Polyphony

As I mentioned in the requirements there's no real short-cut to triggering the SS30 and every key will have to be addressed individually. I thought it would be a good idea to get my thoughts on polyphony down in writing and put to bed some misconceptions about polyphony in general and the SS30 in particular.

A good part of my understanding of polyphonic synths and their foibles came from the excellent Synth Secrets series of articles by Gordon Reid, published in Sound On Sound magazine. Some of what I'm about say is taken directly from the parts 20 and 21 published in the December and January 2000 issues.


The first question most synth people ask is "how many notes can it play at once". This seems an odd question to an organ or piano player. They can always play all the notes at once (should they choose to do so) but it isn't ever that simple for synths.

In order to cut down on the amount of circuitry required in creating polyphonic synths manufacturers came up with a scanning mechanism using digital logic that meant they only needed a small set of circuits that could be assigned to play notes on the fly. So, one of the early such synths, the Oberheim 4-Voice had four voice circuits and was 4 voice polyphonic. When you pressed the first key the first voice module played. If you then pressed a second key before releasing the first key the second voice module would play and so on till you had four notes pressed down. Many later synths were 8 note polyphonic.

This sort of thing is necessary for synthesizers designed to give you as much programmability as possible as you need a large amount of control, but the SS30 is dedicated to one sort of sound and puts it's effort into that one sound. Instead of trying to be clever the SS30 takes the sledgehammer approach of having an individual oscillator for every note (infact two oscillators for every note! But that's not important right now). So, the SS30 get top marks. It's fully, err, multi-phonic. I've read in some places people saying that the SS30 is 8 note polyphonic but this simply isn't true.

So far the the SS30 is only as good as an electronic organ. However it does have one more polyphonic trick up it's sleeve.

In subtractive synthesis (what most analogue synths practice in) there are two ways to change the sound you hear from the oscillator: 1) Alter it's volume (or amplitude) with amplifiers and 2) Alter it's tone, with filters. In order to bring a sound to life you need to alter these attributes over time. The most obvious way is with an envelope. An envelope determines how the something develops over time from the moment you press the key. Typically they have settings that determine how quickly the envelope contour increases and then decreases.

For a keyboard to be truly polyphonic it must have a individually triggered envelope for each key. Monophonic keyboards only have one tone and they restart the envelope each time you trigger it with a new key, as you'd expect (this can be changed on some monosynths though). On a polysynth you can still just have one envelope which starts when the first key is pressed and finishes after the last key is released but it is rather limiting. It's okay for pads but, with slow attacks for example, overlapping notes wouldn't sound right. If a so-called polyphonic keyboard has just one envelope it's only para-phonic and many synths were built like this including one of the SS30's rival strings machines the Solina Strings Ensemble. To be truly polyphonic it needs to have individual envelope generators for each key. They need not be individually controllable, as setting the envelope for every key would be highly tedious. Instead a global setting is used for all keys.

The SS30 is not a synthesizer in the true sense. It has synth like controls but it is fixed to one type of sound and variations of that basic sound. In particular the oscillators are fixed to one wave form. A real polysynth would have envelopes for each notes volume and each notes filter, possibly even it's pitch too. The SS30 has envelope control over the volume but not the filter. This is simply because bowed string sounds don't markedly change their tone as they develop. There's just no need for a filter envelope and it would mean more circuitry. The volume, or amplitude, envelope attack is locked to two settings - Fast and Slow and the sustain is variable .

The envelopes are generated by the the K boards which you can see in the picture below. Look! There's a circuit for every key.

You can see a bunch wires attached at one end and then another bunch leading off to the other. These are the connections from the physical key switches, (some of which you can see at the bottom of the picture) each going through a circuit and then leading off to the G (Generator) boards. The circuit is an envelope generator with settings for attack and sustain. Over on the top right of the board are some more wires and these run back to the attack and sustain controls. There's also a trigger line which switches the vibrato circuit in and out. I'll maybe write in more detail on these boards later

So, is the SS30 a truly polyphonic synth? Yes and no. To be a truly polyphonic synth the SS30 would have to have a individual VCA and VCF envelope for each of it's 49 keys. But, then again, it's not a synth it's strings machine and it does score over a few other strings machines and even proper synths with it's polyphonic envelope generators.

Pictures.

I now have a digital camera so here's a few snaps of the box of junk that used be functioning SS30. Annoyingly some of these came out a bit blurred but you get the idea.

The box of junk.

Examining the entrails. Note the key switches at the bottom.

Switches.

Pots sans knobs.

These are the key driver boards. I've used PCB pillars to stack them up whilst I did some investigations. Originally they were laid flat under the keyboard which flipped up to allow you access.

Here are the 4 voice generator boards laid out with the 3 mixing/FX boards. This is how they were laid out in the original case except they were mounted vertically rather than flat like they are here. Check the 30 cm rule for scale.

And here's a shot of the back of the generator and mixer boards.

I've put the power supply in a case so I could work safely with the mains on.

I fitted the back panel too.

I've tracked down the user and service mannuals from Yamaha. The service manual is original whilst the user is just a photocopy.

The service manual pages fold out!

Tucked in the back of the service manual is this double-sided sheet with a block diagram.

The Requirements

The basic idea is to: a) put the electronics into a rack mountable 19" case with the controls accessible from the front and the connectors at the back b) Build a MIDI interface that can at least make all the keys/notes respond to MIDI on/off messages on a selectable MIDI channel.

This presents a number of unique problems to overcome.

Firstly, the physical size of the circuit boards and their wiring requires a fairly large case. Most readily available 19" cases aren't big enough.

Secondly the front panel should look nice. This is a something that will take up space in my house and a well engineered product should look the part. It's problematic because I intend to use the original tablet switches and getting clean square cuts will not be easy.

Thirdly it's important to note that this is an fully polyphonic keyboard. There is a separate tone generated for each key and if you liked you could play every key at once. CV/Trigger interfaces are only used on monophonic keyboards that can only play one tone at a time. This MIDI interface will need to switch every tone individually rather than having one switch and a control voltage (CV) to set the note. I say this is a fairly unique problem as CV / gate interfaces are readily available and in both ready made form and from designs. More on this later.

I raise these three issues because they are the most particular to this project. If this was a small monophonic synth that only used rotary switches there would be nothing to write about You can already read about such projects here - http://www.synth.clara.net/resources.html and elsewhere.

The project is in two halves really. The mechanical and the electronic. I really need to address the mechanical problems first as they will make it easier to carry out the electronics development. Having all the boards in a cardboard box does not make it easy to work on them

Why?

Why bother.

Why not just get a sample CD of analogue strings sounds? Or get a decent soft-synth which can recreate the sound.

To a certain extent there is no point in resurrecting the SS-30. If I just want the sound I can use a sample or a soft-synth. Even my CS1x does a pretty good analogue strings.

Also it's going to cost a bit of money to carry this out and quite a lot of time. Shoudln't I just be saving that money and using the time to write music instead of just tinkering about?

Yes! Of course I should, but the tinkering about will teach me alot and the next project will be more ambitious and I'll learn even more and so on. Maybe one day I'll be able to make a living doing this kind of thing. Probabaly a pipe dream but it's worth thinking about.

Also the point about sound is interesting. Does a sample or soft-synth really ever replace the real deal analogue? It's a huge debate but right now I'd say no. I recently splashed out on VST of the Yamaha CS80 (see here - http://www.arturia.com/en/cs80v.lasso ) and whilst it's great I personnaly still don't find it as analogue sounding as my analogue synths. It's a personal thing and eventually it may get to the point where I change my mind but for now I'm saying I can hear the difference.

So that's why. I want the sound and I want the experince of doing it.

The loft beckons

We carried on making music after we went to uni, but the SS30 was used less and less.

Part of the problem was the condition of the keyboard. Both synths we bought we 'gigged' or bashed around, in other words. The Moog had/has a dent in the back and had lost quite a few slider caps. The SS30 was painted black and had had a few repairs to the keyboard. The issue with the keyboard was that it gave a rather uneven loudness for each note. Moving from one chord to the next could result in a sudden drop in volume. This was annoying but did give me an idea that I will discuss later.

Another problem for us was it's inherent lack of an interface. As a polyphonic keyboard it wasn't eligible for a trigger/CV interface which only works for monophonic keyboards and MIDI was a dream when it was built. The way we worked, as time became more of an issue, meant sequencing and playing back from MIDI rather than playing live was the norm and so the Strings was left in corner.

Finally it was just too flipping big. I never took it to uni' as it was far to big to cart around and was difficult to have set-up all the time anyway.

Eventually I bought a Yamaha CS1x and the immediate need for a cumbersome, poorly working strings keyboard all but vanished.

However, I'm not one to throw out working electronics and I didn't see much resale value in it. The only thing to do was keep it in the expectation that one day I would cure it's problems.

Post uni' I'd rented for a couple of years but (just before the price boom) me and my partner bought house. Time to clear out the last of the junk from my parents loft and put it in my own roof-space.

The SS30 will rest on it's end quite happily in a corner and had been in the garage for a couple of years not getting in anyone's way. By now I had a fairly good idea that I'd rack-mount the SS30 and attach MIDI interface of my own design (I'd studied electronics at uni). The keyboard and case were surplus to requirements plus getting it in the back of Nissan Micra along with all my other stuff was a problem. A cardboard box was found and the electronics were duly stripped out.

The case hung around for a few more years but eventually went skipwards. This was a probably a waste of good wood but regrets won't bring it back. The innards sat quietly in my new loft until I finally decreed 2004 the year of the SS30-M!

The golden years

So, we had a Yamaha SS30 or more accurately a Yamaha Strings SS-30. But what was it? The SS30 is a polyphonic, analogue strings keyboard. It recreates the sound of bowed string instruments namely violin, viola and cellos through analogue circuitry. I'll save a thorough description for later.

We used the SS30 for a couple of years before we packed off to university.

Here's an excerpt from a track we produced in around 1992

One Of Many

Back-story continued

Here's what the advert said we were going for...



And here's what we took home: A Yamaha SS30

And...

A Realistic Moog MG-1. Not bad.

Introduction

Hi,

This Blog is intended to be a handy way for me to document my project to rack-mount and MIDI interface my Yamaha SS30. I could have just put this in to a Word document (I've already done some of this) but the Blog will allow me access my notes at work as well as home. Obviously having it published will also allow me to share my findings and will hopefully draw some helpful comments from anyone else reading it.

What's the story?

About 12 years ago me and my friend responded to a classified ad in our local paper. The advert simply said Mini Moog £25. Now £25 for a Minimoog is a steal. They were fetching up to £600 even then. Off we went only to find that this was not a Minimoog. "Ah! Now that's not a Minimoog is it?" I said, some what disappointed. The seller looked a bit put out by my observation perhaps thinking that the sale would fall through. What he had was a Realistic MG-1 made by Moog for Tandy (AKA Radioshack in the U.S.). Well, £25 was still a good deal but at the time we had a Korg MS10 and Moog Rogue on semi-permanent loan from our high school. Did we really need this thing considering it was pretty close to the Rogue anyway and we were already pooling meager resources to get this thing. Sensing our reticence the seller then suggested he'd throw this other keyboard into the deal. Enter the SS30. We didn't know what it was but it looked interesting so we took the long term view that we wouldn't have the school's synths for ever and took the pair of them home.

Hello

Hello world