Saturday, 25 April 2020

Synthesizer Build part-29: VCA (Yusynth design).

A good working and easy to build VCA for use as extra VCA or as the endstage and line out for your modular set-up.

This module is a great solution for all your VCA needs. I needed a new VCA module for the second stage of my synthesizer and I wanted to upgrade from the first one I built, although it functions fine I hasten to add. This VCA is a more luxurious version of the first one you could say. And this one doesn't invert the signal like the first one did.

But before I get ahead of myself let me explain what a VCA does for all the people who are new to DIY synth building. A VCA or Voltage Controlled Amplifier, is used to stop your synthesizer from continuously making sound and to only produce sound when you press a key on your keyboard. So it's like a volume knob that is only opened up if it receives a signal from the Envelope Generator. Now the higher the voltage from the envelope generator (or ADSR)  is, the louder the output of the VCA will be. VCA's can of course be used for other things, like in drum machines, as a sort of Gate, to let through short pulses of noise to create percussion sounds but this is not what we're going to be dealing with here. This VCA is primary used as the last stage in your synthesizer from where the audio goes to the HiFi amplifier and the speakers. So to sum up: The VCA lets through audio when it receives a signal from the Envelope Generator and it stops audio from passing through when there's no envelope signal present on the ADSR input of the VCA. Opening up the 'Gain' control will enable you to bypass the Envelope Generator Input and output sound/audio without pressing any key on the keyboard and therefor without any Envelope Signal being present but normally Gain is set to zero.
I hope that's clear but you can always ask me things in the comments if you need more info.

The VCA is capable of handling input signals of + and - 10V and outputs them at the same level if the audio and ADSR potmeters are fully opened up and if you use an Envelope Generator that outputs an envelope of  +10Vmax. This VCA is perfect therefore to pair with the Yusynth 7555 ADSR from article 24.
If you need to output the signal to a HiFi audio amplifier then I advise some little extra attenuation. You can easily do this with a resistor voltage divider that halfs the amplitude of the audio. If you then turn the audio and ADSR potmeter back, the signal will be low enough to go into the Line-In of a HiFi amplifier.
As to running this VCA on a dual 12 Volt power supply; I don't think there will be any problems with that. After all the opamps and transistors all work fine on 12V so I think it's just a matter adjusting the trimmers. You can have an issue where one of the trimmers is turned all the way to its limit because of the lower voltage but I have no data on this so I can't be sure. The first VCA I describe in chapter 10 is purpose built for +/-12V so you can always build that one if you're not sure. I've build 3 of those so far and they work very well.

Here's the verified stripboard layout. Wiring diagram:


Print only. Btw, the green wire-bridges indicate connections to ground:


This is the schematic from which I made the layout:



Bill of Materials.



Calibrating the VCA:
With trimmer A2 you set the initial bias voltage on the base of transistor Q3. This influences the working of the Gain potmeter and you should set it in such a way that with the Gain potmeter all the way closed the signal is just muted. If you turn Gain up the last played note will then become audible without pressing any keys on the keyboard. So Gain is normally closed.
I found that the audio signal initially starts at 10V and then drops to about 6V. To counteract this you need to open up the Gain potmeter a little and then trim again so the signal is muted with Gain slightly open, This will stop the voltage drop of the signal and keep it at full power all the time. You will see this soon enough if you start testing it and connect this circuit to a scope. It's easy to counteract and it is in itself not a real problem because you hardly hear the voltage drop but you know, I strive for perfection ^___^
Trimmer A1 is the Balance trimmer. You set it so that the part of the signal that is above the zero Volt line has the same level as the part below the zero Volt line. In other words, you set it so that the signal has the same amplitude in both the positive and the negative part of the wave. This is best done using a triangle or sinewave on the input, together with an oscilloscope.
For trimmer A3 I advise to use a multi turn one. With this trimmer you trim away any DC Offset voltage on the audio output. Again you absolutely need a scope to do this but a cheap 20 dollar one will do nicely here.
The circuit has a LED that indicates the presence of an audio signal on the input. It's a sort of one LED VU meter and the brightness varies with the strength of the audio signal. If you turn the audio input level potmeter up, the LED becomes brighter.

Here are some pictures of the finished product:





You can see that I put a little white stripe alongside the counter clockwise first 20° of the throw of the Gain potmeter, to indicate to where you can turn the potmeter with the audio staying muted. If you turn it past the white, the signal become audible and normally the Gain should be slightly open but with in the white area.

The day after finishing this module I built two extra VCA's using the old layout and they work fine too. I wanted a few extra VCA's available but there was no need for the luxurious model. I'm going to use that as the end stage VCA in my second stage, with the output going to a HiFi mixer (at Line Out level) and use the other two VCA's for use in different patches.

Here's some pictures of the double model. I also posted these in the first VCA article:




So that's an other one done. One more and I'll have published 30 synthesizer related projects.
Okay, if you have any comments or questions please put them in the comments below and see you on the next one!

Tuesday, 21 April 2020

Synthesizer Build part-28: WAVEFOLDER (Yusynth design).

Here's an alternative way to create awesome synthesizer sounds! It's a pretty easy project to build too.

After first experimenting with a wavefolder design I found on YouTube I decided to build the Yusynth version because I wanted this option in my synth. This circuit produces some awesome and very divers sounds and waveforms.
The build was pretty straight-forward and it doesn't need to take up much room in your modular set-up either. This is a beginner to medium difficulty project but you do need to have a scope available to calibrate the circuit. A 20 dollar cheap one will do nicely. Make sure you use multi-turn trimmer potmeters for this. That will make it easier to calibrate later on. You can use normal trimmer pots if you have no multi-turn ones but it won't be as accurate. The schematic says to used matched pairs of diodes in the diode ladder but when I measured them they were almost all the same voltage drop. So as long as they come from the same batch I think you needn't bother with matching. The two transistors Q1 and Q2 need to be matched also but you can use the transistor tester in your multimeter. I recently built an adapter to change the pinout of my power supply bus system so I can test modules on dual 12 Volt and I'm happy to report the wavefolder works just as well on 12V as it does on 15V without any changes.

Here's the schematic I used from the Yusynth website:


Here's the (verified) layout I made for it and which I used for this project:


Print only:


Bill of Materials:



This wavefolder works best if you feed it a triangle- or sine-wave from the VCO.  This is convenient because an analog filter works best with squarewaves, they have the most harmonic content and triangle or sinewaves don't work that well in a filter. So with the wavefolder we have a use for those triangle and sinewaves. Ramp- or sawtooth waves will sound good too but squarewaves pass through the wavefolder unchanged.
Here's a video demonstration of the type of sounds I'm getting from this module using a Triangle wave only. There's also a very low frequency LFO ramp signal going into the CV input.:




CALIBRATING:
To calibrate this Wavefolder you will first need to set the two trimmers in their middle position. Turn the Shape potmeter all the way counter clockwise and Range all the way open. Connect a sinewave from your VCO to the input and a scope to the output and turn trimmer A1 (above the two transistors) to get the best looking sinewave possible.  It will probably not be a perfect sinewave but try to get the top and bottom part to look the same. Once you set this, turn the Range potmeter all the way counter clockwise and turn trimmer A2 so as to just mute the signal, so the level is 0 when the Range potmeter is turned all the way left.
That's the calibration done.

Here are some pictures of the finished product:





This is what your soldering should look like:


Finally, here's a video I found on YouTube demonstrating the Wavefolder:


Okay, that's an other one done. A very worth while addition to the synthesizer. I can really recommend it and all you need to build it are some very common parts.
As always, please put any questions or remarks in the comments below.
Thanks for checking it out. See you on the next one!

Sunday, 12 April 2020

Synthesizer Build part-27: QUADRATURE LFO Bergman edition.

A very quirky sinewave LFO with 4 outputs with a 90° phase shift to eachother. With extra waveform and an input for Frequency Modulation.

The quadrature LFO is something you won't find in many modular set-ups from the early days but it's a real little gem of a module to have in your set-up. It produces 4 sinewaves that are shifted in phase by 90° each. This can be used to create the 'Barber Pole' or 'Shepard Tone.' effect. "What's that?" I hear you ask. In short, it's an effect whereby it seems a tone is continously rising (or falling) without actually seeming to get any higher (or lower). See this Wikipedia Article for more on this effect. So that's one use. You could also feed four Voltage Controlled Panners with this LFO and have the sound go three-dimensionally around the room. Your imagination is the limit with this module which is why I was keen to experiment with this.

Eurorack 12V vs 15V.
I tested this circuit on a dual 12V powersupply and it works the same as on 15V. The amplitude of the sinewaves stays the same too (+/- 7,5 Vpp). I think this is due to the zener diodes. They keep the amplitude constant. The amplitude of the Trapezoïdal wave however will be lower at +/-10Vpp maximum. You can of course turn the amplitude of the waves down with the Output Level knob to, for instance, the Eurorack standard of +/- 5Vpp. No problem. So this is, in the way it works, a very Eurorack friendly module. For Eurorack you can cut the stripboard in half along the cuts in the copper strips, in the middle and fold it over. Then connect the top 3 and bottom copper strip together again with wire and you have a print small enough to fit behind a Eurorack panel.

I found this module with the schematic on the Yusynth website and set out to make a layout. Once again it turned out I made a faultless layout but it was with building it up that I made a mistake that turned out be an asset later on. This design uses two 5V Zener Diodes and somehow I had managed to stick one of them in the wrong hole on the stripboard so it was not connected correctly. This resulted in the output being Trapezoïdal instead of Sinusoïdal. Not knowing I had made this mistake, I posted about this on the Synth DIY Facebook page and people allerted me that it had to be the Zener Diodes that were at fault and they were right. After correcting the mistake everything worked fine but I then got remarks that I should include this waveform option in the final design of the module. So I did. I adapted the stripboard layout and added a switch to go between the two waveforms. If you want to build it as originally intended, without the switch, then just don't cut the copper between the two connection points for the switch on the print, so the zener diode is connected again.

Here's the layout. It's verified. I used it for my build. This is the wiring diagram. Beware the outputs are not in the right order. I added the correct order by numbering the jacks. All potmeters are viewed from the front.:



(Last revised: 12-April-2020. Corrected wiring orientation of dual gang potmeter and numbering of LEDs. 15-April-2020: Added mounting bolt and pin 5 and 10 warning text.)

Print only:


Bill of Materials:



 The LFO needs a few seconds to start up, when you first switch it on. If the 'Rate' potmeter is turned all the way counter clockwise it won't start up at all. With Rate set to 1Hz it takes a good 20 seconds to start-up and before the LED's light up. So make sure it's not on minimum when you switch on, or you could have a long wait on your hands. Turn Rate all the way up and it'll start up almost immediately.
The normal sinewave output goes from -7.2V to +7.2V with a frequency of about one cycle per 30 seconds to about 140 Hz. You can set the lowest frequency you want available with the trimmer on the print. I had a warning from someone on YouTube not to set the trim pot all the way down because his went up in smoke. I had no such problems when testing this print but I just thought I'd mention it here.
The Trapezoïdal wave has a higher amplitude and lower frequency so beware of that when you switch between them. It's maximum amplitude is -14,4 to +14,4 Volt and maximum frequency is 52Hz compared to the Sinewave's 140Hz. So you can roughly say the Trapezoïdal wave is double the amplitude and half the frequency of the Sinewave.
The amplitude of the waveform(s) can be set by the dual gang 100K potmeter so you can set it at any level between zero and the maximum I just mentioned. The direction of the phase shifting between the 4 outputs can be turned around by the DPDT switch. You can see the direction it has by four 3mm LEDs on the panel. I didn't have an Orange one so I used Red, Yellow, Green and White LEDs and the white one is quite a bit brighter than the rest so that's why it has a 12K resistor as current limiter and all the others have 1K2 resistors. This keeps the brightness perfectly in balance with the other three LEDs. One little drawback is that the LEDs only come on when the dual-gang output level potmeter is at the ten o'clock position or higher. At the lowest levels the LEDs don't light up.
Instead of the LM13700 you can also use the LM13600 and the TL074 can also be a TL084. From testing I also came to the conclusion that the 10nF caps don't necessarily need to be matched so closely. The two PNP transistors do need to be matched but you can use your multimeter's transistor tester for that and matched them to within 2 points of their hfe or amplification factor.

Here's the schematic I made the layout from:



Here's a picture of the finished panel:



Here are some screenshots from the oscilloscope. I only have three channels available because I blew up channel one of my scope and I can't bear to be without my scope so haven't sent it in for repairs yet. ^^

Sinewaves:


Trapezoïdal waves:



Fast Fourier Transform (FFT) image of the sinewave at 140Hz. As you can see, it's not a perfect sinewave. There are some strong harmonics but we're not dealing with an FM transmitter here so we're not looking for perfection. We're looking for usefulness.



Here's what happens to each of the two waveforms when you add a Ramp wave from an LFO to the FM Input:




Finally a little video showing all the different aspects of this module.



Here's a video of the first test I did with the Quadrature LFO. The patch is set up as follows:
3 VCO's are feeding 3 filters with a squarewave. The Steiner, Korg and the ARP filters. The Steiner-Parker receives two sinewaves from the Quad-LFO, one on CV-1 and one on CV-2 which are 90° separated in phase. The FM input of the Quad-LFO is being fed by a 0 to 10V ramp wave from the other LFO. Each filter output goes in a different channel of the mixer where they are summed and the output then goes through the CaraOK effects unit set to preset 61 which is a chorus effect. From there it goes to the speakers. The "da-daa-dang da-daa-dang" drone you hear is produced by the waves from the Quad LFO. :)




Here's an other short sample of the Quad LFO. It's being fed by a slowly rising ramp wave and two of the outputs are going into the Steiner Parker filter. The ARP and the Wavefolder are also in the mix:



Just for my own record keeping, here is an image of the state of readiness my synthesizer is in now. I have 8 free power-buss connections left so plenty of room to build more modules in the near future.



Okay, that's it for this one. With special thanks to the folks over at the Synth DIY FaceBook Group for all their help in the initial troubleshoot.
As always, if you have any questions or comments please put them in the comments below.

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.)
Please feel free to share this or any other article on social media. There are buttons for that underneath every article.
See you on the next one!

Wednesday, 1 April 2020

Synthesizer Build part-26: STEINER-PARKER VCF (Yusynth Design).

An awesome sounding filter with LP, BP, HP and AP modes and a resonance that can be very agressive! (Beware your speakers, LOL). It's way up there with the ARP filter as one of the best sounding filters I ever built on stripboard.

Let's see, we've done the Moog, Prophet One, Korg, Dual Korg, ARP and Digisound so this is filter number six not counting the dual Korg. This is an other Yusynth design and once again I managed to make a Stripboard layout that turned out to work straight-away.

With this filter we get all the different options for filtering sound in one module; Lowpass (LP), Bandpass (BP), Highpass (HP) and Allpass (AP) which is more a phase shift effect although not very pronounced. The filter is self-oscillating in all modes (!) which is not usual for a 24dB/Octave filter I believe.
This filter has a very distinctive sound so it's an excellent addition to the synth because I want as much diversity in sound as possible. Especially the Bandpass and Highpass can have a very cool distortion if you turn up Resonance so it almost sounds like a heavy metal guitar. The filter was re-designed by Yves Usson (YuSynth) to do away with some of the erratic behaviour of the original design, but I noticed he didn't manage to get rid of it completely. The resonance can give a very loud whistle and if you turn it past that, with cut-off freq turned down, the filter stops working with a deep pop that can't be good for the speakers. I've included a 5K trimmer to replace the 3K9 resistor, R18 in the schematic, so I can set the reach of the Resonance control a bit better. This works up to a point but it's not possible to tame the resonance completely this way. The resonance gets better as you reduce the resistance of the trim pot but this reaches zero Ohm before resonance is completely tamed. But then again, that's the character of this filter so you don't want the agressive behaviour to disappear completely. The panel potmeter needed for Resonance is a 50K reversed logarithmic one but in the Yusynth article he explains that you can use a 100K linear type with a 100K resistor soldered between pins 2 and 3 of the potmeter, so that's what I used and it works just fine. That's also the way I drew it in the layout because I figured not many people would have a reversed logarithmic 50K potmeter lying around. If you do have one though, use it.
I didn't have a 2-pole 4-way switch but I did have a 4-pole 3-way switch, a vintage 1970's one too, which I was dying to use in a project. To compensate for missing that 4th position of the switch, I added a second DPDT switch so I can switch from High-pass mode over to All-pass mode. In the layout it's a SPDT switch but I used a DPDT switch and I used the left over pins to switch on some 3mm LED's to indicate visually if the filter is in HP or AP mode. This works very well. The LED's are normally off and only if the main switch is set to HP does the 2nd switch get power to light up one of the LED's. I used one of the left over poles in the 4-pole switch to switch the power for the LED's on or off. This looks really cool and it works perfectly so I now have all 4 options available. I did not add the LED's etc to this layout because I added it as an after thought but it's easy enough to add something like this yourself. Anyway, you would normally use a 4-way double pole switch, so there would be no use for LED's then.

Here's a link to the schematic drawing I used from the Yusynth website. This is the revised re-designed version like I mentioned before.
Here's the stripboard layout and wiring diagram I made for my specific needs with the somewhat odd switch arrangement:



The Steiner-Parker filter will work fine on a dual 12V power supply. No extra changes are needed.
Here is the version with a normal 4-way double pole rotary switch. These layouts are verified, I used them for my own build and they have been successfully used by others, so you can print this one and use it as the wiring diagram. Please note in this layout I left out the second audio input jack and potmeter, the second CV input jack and potmeter and the 1V/Octave input jack, so remember to to put those in! They are just copies of the first inputs with a level potmeter and an input jack for each. Except for the 1V/Octave input which is just an input jack. So in total we have 6 jack-sockets and 6 potmeters.:


(Last revised 2-April-2020: Added Audio output jack and normal 4-way switch and made more room around the caps on the left plus L-Bracket for panel mounting. 4-April-2020: Added earth connection to pin 3 of TL074. 28-April-2020: Labeled rotary switch with filter-modes.)

All my stripboard layouts are made on 24x55 stripboard and usually I use the whole board. Because I use the Kosmo format of 20cm high panels I have room enough to accommodate them behind the panels I make. So the builds on my website are not very Eurorack friendly. I keep the components spread out to make troubleshooting easier should that be necessary.

Print only. (Print this out and use it for your build. Don't forget the cuts underneath the 4th wire-bridge from the left and underneath the chip.):


Schematic:



You can see from the schematic drawing how simple the design is. It's in fact just a diode ladder with 4 capacitors and a few buffers around it. A very effective set-up as you will notice after you successfully built this filter.

Bill of Materials:


(Last revised: 15-5-2020 Added extra potmeters and input jacks that are not shown in the layout.)

Calibrating the filter:
There are three trimpots on this circuit and the way to set them is just to turn them and listen to the filter's reaction. They mostly influence the cutoff point of the filter. The 5K trimmer, as mentioned before, is one I added myself. On my print it is turned to zero Ohm to give the Resonance potmeter as much throw as possible. So you could actually replace it with a wire bridge but I advise to just put in a 5K or 2K trim potmeter.
For the 50K logarithmic pots for audio in, you can use linear types if you wish and the value for the potmeters for audio and cv level is not important either. You can use any value from 10K to 1M for those potmeters. I put in 10K ones myself because I have a lot of those in stock. But do use the right value potmeters for the Cut-Off Frequency and for Resonance. (I guess you could use a 100K for Cut-Off but then the 47K resistor needs to be changed to a 100K type but I have not tried this and I don't guarantee that'll work. So just keep to the recommended values for those two potmeters.)

Here are some pictures of the finished module:

The 'finished' print. Notice anything wrong? Yep I managed to forget 4 components, one 220K resistor, two 10µF caps and the earth connection for pin 3 of the TL074. So when I first tested the filter it didn't work like it should. (Even without the input caps I was still getting audio in. I was very surprised because without those caps the inputs are effectively cut-off from the circuit.)







In the first instance I didn't notice a big difference between the different modes of the filter. That was until I discovered I had forgotten to earth pin 3 of the TL074. Now that I've done that the filter sounds even better than it already did. I noticed that with this filter you can hear the original sound coming through the filtered sound if you turn Cut-Off and Resonance way back. I've done some research and this does seem to be exactly how this filter should sound so my build is spot on. Here's the filter in action in the Arturia MaxiBrute:
https://www.youtube.com/watch?v=7ul95vmNFwM
The Arturia MiniBrute was designed by Yves Usson aka Yusynth with help from Nyle Steiner, the original developer of this filter from whom it gets its name..

Here's a video demonstrating the sounds this filter can produce. It's my usual 'ploink-ploink' on the keyboard, but even so it sounds just amazing! I especially love the Bandpass mode. You can instantly see the squarewave disappear when switching from lowpass to bandpass and you're left with all the harmonic content on top. I LOVE this filter. (Perhaps even more than the ARP filter because of the these different modes.)


And here's a YouTube video by Alan Wolke (W2AEW), demonstrating how to match diodes. Btw, his YT-channel is full of interesting electronics videos. They're not synthesizer based, more radio frequency stuff, but very interesting none the less.:



Finally I want to share with you a picture by a member of the LookMumNoComputer Forum, Duane Kelly (Doolang), who successfully built this filter using my layout only he made it Eurorack size by cutting the print in half and connecting the necessary copper strips together. He did the same with the Digisound 80 filter which also worked perfectly.


Okay, that's an other filter to add to our collection. I have a few more on my wish list and now that I have the second case finished I have enough room to build all the modules in.

If you have any questions or comments, please leave them in the comments below or contact me on Facebook. See you on the next one!