The Stylophone

Well errrrm...  With only 1½ octaves (from A0 to E2) and only being capable of playing one note at a time, it's never been a 'proper' musical instrument.  And it really does sound cheesy....  But it was 'affordable' when it was first launched in 1968 as a 'Portable Electronic Organ' and, looking rather like a '60s 'tranny' radio, was very popular.

My interest in these beasts started when I acquired a non-functioning Chinese copy as a freebie.  It was easy to fix - a broken wire inside - but they're available new from Amazon for about 20 quid.  Then I wondered about the originals that I remembered from my youth but never bothered with - and found they appear frequently on eBay at reasonable prices - so I bought one.  I suppose that when the darker side of Rolf Harris' life emerged in 2014, his association with the Stylophone made some owners whose childhood acquisitions had been gathering dust for decades decide it wasn't kosher to hang on to them.  A bit unfair - Dübreq (the manufacturers) had only hired Harris as a well-known TV personality at the time to promote the thing...

[ Dübreq is/was no more German than I am.  They must have thought it cool to have a Teutonic-looking name by using an umlaut, as did Motörhead... ]

So what's inside the box?  Remarkably little....   [ Battery disconnected to give a clearer view. ]

The original I bought has a paxolin PCB with 4 transistors and about 50 other components.  The Chinese one has a magic chip and a fairly ordinary audio amplifier on another small PCB.  The things they have in common are the 'keyboard', which is part of the PCB, and the stylus that connects with it to play notes.  The only circuit diagrams of the original I could find on the net bore little relevance to mine - but this did reveal there have been several variants, including using resistor networks for the resistor ladder and a unijunction oscillator - see here.
So I set about tracing out my PCB to see what made it tick - here is my circuit:

Click on the image to view it at a higher definition, or here to download it as a PDF.  The main blocks are:-

Overall current consumption is very low - typically 5mA with Vibrato off and no note being played.
Playing a note takes an additional 5mA, and Vibrato a further 3mA.

The Well-Tempered Stylophone?

You've got to be joking!  Since it's entirely analogue, it is susceptible to component tolerance, temperature variations and changes in power supply voltage.  Given this, there is no way it can accurately follow the even-tempered scale, but I have been able to modify mine to get all notes within +/-8 cents (ie. ~1/12 semitone) of where they should be in this scale.  However, this is part of an analogue synth's charm - being too rigid lacks 'warmth'.

The worst problem is supply voltage variation.  As the battery ages, so its voltage drops and internal resistance increases.  The main oscillator pitch goes flatter with lower supply voltage: although this can be compensated for with the master tune, the top 5 or so notes go flatter than the rest, putting the whole thing out of kilter.  The culprit is the bias circuit - a simple potential divider across the battery (R21 and R22) with a smoothing capacitor (C12).
Replacing R22 with a zener (surrounded by a yellow ellipse in the photo above) improves things a lot - choose one that keeps the original bias voltage (with a new battery) of about 5.8V.
[ A 6.2V zener will 'zener' at less than 6V with our less than 1mA bias current.
Replacing R21 and R22 with a 78L05 with its 0V terminal connected via a silicon diode to jack it up to ~5.7V did not work as well - the pitch went sharper as voltage decreased, particularly between 9V and 8V.
The simple zener arrangement is quite stable between these supply voltages. ]

Pitch will still go flat as the battery does so, but it remains reasonably well in tune with itself until the battery voltage drops below 7.5V, so this can be compensated for by adjusting the master tune pot.  By this time, the battery internal resistance will have increased to such an extent that the increased current drawn each time you play a note will drag the voltage down further - evidenced by a note falling in pitch after it has started.  The time to replace the battery will have been sometime in the past - use a decent one (like Duracell Industrial) for best results.

My other two mods are:

Both these are best fitted on the solder side of the PCB, on the 'underside' of the components with which they are in parallel.

Chinese Copies

Can you tell which is the original?

The Amazon offering doesn't suffer from most of the original's tuning problems - the nTuner verified it remained in tune with itself within 1 cent over the whole range.  However, it also goes flat as the battery ages.  It runs off 3 no. AA cells, accessible under a cover in the base of the unit, which is better than a PP3 (you get at this by removing the entire base of the original).  The battery cover bears the words 'Made in China', which are embossed but can be removed if you can't stand the embarrassment...

Note the fluorescent orange tape I added to the ON slide switches - it catches your eye if you leave it on by mistake.  It's fairly easy to fit on the Chinese one, once you've got it open.  You need to take the switch apart in the original - awkward, but not too difficult.

Current consumption is similar to the original - about 5mA when no note is being played, going up to 50mA at full volume (less at lower levels).  Vibrato makes no difference to current consumption.  At least the phone socket cuts out the speaker.

You can get quite a good chorus sound by playing a Chinese alongside an original in unison.

It also has a volume control and an octave switch.  The latter has 3 positions - number 1 is one octave above the original and number 2 is same pitch as the original.
Number 3 is useless - it's a slightly less tinny sound but overall about 25 cents flatter than number 2.

However, INSHO it sounds even more naff than the original.
Vibrato is dreadful - unless you want a sound like that awful organ used by the Tornados in Joe Meek's Telstar.

The Chinese copy has an 'MP3 Input'.  This is simply an audio input to play though its puny speaker, presumably so you can go into karaoke mode - though it beggars belief that anyone would want to degrade MP3 even further by so doing...   However, beware of this - the protruding shells of the headphone output and 'MP3 input' are opposite poles of the battery - so if you accidentally short them, your battery will flatten very quickly!  I removed the entire MP3 jack (the blanking plug I used to fill the hole is visible in the right photo above), but to do so (and fix the original problem of the broken wire) I had to prise open the case...

Our Chinese friends don't want you poking about inside, so they glued it together.  It came apart fairly easily, but then it wouldn't stay together when reassembled.  I remedied this by removing one of the screws holding the large sand-coloured PCB to the top part of the case and drilling a small hole under the middle cell of the battery in the base (see yellow arrows in photo above).  Then a 1.5mm by 12mm screw (arrowed, above right) through the lot retains it.

Note also that the stylus is connected to battery positive - this is of little consequence since the negative side of the battery isn't accessible outside the case once the MP3 connector has been dispensed with.

This is what the PCBs look like.  The black blob on the largest PCB is the magic chip - note that all tracks from the keys go into it.  The space on the top left of this PCB is where the MP3 connector was.

A much better bet...

Fortunately the mid-20th century also produced a considerably better similarly portable keyboard instrument - the Melodica.  Hohner first came out with a 2-octave Melodica in the 1950s, later introducing a more piano-like keyboard.  They're still made, by Hohner and also the likes of Suzuki and Yamaha, though most modern ones have 2½ octaves (F below middle C to C two octaves above), or even 3 octaves.  Pictured below is my rather weird 2½ octave beast - accused by one member of our pub music session of being rather 'Fisher Price'.  I prefer to call it a keyboard player's gobiron - at least it looks better than the 'Fire' alternative, where all blue parts are a gaudy red...

It has a rather strange sound - single reed: nothing like an accordion or harmonica - more reminiscent of a saxophone.  The tube at the bottom that looks like an endoscope allows playing on a table, but you can't get as much expression as blowing it direct.
Anyhow, it has distinct advantages over the Stylophone - though it usually costs between 2 and 3 times as much:-

I rest my case.

Steve Glennie-Smith   July 2017