
• Velocity – controls sensitivity to rate of change of volume level. At min, there will be no velocity response no matter how fast volume is changed. Rotation toward max produces increasing response. At max, the Velocity Control Voltage output will produce a 4 Volt change in response to the quickest possible hand gestures. This CV is a transient with a time constant on the order of a second. Internally, this CV biases the VCA for asymmetrical distortion, with no distortion at the min setting.(asymmetrical, transient distortions are responsible for some of the perceived “punch” in natural instrument) This control also sets Gate/Trigger sensitivity, at max sensitivity the gate will respond to very slow movements of the Volume hand.
• Volume – adjusts the sensitivity of both the internal VCA and external Volume CV output to hand movement relative to the Volume antenna. Output level is adjusted here, but more importantly this control is capable of driving the VCA into symmetrical distortion. (symmetrical distortions are responsible for much of the “loudness” of instrument when played fortissimo)

Jacks

• Mute – a foot switch, or S-trigger to this jack mutes the internal pitch producing circuitry. CVs are not effected.
• Pitch CV – Control Voltage proportional to hand proximity to the Pitch antenna as ranged by Pitch CV control.
• Volume CV – Control Voltage proportional to hand proximity to the Volume antenna as ranged by Volume CV control.
• Velo. CV – Control Voltage proportional to how fast a hand is moved in proximity to the Volume antenna as ranged by Pitch CV control.
• Gate/Trigger – This TRS jack provides a 5 V. gate signal at the “tip” when Velocity exceeds a threshold. The “ring” connection is an S-Trigger compatible closure to ground. The LED lights to indicate a triggered condition. (note that the gate responds to change in volume, i.e. how quickly the volume control hand is moved, not the static location of the hand)
• Audio Out – Output level is adjustable with the volume control but is nominally -10 dB.

I didn’t have the cash for the nice wooden desktop enclosure so I built my own out of spare wood and used metal shish kabob skewers for the antennae (not pictured). The Theremin still works well to this day although I’ve always had a little bit of a problem with the volume control. The 9v DC power supply is hard wired into the unit which was a poor decision on my part. An easy fix if I ever get to it. I’ve used the gate output to trigger an old Alesis D4 with good effect. The voltage control outputs are perfect for controlling various parameters of an analog modular synth.

If you’re comfortable around a soldering iron this is a great kit, an easy build, and for just the electronic kit it’s only $115. Money well spent considering what you’re getting.

Here we have 32 pots temporarily wired up on a piece of cardboard. This was the cheapest and most reasonable way to wire up the amount of pots for just a test circuit. I do this frequently when I need a quick mock up for controls. These are 1M linear taper pots and they’re all wired with a common ground and then each one is individually wired to a multiplexer input. I should be able to just take these out of the cardboard and drop them into the finished control panel when it’s completed.

This is full shot of the prototype prior to some sequencing enhancements. You can clearly see the leads from the pots coming into the 4067 multiplexer. It’s only necessary to run one set of 16 leads to the multiplexer, each additional row of pots can be wired to the previous with only the addition of one unique lead to the control input of the sn76477. A 555 timer is wired as an astable multivibrator for the clock and is sufficiently stable for my purposes. Although difficult to see in the image the sn76477 has a regulated 5V DC output to drive your logic ICs regardless of what your power supply voltage is. The group of black leads with green shrink wrap brings over the 4 bit binary count to the second multiplexer. In this image the binary counter is a 4520B dual binary counter. The original plan was to utilize both counters and a comparator to set the sequence length from 1 to 16 steps. The three switches at the top of the rightmost breadboard are for selecting the mix channels of the sn76477. through a combination of these switches you can include a VCO, LFO, decay, noise generator, and filter as well as bypass the sound completely. Like the pots these will be added for every step in the sequence for tailored sounds on every step of the sequence.

In this photo you can see some changes have been made. I swapped out the 4520B dual binary counter for two SN74LS193N pre-settable up/down 4 bit binary counters. The output of one counter is wired to the multiplexers and controls the sequence and then flows into the 4063B 4 bit comparator. The second counter is manually stepped manually with a push button switch and also feeds the comparator. Count A > count B a high signal is sent to the master reset of the sequencer counter and the sequence starts over at the beginning (0). The two switches off the side of the leftmost breadboard are required to allow for running the sequence in reverse. They serve two functions 1) to switch both counters from up to down counting and 2) to send a preset to the sequence counter on reset. Normally the counters reset to 0, but when going in reverse you want it to reset to 15 otherwise your sequence gets stuck on 0 indefinitely (due to the comparator condition always being met). Make sense?

This is just a close up of the hectic wiring going on. I only have yellow and white wire so it makes for a confusing time tracking down and correcting problems. In the left-middle you can see the 555 timer obscured by a couple yellow wires. Currently the frequency of the clock is variable with a duty cycle of 50%. One of the next steps is to include another timer so I can retain adjustable frequency and adjust the duty cycle to something much higher like 90%. This won’t impact the sound but it will make the LEDs flow from step to step smoothly… a totally superficial enhancement. On the lower right is a 3 input multiplexer to handle sending the reset number to the sequencer clock when running in count down mode. Another next step is to add an analog switch to replace my two toggles to switch from count up to count down mode.

Jacob Lysgaard recently contacted me while he was working on building the Dub Siren I posted here and on Flickr. His documentation and description of the required parts, where he bought them, his findings, troubles, and experience while building it is far more informative than my images and flagrant plug for Bastard Jazz.

I’m happy to see someone has not only successfully built the dub siren but is finding use for it in their performance. All the best to Jacob.  You can find the post on his blog here:  DYI Dub Siren – the complete rubdown.

This is a ‘ring modulator’ similar to the one used in an ARP Odyssey… this version operates by the input of two square waves into a 4011 quad NAND gate. I didn’t have a 4011 available so in this version I use a 4001 quad 2-input NOR with two inputs wired to ground (low) instead of wiring the 4011 with two inputs wired to Vcc. If I did my logic correctly the 4001 works the same when wired this way. I included the logic tables on the schematic if someone cares to check it. The two square wave tones passing into the gates are compliments of a simple op-amp square wave generator circuit. Information on how to wire one of these up is widely available on the web. Here’s one good resource. The original schematic and idea was found on simple-answer.com here. A brief reference to the ARP Odyssey and this ring modulator is mentioned on Wiki here.

Obviously this is in an Alpo Can. The circuit board can be viewed on Flickr (see link below) but it was pretty small so it had no trouble squeezing in there. The knobs were found on eBay for dirt cheap. The hardest part about modifying this can was getting the sharp edges off the holes drilled into the can. To get the top off without cracking open the dog food… and to be able to take the top on and off the can you’ll need one of these: Kuhn Rikon Safety Lid Lifter

More photos, comments, and the schematic can be found on Flickr here:

4001 Ring Modulator in an Alpo Can

Sound Samples:

Dry, without Effects

Wet, with effects

A while back Gil Duross over at Philly Techno was talking to me and was thinking about coming up with a analog step sequencer which would cost less than $100. It got me thinking that this isn’t that crazy and it’s likely someone out there has already done something like this. As is it turns out that’s exactly the case. The following video is of my test circuit of a 16 step analog sequencer based on Mauno Tuominen’s schematic for an analog CMOS sequencer based around at 4067n multiplexer/demultiplexer. You can see a DIY version of the sequencer here at studiomanus.com. I had an old sn76477 which I had been planning on turning into something so I started with the basics… indicator lights, tempo, and a simple oscillator. The eventual plan is to expand this out into a large 16 step sequencer/synth based around the sn76477 allowing for extensive sound shaping of each step in the sequence. Although the sequencer is well under $100 by the time this is completely finished it will likely cost well over that but the result should be substantial. In the meantime, take a gander at the initial test circuit. The sounds aren’t the most musical at this time, but it’s function and simple design is more the point.

I’ve expanded on the original design using a simple 555 timer for the clock and the ability to control the number of steps in the sequence through use of the 4063N. This has not been tested… that’s on my to do list. If anyone who reads this is well versed in these components and circuit design I’d love to hear feedback.

This is a Ring Modulator or similar sounding effect box based around the AD633 (Analog Devices Four Quadrant Analog Multiplier). The original design is taken from Roman Sowa. His website has further details on his design and the schematic I used as a starting point. The above photo shows the finished version albeit without knobs. This is mostly because I, despite better judgment, bought pots from Radio Shack, and didn’t want to waste them. As you can see the shafts are just a bit long. No matter; they work.

I made a few modifications. The first was to remove the option to select AC/DC coupling. I felt that I had no need for DC coupling so I hard wired it up AC coupled. Secondly I added some gain on the clean channel. The clean signal was coming through a little light which I personally didn’t like. Lastly, I added a LED meter on the output volume which you can see in this picture. Using a LB1403N I made a level meter which increases as you turn the volume up. This doesn’t actually monitor signal level but the position of the pot. There’s no real purpose other than I like blinking, flashing, pulsating and adjustable lights on all my gear. Who doesn’t? It’s wired through a dual ganged pot with a trim pot to adjust sensitivity. The detailed photos can be seen at the full Flickr photo set.

From a distance the paint job looks OK but as you can see in the first photo there’s definite room for improvement. Wet sanding, Clear Coat, and Polish would definitely help but it’s not a bad first run. The fluorescent paint however had a tendency to get ‘powerdery’ and presented some problems. Check the sound samples below to hear what it sounds like.

Many more photos and comments on the build can be found on Flickr here:
AD633 Ring Modulator

Sound Samples:
Before & After Number 1
Before & After Number 2
Before & After Number 3
Before & After Number 4

This is my second design from scratch that I put together for DJ Paul Diggs. He mentioned to me he wanted to add some fuzz to his Fender Rhodes and this seemed like a great chance to take a stab at an original design. Well, almost original. The distortion circuit is a portion of a larger circuit which I found on the web but unfortunately did not document. The remainder however, the sweepable low pass filter and second tone control I added in myself. Overall this is a pretty versatile sounding fuzz box with a pretty wide range of tones. It utilizes diode clipping so it still can be a little harsh although with the filter and clean/dirty mix you it can be tweaked for a nice sound. This is hopefully only the first version, I’ll be working with Paul to refine the tone and the layout to hopefully make this a perfect compliment to his Rhodes and bring about the sounds of classic rock years gone by like those from Joe Zawinul and the likes of Weather Report… though that’s just my taste, I’d bet it will end up a bit different.

This time I actually took notes and threw together a schematic. I’m hardly an engineer and my understanding of analog circuits is elementary so I welcome suggestions and criticisms from anyone familiar with these types of things. As with the other projects you can see detailed photos on the build at Flickr.

More photos, comments, and the schematic can be found on Flickr here:

Paul’s Fuzz

Sound Samples:

Unfortunately I neglected to sample this box before popping it in the mail. Version II will definitely have samples. That will be better anyway.  Incedentally I’ve repalced this fuzz with a better one.. the Big Muff Mod.

The Crash Sync is a John Hollis design who’s schematic can be found here. There are dozens of examples of these on the web.  They’re pretty popular among DIY enthusiasts and not terribly difficult to throw together.  John’s site has a number of great projects that center around Op Amps and are very affordable to complete.

I typically use whatever components I have available, either bought or raided from old gear, so when putting a project together there are some inevitable changes.  In this project I used different Op Amps and added in a bypass switch (with lights of course) to pass the original signal.  As far as I can tell using a different op amp hasn’t had a noticeable impact on the sound of this awesome little box. Lastly, like all of my boxes so far, I haven’t wired them up for use with a 9V… which is fine for me, but others might find it an inconvenience.   See the full flickr set for detailed photos.

Many more photos and comments on this build can be found on Flickr here:

The Crash Sync

Sound Samples:
Before #1
After #1

Before #2
After #2