4 – Four Voice Oscillating Synthesizer (B.E.2)

While looking around at circuit bent electronics, I discovered casperelectronics’ Drone Lab V2, and was immediately in awe. While the website has the schematics, parts list, and assembly instructions, it’s a fairly hefty undertaking, with a great deal of precision soldering on a pretty detailed circuit board. It’s also the sort of thing that would be a nightmare to debug, if I had a cold solder or bad component. In other words, diving into an undertaking of this size and complexity with the little experience I have under my belt would be a foolish, frustrating and likely expensive, fruitless endeavor. That being said, after watching the sample videos, I still considered buying the kit or maybe even a pre-assembled unit… until I saw it was $350 for a tested and assembled model, and $200 for the kit.

Basically, the Drone Lab V2 is a four-voice oscillator with effects. That is, it plays up to four separate tones at once, the sound of each being adjusted manually, and run through a mixer, low-pass filter, distortion, and band-pass filter. Their website does a far better job of explaining than I ever could, but watch this video (the part from about 00:45-01:00 is what really grabbed my attention), or this one to see it in action.

Disparaged by my inability to add this amazing thing to our musical arsenal, I sent the link to our singer over instant message, and explained what it did. While I was listing the features, something occurred to me: I didn’t need to buy it or build it at all. Using duplicate parts leftover from my first synthesizer, I could simply build a four-voice oscillator, then run it through guitar effects to do the rest. Our singer had recently begun using a series of individual guitar pedals in lieu of his Boss GT6 effects processor, so it was now conveniently unused and available.

Aaaaaaahhhhhhhhhhhhhhhhhhhhhhhh (Heavenly vocalizing, not surprised screaming.)

Ahh, re-purposed electronics: saving me from days and days of frustrating labor since at least a couple of weeks ago.

All I needed was an enclosure, some potentiometers and knobs, and I was in business! I already had a re-purposed, scavenged enclosure in mind, sitting at home waiting for me, so after a quick trip to Tanner for the rest of the items, I was ready to get started.

The theory behind this synth is simple: the 40106 chip I used in the first synth can actually output up to six ‘voices’ at once (I considered doing all six instead of four, but decided it was overkill. For now.).

The 40106 IC pinout.

The way this works is to take an output, for example, pin 2 in the diagram to the left, add a resistor and a potentiometer, then feed it back into the input- pin 1, in this case; the output will then also be connected to pin 2. There are several sites out there that detail how and why this works, if you’re interested, and there are a lot of different ways to build an oscillator using different chips and methods.

Once this was breadboarded out, and tested, I found the pitches weren’t quite low enough for my liking due to the potentiometers I chose, so I added a  resistor to each in order to lower the notes. The final design ended up with  the fourth oscillator at a higher frequency, in order to include a higher octave in the drone.

[I’ll update this with a schematic once I’ve drawn one up, but it’s extremely simple. ]

Yes, I forgot to take a 'before' picture again.

Picture this, without the JENSEN logo emblazoned on the front. That's it.

For the case, I emptied out an old RF modulator (for attaching a VCR or old-school game console to a TV with no input jacks), and mounted the output jack, power switch and indicator, the four buttons to activate each oscillator and the potentiometers to control them.

There wasn’t room to mount the 9V as I would have liked it, so I settled for hot-gluing the clip against the inside front of the box, facing the back side, so that the 9V’s bottom end would slide into the clip. The clip was bent open slightly more than usual, so it doesn’t offer too much resistance when removing the battery, and the hot glue holds it nicely in place. My only concern was that the battery was close to a set of potentiometer terminals, so I went ahead and insulated all of the exposed terminals with hot glue, for good measure.

Once everything was wired and soldered, I fired it up, and was pleased to discover that it worked beautifully. The sound it produces is still a somewhat harsh square wave, but once it is run through the GT-6 effects, it sounds amazing.  I’m still learning my way around the GT-6, but once I’ve got the effects down, I’ll upload some demos.

As you can see in the above picture of the RF Modulator, the back panel had a number of jacks on it, which obviously weren’t being used in the synthesizer, so I left that panel out entirely, and started looking for a replacement. I was originally planning on using a front panel for a computer drive bay, cut to size, but I ended up cutting a piece of clear acrylic from the face of a broken clock. I cut it out with a dremel cutting disk, which I wouldn’t recommend; the resulting cuts weren’t as clean as I’d have liked, and it left visible white marks on the edges. I realized it was happening as I made the first cut, so I just cut out a larger piece than I needed, and took off the excess with a regular dremel bit, which ended up leaving marks anyway. Lesson learned: I think it would have been much better to score the outline with a knife, then break it cleanly using a straightedge.

The transparent back panel, marks and all.

Future Ideas/Rebuild – I’ll probably rebuild this one to make a few adjustments to the design. When I do, I’ll be resistoring the unused leads of the 40106 to ground, since I’ve discovered that’s considered a ‘better’ implementation which is more efficient.

I’m also planning on going with panel-mount potentiometers and ferrite beads to reduce noise and make the output a bit more steady and reliable, since this one’s a bit more ‘controlled chaos’ than the other synth. As it stands, each oscillator produces a steady tone that can be adjusted until it’s a perfectly-tuned note, but the octave range occasionally varies between sessions.

It’s always exactly one octave, but the starting note can be… mercurial: sometimes it ranges from low to middle C, sometimes F# or D. It doesn’t vary while the unit’s on, so the knobs can be adjusted until it’s tuned to a perfect chord and it will drone away on that set of notes without wavering, but if you turn it off and back on, each oscillator will be equally lower or higher. I don’t know why that is, but I’m assuming it’s either noise introduced through parallel-running-wires, panel-mounted (ungrounded) potentiometers and shoddy soldering.

I may also combine new, improved builds of the first synthesizer and light controller module with this synth in a single enclosure. Wall transformers are easy enough to come by that it shouldn’t be a problem to run it off of A/C power, and it would be more convenient to have all three units in a single form factor that looks more like a retail purchase, and less like something that wouldn’t clear airport security.

Pictures – I knocked this entire build out in about two hours, and didn’t really photograph the process, so I’ll have to open it up and take some more. In the meantime, here are a couple I took in the studio while playing around with the synthesizers and the GT6 through the PA.

The new synth (middle), original synth (left), and headphones, in front of the GT6.

Ooooh, ahhhhh.

Both synthesizers turned on and pointed lights-up for dramatic effect.

3 Responses to “4 – Four Voice Oscillating Synthesizer (B.E.2)”

  1. how can ı make a simple read out loud device

  2. I’m not entirely sure what it is you’re wanting to know, but the only real advice I can give you would be to search the internet or electronics texts for schematics or ask for help from someone that has already made one.

    I’m just about the furthest thing from an engineer you can get. Everything I’ve done or that I’m currently working on is an example of extremely basic, simple electronics, and I’m sure that even a beginning engineer could laugh at a million things I’ve done wrong.

    The only reason I post anything about working on these projects is to demonstrate that it’s possible for anyone with an interest in such things to get started, even if they have no experience.

    Sorry I can’t be of more help, but good luck!

  3. Sorry for my bad english. Thank you so much for your good post. Your post helped me in my college assignment, If you can provide me more details please email me.

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