Thursday, August 25, 2016

Yamaha's Quality Design and Manufacture

I was browsing around the web looking at Yamaha organs (uh-oh!) today and came across this image which tickled me.

It's from an fact-sheet/flyer of their new organ around 1978, so contemporaneous with the SS-30.



Tuesday, August 23, 2016

A switch to variable controls?

A bit on the slide?

As I've been too busy to get into the garage again these past few days (and will be until next week) I was instead meditating on the idea I had during the front-panel rewiring exercise.  The idea was that for some of the switches I could instead have a variable control. I liked the idea of using sliders for some of these as you can more easily switch them on/off.
Let's see how that might work.

Orchestral Manoeuvrers 

Here is the Orchestra section.

Orchestra Section - Controls

 The Depth control set's the mix of signal that's going to the output unaltered (dry) and the amount that is going through the of the effect (wet).  The only difference between the minimum setting and having the instruments bypassed is that when with the minimum setting a small anout of signal will still get through from the Orchestra block.

The other controls are all switches, but what would happen if they were variable controls too?

Speed Control

SPEED is a switch which alters the voltage to a Yamaha IG00150 LFO chip. It's speeds '1' and '2' could be any value between those two voltages but with the switch they are fixed. It could even be a voltage beyond those limits.  Replacing the switch with a suitable potentiometer would be a useful addition.

Switch controls

The instrument switches are more problematic. Each tablet switch is dual-ganged and has two 2-way switches.
For each instrument (CELLO or VIOLIN) when the switch is 'off' the Orchestra effect is bypassed. In bypass mode the signal goes through T1 switch, through a resistor and then on to the T2 switch and onwards to the output.
When the switch is 'on' the signal goes from T1 switch to the Mixing Amp, then it's split to go to both the Orchestra section and the depth control. The depth then balances between the original dry signal and the wet. Then it's back to T2 and onwards to the output.
In other words, when it's bypassed the Orchestra inputs and output are disconnected. Otherwise you would get both Cello and Violin input when you only select one and the noise from the choruses would leak through even if nothing was being input.
Therefore the level of each instrument into the orchestra could be controlled but there will need to be some care taken to ensure that 'off' still means off. The easiest way would be to retain a switch and add a variable control. A rotary pot with a switch would allow both to co-exist but I want a slider then a button would be needed. 

In the mix

Here is the mixing section:

The best form of attack is a switch?

The ATTACK switches set the period of the 'attack' phase of the envelopes - i.e. how long it takes each key to rise up to full volume. When not engaged the AT signal to the key switch circuits is switched to ground. In the keying circuit that means that when the keys switch to ground the transistor controlling the signal to the VCA switches immediately to ground too and the attack is period is fast. However when the switch is engaged and switched to SLOW the AT signal is disconnected from anything. Now a capacitor in the key switch circuit comes into play. This capacitor sits between -7V and the emitter of the transistor.  The ground from the key switch will now cause the emitter to rise to 0V but because the collector is no longer at 0V there is no current through the transistor. In order to bring the signal to the VCA up to 0V now the capacitor has to be charged up which slows the increase in voltage from -7 to ground. Phew!
In short the switch governs if the charging is significant to the switching, but the time period of the charging is set by the RC constant of the capacitor. As the AT line is not connected to anything in the SLOW mode there's no point trying to replace the switch with a potentiometer.
I'm not sure my circuit analysis is totally on the money there but it might work with suitably large pot' if the so some experiments are in order. I might have to see if there's a non-trivial but still feasible way to do this with some sort of circuit to control the current. Maybe... 

Mix selector

The selector switches turn the signals from the 'Mixing Amp & Filter' circuits on or off. 'Off' means the signal is switched to ground. 'On' means it is routed on to the next part of the chain.
Therefore it's a simple matter to replace each switch with a suitably rated potentiometer which would allow each instrument to be balanced rather than just switched.    


Most, if not all, of the switches could be replaced by controls, but should I? Putting aside the fact that I've swung back to not reusing the original controls again, are these useful changes? I think changing the Orchestra speed is useful. No respectable chorus effect would really want to limit the user to two speeds so this is definite improvement. Similarly all effects allow you balance how much signal is fed in so the orchestra switches would be better off as variable controls (or both). For the attack control is would be nicer to be able to control the time. again no self respecting synth has only a switch and the sustain time is variable after all, so that is preferable too. The mix of instruments is easy to do but is it worthwhile? I do think it is. It seems that no stringers offer this feature though. They were seen as organs and followed the switch per instrument approach (where they offered anything at all). But why not? Synths almost always allow you to mix the tones, even when they come from the same oscillator. In summary then, I should seriously consider this option.

Thursday, August 18, 2016

Rewiring update 2

Cello, again!

Back one day later with more updates!

I fixed the issue with the Cello. Well, almost. The issue with broken wire to the volume control was easy to fix. However the signal had another break further down the chain. At the Orchestra section the signal is either passed through the chorus it bypasses the effect. In other words the it's a 2-way switch*. The problem was that the open backed switch for the Cello has had it's contact bent at some point and it was only operating as a one-way switch. The Cello Orchestra (wet) worked but not Cello without Orchestra (dry).  I bent the contact back and it's work okay now. No great, but okay.

Vibrato delay fix

Next, I wasn't sure that the Vibrato was working right so I did some measurements around the LF board and found a couple of broken wires. An earth wire and a control line for the Vibrato Delay. After that fix the Vibrato seems okay too.

The 100Hz Mystery

Yesterday I said it sounded like there was a noise floor of all the voices bleeding though. Last night after fixing the Cello and the Vibrato wires I again turned up the volume to listen to that noise. I can't be sure, but I think it has changed. Now I hear a single tone coming through. Like the stuck note I have on A# on K4 board, but this time much quieter. To be clear maybe my ears were deceiving me previously but now, for sure there is something there at one tone.

100Hz noise

There could be a bleed of everything else under that, but as you can see there's something quite loud. It's around 25mV at 100Hz and crucially it varies frequency with the pitch and detune controls. That means that it must be coming from the voices and not the power supply or some other circuit. I traced it back and it is present all the way back to G1 board.  I started there as it seemed likely that this would be coming from a whatever note is around 100Hz, and that is the lowest frequency board. However, I could also see it on the G4 board outputs. This isn't surprising actually. The outputs are mixed together (crudely without buffers), but I would have expected to see something stronger at the source, probably on G1. I didn't, so I will need to go deeper.

Make like a banana...

Something else I noted is that as I switch the split-gate upwards it lessens. So at split 0 it's loudest and at split 3 it's quietest. It's also present from all sources - Cellos and Violins.The split gate is quite fiddly to describe without a few pictures and tables but some voices are always open to be switched. The lower part the G1 board 16U and 16L are always present. In split 0 G1 16U/L are present as part of the Viola, mixed with the G1 8U/L. At split 1 (and above) G1 16U/L is present (alone) as part of the Cello sound. 

On the down low

If we assume some note in the lower part of the G1 board is the source of the noise then it should go away if only the Violins are switched in and the split is 0. This sort of matches the effect I got when playing around. It didn't go away completely though. I could get a trace of it in G4 so that does make sense. It could still be bleeding back even though the Viola and Violins are mixed separately.

How low can you go? 

Therefore the theory that it's coming from G1 makes sense, except for one thing. If I played through the notes on G1 I should have found the same note somewhere on there. I think I did, actually, but it wasn't quite right. I played note G and got something much louder but sounding the same. But I couldn't get a trace that matched. I think that the lowest G is G3 not G2 and my ears tell me it's more like 200Hz than 100Hz. I must redo this but I think it might just be because that G is a fundamental of 100Hz I'm hearing. G2 is 98Hz and G3 is 196 Hz. I think I'm hearing the first fundamental at ~200Hz because of the natural high-pass filtering in my listening environment from strip lights etc. (and yes, I tried turning them off to make sure it wasn't EMC). What I measure is 100Hz, but what I hear is a mix of harmonics from that pulse trace - I think! 

All very interesting (in a way) but if the fundamental is 100Hz then where is it coming from? The lowest note is C1 at 130.81. If it was the low G and I was wrong about the lowest note frequency it would probably be because the key circuit was broken. But I also shorted that key to -7 and it made no difference.

Pulse, a ting?

Finally the shape of this tone is not 'right'. Firstly it's a pulse, not a square -which is the source of the tones - or the more saw-tooth like shape - from the wave shaping (the subject of another post). If some wave shaper on the G board is faulty and bleeding through the raw oscillator then maybe a pulse is the result. The most obvious fault would be a shorting capacitor, but how that would get to a pulse I don't know.

Enough. Let's see what I find, next time...

* Idea - Replace the switches with a mix control? In fact all the switches could be replaced with such controls. Then instead of switching things in or out they could be balanced instead. Sliders would be faster for a quick switch in/out.

Wednesday, August 17, 2016

Front-panel rewiring update


Temporary front-panel rewiring

Progress has many enemies: perfection; comfort; greed; fear; indecision; indifference and (it says here) free-time(?). 

I can't point to any of those and blame them for the lack of progress on the SS-30M. Free-time is the thing I lack the most.  Okay, maybe comfort. I don't like working in my garage when it's below 10 degrees. No, the real enemy of progress has been Eurorack.


 I made a rack case

Eurorack case sanding

Eurorack case rear

Eurorack case ready for loading

And I made some DIY modules

DIY Mutable Instruments Braids

And I got a Roland System 1M and then a System 500.

My Eurorack set-up taking shape

I even started another blog about the System 500 - http://system500.blogspot.co.uk/

Now all that is (mostly) done (for now) I am keen to get the SS-30M show back on the road!

Front-panel rewiring

You probably won't remember that last year I was wiring up the temporary front-panel when I stopped. Most of the controls had been removed some time back and the challenge was to reattach them all. In the bigger picture this would allow me to test the SS-30 and see if there were any major problems before starting on the MIDI interface.

Rewiring was quite slow because although each wire is colour-coded I still wanted to check that it came from where I was expecting. With the black ground wires this was quite hard as most are still bunched together and it's hard to tell where they go to. Note that there isn't just one ground for all the controls. They are all grounded to different points on the F, LF and OR boards so there are several black wires. I think I got them all in the right place in the end.

After a couple of evenings work everything seemed to be back in place and I powered up to see what was happening.

A sharp pain

The first thing wrong was that there was a stuck note. A# on the top K4/G4 boards was on and staying on. I traced it back and couldn't see any wiring issues with it. I fixed another couple of broken connections on K4 and then disconnected A# from the G board. The output should have been -7V but it was 0V. I poked around on the circuit for a while and after a bit it sprang into life. Hmm! Well, it is a very dirty board. K4 sits at the top of my stack of K boards and has collected a lot of dust and fluff over the years. I will just have to wait and see if it fails again, but for now all is well.

Yo! Yo! where's my Cello, Ma? 

The next obvious problem was that although I could switch in the Violin section (Viola, Violin1 and Violin 2 were present and seemingly correct) the Cello switches weren't making any difference to the sound. I switched through the KYB.SPLIT options to no avail and it was clear that the Cello audio was missing in action.
I traced it back to the Cello Brilliance control. At that point the Cello signal comes from the Cello Amp circuit and splits. The signal goes into the Brilliance control as part of the low-pass filter circuit. The control sets the resistance to the signal going in to the capacitor to ground. If there's nothing going in, no filtering - brilliant! Another wire goes direct to the Cello volume control and from there onwards to the Orchestra section. When I looked, the two wires had split apart and only one was connected. The signal in to the volume control was waving in the breeze.
It was too late to fix that so it's next on my to-do list.

Bleeding hell?

All the Violin section was working though and I checked the Pitch, Vibrato, Brilliance and Orchestra which all seemed well. I was particular happy to hear the familiar woozy chorus taking over as I increased the Orchestra depth. I was tempted to immediately try and patch in another synth and have a play with it as a stand-alone effect. I resisted though and pressed on with my checks.

The only other problem I found was that the noise floor was seemingly quite high. I say noise but in fact it's the sound of all 49 keys bleeding through at once. The only thoughts I've had so far are that either this is normal or that there's something wrong with the -7V or 0V around the key switches. If -7 isn't low enough you will get a bleed through. I need to measure and think about that. Maybe I have 49 capacitors that need replacing :-(

Friday, July 01, 2016

YAMAHA SS-30 plays The Cure - And MIDI Solina?

The Cure on SS-30

Here's LibreCandombe  (from Uraguay?) running though a selection of hits by The Cure on a nice looking SS-30. A good range of sounds and styles on show here.

Solina with MIDI? 

I don't think The Cure ever used an SS-30 themselves . It seems they were an Eminent Solina band. Interestingly it's claimed in this auction that this one - their actual machine - was MIDI retrofitted. 

The pictures are preserved by MatrixSynth and you can see they went with an XLR connector.

It's beena while since I looked around for such things but seems both a few people offer solutions for the Solina. There's lot's a of ribbon cable being used, which is an intriguing idea.



 The Dopefer solution is based around their MTC64 MIDI TO CONTACT / GATE . 

It's actually a design one of their customer's has documented and provided for everyone's use.

The interface is based on CNY74-4 opto-couplers. This would work just as well for the SS-30.

Kenton Retrofit

The Kenton solution is a bit obscure and there's no clues on the website on how it works. 


This one is discontimued


Monday, June 20, 2016

The Fonts Of SS30 And YAMAHA

This is getting way off topic but I get spare time in front of a computer and I like good design so here we are with a post about fonts.

Owners Manual Cover

Here on the front page there are four fonts.

 YAMAHA- Helvetica Black Condensed

Yamaha's simple logotype is famous the world over and Helvetica is the about a as famous as a font gets. Helvetica Black Condensed is the font variation they used here.

Strings - Faktor Condensed Extra Bold

STRINGS is rendered in Faktor Condensed Extra Bold a font popular with Yamaha at the time. Here it is again on the SK30 brochure.

SS30 - DDT Extended Heavy

SS-30 is printed here in DDT Extended Heavy although it seems to have been made heavier and extended even further than normal.

Owners Manual - AG Book Rounded

This is where it starts to get difficult. The previous two fonts have some unique features which make it easier to identify them. and the YAMAHA logotype is so famous you can simply look up the answer (although there are several wrong guesses out there). This one is unremarkable in every way. I was sure that it was Akzidenz-Grotesk Book Rounded , but extended.
AG Book Rounded seems closest though

But that was designed in 1980, which is too late.
There are more fonts that fit the bill almost but not exactly. 

Owners Manual Inside 

The section headings have a friendly rounded font

This has lot in common with Arial Rounded.
Except the bottom of the 't' and the top of the 'r' aren't curly enough and the 'O' isn't round it's oval. So, it's not that.


Elsewhere Yamaha were very keen on this Dynamo font from 1930 which shares some features with Faktor.

Mystery 70s Yamaha font 

Another font from that era was used for the CP, CS, SK and GS ranges of synths. 

Often this font was just used on the owners manual or brochures but sometime it was emblazoned on the synth itself. I can't find what it is though.

Monday, May 09, 2016

Voltage Controlled Pitch à la Tomita?

I had this post drafted for a while but with the recent passing of Isao Tomita I finished it off.

Whilst researching the SS30 I noticed that it had been used by Tomita.

Isao Tomita - SS30 not pictured
Specifically our favourite strings machine was credited on his Daphnis et Cloe album (also called Bolero in the US)
As you might expect from someone creating synthesizer arrangements of orchestral pieces the albums credits also list a number of other synths which can perform strings duties, and another dedicated stringer, the Roland RS-202. It's hard to pick out the SS30 in amongst all that, but what struck me was that some of the string sounds seem to have pitch bend and even portamento applied.

The SS30 can't do that, but can I modify it to?

First I looked at the pitch control. Would it be possible to simply add voltage control to the existing pitch/detune control? The answer is yes, but the range of control would be very limited. The pitch and detune controls on the SS30 provide minimal control. You can tune it within a very narrow range but to get the kind of variation that's worthwhile it would need to be much wider. That would mean a completely new master oscillator design.
Also, the way that the square waves, produced the divide-down design, are converted to spiky saw-tooth-like waves depends on the frequency of each tone. If you shift the tone up or down you would not only change the pitch but also the wave shape and associated harmonics. So, pitch control isn't a good fit for this strings ensemble, or indeed any other of a similar design.

Rest in peace Isao.