Little Jenny – the resurrection of a simple Italian 70’s synthesizer & other waffle

Since 1987, at the age of 17 (you work it out!) I have always owned at least one pro synthesizer, not including owning a keyboard overlay for my Commodore 64 a year earlier.  Various trends have come and gone, along with my hair and most of my youthful exuberance, I even had a spell being really into hard heavy rock & metal bands, solely playing guitar, but still… I’ve always owned a synth or two (three, four, five etc 🙂 )

Recently, coinciding with the analogue synthesizer revival, I have been hankering for the old analogue sounds (see my previous blog why I love them).  Due due to selling some unused kit and a small windfall a year or so back I managed to purchase a ‘modern’ analogue monosynth, the Arturia Minibrute.

That machine is amazing and has brought back all I loved about my personal ‘golden age’ of synth based music, for me it was the years 1978-1983-ish. Following using this I got myself a little Korg monotribe and immediately modded it for MIDI use. I’m back in bleepy noise heaven 🙂

Loving the ‘no preset’ use of these synths reminded me of my old Roland Juno6, SH101 and Yamaha CS30 beast. As much as no memory can be a pain in the arse when trying to recall a particular sound, it does force you to be creative and learn how to use your synth.

So, due to using these modern synths on a few tracks with my electronica based project recently ( if you’re interested), it really kick-started the synthesizer freak in me again and I went back to hunting down any old kit I could find cheap (as now skint due to 2 kids and big mortgage!). I have a love of restoring kit back to it’s best or even better, as I hate seeing things thrown away.

Basically I began asking around at independent charity shops (the big ‘corporate’ ones sell working to ebay, which end up going in auction for current ridiculously inflated prices – fair play to them though as they are a charity, but the non-working/failed PAT test stuff quite often gets binned! aargghhh!)

I also asked anybody I know whether they know anyone who had ‘one of those old keyboard with knobs n sliders all over them’, unsurprisingly I didn’t have a lot of success initially…. that was until I asked one friend who I remembered used to gig with a Roland MC202 with his doom metal bands 10 years or so back. It turned out he still had it in his living room, sat behind his couch (!?). It wasn’t working correctly, sticking sliders, 3 potentiometers were broken/seized and it was filthy from years of exposure to smoking and countless gigs.

Still, I handed over some cash, retrieved the 202 and set about restoring it, which proved a little difficult due to the rarity of some components and the fragility of the early 80’s Roland kit, which had paper based PCB’s (yes.. really!). I finally got the Roland near minted and it sounds great! Definitely a keeper, although I would like to mod it at sometime in the future, if I dare!.

Well, by now the synth bug has well and truly bitten again (and also my personal issue of having to modify anything I get my hands on, but we’ll get to that later).  I started scouring free ads, eBay, gumtree etc etc but everything from the 70’s and 80’s seemed to be waayyyy overpriced. Even much derided budget synths and ‘almost destroyed beyond repair’ stuff was way out of my price range, which got me slightly angry.

For example, and is the main part of the article too, I found an ebay auction for the much derided 70’s Italian monosynth, the single oscillator Jen Synthetone SX1000. It was smashed, not working correctly, had more than half of it’s keyboard missing,  split wood end cheeks, dented and scratched panel, missing knobs and probably many more faults with it. Even so, I thought ‘I can do something with this’ as they are reasonably plentiful (in the UK).   So with this, I made my bid within the last 15 seconds, with the absolute max bid at £50, which I thought is a little over the odds personally for a basic synth requiring that much work. Well, it went for well over £100 in the last 3 seconds and I wasn’t happy!

If anyone’s interested the Jen SX-1000 vintage synth review page is here, along with a little piccy of mine 🙂 :
jen boards 030

I’m a member of a Facebook group that’s called Synthesizer Freaks (naturally!) and expressed my rage on there regarding this, and the vast majority of the members, well OK maybe about 15 of them, agreed and raged along with me! (FB community pitchfork waving FTW)

Way down the long thread replies, one guy replied with… ‘I have a Jen that I’m not using, you can buy it if you want?’ or something similar along those lines. It wasn’t working correctly but it was complete and at a VERY reasonable price!  A week later, a few emails with the owner (top feller btw!) and a little trouble with courier company (as usual) and the Jen was sat on my desk!

It was all original, and in pretty good condition seeing as it was probably made in late 1978 or 79 looking at the early-ish serial number.

Unfortunately the courier had dropped the synth despite it being packaged well and having large ‘FRAGILE’ stickers all over it.  The result of the drop included one smashed potentiometer knob & shaft (‘snigger’) and dented panel around that area, plus the power switch on the back was cracked… grrrr.

I plugged ‘her’ in (she’s called Jenny 🙂 ) and almost everything seemed to work, well apart from the fact that no matter what key I pressed the same note was produced.  Following this I went a bit mad researching online scouring everything I could find, including sites long dead on internet archive sites and found a few pages dedicated to this particular little synth.

One thing I noticed straight away in these articles was reference to the keyboard processor circuit and the large Italian made M110B1 IC chip that controls all this.  All the articles mentioned the strange way in which the Jen uses this IC produce accurate keyboard pitch scaling, non standard to any other synth made outside of Italy and only fitted to a handful of Italian synths of this era (Farfisa/Crumar/Siel’s).  If this chip had failed, so the articles stated, you’ll have a hard time finding one as they’re rare as the proverbial rocking horse shit!

hmmm, It’s at this point I’d like to note that although I can solder and know how to take pretty much anything apart and put it back together (usually in the way intended and with no… well not many parts left over 😉 ), I am no electronics expert and as far as repairing circuit boards or following circuit diagrams etc I am firmly in the ‘enthusiastic novice’ aspect of it all.

Feeling a little down about the possibility of having an almost dead synth with potentially failing rare IC,  I stripped it down, gave everything a good clean, repaired the dented panel and smashed potentiometer shaft then went looking for a replacement knob online.  I found an Italian guy who had a few replacement parts for sale on ebay,so I bought the spare knob and casually messaged him if he by any chance had a spare working IC…. Which he did and at a very reasonable price, Result!

After going over all the potentiometers with a liberal application of switch cleaner and replacing one, Jenny came back to life! turns out I didn’t need to replace the IC, it was just the glide potentiometer at fault.  Still good to know I have a spare IC in case it fails in the future.

Well this little Italian sure has a lot of character for such a simple, single oscillator synth.
I love the fact that it has separate envelope generators for the VCF & VCA sections, usually only really found in more expensive old kit.  Also I especially like the way the LFO * can be routed to modulate the Pulse Width – that gives the sound a lot of movement and makes it sound much more powerful. *the vibrato & filter modulation speed is also controlled by this LFO 🙂

Issues? well I did notice it does have some nice bottom end grunt… but only as long as you have the resonance turned right down.  If you turn up even just to the 1 mark then this low end just disappears, which is not great for those beefy/squelchy basslines.  They do still sound good but a bit more ‘ooomph!’ wouldn’t go amiss.

Another ‘issue’ was that the white noise seemed really quiet in relation to the pink noise (which itself is much quieter than the normal saw/square/pulse waveform generator) so that limits it’s use when combining with the main waveforms and it gets drowned out very easily.

I read in other articles about these issues I’d noticed plus others and it seems it’s just the way the Jen’s circuitry was designed initially.  not bad at all, just a bit quirky, designed to a budget and probably the reason it was maligned for being thin sounding.

So after reading every article I could lay my eyes on, I noticed that the Jen is ripe for modification. It was a daunting task as the last electronics training I had was way back in 1987, which consisted of etching a couple of PCB’s (and getting ‘off my tits’ on fumes in the process) for a simple led flip/flop circuit.  I can’t remember much of what happened from last week let alone a couple of weeks training 27 years ago!!

My very first mod was to do away with the power lead and fit an IEC (kettle lead) socket and new power switch.  I found that the hole for the old power switch was almost exactly the right size for a push in IEC socket and the hole where the old power lead was was exactly the right size for a new power switch, nice result there! (remember, this is with MAINS voltage, so be careful with this one if you tackle it, however simple it is!)

I was determined to have a go at the internal sound mods and found a very simple circuit to add a -1 octave square wave sub oscillator, which involved a small 4013 IC mounted on a piece of perfboard and soldered to four points inside the Jen, with no external visible modification.  This looked easy enough, even for a numpty like me 🙂 .  When I completed it and after blowing one chip due to holding soldering iron on too long (oops!), I fired her up and dialed in the sub oscillator… WOW! what a difference and what a great mod. fully recommend anyone with a Jen needs to do this mod.

That was it! My mind is running riot now… back on the net looking at all the other mods available.  The next one I tackled is trying to stop the high pass cutting of the low end frequencies in the filter section.  That mod involved snipping out and bridging the input capacitor in the VCF section… again looks simple enough.  But this mod also involved soldering a new capacitor (the right way round too 😉 ) onto the output on the waveform VCO board and cutting a trace out of the PCB… errrrrm rrrright! time to look at circuit diagrams and relate it to the actual board.

It wasn’t that hard to do at all, just my fear of destroying a 36ish year old rare circuit board was making me a tad hesitant.  After I completed this I once again reassembled her and tried it out… hmmm it’s quite a bit better but it does still filter out the low end further up the scale to a lesser extent.  Still it was worth doing this mod and is a definite improvement over stock.

The next mod was to replace the filter’s disc ceramic capacitors with polystyrene equivalents. A real easy mod as they’re very easy to spot and replace.  This made a great difference to the filter’s sound, although I do wish I had made a reference recording of it pre mods.  I could still tell, even though the synth had been apart for a few days, that the filter definitely sounded better… hard to explain exactly how but it does.

The last mod for the moment was to follow an old site from the internet archives and try and boost the main oscillator waveform & noise circuits volume to something close to equal (ish).  This was the hardest (*note: until I completed LFO mod – see end), not because it’s a difficult procedure in any way, but just because it involved looking at circuit diagrams, tracing each of them along the boards and finding the relevant resistors to swap out or add another in parallel.

I completed that mod, reassembled yet again and tested… Yes! the white and pink noise are equal and the overall waveforms ‘seem’ louder.  The noise circuit is still a little quiet in comparison to the main waveforms but it’s better overall and much more usable.

**** UPDATED 29-1-2014 ****

I’ve completed some additonal mods,  the first was to add a 1/4″ jack socket on the back and route it through the filter for processing external sounds, this one was easy, apart from when drilling the 10mm hole in the back panel for the Jack socket,  the drill bit snagged as it went through, causing the pabel to twist slighty round the hole and much swearing from me!  After straightening it and filing the burrs off I got the socket fitted fine (that’ll teach me to use a vice in future!).

The mod is basically a switched socket wired from the sub osc board output and onto the noise off pin where the sub osc was soldered to before. Therefore when a external source is plugged in it runs through to the filter section of the synth, allowing some nice filter sweeps etc., and also allows the LFO to modulate this source…. which is nice! 🙂

The downside of this mod is you have to hold a key down to hear any input (it also cuts the sub oscillator, no big problem though). Nice simple job.

The last mod, as of end Jan 2014, was to add two more waveform shapes to the LFO, basically sawtooth up/down ramps in addition to the existing triangle wave and also to increase the LFO’s usable range overall.  Now this was a touch more complicated, but that’s probably more of a statement of how little electronics knowledge I have more than anything.

This involved the usual swapping of resistor values, soldering diodes for the wave shape, changing the LFO’s pot value and fitting a DPDT switch to the front panel. I completed this (and only asking my mate Lee to help interpret the circuit diagrams 4 times for me!! a new record 🙂 )

I reassembled for the umpteenth time and fired her up, dialled in the LFO with the switch off, yep still works and woah the speed has increased dramatically, great stuff.   Now hold breath… flick the switch… sawtooth up ramp brilliant! Flick switch down……. sawtooth down ramp! whoop!   About 45 minutes later I finally stopped messing around on the synth 🙂

What a fab mod this is, as the LFO shape affects the vibrato, PWM & filter LFO it’s now greatly enhanced the usability of old Jenny.

There is only one mod left that I would wish to do, which is the sawtooth multiplier circuit (which is a little bit like the ultrasaw circuit on a Mini/Microbrute if you’re at all familiar with it).  I’d like to keep the synth panel free of extra pots etc so I’ll have to do a little more investigation first and post that later.


For anyone who is still awake at this point, and is a little synth-savvy, you might probably be asking why I haven’t added CV/Gate sockets and/or MIDI capability as that would surely be the best mod and make the Jen much more usable in a modern setup?  Well I looked into this and it’s MAJOR work to install either.

One: because the Jen actually runs on Hz per volt, not CV and two: the way in which the oscillator (hydrid DCO/VCO) and the keyboard M110B1 IC work requires a complete new oscillator circuit in order to accomplish it. Wayyy over my abilities so I’ve ruled that out for now.

I’ve attached a PDF detailing my mods at the bottom of this blog, they may help people like myself who are not so electronics savvy but willing to have a go.

PLEASE NOTE:  I hold no credit for any of these mods by the way.  These were all designed and uploaded on the net by people far far more electronics savvy that myself:

All the credit needs to go to these guys below:

(don’t know this guys name, but just look at his synth mod list!)

Neil Johnson’s site is the holy grail of Jen SX1000 mod info:

Hakan Erikssons site from internet archive:

Bluebears site from internet archive:

And I got the initial basic sub oscillator mod from this page*: (which I think is Bluebears page also):

*note: the chip has 4017 showing on the diagram whereas the description mentions 4013, I fitted the 4013 IC.

Cheers for reading,  hell-fire I can babble on forever about synths, really sorry about that ;-D


P.s. Below is the PDF with my instructions on the mods (if you find any errors, please contact me and I’ll correct them). thanks:

Jen SX1000 mods

*** UPDATE 18-3-14.  I have another Jen in my possession which is getting the full works!

sawtooth multiplier mod, 2 octave range sub osc, cv/gate, midi in (hopefully), filter env inversion plus all the mods listed above.  It’s also very nearly complete, I have refinished the (originally very rusty) panel, new knobs and walnut wood cheeks.

I’ll post a blog on the build of my 2nd Jenny soon.

If you want to see the progress and are on Facebook.  there is a Jen SX-1000 owners group just been started on there (I’m an admin).  check it out! 🙂

*** UPDATE 18-7-14  It’s been a while as I’ve been really busy with the little ‘uns and also trying to setup a new business, more on that in the future.

My 2nd Jen SX is looking amazing, complete overhaul and every mod I could find 🙂  I’ll also post a blog on that too once finished.

Here’s a soundcloud link to a demo of my first Jen documented above:

10 thoughts on “Little Jenny – the resurrection of a simple Italian 70’s synthesizer & other waffle

  1. good work, sir, & i hope your account spurs others into action. doing mods to enhance an instrument rather than painstakingly restoring it to “concourse” condition is far more interesting, in my opinion.

    • Thanks Duncan, agreed!

      I think you’re going to like the ‘other’ project I have going on then.

      not releasing anything about it just yet, until I’ve got a bit further along with it. But it involves modification of yet another misunderstood cheap 80’s analogue. 😉

  2. Hi kevin, I had a jen for 15 years or so and in its later time with me modded it. I had the kenton Osc mod which gave me cv and gate inputs, the filter env (positive and negitive values), sub osc and the lfo three level speed switch. sold it a few years ago but I must say I miss the old girl. warm and soft she was but it fitted a mix nicely. It had a very FSOL sound.

    • Hi,

      Yeah it is a nice warm little thing, even better and less thin with the filter mods.
      Thought about the envelope mod, but keeping as it is for now I think and use it more (that said the sawtooth multiplier circuit looks fun!)

      Does sit well with my others in a mix as you said. I need to get recording with it more now.



      • As a note paul, do you have the schematics for the envelope inversion mod? is it an easy mod? Could you possibly send me some details on it by any chance 😉

      • I don’t think I will have kev, it been a long time since. If your in no rush I ll dig through the synth paperwork at some point.

      • It’s OK Paul, I found it and modded my 2nd Jen SX with it….. yet to test though as it’s an epic mod list this time (refinished wood cheeks, repainted panel, sawtooth, cv/gate & midi in etc 🙂 )

        I’ll more than likely do another blog on that one v soon.

  3. Hello, any chance you would know the weight of one of these? Just bought one, but the seller doesnt have scales to weigh it and i need it for the courier!!

  4. Pingback: Reviving Jenny, or: contacts cooked to life | untergeek

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