Stylophones 3 – The Stylophone 350S, Part 1

A series on the Stylophone can only reach a climax with the mighty 350S!

The question of why the original Stylophone sold in its millions and became a world-wide success story, and the 350S didn’t, has long been debated.

According to http://stylophonica.com (‘The official home of the Stylophone’), it was ‘too costly, and lost the key uniqueness of the Stylophone itself, which was its small size and mass-market appeal’ – but it certainly wasn’t through of a lack of features.

You may be familiar with the Stylophone, but not the 350S: if so, then to start with, a run-down of its capabilities is required:

First of all, it’s certainly true to say that it’s much larger than the regular Stylophone – which is, after all, about the size of an inch-and-a-half thick postcard.  Here’s my 350S together with the regular-sized ‘New Sound’ Stylophone with which it shares many of its design cues:

The 350S is a souped-up Stylophone in every way: instead of the Stylophone’s 20 notes – an octave and a half – the 350S has 44.  That’s three and a half octaves, and you can see in the picture the difference in length between the two keyboards.

Not only that, the 350S has eight voices, as opposed to one (or even the S1’s three), and some of these are themselves in different octaves.

The voices are designated ‘woodwind’, ‘brass’ and ‘strings’.  In these days of sample-based synths, none of these sound terribly much like what they say they are, but they have the general qualities of these instruments – and, despite what you may read, one or two of them are quite like the distinctive tone of the regular Stylophone that we all know and love!

These voices are:

four ‘Woodwind’ voices pitched at four different octaves, and described (like organ stops) as 16′, 8′, 4′ and 2′;

two ‘Brass’ voices at 16′ and 8′; and

two ‘Strings’ voices at 4′ and 2′.

Because these voices are pitched at different octaves, from 2′ to 16′, in all no less than six and half octaves are available from the bottom of the keyboard to the top.  This is almost as large as a ‘professional’ 88-note synthesizer keyboard.  Up to two of the voices can be combined at any time, one each of the four octaves.

As well as this wide range of voices, the 350S has a variety of built-in effects.  Like the regular Stylophone, one of these is Vibrato – and two speeds are available, rather than one.

There is also a two-speed ‘Decay’ facility: as well as the usual Stylophone ability to hold a note as long as the stylus is in contact with the keyboard, when the Long or Short (actually, ‘short’ or ‘very short’) Decay button is pressed, the note will fade out while the stylus is still in contact.  According to the nicely-produced, LP-sized User’s Guide that comes with it, this enables the player to obtain ‘a percussive effect rather like  piano.’

However, as can be seen from the above picture, this is only the beginning of the 350S’s abilities.

The fast or slow ‘Reiteration’ button (second from the left) can be used to imitate the sound of a banjo or mandolin, and the 350S even has a second stylus which is used to produce these effects.

Normally, whichever stylus is being used, the ‘regular’ or ‘reiteration’, it’s held in the right hand; but it’s possible to play two notes at once in reiteration mode by using the reiteration stylus with the right hand, and playing lower notes with the regular stylus in the left hand.  It doesn’t work the other way round, and it doesn’t work in ‘normal’ mode, i.e. without either the fast or slow reiteration switch pressed.

The white tuning control can also be seen in the above picture – handily placed on the front of the instrument, unlike its counterpart in the regular Stylophone, which is always hidden underneath.

The most unusual effect, though, has got to be this:

Above the volume control is the 350S’s secret weapon – the ‘Photo Control’.  This device, operated with the player’s left hand while the stylus is wielded in the right, can be set to control the volume, amount of vibrato or low-pass filter cut-off point – acting as a ‘waa waa’.

On the side of the 350S, next to the Photo Control, are three 1/4″ mono jack sockets.:

While one of these is ‘sound in’ and another ‘sound out’, the middle one is a socket for a foot pedal that replaces the Photo Control – either because the player would prefer to control volume, vibrato or waa with their foot, or because the ambient light level is too low for the Photo Control to be effective.  A 50k – 100k potentiometer does the job, according to the User Guide.

My experience of light-dependent controls like this – and I’ve made a number of them – is that they are really only fully effective when quite a bright light is shining on them, which is not always the situation when you sit down to play.

Unsurprisingly, this magnificent machine requires a fair amount of juice, so it’s powered by not one, but two weighty PP9 batteries, connected in series to provide 18v of power to the 350S.  [Edit: but see notes below about powering the 350S].  The batteries are housed underneath the rear of the instrument:

The battery covers look as if they’re held in place by screws, but these aren’t really screws: they click into place when pushed, and just require a slight turn with a screwdriver or a thin object to loosen them.  (The User Guide suggests a coin, but in my experience modern coins are too thick to perform this function.  Maybe a 5p would do it).

This is the User Guide that came with the 350S:


Reliable information on when the 350S first came on the market, how many were sold, etc. seems hard to come by.  http://stylophonica.com says: ‘No more than a few thousand 350S’s were ever sold’; http://stylophone350s.com/ says ‘Dubreq, the manufacturer of the original Stylophone created and produced the Stylophone 350S beginning in 1971 . . . fewer than 3000 were ever produced’ and quotes a Ben Jarvis (son of Stylophone inventor Brian Jarvis and re-founder of Dübreq in 2003) estimate that only 200-300 working units are probably still available worldwide.

I’d be surprised if the numbers were quite this low, but they’re certainly not common, and those that appear on eBay in the UK frequently command in excess of £100, rarely less than £70. Stylophone350S.com in the States have access to a recently discovered cache of mint condition boxed examples, which are now on sale.  Their website tells the story of this amazing find.

The back of the 350S is removed by undoing 4 large screws in the corners and two very small screws under the front, and reveals two printed circuit boards: a thin, narrow one at the front containing the keyboard and the resistor chain – not discrete resistors, but what I’ve previously called ‘resistor modules’, since I can’t remember what the proper name for them is – and a large, rectangular one with everything else on it, including potentiometers, sockets and switches:

The circuit boards themselves come away quite easily: there are 4 screws, clearly visible in the above photograph, which hold the keyboard in place, and 6 similar ones for the larger board.  The volume control knob doesn’t need to be taken off – it fits through the hole surrounding it – but the plastic nuts on the three sockets need to be removed.

This is what the other sides of the boards look like:

Here we see the larger items across the middle of the board, from left to right: the three sockets, the volume control, the eight voice and effect switches, the pitch control and the on/off switch.  If I was an electronics expert, I could tell you what the rest of the components do; but I can’t.  I can only surmise that the round inductor next to the left-hand switch is to do with the waa circuit; the LDR (light-dependent resistor) to the left of that is the ‘Photo Control’.

The black ‘hood’ that partly surrounds the LDR was slightly damaged when I came to look at it, and it’s quite possible that I did this myself when I opened the case.  It was easily repairable with a spot of superglue, but watch out for this if you’re looking inside yours.

The ferrite core inductor is a Mullard FX2236.  In this close-up you can see that mine looks a bit broken.  I don’t know enough about these things to know if this means it isn’t working properly, but, while by no means common, they can be found – perhaps more easily in the UK than elsewhere – so I shall certainly consider replacing it.

According to the experts at www.stylophone.com, under the heading ‘VITAL INFORMATION WHEN BUYING A 350S… PLEASE READ CAREFULLY!’, one of the components you can see here – which they describe as the ‘Amp-ic’ – is highly prone to failure.

The related website, the Stylophone Information Centre at www.stylophone.fsnet.co.uk says: ‘The circuit board carries an IC which controls sound output, and this component (long since obsolete) is the single- most likely cause of the 350S to break down. If this happens . . . the unit will only be heard if played through a separate amplifier, if at all.’

The symptoms to look out for are: ‘when the stylus is applied to the keyboard, only a very faint sound is heard (if even audible at all), which fades away rapidly . . . Even with the volume control turned up to max, the sound will still be very low – then quickly fall away. The user will then be left with a ‘dead’ 350S.’

The chip in question is this one – the black one with six legs in the top left-hand corner of the picture:

It’s a Motorola MFC 6070, 1-watt power amplifier  – ‘designed primarily for low-cost audio amplifiers in phonograph, TV and radio applications’, according to the datasheet.

If you don’t know what a phonograph is, ask your grandad, he’ll remember them!  The use of this antiquated vocabulary confirms what is said above.  If you find the datasheet for this chip, it says ‘Device discontinued – consult factory’; if you try to buy one on the Net, you’ll mostly find specialist sites, dedicated to sourcing obsolete parts.

As a matter of fact, you can, at the time of writing, get one on eBay for about £20, but you aren’t going to want to do that: the problem doesn’t arise, apparently, just because 350S’s are now all old – it even used to happen to quite new ones.

Stylophone.com told me that ‘the original chips as fitted . . . were working very close to their breakdown point voltage-wise. Although theoretically all the chips supplied to them should have worked, Dübreq actually had to batch-test the chips to find those with an acceptable working voltage range, especially the maximum voltage’ (which is meant to be 20v). ‘We’ve seen some of these chips.’ they said, ‘ running extremely hot (basically too hot to touch) by simply switching the instrument on, before even playing a note.’

That’s not to say the MFC6070 was a particularly unusual part at the time – they were used all over the place, and even the venerable VCS3 synthesiser used one as a driver for its spring reverb circuit.  However, as the site offering VCS3 spares, http://www.synthi.com, says: ‘The Achilles heel of the VCS3/Synthi AKS are the now obsolete and ultra rare semiconductors that it uses’ . . .

This made me think twice about powering the 350S with a mains-powered adapter: the increased risk of overdoing the voltage and blowing the chip might not be worth it.  Dübreq themselves did apparently produce some 350S’s with an ‘adaptor socket factory-fitted’, but ‘this led to many of them blowing the chip.’

I’m not quite as worried as I was, however, as stylophone.com are now marketing a new module, the ‘Stylophone ACM’, which can be retro-fitted to an ailing 350S – or even to a working one, as a precautionary measure – to get round this problem altogether.

The circuitry inside this unit is not operating close to its limits, and makes it much safer to run the 350S from an 18v adapter.  (And if you buy a reconditioned 350S from stylophone.com, it will already have one of these in it).

[Edit: see comments from Christian Oliver Windler below relating to powering the 350S.  He concludes from his tests that the 350S could – and should – be powered at less than 18v, and preferably less than 15v.  Some of the above problems and their expensive solutions can thus be avoided.

As with the original Stylophone, by the way, there appear to have been various upgrades during the course of production, and it’s interesting to note that some of the components inside Christian’s 350S differ from those in mine].

As a matter of fact, this is not the only ‘obsolete’ component in the 350S.  Although the resistors, capacitors and transistors that fill the circuit board are not commonly used in new designs nowadays, they’re still readily obtainable; the round silver integrated circuit over on the right-hand side, just above the tuning control, isn’t.

It’s a General Instruments AY-1-5051, and what it does is frequency division (presumably for the 350S’s different octaves) – the kind of thing modern CMOS 4000-series chips do with the greatest of ease.  There’s a description on this website: http://www.divdev.fsnet.co.uk/repair2a.htm of how one might make such a replacement (using the example of a 1960s Elka electronic organ).  All I can say it, it looks feasible in theory, but not something I’d want  to be faced with in practice – let’s hope this isn’t a part which is going to fail!

Returning to my 350s, it looked badly in need of a clean up.  There was a lot of dust inside it, and over the years the keyboard had got very dirty:

The switches sounded OK – no crackling or intermittent operation, so I left those, and just cleaned the circuit board and keyboard.  The keyboard in particular needed attention from, in order, a soft brush, switch cleaner, WD40 and Brasso.   This seemed to do the trick, and it began to look shiny again.

I cleaned everything, including the switch rockers, the case and the tips of the styluses, and put it back together again.  It now looked much better, and sounded clearly and reliably on every note.

In my next post, I’ll take a longer look under the bonnet of the 350S and see what there is to see.


14 Responses to “Stylophones 3 – The Stylophone 350S, Part 1”

  1. 1 mbbmbbmm
    August 27, 2012 at 1:13 pm

    Wow, this is a great source of information- especially about the Amp-IC and the battery eliminator. Thanks!


  2. August 27, 2012 at 8:27 pm


    Thanks very much – it’s surprising how little there is on the 350S on the web, isn’t it?

    I’ve added a little extra information and improved some of the photos since the original post.


  3. August 28, 2012 at 12:49 am

    Hi Andy,

    You were correct about RetroTech being the owner of stylophone350s.com. I’ve been quite slow to get the actual site up and running because of some family and health issues these past few months, but hope to have at least the beginning up by the end of this month. It’s my hope that it will become a place for a 350s community of sorts, and I hope that those who purchase units from me or that are fans of the Stylophone in general will share their creations and learnings with others on the site.

    I came to the Stylophone world quite accidentally, as I had the great fortune to discover a large cache of brand new in the box units in a storage space in Beverly Hills, where they’d been since at least the early 80’s. If you’re curious, I have written a draft “press” release that I’d be happy to send you with information about the find. (Oh, also the quote from Ben Jarvis was from he and I’s correspondence.)

    Feel free to e-mail me if you’re interested, and I’ll certainly let you know when I have more than the splash page up and running. Thanks!


    • August 30, 2012 at 8:18 am


      Thanks for confirming the RetroTech connection – looking forward to stylophone350s.com and those ‘brand new’ Californian 350S’s.

      Thanks also for placing the source of the Ben Jarvis quote. 350S owners are a more exclusive bunch than I realised!

      Good luck with your project,


  4. August 25, 2015 at 10:43 pm

    Love the page,Andy.Keep up this good work.

  5. August 27, 2015 at 10:45 pm

    (btw Andy.In mid-1970’s I owned the ‘Bass’ stylophone purchased from an Erdington,Birmingham music shop-long closed.It was a browny/caramel colour and I wish I knew then what I know….)
    all the best.

  6. September 1, 2015 at 10:37 pm

    Out of interest, VBS,tv Flickr photostream has pics of the Bass and Treble Stylophones

  7. March 18, 2016 at 4:19 am

    I just got a Stylophone 350S and repaired it. My PCB (revision “6510 C”) strongly differs from from yours and is likely later.

    My main ICs are the CMOS 7-stage ripple counter “Motorola MC14024BCP, M 9 38” (14 pin DIL) as the octave divider and the power amp IC is “National Semiconductor LM380N, /925” (14 pin DIL). Despite the 2 huge 9V battery compartments this model can run very well on 10V (tested with halfway empty 9V transistor batteries). Both batteries are wired in series (no intermediate tap) for supposed 18V, and there is also a 3.5mm power supply jack (labelled “BATTERY ELIMINATOR”, positive center). I recommend to feed it with not more than 10V to 14V DC (“6V” or “7.5V” setting of unregulated PSU) to avoid damage.

    The foam rubber on battery lids were very crumbly and fell apart by any small touch, thus I had to vacuum the residues out. Also 2 Piher trimmers had strange white blooming (like mould fungus) on them that could be easily wiped off; may be the plastic sweated out some chemicals. Another Piher pot looked ok. The volume pot is made by ITT with white plastic package.

    My Stylophone made only creaky noise mess because none of the rocker switches did work. The previous owner even had soldered a diode (1N4007) across the power switch to short it, because it obviously failed.

    CAUTION: The switches are held by each 2 screws at the PCB back and fall apart when removed. Thus to avoid mess, only remove and clean one switch at a time and hold it with the other hand during removal. These switches contain up to 3 metal contacts, each with ends sticking in 2 holes of a L shaped sheet copper leaf spring. Look carefully how they are placed (if in doubt, carefully unscrew another switch to compare). Clean the contacts with cotton swabs and isopropanol. The opposite contact side are solder nails on the PCB. These may fall out or misalign if you try to resolder them without switch in correct “on” position holding these nails down. (I acidentally broke a leaf spring when I tried to bend it higher; fortunately it could be soldered back together.)

    After I got the instrument to work, I installed a polarity protection diode (will also reduce voltage by 0.7V). I can run my Stylophone safely on 10V. Even switching to 8.9V during operation works, but it can not start that low (possibly a low battery detection). My unregulated power supply makes it hum a bit. Thus particularly for owners of the older version with the delicate “Motorola MFC6070” amp IC I recommend to install an additional voltage regulator. E.g. a 7812 makes 12V output; if this is not enough for it (my newer model runs on 10V) you may install one or more diodes in series with the GND (reference) pin of the regulator to increase the output voltage.

    I conclude that the 18V operation was only done because the at that time only available zinc carbon cells had strong voltage drop when running empty. Suitable voltage regulators did not exist in 1970th or were expensive discrete circuitry, so the maximum possible initial voltage was used to extend battery life. But perhaps the manufacturer also wanted to squeeze out as much output power as possible through that tiny amp (installing a heatsink on MFC6070 may be a good idea if it runs hot). Reducing voltage may cause distortion at maximum volume setting, but unlike 1970th nowadays it is anyway uncommon to play instruments loud on stage through a that small internal speaker or amplifier (and who wants to use an external 35 Ohm speaker?!). It also may be that semiconductors were simply too new technology, thus manufacturers did not know that they will decompose from operation near their maximum possible voltage despite they work well in short laboratory tests. In modern IC datasheets are often sentences like “Product is rated for operating voltage of 15V. Absolute maximum voltage of 18V may not be exceeded. Running near this voltage will reduce reliability and may cause premature failure…” Thus I conclude that by modern terms the MFC6070 would be only suitable for 15V and rated wrongly.

    But the big warning on the official Dübreq Stylophone sales website (and the many websites copying from it) IMO sounds very much like propaganda to raise panic for selling expensive snake oil (like the “Stylophone ACM” voodoo) for the sheer sake of moneymaking. Even owners of a 1st generation Stylophone 350S can certainly easily buy a cheap regulated 12V power supply to operate it without any risk of damage. Also installing a chain of about 5 1A silicon diodes (e.g. 1N4007, each dropping 0.7V) in series with the battery is a cheap and simple measure to reduce the operating voltage by >3V, which should be enough to keep the MFC6070 in its safety margin. I even doubt that the instrument is that ultra-rare; may be that Dübreq only counts their customer list as the total number of owners.

    The Stylophon 350S is IMO quite similar like the Gakken SX-150 mini analogue synthesizer, thus for use as an instrument do not pay too much. Especially people should not fall for the false myth that it is duophonic (2 note polyphonic). The only thing it can do is to alternatingly toggle its monophonic VCO between the notes of both stylusses at a fixed speed (like the dumbest possible arpeggiator), and this even only so long one note is lower than the other. I particularly don’t understand why Dübreq used these stupid rocker switches for setting each only 2 speeds for decay envelope, vibrato and “reiteration” (chopper or toggle mode – unlike mandolin ring at least mine does not decay). I definitely would prefer here each a potentiometer + on/off switch, which would have taken not more space. (Likely in 1970th “preset” switches were believed to be easier for novices.) The 350S also seems to be the only monophonic instrument with a drawbar IC for 4 footages. Despite the 350S contains 2 LFO (for vibrato and chopper), some kind of (LC based?) VCF and even a light sensor (for volume, vibrato depth or cutoff) it IMO lacks many features (e.g. attack rate, pitchbend, modulation matrix, combining both stylusses differently, additional ribbon controller) I would expect in a basic monophonic synth.

    Interesting is only that the technical concept has many similarities with the “Clavioline” (a compact monophonic tube organ with vibrato, timbre switches and in some models mandolin-like effects, that was widely used in 1950th – I own one made by Jörgensen). Perhaps the original idea of Dübreq was to create a solid state miniature version of it.

    The light sensor needs bright light to respond well, thus I recommend to play it with the small hand-mounted LED lamp that can be covered by fingers for full modulation depth. Also a glove with finger contacts instead of a stylus may be used for play tricks.

    During repair I quickly measured the hardware with my analogue oscilloscope. The key contacts respond on connection to GND (that is what the normal stylus does), which triggers the decay envelope (if enabled) and plays a tone with pitch depending on the resistance of that connection (much like Gakken SX-150; due to their wiring as a resistor chain, pulling multiple “keys” to GND makes the higher note succeed). With “reiteration” (chopper) enabled, the reiteration stylus apparently pulls to GND through a pulldown transistor modulated by a square LFO. Because the other stylus stays always GND, using both together makes the tone only toggle between notes when the normal stylus is on a lower note (a multivibrator with 2 real toggeling stylusses would have prevented this). To prevent waiting on a note, the chopper LFO starts only when its stylus touches the keyboard. The octave divider IC derives from the VCO squarewave undertones , those are mixed through 4 switches (with different capacitor filter on both ends). For professional circuit-bending it has high potential. Because everything is analogue, potentiometers may be installed as drawbars or to change the LFO and decay speeds. Connecting a capacitor to GND at the decay switch makes slow attack. The LFO signals may be also routed elsewhere. Strange is that vibrato (intentionally?) fades in very slowly when the switch is pressed.


    I CYBERYOGI Christian Oliver(=CO=) Windler I
    I (teachmaster of LOGOLOGIE – the first cyberage-religion!) I
    I ! I

  8. March 4, 2017 at 9:58 pm

    Hi Andy
    I have purchased a 350s that all works bar the wah function. On inspection I noticed the inductor wires that drive the wah function had snapped off the connectors and couldn’t be resoldered. Can you recommend a replacement coil? I tried purchasing using the code on the core fx2236 but only recieved more cores and no coils!

  9. 12 DON COOPER
    May 2, 2017 at 8:42 pm

    Hi Andy.Have you had a look at the (hopefully) forthcoming Stylophone GENX-1 on the Dubreq page? Looks tasty-much like Korg Monotrons etc.If you express interest via em they offer 20% discount on release,(again,hopefully)
    All the best from Brum

    • May 14, 2017 at 10:38 am

      No, I hadn’t seen that! – I like the look of it more than the S2.

    • 14 DON COOPER
      May 17, 2017 at 10:42 am

      Price looks reasonable.I imagine Dubreq have ‘clocked’ the Gakken SX-150 synth ( which I managed to grab prior to silly-money prices).
      Gen X release now July-hope that is increased orders rather than production problems…

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