Friday, 17 September 2021

Synthesizer Extra's No.3: THE GRISTLEIZER.

An effects unit made famous by British 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.

IF YOU BUILT THIS UNIT BEFORE THE 16TH OF NOVEMBER 2022 THEN YOU NEED TO MAKE A LITTLE CHANGE AND PUT A WIREBRIDGE FROM PIN 5 OF THE TL074 TO PIN 3 TO CONNECT PIN 5 TO GROUND! This was a mistake that had slipped into the layouts I published earlier and was noticed by a kind observer who drew my attention to it in the comments below. 
All layouts are now corrected so the layouts are now really verified. I'm sorry this mistake occurred guys. I pride myself on publishing faultless layouts but sometimes mistakes do creep in.

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. Next to the link above 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-


SCHEMATIC:
The schematic below is a modern update of the original one from the article in Practical Electronics, and this is the one I used to build mine. The two diodes in this circuits are 1N34A Germanium diodes but I used 1N4148 and this works just as well. 
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. 

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.

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 if 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 print 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 peak to peak.

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 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.

Here's the print 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, especially not if you feed it with batteries:


Cuts and wirebridges, component side view:


Cuts only, copper side view:


Here's the Bill of Materials:



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 print and the wooden case which I also built myself from 3,5mm plywood. I forgot to take pictures of the print 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.



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. This first one is in VCF mode using a sawtooth wave as input. The Bias control influences how many squarewaves are inbetween the resonant sawtooth waves and the rate between the two sorts of waves is set with the Speed control.


Resonant sawtooth waves with amplitude variation created by the LFO Speed control (resonance with tremolo effect). The same as the image above only now the Bias control was turned counter clockwise which makes the squarewave less prominent or even make them disappear altogether.


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. The amplitude of these waves can be many times higher than you see here because I had the Level potmeter about one third open.

The next two screenshots are taken from the wiper of the rotary switch and show how the LFO wave is influenced by the Shape potmeter (orig. a trimmer) when the rotary waveform switch is set to triangle:
Fully clockwise:

Fully counter clockwise:


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 --

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.

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