Synthesizer Build part-66: ROLAND TB-303 VCF.

The famous acid house filter from the Roland TB-303. A Eurorack friendly project and a ladder-filter that sounds amazing. 

This is the 14th filter on this website and this is one with a very specific sound so I thought let's make a project out of this because I think that this filter in particular will be of great interest to many people because of it's unique sound. I based my layout on a layout that Jake Jakaan made from a schematic he found online in combination with the original service manual schematic of the TB-303 (TB 303 stands for Transistor Base 303). 

I have to warn you, the filter sounds great in itself but to get that Acid-House sound out of it requires more than just this filter. That specific sound is a delicate balance between filter settings and envelope input and maybe some LFO or offset voltage added. When I first tried this filter I didn't get anything near that classic sound. However, I found some tips and instructions online which helped a lot. I posted a very helpful short video at the bottom of this article below the video demo's that tels you how to get that sound.

I got close in the end though as you can see in the demo video below. My mate Jake Jakaan built a few of these filters and he can really make them sound like a 303 should sound but then he's a professional musician. 

This is really the first filter I ever built that you have to learn how to use. I'm getting there tho ;)

A LITTLE HISTORY:

The TB303 was a bass synthesizer made by Roland and released in 1981. It was supposed to simulate bass guitars but it sounded nothing like a bass guitar and it became a commercial flop. It was taken out of production in 1984 after a run of 10.000 units. These were sold off cheaply by Roland. (If only we knew then what we know now @___@)  However, cheap second hand 303's were picked up by electronic musicians and the twirping, squelching sound became a main stay of electronic dance music genres like Acid House, Chicago house and Techno. There are now numerous clones on the market and original units fetch prices of over $3000,- on the second hand market. Originals were also modified in the 80's, adding distortion and external inputs (Nova mod).

The TB-303 was designed by Tadao Kikumoto who also designed the TR-909 drum machine. It has a single oscillator which produces a sawtooth wave or a squarewave. This goes into a 24dB/Oct lowpass ladderfilter which is manipulated by an envelope generator. 

I have read that it's actually an 18dB/Oct lowpass filter instead of 24dB but I don't know if that's true.

SCHEMATIC:

Here is the schematic. It's a bit low resolution because this was originally a file with a black background and bright green lines. I took it into Photoshop and inverted the image and brightened it up and made it more legible. I also included the transistor pinouts. All transistors on the schematic are NPN 2SC945's except for the two at the bottom marked 733. Those are two 2SA733 PNP transistors.

The capacitors in the schematic are not marked as polarized but the 10µF electrolytic caps are obviously polarized and for the 1µF you can use either type. Polarized or non-polarized. I used polarized caps in the layouts below so that you can see where the minus pole goes if you choose to use polarized caps.

Here's the filter part of the service manual schematic for reference. It has two 2K2 resistors from +12V to T1 and T2 but I think that's a misprint. It needs to be 22K:

The filter does not use any negative voltage. It is powered by +12V and it also needs a +5V powerrails which is provided by the onboard voltage regulator. The +12V goes through a 100 Ohm resistor. I wondered whether or not to include that but I wanted to see how much voltage that resistor takes off from the original 12V and it's only 0.2V so I left it in.

Staying true to the original includes using 2SC945 transistors for the NPN trannies and 2SA733 for the PNP transistors. You can however use other transistors like the BC547 and BC557 but beware when you do because you'll have to redo the layouts. The 2SC945 and 2SA733 have an unusual pinout. It's emitter to the left, collector in the middle and base to the right. I had to constantly keep this in mind when designing the layouts and it wasn't easy but I managed it in a day.

The transistor pairs at the top and bottom of the ladder and the transistors next to it with the common emitter connection need to be matched pairs!! Very important with this filter.

I came to the conclusion that my usual method of matching on Hfe didn't meet the case here so I did it with setting up a differential amplifier on a small breadboard. The method is shown below.

I ordered a hundred of the 2SC945's and made 10 matched pairs and I used those transistors in this project even with the middle trannies in the ladder. I thought I might aswell use all matched transistors but you don't have to do that. You can use other transistor types like the BC547 and BC557 which are used in the Doepfer A-103 VCF6 filter but you'll have to redesign the layout because their pinout is different from the 2SC and 2SA transistors I used.

Two resistors in the circuit have been replaced by trimmer potmeters so we can tune them in to our liking. These are in the Cutoff and Resonance control so they are important to the sound and they do make quite a difference. The way I set them was almost fully open for both (max. resistance).

To make things extra clear I just completed the KiCad version of this schematic:

MATCHING TRANSISTORS.

For this filter I didn't want to rely on just measuring Hfe and matching the transistors on that value. I used the Ian Fritz methode. I took a small piece of stripboard and set up a simple differential amplifier with two transistors. If the transistors are matched then the voltage measured between the two emitters should be zero. Make sure you let the transistors cool down after handling them with your fingers.

For D1 any silicon diode will do. The voltage drop over this diode ensures both transistors get exactly the same Collector Base voltage. Beware this setup requires a dual voltage source of +/-12V. You also need to make sure the two 100K resistors have exactly the same value.

You then need to switch the transistor positions and measure again. I didn't bother with that though. An other method is to leave one transistor in place and change the second one. If you find two transistors that display the same voltage difference from the fixed transistor, those two will be matched.

This method worked very well. I used matched pairs throughout the ladder filter and also for the differential amplifier made up of T1 and T2.

Please read the full article on transistor matching by downloading the article by Ian Fritz. 

Below is a picture of my transistor matching stripboard. I can get them matched to within 1/10,000th of a Volt or 0.1 milliVolt. I cut a DIP8 IC socket in half and connected the top and bottom pin together. I use that as socket for the transistors under test and with this setup I can measure NPN transistors with different pinouts because I have an emitter contact at the top and the bottom. I placed the sockets away from eachother to make it easier to change transistors without influencing the other transistor. I usually accept transistors that measure a difference within 0.3 milliVolt or lower. If you go to extremes with accuracy you'll be measuring until doomsday before you find a match.

LAYOUTS:

Below are the layouts for this project which are verified as ever. I used them to build my filter.

Wiring:

I numbered the transistors that are not part of the ladder, using the same order as in the schematic so you can easily understand which transistor is which when you compare it with the schematic. The light grey transistors are the 2SA733's. I included an extra CV input with the same level control as the Envelope input. 

The transistors in the ladder have the base and collector connected together so they actually function as diodes.

As you can see the envelope and CV input level potmeters have pin 3 connected to a 10K resistor and not straight to ground as is usual with input level potmeters. This is done so that the Envelope input is never fully closed. This is also the case in the original Roland TB-303 because the envelope input is very important for the characteristic sound of this filter. In my own build I did connect pin 3 of the CV potmeter straight to ground instead of the 10K resistor because I wanted to be able to fully close that input. So I leave it up to you how you want to wire that up.

If you look closely at the audio input you can see a 220K resistor on the stripboard that isn't used. I have the audio going straight into the filter through the 1µF cap. Originally that 220K should be in series with that cap but I think the value is too high. I later experimented with a lower value but you can also leave the resistor out.

Stripboard only view:

Cuts and wirebridges seen from the component side. As always, mark the cuts on the component side with a Sharpie or Edding marker and then stick a pin through the marked holes and mark them again on the copper side. Then cut the strips at the marked positions with a sharp hand held 6- or 7mm drill bit.

Bill of materials:

PICTURES:

Here are some pictures of the build proces:

Cuts and wirebridges done:

Everything is soldered in.

Here's the design I made for the panel. Feel free to us it if you want.

And here's how the panel came out:

You can see the colours don't come out as strong with clear waterslide paper as opposed to using white waterslide paper. But I like this effect. The design shouldn't be too overpowering I think.

Here's a look at the finished module:

Side/rear view. I had built a version before this one but it didn't work but I re-used the panel I made so the mounting holes are not positioned where they need to be so that's why the M3 bolt is bent sideways.

VIDEO DEMO:

This filter has that typical ladder filter quirck where if you turn the resonance up the volume goes down and you get less bass. Most ladder filters have this characteristic. The Moog ladderfilter does it and even the Doepfer A-103 VCF-6 does it. 

Here's demo, trying to get that Acid sound using some of the tips from the YouTube short video below. I came close but it's not quite there. I had a slowly rising sinewave on the CV input and a short pulsing envelope, with just some decay and all the other parameters of the ADSR closed. Instead of an LFO I think an offset voltage alone would be better. You can hear it reaches that "eeeuuurrrghhh" sound as the LFO rises in voltage but then it gets too high and it starts to whistle more. I'm going to do more experiments, using the voltage processor and see where that gets me.

Here's an other short test. Beside the envelope input I also had an offset voltage going into the CV input. That offset voltage came from the dual voltage processor to which I also had a sawtooth LFO connected. I set the processor in such a way that I always fed an offset voltage to the filter but the voltage would swing between about +2V to +4V. You can do this by raising the offset and then using the attenuverter to limit the maximum voltage. A very useful module to have in combination with this filter.

Here's a YouTube short explaining how to get the characteristic 303 sound:

Documentation:

Here's the webpage of Tim Stinchcombe about the TB303 ladder filter.

Here's Ian Fritz's original article on transistor matching in PDF form

PCB Service:

A PCB for this filter is available. It's 6.6 by 9 CM

It costs €10 incl. free shipping inside European union. Use the paypal link below to order. 2 in stock.

(PCB only, no components.) 

That's all for this one.

If you have any questions or remarks about this project then please put them in the comments below or post them in the special facebook group for this website.

Synthesizer Build part-65: YAMAHA CS FILTER w IG00156

 A LP, BP and HP filter in one chip. Not a filter you can just decide to build on a whim though. It uses Yamaha's own IG00156 VCF chip which is very rare and very expensive if you can find one. Like three figures expensive. This projects deals with a Eurorack version of this filter but of course it will work equally well for Kosmo sized synths.

PCB'S AVAILABLE ON REQUEST. Contact me on Facebook messenger. (2 in stock). They are 6 by 8 CM in size. The boards work fine but miss a connection you must make yourself but it couldn't be easier, just connect pins 1 and 9 of the IG00156 chip with a wirebridge.

A good friend of this website, a fellow Dutchman who happens to be an amazing psy-trance producer by the name of Jake Jakaan, signed to a top record label, who uses modules from this website gave me one of these chips. He managed to get hold of a few of them. He states this filter is great for filtering FM sounds from the TH VCO555. It's very low-mid heavy.

It was not easy to find a good schematic for this filter. In fact, all I had was the service manual for the CS-5 and a stripboard layout that someone put together which looked very dodgy and had some mistakes in it (although it did seem to work for my friend but I didn't use it).

I made a completely new schematic for this filter using the original circuit from the service manual and from that I made a new layout, small enough to fit a Eurorack system. The layout turned out to work faultlessly straightaway for which I was very grateful because the IG00156 is not a chip I'd like to blow up. The chip is actually quite robust, I found.

There are two things that are unique to this filter; it has a frequency dependent Q (resonance peak) and a gentle single pole lowpass effect. Resonance (Q) is achieved by damping rather than using a positive feedback loop and because damping will not go to zero the filter can not self oscillate.

This filter is used in all of the Yamaha CS range of synthesizers. Even in their flagship synthesizer, the CS-80. It's a two pole 12dB/Oct. state variable filter. In the CS-80 one chip is used for a lowpass filter and a second one for a highpass filter and in other CS synths like the CS-5, one chip is used for lowpass, bandpass and highpass. The filter I present here has all three functions under a switch although you could have each output go to its own socket but then you have to redesign the output stage or simply bypass the output opamp which I wouldn't advise. You should have opamps with a little bit of gain on the outputs.

Here is the schematic I made and on which I based the layouts below:

Here's a block diagram of the inside of the IG00156 chip:

Source: Yamaha IC Guidebook.

There's an in depth analysis of this filter on the Modwiggler forum: CLICK HERE to read that.

I added an audio level control on the input because this filter is rather sensitive to high volume levels. I also added a gain potmeter on the output that gives you the option to set the gain from 2 to 4 times with a 100K potmeter. That is more than enough, but if you want more gain, put in a 500K potmeter which will give you 12 times gain, or 1M which will provide 23 times gain. It will just clip. There's no use in doing that. I really wouldn't advise it.

The schematic says to use +/-15V but I tested it on a dual 12V powersupply and it works fine. The chip inputs for the cutoff and resonance functions are very sensitive and the complete cutoff range is controlled by a voltage that goes from 0 to 0,25V. Only 250 milliVolt for the full range. This is achieved by the voltage divider consisting of the 22K resistor in the cutoff line and the 470 Ω resistor between pins 7 and 8 (or pin 7 and ground really). The potmeters for Cut-off and Resonance need to be fed with +10 volts so I added 1K8 resistors to the pins where the power comes in to cut off roughly 2 volts. You can actually use other values for these potmeters because they're only used as voltage dividers but then you will have to re-calculate the values of those two resistors to make sure the pots receive +10 volts. For instance, if you use 100K potmeters you're need to use two 18K resistors.

I used this schematic to make my stripboard layout which wasn't that difficult because it's quite a simple filter. There aren't many components in it. It worked straight away although at first I couldn't get it working because I had not wired everything up yet. I thought I had connected all the knobs I needed for testing but I forgot the V/Oct input. That needs to be connected to ground if it is not in use and once I had done that the filter sprang to life. After testing I added a V/Oct section to the stripboard layout as explained in the next paragraph.

VOLT per OCTAVE INPUT:

At first I had the V/Oct socket grounded through the socket switch but then I realized that isn't needed because the V/Oct input is always connected to ground via the 470Ω resistor. 

I applied a voltage divider to the V/Oct input consisting of an 18K and a 470Ω resistor, I went with an octave range of 8 octaves, meaning that the input would get 8 Volts at maximum which would need to be reduced to the same range as the Cutoff input because they all enter the same summer inside the chip (see diagram above). 18K with a 470Ω would give 0 to 203milliVolt which works out perfectly.

Because the filter can not self-oscillate anyway, the filter can not be used as a sinewave oscillator with the resonance fully open. So accurate volt per octave tracking is not an issue and therefore none of these calculations need to be super accurate, it just needs to work so that it sounds good and the filter now tracks nicely up with the octaves.

LAYOUTS:

Here are the layouts I made for this filter. As always they are verified, I used them for my build. As you can see it's a really simple project. There's only 25 resistors, a few capacitors and wirebridges and the chip sockets to put in. The biggest job will be the wiring up of the potmeters and sockets and the making of the panel.

Wiring diagram. Note that the Resonance potmeter is connected the other way around from all the other potmeters, with ground at the clockwise lug. This is usually the case in VCF's.  

Stripboard only:

It's best to use bi-polar or none polarized capacitors for the 1µF caps in the filter outputs and on the audio input. This is because we're dealing with bi-polar signals that go through the zero Volt line. The caps don't need to be this specific value. You can use anything between 1 and 10µF without problems.

As you can see all three filter outputs have a 100K resistor to ground. Together with the 1µF capacitor this forms a highpass filter with a cutoff frequency of 1.6Hz so in effect it keeps DC voltage from passing and all the other frequencies get through. Make sure you use high quality capacitors for the two 1,5nF filter caps. I used Polystyrene ones which always sound the best.

Cuts and wirebridges. As always, mark the cuts with a Sharpie or Edding pen on the component side and then stick a pin through the marked holes and mark them again on the copper side. Then cut the strips at the marked positions with a sharp hand held 6- or 7mm dril bit. Make sure you work accurately!!

And here is the bill of materials. It won't be easy to find an IG00156 chip. They are long out of production so your best bet is websites that sell rare synthesizer components. They go on Reverb for $189,- but that is top dollar. They should go for between $70,- a $100,- 

I did not include any bypass caps or extra electrolytic caps for the voltage rails. If you want to include those you need to add them to the list (2 x 100nF and 2 x 10µF/25V). They're not on the layout or schematic either but there's room enough on the stripboard to put them in over the voltage rails.

The two trimpotmeters should really be the normal kind and not multiturn trimmer. There's really no use in having multiturn trimmers because there's no need for that kind of accuracy.

NOTE: There is a Hongkong based listing of the IG00156 chip floating around on the internet selling them for €10,- Don't fall for that, it's a scam!!

PICTURES:

Here are some pictures from the build proces:

All components soldered on:

Testing:

Drilling the panel using a copy of the panel design I made in Photoshop as a dril guide:

Waterslide design applied to the faceplate and now drying on the central heating. All the creases you see will be gone by the time this is dry.

Finished panel ready to receive the pots and sockets etc. After the waterslide design has dried we cut out the holes with a very sharp hobby knife and then apply two more layers of clear acryllic lacquer and let it dry overnight.

Finished module. The module is 14hp wide (7 CM) and 3.7 CM deep.

I only had a 4 way rotary switch, that's why the HP mode on the panel has 2 settings. Lugs 3 and 4 of the switch were connected together.

Side view:

Side and back view:

Here's an oscilloscope screenshot of a squarewave wave in LP mode with full resonance applied:

CALIBRATING THE FILTER:

There are two trimpots on this filter that need to be set.

The first one is the 100K trimpot. You use this to set the throw of the Cut-Off potmeter. Set it in such a way that you get the most resolution of the Cut-Off potmeter.

The other one, the 200K, is used to set the Resonance to maximum. Turn up resonance and turn the trimmer until you're at max resonance. This will probably be around the middle of the trimmer at about a 100K.

It's best to have normal trimpots not multiturn ones. There's no need for those and the normal trimpots are easier to use.

VIDEO DEMO:

Here's the first test I did after finishing the project. This filter literally makes the room shake. If you turn up the volume (with good speakers or headphones) you will hear stuff starting to rattle in the background. It's a very bass heavy filter which really sounds great!

Here's a short demo I made with the X4046 VCO hard synced by the 555 VCO going through the filter.

Here's an other video I found on YouTube dealing with the CS-5 Lowpass filter:

https://www.youtube.com/watch?v=5F8_RfVzO2A

Here's a Facebook video of my friend Jake Jakaan using 3 of these filters in bandpass mode to create a formant filter that makes sounds akin to human speech.

https://www.facebook.com/share/v/1A2Q6Ws1AE/

Okay that's it for this article. Not a filter anyone can build alas but this website is an archive of all the modules I built myself so it certainly belongs here. I also noticed that Yamaha filter schematics that specifically deal with the CS filter are almost non existent on the internet except for the service manuals. So I hope this article will provide at least one good schematic for those looking for it.

If you have any questions or remarks about this project then please put them in the comments below or post them on the special Facebook group for this website.

Synthesizer Build part-62: 2164 VCF/VCA by Thomas Henry.

This is the Fonitronik Thomas Henry AS2164 state variable filter and VCA in one. THIS FILTER SOUNDS DELICIOUS!!  It's a great sounding combination. I used two stripboards that connect together with pinheaders making this a very eurorack friendly design. However this is not a beginner friendly project. You need good soldering skills for this one. Even for me this was not a 'hole in one' like a lot of the previous projects. I made a few mistakes but I found them in the end so all is well. But this project is certainly in my top 5 of best projects on this website.

This filter uses the AS2164 or V2164 chip which, in its original form, was a chip from SSM (Solid State Music). These chips were used in many late 70's polyphonic analog synthesizers like the Prophet 5 for instance. The V2164 is made by CoolAudio which is a company owned by Behringer which they use to create all the old obsolete chips for Behringer's line of vintage synths that they are reproducing.

The 2164 is not actually a filter chip. It has four independent VCA's on board and in this design two of those are used to make a great sounding 2 pole filter (12dB/Oct.). This filter has that vintage liquidy feel to it when you add a lot of resonance. It sounds amazing.

The left over two VCA blocks in the chip are used to make a single VCA. Of course you don't have to build the VCA if you don't think you need it. You can build just the filter board if you want. However you can not only build the VCA board (using my layouts) for the obvious reason that the 2164 chip is housed on the filter board.

The V2164 chip is very sensitive to missing negative voltage. If negative voltage falls away the chip will be distroyed. There is a diode in the layout that protects the chip however.

If you buy the AS2164 instead of the V2164 then you don't have to worry about this because the AS2164 has internal protection against negative voltage cut out built in. BTW, you can buy the chip(s) from Electric Druid amongst others.

Here's the finished module (on the right) fitted into a Nifty Case. Dispite the depth it still easily fits.

Here is the schematic:

This project will run on both a dual 15V or a dual 12V powersupply. It's designed for 15V as you can see on the schematic but I built it for Eurorack dual 12V and it works fine.

As you can see it's quite a simple design and in my experience those produce the best sounds. The top part of the schematic shows the filter and the bottom part the VCA. I decided to make the two parts that make up this module on two separate pieces of stripboard so that I could make them small enough to fit flat behind a 14hp faceplate, with one board on top of the other. They connect together using pinheaders. The VCA board is connected to the 2164 chip via those pinheaders. The depth of the finished module will be around the 4 CM mark.

LAYOUTS:

Below are the layouts I made for this module. As always they are verified, I used them for my build.

Here's an overview of both boards. In the layouts you can see a Coarse and Fine control for the filter cut-off. The fine control is there in case you want to use the filter as an oscillator in full resonance, so you can tune it, but I never use a filter like that so in my own project I switched the 3M3 resistor for a 100K one and put in an extra socket so I can use that as an extra CV input with level control, So the potmeter labelled as Coarse is in my case labelled as 'Cutoff' and the 'Fine' control is now my CV2 Level potmeter. I placed it all the way down on the faceplate. 

The PTC is an other component you don't need if you don't want to use this filter as a sinewave oscillator. Just put in a 2K resistor instead. That's what I did too. There's also a 7K5 resistor which I coloured purple, in the layout. Leave that out too. If you include it you change the VCA amplifier type from a class AB to a class A type. Totally unnecessary.

I used miniature potmeters in this project to save space and I made my own custom potmeter symbols in the layout software, the little green ones.

Here's the wiring diagram for the filter part. All potmeters are viewed from the back. It may look to you that the Resonance potmeter is wired the wrong way around with ground at the clockwise position but I found out that this is the right way to do it. Resonance is usually wired the other way around in most filters. This filter, I have to say it again, sounds sooo good. I love 2164 based filters and I think this is now my favourite filter on the website. It has a liquidy watery feel to the resonance which is just amazing. Anyway..... here's the layout for the filter board.

VCF stripboard only view:

Below is the wiring diagram for the Linear VCA part. The VCA has two audio inputs. One direct input without level control which is intended more for LFO signals. On the Fonitronik panel it is labelled as DC IN. In my design I did give it a level control but that potmeter is not on the layout. The top audio input has a level control and an AC/DC switch. AC is usually used for audio signals, filtering out any DC components like offset voltages that might be present. DC is used for very low frequency signals like from an LFO or envelope generator; signals that would be distorted if they went through a capacitor first. The VCA is very snappy, it can switch on and off very fast so you can use audio rate signals to open and shut the VCA and get a sort of ringmodulator effect.

The 'initial' potmeter regulates the output volume of the VCA by adding an offset voltage to the envelope input. You can use it to open the VCA without pressing any keys so you hear continuous sound. If you close it, the sound will only come through when you press a key and an ADSR signal comes in on the CV input. 

(Last revised: 16-12-2024: The two potmeters with ground connections were wired the wrong way around. That is now corrected)

I know that in the schematic the 'Initial' potmeter goes through a 300K resistor and not a 100K like on the layout but I lowered it to 100K because that worked better for me. Should you feel that the Initial potmeter is too overpowering or doesn't work right, then put in a 300K for the bottom 100K resistor.

VCA stripboard only view:

Here's an overview of the pinheaders, wirebridges, and cuts to be made for both boards, seen from the component side:

The VCA board has male pinheaders soldered directly to the copperside so the board connects to the filter board with the copperside facing the component side of the filter board.

This is a bit fiddly to solder, especially because I used a double row of pinheaders to make sure the connections are solid. I used the same method I used with the wavetable oscillator. I put some solder down between the holes where the pins sit and I put some flux on the solder part of the pins and pre-soldered them too. Then I put them in place and I only needed to heat the solder already there to make them connect to the stripboard. Do this before you solder in any components so you have enough room to work and fit the two boards together regularly to make sure it all aligns like it should. 

Be careful not to overheat the pinheaders because the plastic that holds them together can melt. When I solder male pinheaders I always connect female connectors to them so the heat can dissipate

Finally here's the Bill of Materials:

You can use other types of Schottky diodes if you want, like the BAT41 or 42, 43 etc. It doesn't matter as long as they are Schottky diodes.

PICTURES:

Here are some pictures from the build proces:

The stripboards with wirebridges installed:

Here's how I soldered on the male pinheaders:

Both boards finished but without their chips. I only put those in at the last moment to prevent damaging them.

The faceplate with the holes drilled in and de-burred, with the waterslide design applied to it. You can see there are still some bits that are not completely flat but when it is dry it will all be tight.

As you can see in the picture below, it dried up beautifully. Now to cut out all the holes with a very sharp hobby knife and then give it a few more layers of clear lacquer.

Here's the end result, not yet wired up. I put in two 3 CM M3 bolts with counter-sunk heads and screwed them tight with nylon ringed locknuts. Then I put some white paint over the heads and applied the waterslide paper overtop of that. It doesn't make the screw heads totally invisible but it works. I forgot to put in a hole for the 3mm LED. I later drilled one in just underneath the top text.

While I was waiting for some components to come in the mail I wired up the backside of the panel as far as I could. I connected all grounds together with one copper wire and I also soldered all the potmeter pins that needed to be grounded to that same wire. This way I will only need one ground wire going to the stripboard to ground everything. This is how I usually wire up ground connections. Do not rely solely on the metal of the faceplate to be the ground. Remember Aluminium oxidizes and oxides are not good at conducting current.

When all components were in, I wired it all up which took me almost a whole day and then I plugged it in and.... it didn't work at all. I tried to troubleshoot it, I posted in the Facebook group about it but it wouldn't work. Then I left it for two days and came back at it with fresh eyes on a sunday morning and I found the mistakes within half an hour. I made two little errors in the layout and I soldered one wire to the wrong place and I forgot to connect the ground copperwire, which has all the socket grounds and potmeter grounds connected to it, to the stripboard. After I corrected that, it all worked fine. Strangely enough the missing ground wire connection was something I noticed later on, but even without a ground connection everything worked! I was really surprised by that.  

Btw, I normalled the lowpass output of the filter to the input of the VCA so the filter output is automatically enterred into the VCA. To replicate this all you have to do is solder a wire to the audio output of the VCF and then solder the other end to the switch connection of the audio input socket of the VCA. When no patch-cable is connected to the VCA audio input, it gets its audio from the VCF output. If you connect a cable to the VCA input that VCF connection is broken.

Here's a look at the finished module:

As you can see, the boards bend back a little because they are only connected to the panel at one end and there are a lot of wires pushing it up. To pull the other side down, I soldered a wire from the socket ground to the ground of the eurorack powerheader. These points are directly above eachother and the copper wire now pulls the boards down which looks better and helps keep the depth to a minimum. It also takes care of grounding everything on the panel.

It is still a pretty deep module. It's 47mm deep. But it will fit most eurorack cases like the Nifty Case just fine. 

VIDEO:

Here's a cool demo video I found on YouTube by Fonitronik:

A few final notes:

I based my panel design on the original Fonitroniks panel and the labeling on that is somewhat different than on the schematic. This caused me some confusion as I only really noticed it after I had finished the panel. For instance the DC IN on the VCA is actually an extra audio input that can also take CV signals. The Linear AM on the schematic is labelled Lin. FM on the original panel. So I would advise you to keep to the labeling of the schematic and the layouts and not use the Fonitroniks panel as inspiration, like I did.

Here is the original panel of the Eurorack module:

Note how it says Linear FM at the bottom right input but with a VCA the control voltage influences the amplitude or volume of the output, not the frequency. So it should be AM.

Here's an explanation of the input options of the panel design above. They can be very confusing.

I took my panel design and added more understandable labels. It used to look like the design above here but I think this will make more sense. There's four designs for an A-4 sized waterslide paper so you have some spares should you mess up. I also added a place for the LED which is connected to the filter CV-1 input (that's the envelope input for the filter). This image is to scale for a 14hp Eurorack panel. You can save it and print it out onto waterslide paper and use it to make you panel.

Okay, that's it for this one.

If you have any questions or remarks about this project then please put them in the comments below. Comments are moderated and don't appear until I approved them which can take a while if you're in a different timezone than me. You can also post questions or show your work in the special Facebook group for this website.