Synthesizer Extra's No.3: THE GRISTLEIZER.

An effects unit made famous by British Electronic Industrial Band 'Throbbing Gristle' from the late 70's. The band used it on everything, from guitars to synthesizers and even microphones and it will take all the different input levels without problem.

I have some PCBs for the Gristleizer in stock. I built one up and tested it and it all works perfectly. The PCBs are 155mm by 55mm so they're quite wide and therefore a bit more expensive to have made in China. They go for €12,-  excl shipping. PM me if you're interested.

HISTORY:

I built this as a stand-alone effects unit, as it originally was. There are now numerous variations of the Gristleizer (pronounce as: Grissel-eye-zer) available. Even as Eurorack modules with lots of extra functions but I wanted to build the original one as used by Throbbing Gristle back in the day. Band member Chris Carter built the unit from an article in Practical Electronics Magazine (July 1975 issue). 

(The above link will lead you to a downloadable PDF of the entire magazine. The article starts on page 29.)

The circuit was based on a design by a then 15 year old Roy Gwinn. Alternatively, you can get just the relevant article in PDF form in the 'Files' section of the EDDY BERGMAN Discussions FaceBook Group.

I first became aware of this sound effects unit when I watched the documentary 'Synth Britannia' on YouTube. (Click here to see the part about Throbbing Gristle).

Here's a picture of the original unit built by Chris Carter. This was Cosey Fanni Tutti's original unit used until 2009 when it stopped working:

Here's a look at the inside (low resolution):

Below is a link to the website of Chris Carter which has tons of links on it to all sorts of Gristleizer related webpages. It starts with a lot of videos but if you scroll down you'll find links to the various webpages.

Chris Carter's webpage about the Gristleizer:  -CLICK HERE-

The Gristleizer on Boing Boing.net:  - CLICK HERE-

Here's the website of Throbbing Gristle.

SCHEMATIC:

The schematic below is a modern update of the original one from the article in Practical Electronics, but it's exactly the same circuit and this is the one I used to build mine. The update was just cosmetical. The two diodes in this circuits are 1N34A Germanium diodes but I used 1N4148 and this works just as well. I did later change the 1N4148 diodes for Germanium type 1N60 diodes but it didn't have any effect on the signal.

This circuit runs on a dual 9V powersupply but I used a dual 12V powersupply built into the case. It's not an issue because the opamps can easily take it. In the picture above you can see the original used two 9V batteries to create a dual 9 Volt powersource. The circuit itself is really rather simple. The only thing that can be confusing is the wiring of the 4 way switch. Luckily I got that right at the first try.

In the version I built, all the potmeters are mounted on the front panel, even the ones initially intended to be trimmer pots that you only set once, like Shape and Offset, I thought it might be handy. 

Please ignore the 'Max1044' chip in the schematic. This is a voltage converter chip which is not used in my layout because I use a custom built powersupply. The chip generates a negative 9V source so you can have a dual 9V power source with one 9V battery.

WHAT IT DOES:

It's difficult to describe the effect this unit has on any sound you put into it. It has a built-in LFO with a choise of 4 waveforms, that gives a tremelo effect to the sound but that can be cranked up all the way into the lower audio frequencies which gives a cool sort of filter sweep sound combined with distortion. See the demo video below to get an impression of what it can do. 

I did some internal measurements and I measured an LFO frequency from one cycle every 70 seconds to 115 cycles per second (115Hz).

It also has a resonant filter that is mixed into the sound. but you can't set any Resonance like a normal VCF. Watch the demo video below to see what it does. It's quite unique. I can see why it fitted the music of Throbbing Gristle so well.

One cool thing about this circuit is that it can handle a really wide range of input signal amplitudes. You can feed it line level signals or signals at the synthesizer level of -5/+5Vpp or 0-10Vpp. It's fortunate that there is an output level potmeter because the output can be very loud because this unit can amplify the audio, but if you turn the Bias down the audio level can go down too and with the output level potmeter you can crank it up again.

I would advise to put a level potmeter on the input aswell. This will give you the option of turning down synth level signals and prevent clipping which will give you more sonic diversity. Just use a 100K potmeter like in any other project with attenuated inputs.

EDIT: I have tried it with my Steinberger Spirit XT-2 bass guitar which has passive pickups and the signal gets through quite loud. In many ways this works mostly as a distortion and also as tremolo effect. If you turn the rate up you get a nice beating of 2 frequencies against eachother as the bass frequency comes near the LFO frequency. When they used the Gristleizer on Genesis' voice they must have had it in VCA mode. You can hear that in songs like 'Hamburger Lady'.

Overall I was not very impressed with the sound it produced when using it with my bass guitar. I think synthesizers sound better. 

CV CONTROL:

I have not experimented with CV control for any of the parameters but I don't think putting Vactrols over the potmeters will work very well, but you'll have to experiment if you want CV control. I am however reliably informed that you can put an external signal (LFO) on the wiper connection, pin 2, of the Depth potmeter. You can use a toggle switch to switch between internal LFO or external CV or use an input socket with built in switch normalled to the internal LFO. Then you can connect and external ADSR and use it as a weird sort of filter. I have not tried this myself however.

LINE LEVEL SIGNALS:

When I first tested my unit with line-level input signals I could hear a ticking noise mixed in with the audio. I first thought this was a power supply issue but then I found out that I had forgotten to put in capacitor C6. This is the 100nF one on the left of the stripboard from the cathode of the diode to ground. I soldered it in and, because I had an ON/OFF switch on the front panel that I hadn't wired up yet, I used the switch to turn on or off capacitor C6. You can just hear the effect it has. It smooths out the audio a bit. I can see why the cap is there. If I turn the capacitor C6 off, the sound is slightly rougher.

Btw, you can connect a dynamic microphone straight to the input of the Gristleizer and experiment with the effect is has on the human voice. Should you experience noise or weird sounds in the line-level audio then turn down the voltage from the powersupply a bit (if you can). I just did a test with dual 9V and dual 12V and a lower voltage is definitely better for line-level signals. I made my powersupply with LM317 and 337 regulators so I can easily adjust the voltage. Dual 12V is better for synthesizer level signals.

Btw, when I say 'line-level' I mean signals that come straight out of a guitar or microphone. Signals in the range of 100 milliVolts to 1 Volt peak to peak.

I've had some feedback that, if you hear a ticking noise in some settings, you can connect a 10µF cap between the wiper of the Depth potmeter and ground and that will get rid of most of it.

I strongly advise you to put a level potmeter (100K) on the input socket. That way you can turn synthesizer level signals down and get the most from the different waveform, otherwise it will clip the input. That also sounds great btw but a level pot on the input gives you more sonic diversity. Take a 100K potmeter, solder the audio input from the socket to pin 3 (clockwise), solder a wire from pin 2 to the audio input of the gristleizer and connect pin 1 to ground of both the audio socket and the gristleizer. This option is not included in the layouts below but do put it in.

LAYOUT:

Here's the new (verified) layout I made for it. The previous version that was up here until the 16th of November 2022 had a mistake in the layout. I had forgotten to ground pin 5 of the TL074. Now that that's all corrected the Gristleizer works like a charm. I included a bypass switch in the layout which I thought might be handy to have. (The weird thing in my unit is that if the Level potmeter is fully clockwise or fully counter clockwise, the bypass signal doesn't get through.) 

The Bias potmeter is wired the other way around from what you would expect. I thought this was the best way but it doesn't really matter which way you wire it up. The layout below has the supply voltage at +/-9V but I run mine on +/-12V which works fine too. (There's an alternative layout with trimmers for the Shape and Offset potmeters further down the article if you want to build it like the original unit but I find putting those potmeters on the front panel much better.)

Wiring Diagram:

Be very accurate with soldering up the 2 pole 4 way rotary switch. Solder the resistors and jump wires straight to the switch first, before you wire it up to the stripboard.

You can connect together all the potmeter lugs that need negative voltage and all the ones that need positive voltage with hookup wire and then power them all at once with two wires coming off the power rails on the stripboard. That way you keep the wiring to a minimum.

Here's the 'stripboard only' view. There are no bypass capacitors in this design but in my own build I did put a 100nF cap over the plus and minus rails near the TL074, but it's not necessary if you feed it with batteries:

Cuts and wirebridges, component side view:

Cuts only, copper side view:

Here's the Bill of Materials. Remember to get an extra 100K potmeter for the input level and four 100nF ceramic bypass caps. Two for each chip going from plus to ground and from minus to ground:

ALTERNATIVE 4 POTMETER LAYOUT:

Here is an alternative layout which lets out the Shape and Offset panel potmeters and replaces them with trimmers on the stripboard. This is the version as used by Throbbing Gristle. Beware that the stripboard is a little bit longer (43 holes in total) and that it has two extra cuts in the ground strip next to the trimmer potmeters, so the wipers don't connect to eachother or to ground.

Once again, be very, VERY accurate when wiring up the switch. You must get that right before doing anything else otherwise it won't work right.

Here are some pictures of the stripboard and the wooden case which I also built myself from 3,5mm plywood. I forgot to take pictures of the stripboard alone during building. In the pictures capacitor C6 is not yet put in. I had forgotten it first and after I put it in I could notice that it smooths out the rough edges of the sound, so to speak. In certain settings it acts in the same way as the Bias control, adding a little more Bias as C6 is turned on. But it's not necessary to use a switch. Just solder in C6 as it normally should be. It's not a useful feature to have this capacitor switchable.

The picture below shows the powersupply print glued to the inside top of the case:

This is the front panel: 

The finished product:

DEMO VIDEO:

Here's a new demo video I made of my Gristleizer directly as I tested the revised version. After correcting the mistake of forgetting to ground pin 5 or the TL074 everything works much better as you can see and hear. You might have to turn up the volume a little.

If for some reason the video doesn't appear then here's the direct link to YouTube: https://www.youtube.com/watch?v=akE6kQEMy28

The effects are I think very useful. You can get a tremolo effect going and turn it up into audio range and then mix it with a resonant filter so you get that filter sweep sound. Very cool I think. And I haven't even tried it with other sound sources like guitar or a (dynamic) microphone.

To close off this article I'll show you some screenshots from the oscilloscope.  These are the different LFO waveforms in each of the four switch settings:

The next one shows waveforms created in VCF Mode with an audio Sinewave as input:

This is in VCA mode. The LFO shuts or opens the VCA giving a Tremolo effect.

The above screenshots give an impression of the main effect the Gristleizer produces. There are of course numerous shapes in between with all the different potmeters you can set in so many ways. 

I want to leave you with a video of Roy Gwinn, the inventor of the Gristleizer circuit, which I recently found on YouTube. Hear the man himself talk about the circuit and how it came to be. The video was uploaded in 2017 and it mainly deals with the Eurorack Gristleizer that had just come out but it's very interesting to watch. He had no idea his circuit was used and made famous by Throbbing Gristle until 2007 when he learned about it.

If you can't see the video then click this link: -- Roy Gwinn Video --

I made a Falstad simulation of the Gristleizer circuit which you can view by -- CLICKING HERE --

Here's a build guide for the Eurorack module Gristleizer from Instructables.com. It has a schematic and a good description of the function of all the changeable parameters.

As I mentioned at the beginning, I have PCBs available for the Gristleizer. They are tried and tested.

PM me on Facebook if you want one. (€12 a piece) 

Okay, that's it for now. If you have any questions please leave them in the comments below or post on the EddyBergman DIY Projects Facebook group.

Synthesizer Build part-11: ECHO and SOUND FX UNIT and LINE OUT.

100 different sound effects combined with a line-out and head-phones connection for the DIY synthesizer.

Here's a little item I found on eBay and thought it would work great in the synthesizer; and luckily I was right. It is a fantastic asset and makes the synth sound really professional and full. 

A word of warning though, this is not a beginners project. You need to know your electronics to follow my plans. This unit also needs two voltages to run on. The effects unit runs on +5V and the stripboard runs on +/-15V or +/-12V. So you must make sure you have those voltages available in your modular set-up or add a +5V regulator to the print. I recently added a Dry/Wet control so you can dial in as much of the effect as you want in your sound. This makes this unit really useable and perfect for modular synths. (see further down the article)

The unit goes under different names but mostly as the Cara OK ("Karaoke" get it?) or DSP 5V Red Digital Stereo Mixer Reverberation Karaoke Reverberation Board Module (if you copy and paste that into the search bar on eBay, you'll find it). The prices vary from $15 to about $30 us. (DSP stands for Digital Sound Processor)
This is the cheapest listing I could find on eBay: click here.
It offers 100 presets with reverb, echo and even chorus, phaser, flanger, phase shift and reversal effects and combinations of them together. There's a rotary encoder with which you choose the preset of your choise and then you just press to confirm and engage the effect. It's a favourite with many synth builders I noticed.
I made a special panel for it and combined a 'Line-Out' control and bypass switch option with the module. Here is the schematic or wiring diagram to make this unit part of the synthesizer. This was one of my early projects and at first I didn't have dry/wet control in there so this is the version just with a switch between normal line out or line out with effects:

I had to put extra attenuation on the bypassed (normal) signal because it was much louder than the output from the Echo Module, but that was easily fixed as you can see in the diagram above. The panel that I built into my synthesizer also includes a headphones out stereo jack which is not included in this article but it's just an output jack soldered straight to the negative poles of the Left and Right output Electrolytic Capacitors. Weirdly enough, if you listen through the headphones, the echo module is much louder than the normal line out. This is probably some impedance matching issue but it doesn't bother me. It's easy enough to turn a volume knob so I'm not bothered.

The Stripboard can work on +/-12V also. It doesn't matter if you use 15 or 12V. The CaraOK effects unit must have it's own +5V powersupply! You can use a 7805 voltage regulator and connect it to the 15 or 12V of the stripboard to get 5V for the effects unit. This is not further described in this article. I'm assuming you have the knowledge to make powersupplies. If not, check out my article on this subject here or see the datasheet for the 7805 voltage regulator.

Here's the stripboard layout (older version). This one has a 3 pole switch but that's not necessary. Just connect the wires on the left hand side of the switch together; the red line coming from the 'normal level pot', the blue line from pin 1 of the chip and the effects unit input. They can all be connected together and then you just need a 2 pole dual throw switch (DPDT).
(All potmeters viewed from the front)

Please note: The GROUND connection of the Effects Unit must be connected to the GND of the stripboard. Everything must share the same ground. I myself made a central grounding point with a solder eye connected to one of the M-3 bolts holding the Effects Unit to the panel. To put it in a simple way: the ground of the 5V powersupply for the Effects Unit must be connected to the ground of the +/-15 or 12V powersupply of the stripboard. The Grounds of the Line Out cables are also connected to this common ground. You can tap that off from the 4th strip above the Left Line Out connection. (2nd strip below the chip).

Print only:

(Last revised: 14-Aug-2020: Corrected mistake with negative voltage supply to the TL074.)

I used a 3 pole double throw toggle switch (ON-ON type) to be able to switch the synthesizer between normal output and output through the effects unit. This is a bit of over-kill because you can just as well connect the inputs together (part S1-A of the switch) and then use a 2 pole switch to switch between the outputs. Better still. I describe down below how you can put in a dual gang potmeter instead of a switch and so have a DRY / WET control. 

I'm going to adapt this article soon and make a new layout to put in this Dry/Wet control permanently. 

[EDIT] March 2021 DRY/WET CONTROL:

I wanted a Dry/Wet control on this effects unit for a while now and I wanted to install it without having to rebuild the whole module.

I changed the 3 pole toggle switch for a dual gang potmeter and I connected the inputs, normally connected to part S1A of the switch, all together. If you do this make sure you keep to the right order with the wires. Best to make a few pictures of the switch connections first before you solder in the dual potmeter, that is, if you built this module already.

Below here is a schematic. You can see the switch has been replaced by a stereo potmeter. This MUST be a linear type potmeter!!

There is a half drop in volume at the half way stage of the potmeter because we have 50K of resistance in our signal path there but other than that it functions fine! It's just a matter of turning up the input or output levels to get it where you want it. You must make sure the output audio goes into a very high impedance input, like a HiFi amplifier because if you pull even a tiny bit of current from this circuit it won't behave normally anymore. But it works fine on audio amplifiers, I guarantee it.

Here is Juanito Moore (Modular for the Masses) schematic for this unit with a properly implemented dry/wet control

The Dry/Wet control really makes a world of difference! Now you can set it to reverb and then precisely dial in the effect to where you like it. It's fantastic sounding!

Here is a picture of the panel with the Dry/Wet control where the switch used to be:

I made a little demo video. You can hear the drop in volume at the midway point of the Dry/Wet control. (I know it's wired backwards LOL :)  But being able to dial in the effect makes a world of difference and the volume can easily be crancked up by the level controls.

Continuing the original text:

I've put in 4 buffer stages, using the TL074, for the input, normal output and FX Unit outputs Left and Right channels and I gave the latter two adjustable gain by means of two 50K potmeters in the feedback loops of the opamps; one for each channel. The gain is adjustable from 2 to 5.3 times. You can increase that by using 100K potmeters instead of 50K ones. That would give a maximum gain of 8.6 times.

When I first tested this unit I noticed I was receiving an FM broadcasting signal through the effects unit. (There's an FM Broadcast transmitter and antenna on a flat 100 meters from my location). So I took a ferrite ring and wound the audio input wire around the ferrite ring about ten times. I also put ferrite beads in the 5V power-supply line to the effects unit and to the print with the opamps on it. This solved the problem. One more little thing: beware of the little crystal X1 near one of the screw holes on the circuit board. It is rather flimsy and fragile. Take care not to damage it.

The Cara OK is a really versatile unit with lots of really cool sounding effects. Here's an overview of the possibilities it offers. I myself printed a small version of this list out, laminated it and stuck it at the bottom of the panel I made for it. Handy to have around I thought :) :

This picture shows all the connections to the circuitboard:

It's small so it won't take up too much space. Beware that it needs just +5V for power supply. Luckily in my synth build I made a power-supply that delivers dual 5, 12 and 15 Volts so I can feed it right from there. I can really recommend you picking this up and trying it in your build project. It will add a lot of options and is a very useful addition to the filters and its output is in stereo! The sound quality is just great so no problems there. The only thing is the difference in volume I mentioned earlier but that is easily fixed. You can use opamps buffers with it, like I did, but it's not absolutely necessary. I did without them at first but then installed output buffers with variable gain as I mentioned before.
The audio response of this module is so good that it even lets through the ultra low frequencies the Korg MS20 filter produces (see next article) and that can go as low as 10Hz. You can really see the speaker cones move bigtime!
Before I installed the 3-pole toggle switch I had a single pole and a double pole switch side by side to switch between FX-unit and normal line out. So after installing that 3-pole switch I had a hole in the panel left over. I mounted a 3,5mm stereo output jack in that hole as a connection for head-phones. The output jack is connected straight to the audio output on the stripboard. One thing I noticed with this arragement is that the normal line-out through the head-phones, sounds a lot quieter than when the effects unit is switched on. That's probably due to a difference in output impedance because we're effectively putting an 8 Ohm resistance between Line-Out and Ground in the form of the head-phone speakers. This doesn't occur when I listen to it on the normal audio amplifier, at least not if the head-phones are not plugged in. It would be a good idea to build a little head-phone amplifier for this purpose.
Here is a picture of the finished module in my synthesizer:

Here's a picture of what's behind the panel. Now you understand why this is not a beginners project ^_____^  You can see the yellow Ferrite ring with the black 'audio in' wire wound around it above the blue circuitboard and there's also one on the stripboard. I advise you to include these in the power supply line and audio in line. In red you can see the 3 pole toggle switch. This panel works really well like this.

Here's the Line Out Panel I made on the back of my synth, with two gold plated RCA outputs and a 6,3mm (1/4") Stereo Output Jack, which is connected straight to the RCA left and right outputs.

ONE LAST REMARK:

I have had feedback that some chips on the CaraOK board can run hot when run for a long time and even fail after a few years so it is advisable to add an ON/OFF switch to the module so you can turn it off when it is not needed thereby preventing the chips from being on needlessly for a long time.

(see comments below)

Okay, that's the 11th module I put in the synthesizer. We're nearly there. I have just room enough left for one more module and that has got to be the Korg MS20 filter. But I'm waiting for some supplies from China before I can build it. (Circuit boards for one, coz I'm fresh out at the mo.)

Okay here's an excellent video by Juanito Moore that shows you how you can circuit-bend this device and make it voltage controllable. Click here

Right, that concludes this article. Thanks for stopping by and while you're here, why not leave me a comment or if you have any questions put those in the comments too and I'll get back to you asap.