Sunday, 5 April 2020

Synthesizer Extra's No. 2: JOYO Instrument Tuner Hack.

This article explains how to connect a JOYO Instrument tuner to the VCO('s) of your modular synthesizer.

Inspired by LookMumNoComputer's Preformance VCO with built in tuner I bought three of these small Joyo tuners on eBay to see if I could adapt them to work with the synthesizer. I managed to do it and it's not difficult to do at all. Many people seem to do this too going by the Facebook reactions I got on this hack. :-)
The JOYO instrument tuner is a very useful bit of kit that you can buy on eBay or AliExpress etc. for around 5 US Dollars including shipping. It's pretty easy to hack these things so you can connect a jack socket to them and so connect it to the VCO's in your synthesizer. Because my synth is monophonic I can not play cords on it but having three VCO's and three of these tuners connected to them, I can easily tune each VCO to a different note and so simulate a 3-note cord.  It makes tuning very fast and very accurate.

Now, before we begin I want to mention that the method below is just the way I did it. I've had lots of reactions to this hack and people do it in all sorts of ways, for instance connecting a jack straight to the piëzo wires without a resistor divider and not having the piëzo mic connected. Using a capacitor instead of resistors and it all seems to work so this is just my way of doing it but it's certainly not the only way, or the best way, to do it! Just so this is clear.

Here's what we do. You'll need to carefully open the tuner case by turning loose 4 little screws at the back and then take out the two screws that hold the print in place and now you can lift out the print. Leave the actual LCD display safely inside the case and make sure not to get fingerprints all over it. On the back side of the print, you'll find a very thin Piëzo-electric disk-microphone. Carefully bend the white display lighting out of harms way and solder a thin wire to both the earth connection, which is the solder blob on the outer part of the Piëzo electric microphone, and to the red wire that goes to the center of the disk microphone. Do not disconnect the red wire from the microphone otherwise this won't work. (If you leave out the 20K resistor, it will work without connecting the Piëzo microphone, according to some comments, but I have not tried this so I can't be sure.)
Now make some small notches in the side of the tuner case to lead the wires outside. Put the print back inside the case first, to make sure where the notches need to go, then mark the right spot and take the print back out and make the notches in the case. Assemble the tuner and put everything back where it was. Now you can solder on the resistors following the diagram beneath. Solder them straight onto the input socket. Now solder the wires to the input jack socket (3,5mm) and the resistor and then glue the input socket, with the resistors and wires attached, to the side of the tuner case. Make sure when glueing that you don't go past the bottom of the tuner case so the underside stays straight and flat. I myself then hot-glued the tuners to my synthesizer by putting hot glue on the battery cover, which covers about 3 quarters of the backside, so the tuners are held in place by the battery cover. I later carefully drilled a 2mm hole through the covers into the wooden panel of my synthesizer and put a small screw in each one, that sits flush with the battery cover inside surface. That way I know it won't fall off at some point.

Powering the tuners:
I soldered two wires to the battery connectors. The spring connector in the middle of the battery compartment is the negative pole and the metal contact at the side is the positive pole. I drilled a 3mm hole above the screw that holds the battery cover onto the synth, right through the wood so I could lead the wires through. Then I connected all the positive wires from the three tuners together and all the negative wires. I soldered a 10µF/16V electrolytic cap to the point where all the wires come together to make sure there's no interference in the power supply and then I soldered a connector to the wire junctions that goes straight into my synth's powerbus system at the 5V point. (My synth provides +/-5, 12 and 15V). I soldered three 1N914 diodes in series with the positive pole on the power connector to bring the 5V down to 3V. This worked perfectly. Then I insulated the connections by putting hot glue between the two wires so they can never touch. When that is dry or cooled-off, I put some hot glue on the edge of the battery case and pressed the tuner onto the battery case quickly and held it in place until it was cooled-off. That's a matter of 30 seconds. Now, if I turn on the power, the tuners switch on automatically without the need to press the on/off buttons.
It's much better to give them their own internal power source because if you run them on the batteries the screen will flicker and vary in brightness. This way is all nice and stable.

Here is the way I wired up the audio inputs. I believe the input of the Joyo tuner is capacitive so a resistor voltage divider like this will work fine and there will be no need to use a capacitor. This resistor voltage divider brings signals with an amplitude of 10Vpp down to 2Vpp.

This is the print lifted out of the case. The white panel on the left is the LCD back-light. The gray and pink wires are the ones I soldered on myself:

Here's one of the finished hacked tuners without the battery cover because that is glued to my synthesizer. I blackened the glue with a permanent marker. As you can see I cut off the mounting eye for the clamp and made sure it was all sandpapered nice and flat. The fact that this particular model of tuner has a straight back and sides is why I chose this one. There are models out there with curved sides which make mounting more difficult. Bear that in mind when you buy one of these tuners.

Here are two of the three tuners mounted on my synth above two VCO's:

And finally a little video showing the tuners in action. As you can hear at the end, I was really pleased with the result. It looks very cool too on the synth I think.:

Oh and one final thing. You can use the left over clamps, from the backs of the tuners, to make a so called "Third Hand" to help with soldering :)

Leave the little screws in there and take some thick electrical copper wire (about 50 Centimeters long) and bend an eye at each end and mount the clamps to them with the little screws going through the eyes. Then hot-glue them in place and glue and/or tape that to a heavy enough metal base and there you have it. Super useful! ^___^

Okay, that's it for this one. If you have any questions please put them in the comments below or message me on FaceBook (only if we are officially friended, otherwise I'll get no notification.)
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See you on the next one!

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