Archive for May 15th, 2012


The Touch-Radio

The Touch-Radio was, design-wise, by far my easiest project to date.  This was for the simple reason that it’s essentially the circuit board out of an old transistor radio, more or less unaltered!

Touch Radio 1 DSCF0011

I had had the radio for about 40 years: about 20 years ago, I took it out of its case – which has subsequently disappeared – and rewired the tuning and volume controls, evidently intending to do something with it.

I forget now whether I ever did – probably not – but I found it again recently, just as I was finishing the Cracklephone, and thinking about touch-controlled sound-makers; so I decided to connect a battery clip and speaker and see if it made a noise.

It did!  And I soon discovered that by touching certain parts of the exposed circuit board interesting sounds could be coaxed out of it – often not entirely unlike the Cracklephone, but with an element of speech incorporated.  Touching the aerial did frequently amplify the received radio signal, but it was rare for speech to become readily intelligible.

So I decided to leave it at that! – apart from putting the speaker, volume control and power in a box, to keep it neat.  A PP3 battery would just about fit inside, but it also has a socket for  external power.

Touch Radio 2 DSCF0014

I’d recently obtained some small plastic jewellery boxes, which looked good for small projects (some more are described elsewhere in the blog), so I used one of these.  There was also room for two 3.5mm sockets and two 4mm banana sockets, which I added, as I had done for the Cracklephone, to allow a microphone to be attached to the Touch-Radio or the Touch-Radio to be connected to an external loudspeaker.

Touch Radio 3 DSCF0015

I’ve always been interested in manipulating speech sounds, and have a number of projects in mind utilising radios in different ways.  I haven’t started working on these yet, but the Touch-Radio is the first in the series.


The Cracklephone

The ‘Cracklephone’, nicknamed ‘The Blue Parrot’, is my second project recreating a classic design.  The first, The Hedgehog, was a version of the famous Atari Punk Console; this one was my take on the ‘Cracklebox’ (or ‘Kraakdoos’ in the original Dutch).

The original Dutch Cracklebox was created by Michel Waisvisz at STEIM (the Studio for Electro-Instrumental Music) in Amsterdam in the 1970’s.  Waisvisz died in 2008, but his description of the Cracklebox can be found here:

This is what it looks like:

Cracklebox - Sascha Pohflepp

Photograph by Sascha Pohflepp.

You can buy one like this from STEIM at

Waisvisz’s early experiments with electronic sound were of the type now known as ‘circuit-bending’, and the Cracklebox was developed as a natural extension of this: STEIM’s philosophy is very much in favour of low-tech electronic music-making and the ‘creative misuse’ of technology.  In particular they emphasise the importance of human touch in musical performance.  Accordingly, the Cracklebox is based on an early op-amp chip numbered 709 (LM709, MC709, uA709 or MC1709CG), provided with 6 pads or touch points which cause it to oscillate in a not entirely predictable way.

The 709, as a matter of fact, was the first widely-used op-amp on a single chip.  It was invented by legendary designer Bob Widlar – an ‘irrational, eccentric, and outspoken personality’, ‘alcoholic loner’ and ‘celebrated dropout’ according to his Wikipedia entry at  Whether or not STEIM knew of it, I don’t know, but I feel sure they would have approved of the physicality of his practice of ‘widlarising’ – ‘methodically destroying a faulty component or a flawed prototype with a sledgehammer’ . . .

Be that as it may, the 709, as a very early design in the field, required more external circuitry for ‘frequency compensation’ than later and more familiar op-amps like the ubiquitous 741, so lends itself to greater possibilities of interference by touch.  As people are different, so the Cracklebox sounds different when played by different people – the player and the electronics combine to make a unique instrument between them.  (Indeed, it is possible for two or more people to play the Cracklebox at once, by touching separate pads, or each other.  There are videos on YouTube demonstrating this).

I had been using the computer a lot in recent projects, but the low-tech approach is another strand I’ve been following.  Fortunately, circuit diagrams and advice on the Cracklebox were available at this website:, and there was much discussion of it on the electro-music forum, for example:

In some places I read that the 709 could be difficult to get hold of, but I had no trouble in getting them from one of my regular sources, Cricklewood Electronics, at a perfectly reasonable cost.  I have also read that the NTE909 works as well, but have not had cause to check this out.

The circuit I used looked like this:

Cracklephone Circuit3

The reason why there are 13 touch points, rather than 6, is to do with the case I built it in.  I mentioned in an earlier post that I had acquired a number of broken Stylophone Beatboxes.  I had used one for the ‘Big Boy’ Stylophone mod, and had been looking for a project in which I could use another.  As the Beatbox has a large and attractive circular ‘keyboard’, divided into sections, I thought this would be ideal for a series of touch pads, as used in the Cracklebox.

The Beatbox keyboard – or as it is now, ‘playing surface’ – has 13  segments, hence the duplication and addition of extra touch points.  The original 6 are marked  *  on my circuit diagram.

As many as possible of the Beatbox’s original switches were retained – mostly with different purposes, of course – and the volume control, in particular, proved useful to keep, as it could be manipulated with the right index finger while playing.  The odd arrangement in the middle of the circuit diagram is designed to make use of this – the first variable resistor sets an average, maximum or minimum volume, and is not much used when playing.

Other additions to the basic circuit are:

– voltage starve.  I added a switch to this arrangement, the idea being that the voltage starve could be applied or not, as required, and there is a choice of direction of turn of the control pot.  After practising with it for a while, I prefer position 3, with voltage starve on, turning clockwise to increase voltage.

– resistor bypass.  There’s only one resistor in the circuit, so I added a 1M potentiometer in series with it, to increase or decrease the resistance between pins 2 and 6.  I know that knob-twiddling isn’t entirely within the philosophy of the original Cracklebox, but I found it a useful addition, affecting the pitch of the sounds produced.

– LDR.  When I had finished, there was an unattractive hole remaining where the Beatbox tuning control used to be.  I decided I needed to fill this in and calculated that an ORP12 LDR was the perfect size to do this.  I put this in series with the 1M resistor, and added a switch so it could be selected in place of the 1M potentiometer.  The effect it has varies considerably according to the ambient light level and the type of sounds being produced: sometimes it acts almost like an on/off switch, allowing for ‘gating’ effects.

The  op-amp section and the transistor section were built on two very small scraps of veroboard to make sure they could be fitted inside the case – there was very little room above the large keyboard PCB.

There is an LED shown in some versions of the Cracklebox circuit diagram.  I intended to incorporate this as shown, but I wired it as an on/off indicator at some point when I needed to know whether power was getting to some parts of the circuit and in the end I left it that way.

Here’s what it looked like when I finished:

Cracklephone front high angle

As soon I started to use it, however, I realised straight away that the best way to play it was to turn it upside-down, with the keyboard and speaker facing away from me.  This made it easier to touch the playing surface with my finger tips: seeing where they were wasn’t important, as playing was all done by feel.  This meant the underside of the instrument  – now the upper side – had to be decorated, too.  It now looks like this:

Cracklephone back high angle

In fact, the Beatbox keyboard turned out to be a very good playing surface, allowing for a certain amount of variation in the strength of touch and the possibility of sliding gradually from one touch point to another.

There is much discussion at the links mentioned above about whether a direct output could – or indeed should – be included, and if so, how this could most effectively be done.  As the principle behind the original Cracklebox was that it should be a ‘stand-alone’ device, I decided to deal with this issue by purchasing – for under £2 – a small goose-neck mic.  This plugs into a 3.5mm socket on the rear of the Cracklephone, and is bent to point at the speaker; adjacent to this is an out socket going to the amp.  These sockets aren’t connected to the rest of the electrics in the case, so this is just a simple way to mic the instrument up, enabling it to be amplified or recorded however or wherever it’s being held or moved.

Cracklephone rear DSCF0003

At the moment, I can only get this to work when plugged into my laptop, not through my general effects and amplification system – but I’m working on it.

I also added two 4mm banana sockets so the instrument could be connected directly to a (better) external speaker.  The external speaker arrangement is described in another post.

Cracklephone rear 2 DSCF0004

The working title for the project was the ‘Cracklephone’, since it’s a combination of the Cracklebox and a Stylophone Beatbox.  I liked the look of the blue parrot stickers, and it sounds very reminiscent of a parrot, so it acquired its nickname – also a reference to Sydney Greenstreet’s bar in Casablanca.

Here’s what it sounds like:


May 2012

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