Friday, July 14, 2017

MIDI Interface - Test #1

I am conscious that this project is taking a long time. As you can see I'm going through another rush of activity whilst the weather is warm and I can sit comfortably in my drafty garage but how long it will last, I don't know. In the last post I said I would pack the boards carefully into the rack enclosure before making a start on the MIDI interface at long last. Well, last night I thought again. Now I have my new bench power-supply I decided I would just check if the j-Omega MTP8 I bought back in (checks blog) 2009 was powering up okay.

I'm pleased to report that when I set-up a 15V supply the MTP8's power LED came on. At this point I couldn' t resist trying a simple test with an LED. And it worked.


The MIDI keyboard I'm using is my trusty old Yamaha (of course) PSS-580. A lovely example of the Portasound breed with a programmable 2-operator FM synth and useful MIDI spec. It says it's a Workstation and it really is. The fact that it's nearer in age to the SS-30 than to now is slightly amazing to me though. It is possible to record sequences on this keyboard too so for testing it will be possible to set up a simple note on, note off for each key which I can play at will. I could do this from my phone or iPad with a MIDI interface too. I might re-think and do that but for now I like having a keyboard and I can easily use it for a tuning reference.

Here's a fun demo I found on YouTube of some of the more extreme possibilities of the synth section.

Handily, the keyboard is exactly the same size as the SS-30 - 49 keys from C1->C5 - so it's ideal for this project. And although I still have a soft spot for this keyboard  - it was my first ever synth - it's not in use in my studio these days. I have a Volca FM performing FM duties, so it's not really required.
Something else I will need to do is check the range of the keys used by the MTP8. I connected output number 32 (of 64) and that mapped to G3. If output 1 was C1. C2 would be on 13 and C3 on 25, C4 on 37 and C5 on 49. G3 would then be on 32 so it is mapped exactly as I would have wanted it to. Great!

With the MTP8 working and the SS-30 ready and working I still had time to take the obvious next step -  try to control the SS-30 from MIDI! At long last.

First though I had to find something to handle the switching. As you may remember from this post, on how to switch the -7V keys to ground, there are a few options but the obvious choice is some sort of opto-coupler/opto-isolator. I thought I must have one somewhere and remembered that I have a CNY17 chip. Originally this was used for a failed attempt at a DIY MIDI CV converter. And then it was stolen for a Gameboy MIDI interface. For MIDI it's always recommended to use an opto-isolator and on the MTP8 there's a similar chip for the same purpose. The CNY17 is a passive component of the type I expect to use so I de-soldered it from the GB interface and with a bit of wiring and a couple of resistors on the bread board I could switch the LED on/off through the opto-coupler.

It was the moment of truth. I knew it should work, but could I play one note of the SS-30 via MIDI? Yes, of course  :-)


So there you have it. All I need to do now is make another 48 similar circuits and it's job done!

Thursday, July 13, 2017

Jitter Bug

Fix the jitter bug...!

Well, that's a relief! Last night I fitted a new transistor on G3 and the clock came back to life with a far more healthy looking waveform.

Tr1 Replacement on G3 - A bit wonky as I'm trying to be careful handling these boards to avoid breaking more wires.

 To be frank I'm still not totally happy with it though. I need to spend a bit more time measuring and checking because it still seems a bit, jittery... Not as bad as before but on the scope it's not as stable as the clock on G4.

I've Got The Bench Power

Before trying the transistor I thought I would have another go with a bench power-supply. But this time it was a linear supply, not the switch-mode one I borrowed. Ah, yes, this one is mine! I decided I needed a new toy for when I start work on the  MIDI interface so I bought cheapest one Farnell offered - a Tenma - and it's rather good for fifty notes. It'll appear in a later post no doubt.

Transistor Saviour

Initially I was a bit worried that I couldn't find a replacement for the 2AS509 transistor. I could find expensive ones or cheap ones in the states that would be expensive to ship over but nothing in the UK. Eventually I noticed that BC636 were close match and were cheaply available at Farnell. I bought a few just in case, as there we so cheap.

Back in the S.S.3.0

In any case, it works with the new part fitted and I plugged the output back into my mixer and had a listen - More noise! Oh, but this time I know what to look for. Sure enough a ground wire had snapped off G3. A quick fix and I was finally listening to the SS-30, as it should sound. Hurray!

To celebrate I decided to create a short video of me fiddling with the temporary front panel. Not the most exciting thing you'll watch today I would imagine but it's nice for me to have a record of these things.


You will notice that some of the pots are a bit noisy and sometimes when I switch things in it gets quieter, but overall things are working.

After a few more checks I should now be able to put everything back together in the rack case and after verifying it still works turn to the MIDI interface. The idea is to keep all the SS-30 boards inside the case, have the front-panel easily accessible and then just have the switch PCBs available to connect up with the interface. 

Tuesday, July 11, 2017

Panel Design Re-think & Yamaha's Design Language

Panel Games

I've been thinking about the front-panel and a few ideas have crystallised
  • Don't use the original parts. 
    • I want to use faders/pots for many of the controls.
    • Many of the switches are a bit damaged 
      • and twisting the contacts back into shape is unsatisfactory
    • The huge tablet switches are a bit difficult to accommodate 
    • Brown
      • From an aesthetic point of view brown is difficult 
      • I did envisage having a wooden front-panel at one point!
      • Brown tho?
    • The layout is fixed and limits options when adding other features etc.
    • I have identified some possible modifications which the old parts don't allow for
      • e.g. swapping a switch for a slider. 
  • Base a new design on the look of the CS and SK ranges. 
    • Black with white text
    • CS80-CS5 range
    • SK combos
    • EM Mixers
    • Same era as SS30
    • What a real SS30M would have looked like
  • Use the new Schaeffer UV printing option
    • Means fonts can match exactly
    • Much cheaper than engraving
    • easier to mock-up
    • almost as good as a screen print(?)

The Past Inside The Present

The idea then, is to make a front panel that looks just like something Yamaha would have made circa 1982/83 when MIDI was first introduced, but somehow still from 1977 or earlier, because by '83 the string ensemble idea was archaic. This is only recently more easy to achievable thanks to UV printing. Previously, I had looked closely at engraving, transfers and screen printing - which would have been the ultimate. Now, UV printing means Schaeffer (and Front Panel Express) can offer full colour images in any design for a very reasonable price. This means I am only limited by my imagination and my dream of having something that looks not only professional and pleasant to use but also ersatz Yamaha, circa late 1970s.


MIDI started to appear in 1983 and that was the year Yamaha unleashed FM on the world (GS1/GS2 excepted) and it's not that era that I want at all. The year before was the last of the analogue's, but apart from the SY20 the design language had already started to move on. 1981 say the mighty CS70 and SK15. 1980 was all about the SKs with, SK20, SK30 and SK50D. 1979 saw the first of the SKs with SK10 and the last of the CS beasts with CS-15D, CS20M and CS40M. In 1978 they kept it simple with the all black and no wood CS-5 and CS-15. 1977 was the year of the SS-30 and Yamaha was very busy with the CS range  - 50/60/70 - and CS range - 10/30/30L - both kicked off. Finally the SY1 started it all in '74 followed by the expanded SY2 in '75 along with the jaw-dropping GX1.

Meanwhile Yamaha were putting out mixers with similar in-house styling. There we desks and then some cabinet, PA mixers and then rack mixers. Some of these share the same knobs, fonts etc as the synths.
Yamaha's other rack gear was generally for PA systems. The design and 'look' is quite different to the synth and mixer ranges. There are the analogue delays E1050 and E1010 from 1989 but still not very useful as a reference unfortunately. 

I want to plunder this entire period to some degree, so let's look at all of it - or just jump to the summary at the end if you prefer.

CS Polysynth Range - 1977

CS80 CS60 CS50



These synths have a gun-metal grey finish with white Univers Condensed


 The CS50/60/80 knobs are the same as the SS30 - but in black. These would be the closest match but obtaining them is going to be a problem I think. I have seen nothing even close available from modern suppliers.


There are a variety of different switches used, including the same tablet rockets as on the SS30.
The presets on the CS 50 and 60 are extra chunky tablets with lips on the front. Proper organ style.

Some are smaller rocker type switches and something similar should be possible to source still but the dimensions and finish will probably not be.

The push type might still be available but I'm not currently thinking I will need anything similar.

And there are some are a sort of lever type 


These lever types take the same kind of slider caps as seen below.




CS Mono-Synth Range - 1977-78

CS5 CS10 CS15 CS30

For the range of CS mono-synths a more 'functional' or industrial aesthetic was adopted to compliment the cheaper price. Wood was eschewed in place of the plastic end cheeks and the look is similar to the Korg MS range.



The legends are Univers, like the CS80/60/50.


These look quite chunky and robust compared to the CS range ones. They look almost military spec. Note the 'U' shaped knurls. In the CS30 parts list these are 301000 CB810130


Slider Knobs

Theses CS synths have the same slider caps in the player control section as their poly forebears, but in plain b/w. These are part number 301000 CB811280.

The CS15 and 30 envelope section uses a smaller slider cap. Part number CB811290.


There are some fat red push buttons on the CS30 but for the most part it's bog standard slide switches all the way. The main difference is that they have natty caps on them so they are protected from dust and other unwanted crud falling to them and the sit flush under the panel. They are stand out prouder from the panel so they are so fiddly. I've looked around for these caps but I haven't seen anything similar.

CS & SK Range - 1979-81

CS70 CS20 CS15D SK10 SK20 SK30 SK50D & SY 20 - 1982


The 'hero' font is URW Corporate


The legends seem to be Helvetica


These seem to vary a bit but basically they are the same style as the CS mono-synths.

The CS40M and CS70 knobs have a fairly standard caps. The knobs themselves are a slightly less common.
They seem the same as the earlier. 
CB812140 ivory
CB812130 yellow

CS40 - 1979

CS 40 parts list 

SY20 - 1982

SK knobs



For the push buttons these synths use a variety of common designs from the era, some with a LED integrated. I guess these are momentary switches which don't latch 'on' but send a pulse to the computer to make settings. The LED is then driven by the computer as or electronic latch.

There are some other chunky style push buttons used but there are of no interest to me as I said before.

Slide switches are used as on CS mono-synths with the nice covers again. These covers don't have a separate part number so the issue is.

The SK10 is using tablet rockers.


 The CS40M, CS15D and SK10 sliders are the similar to the CS80/60/50 ones but have the special tan/sandy in-fill colour. They also seem to be a matt finish rather than the silky smooth finish on the earlier CS polysynths. 


The sliders on the CS70M, SK50D, SK15, SK20, SY20 are a curious, rectangular design with coloured caps. I have seen nothing like these anywhere before. Also, I'm not keen on the look of them/

Add caption


Yamaha produced a plethora of mixers in the era I'm interested in and I have tried to list them below with the years they appeared on the market. 

EM for Ensemble Mixer. With power amps for speakers and onboard FX - For practice and small stage set-ups
PM for Profeessional Mixer. For sound reinforcement duties  - i.e. live mixing.


These cabinet style units in sturdy Tolex covered wood with metal corners. Clearly intended for live use these mixers provide enough power for speakers. They also sometimes included  built-in effects! The EM89 and 95 had analogue delays (echo) and the EM120 has a spring reverb. I'm tempted to build something based on these as a companion to the SS30M.Or maybe even buy one of these old things and reuse the parts. They still command a reasonable price though so it would be a serious investment. 

EM-120 - 1977
EM-85 - 1980
EM-95 - ?

EM85 1980


 This post is already too long so let's keep it short on desks.

Ensemble Mixers

EM-80 - 1977
EM-100 - 1977
EM-100 II
EM -150 - 1977
EM-150 II

Sound Reinforcement Profesional Mixers

PM-210 -1977
PM-430 - 1977
PM700 - 1977
PM1000-16 - 1977



Rack  - Sound Reinforcement Mixers

These are the closest thing to an SS-30M in a rack  that I can find.

PM-170 - 1978 - Unbalanced Phone Jacks
PM-180 - 1978 - Transformer coupled XLR
M406 - - Balanaced MIC inputs



The knobs are the familiar rugged style

PM-170 Knob

Guitar Units



  • Panels
    • Black or very dark grey, silk finish. 
    • Powder coating, but later mixers were anodised
      • Note: Schaeffer don't offer UV printing on powder coated panels at present.
    • The cut-outs for faders and switches are rounded in the earlier models
      • Need to think about the edge of the cuts too as anything that is visible should not be shiny bare metal.
  • Knobs 
    • Two types of rotary knobs - the SS30/CS80 style and the rest are rugged - both have skirts/nut covers.
    • Fader knobs are either the split marker style or the rectangular capped style - but I don't like the capped ones.
      • These Yamaha fader caps are rare.
  • Switches 
    • Rocker switches are PCB mount with no obvious panel mounting.
      • Switches are smooth and silky. 
    • Slide switches have covers
  • Artwork
    • Rather than use the standard markers on the rotary knobs - like a clock face - Yamaha synths went for line markers that start at an angle and then bend to a horizontal.    
    • Fonts were Univers, then Helvetica and URW Corporate was used for the large logos.
    • Colours went a bit tan and yellow on black instead of plan white at one stage.

Monday, July 10, 2017

Transistor coming off the rails

Bench Press

With the help of the borrowed bench power-supply I manged to narrow down the -26V rail issue to board G3. Without that board the total current was less than 200mA, but with it the power-supply would switch the voltage down instantly. The current was probably lower than normal because the clock signals generated on G3 were off , which in turn meant that the other boards were not active.

Bench Power-Supply On Loan

The next step was to isolate which part of G3 was causing the problems. I started by lifting resistors to the -15V and -8.2V regulators and Master Clock Oscillator but the problem remained. Then I realised that the transistor on the -15V regulator was also connected to the -26V and I would need to remove that too.

Once that was out the problem stopped immediately. So now I had a prime suspect.

Checking the resistance between collector-emitter showed it was blown. Practically short circuit between the two pins. As I don't have a replacement to hand the next step was to connect the other side of the bench supply to the -15V rail and verify that there were no more problems there.

On doing this I was relieved to see that the unobtainium parts - the YM25400 octave dividers - were still running. However, I'm not out of the woods yet. The Master Clock Oscillator on G3 not looking good, to put it mildly.

The effect of this on the dividers that it feeds varies but it's possible that the bench power-supply is the problem here. I will reserve further judgement and investigation till I have the -15V supply back in place.
Perhaps I'll just piggy-back off the G4 -15V supply and see what that does. My HW engineer colleague agrees and points out that the bench power-supply is switched-mode and this could be an issue.

Transistor Sourcing

The 2SA509 "Silicon PNP Epitaxial Transistor for audio power (1W) amplifier applications".  As this is a regulator though it's not used in that way on the SS30.
A voltage divider is used in place of the more usual zener diode to set the voltage at the base. The divider gives -9.5V. which means a difference of 16.5V base to collector. A voltage of -26V here would switch the transistor fully on, it being most negative with respect to the emitter.  Whilst if it was gnd/0V the base and emitter would be at the same potential no current would flow. Therefore the voltage  of -9.5V at the base results in approx -15V at the emitter.

It's possible to get the original parts - which are Toshiba - but these are pricey. There are equivalents which are cheaper but these all seem to be in the US and cost a ridiculous amount in P&P. I have found an eBay seller with the right part at a reasonable price, but not much information. I've contacted them to check that the pin-out is the same.  

Friday, July 07, 2017

The answer is blowing in the fuse.

A very frustrating and worrying night last night.

I re-stacked all the G boards and fixed the broken -26V wire. But as soon as I powered up the fuse blew again.

So, I started removing wires and measuring impedance and trying things but after another couple of fuses had gone I gave up for the night, dejected.

It seemed at one point that I had identified which rail on which G board was the problem. But, when I left it disconnected and reconnected some of the other boards I was back to square one with another blown fuse.

From that it appears that no single board is the problem alone. When a few are connected simultaneously the overall impedance drops and the current rises, killing the fuse.

The voltage is lower than -26 but it's always been like that. Back in this post I measured -23.6V

And if the impedance is above around 2K ohm all is well. When I keep adding rails though, it drops to around 1K ohm and the fuse is blown.

Luckily I work in an electronics company and after a quick chat with some hardware engineers (I'm software) a bench power supply was tossed my way and I have another way to investigate.

With a bench supply I can just use this to power the boards investigate and save blowing more fuses. I can set the maximum current to 500mA, or less, and then add rails till it clicks off. I can also measure the current being used for each board and try and work out which is taking the most to help trace the fault. My plan is to test each board in isolation first, checking the current as I go. I should find one that is taking more current than the others - although they will not all be equal, so I have to use some judgement. I was also advised to check for heat. Anything getting warmer than expected is probably the source of the trouble. I can also test all the ICs on each board and hope and pray that none are blown [shudder].

This is all very annoying. I seem to have precipitated this fault when fiddling around with the noise problem which was a silly mistake and should have been diagnosed without all the messing about I did. It's also worrisome because if I've blown one of the custom Yamaha chips the replacement might be costly and difficult, or even impossible.

Wednesday, July 05, 2017

Don't cut the black wire!

Sometimes the obvious answer is staring you in the face.

I found that I had cut the ground wire to the G boards at some point. Why? I forget. The perils of stretching this project over so long is things like this slip your mind.
Anyway, I found the two ends tied together.

Knot what I was hoping to find

As for why I didn't check that the earth wire was connected to ground before, I can only say I need to think a bit harder!

I reconnected the earth to the G boards and the problem was solved. Just the faint hiss of old electronics was left.

G Board output connectors cleaned and ready to reconnect.

I set about reconnecting the outputs and all was well until I realised that I couldn't get any tones to come out anymore. Nothing from the clock dividers, nothing from the tone generators at all. Then I checked the power supply and the -26V rail had gone. Just that rail though. After checking the PSU (during which I managed to spike the ground and trip my whole house's power, even with an RCD connected!) I could see that the fuse for that line was blown. I replaced it but it just blew again. I disconnected the PSU from the boards and it then held up okay. I couldn't find any obvious shorts to ground - maybe there was something touching somewhere - but I'd run out of 500mA fuses, so I finished reconnecting the outputs and started stacking the G boards back together. During that I found a loose -26V wire too. Hmm!
I've ordered some more fuses so next I will reconnect that wire, test the connections for -26V, check for shorts again and then see if the issue has gone.

If that works then everything should be okay, finally. A fully working SS30 in a rack case without MIDI! And that means I can, at long last, start on the MIDI interface.

In the background I have been rethinking the front panel again. More, much more, on that to follow.

Monday, July 03, 2017

It's oh so... noisy

Annual Apology

13 years it's been since I started this blog. Many things have changed since then but my desire to have a Yamaha SS30 in a rack mount with MIDI is undimmed and just as subject to my whims.

Anyway, 9 months since the last post and 11 months since the last update on the rewiring; where was I?

Bring the noise (down)

Last night I worked on locating the source of noise when no notes are being played. To begin with I confirmed that there is still an unacceptable level of noise but gave up trying to locate it in one place. My scope might show a specific signal but my ears discerned general bleed-through from many tones. Maybe all of them!

After a bit of messing about and reacquainting myself with the boards (it has been a while) I decided to be bold and disconnect the outputs from the G boards until I found the source if the problem. Eventually I concluded that not only are there tones bleeding through every output on every G board - to a greater or lesser extent - but the noise is also present on the earth for each output too!

Once I had disconnected all the outputs and all the corresponding earths the output noise-floor dropped to a more acceptable level. I would like to able to put a figure on the noise before or after but I a) don't need to when I can hear it without any trouble and b) can't be bothered with setting up the extra cabling etc and trying to find an app to do it. As I'm in the garage, as far from my studio as possible on my property, it would have to be a phone or iPad app - but I digress. With the SS30 volume control at 50% and the mixer gain at 0 and the fader set to 0dB I can hear noise. Once the G boards were all disconnected it was not silent, but the kind of quiet I would expect given the SS30 is old and the mixer is no spring chicken either. 

Reconnecting the earths for each part of each G board in turn I could hear the various components of the noise return. Even in the same board the sound of each part varied. This means that as the noise is getting on to the ground track it doesn't come through as strongly at the far end as it does the nearest node.

All of which is to say I have a serious problem. But what is the source? What is the root cause? 

The blame game

My initial, gloomy diagnosis is that the vast number of grounding capacitors (four per tone) are all to some extent leaky, and all that is adding up and causing the noise. 
This is an irrational fear though. Why should they be leaky and why should that mean the ground is noisy? There is a bit of a myth in the synth community about re-capping. Sure, tanatlum caps in the power supply should be replaced in case they short. And electrolytics can dry out or leak and I have had to replace one on my Roland MKS-50. However these caps are low voltage and connected to ground. If they shorted out the worst that should happen is that the audio would go down the plug-hole run to ground or be attentuated. So, I should probably not assume the worst.

Therefore, my second thought was that blaming the caps might not quite work as an explanation because it's not a likely explanation. But, there is a more fundamental reason why blaming these caps makes no sense. To understand why,  you need to understand the whole method of generating keyed, string-like tones from square-waves. 

 The tones start as square-waves from clock dividers. That signal is then put through a series capacitor. This cap achieves two things. Firstly the signal is DC biased by whatever voltage is on the other side of it and secondly the wave is shaped into charging curves as the capacitance charges and discharges. This how the square-waves start to become the 'spikey' wave-forms needed for string sounds. 

Offset VCA

The DC voltage on the other side of the capacitor is -7V when the key is up. When the key is down it is 0V.  That means that when the key is up the signal is all offset to less than 0V and the current is all flowing - more or less, as it oscillates -  in the negative direction. When the key is up the signal is centered on 0V so the signal flows half in the positive direction and half in the negative.

 The next device in the circuit is a forward biased n-p diode. When the key is up nothing should get through that diode. With -7V offset on the signal, nothing can get through. Bit at 0V the positive half passes through the diode. In fact the amount can be between -7V and 0V as the attack and sustain controls set the raye of change. This means that the amount of signal gettig through the diode is controlled by the keying circuit effectively making it a VCA and explains why the SS30 is partialy polyphonic. Pretty neat huh?

This is just the first of two diodes in series, with a grounding capacitor after each. Even if the capacitors had become short circuit nothing should be getting through the first diode until a key is pressed and the DC bias voltage rises to 0V.

When I probed the output side of a the first diode on a circuit on G4 I saw plenty of noise, but it seemed to be unrelated to the signal on the input. If anything it seemed to be getting in through the capacitors or bakc through the diode. From where though is unclear. On the diode I probed, the signal on the input side seemed to be safely under 0V, but maybe others are not so well behaved. 

If we assume that somesignal is getting through the diode it's either becaise the diode is not functioning properly or the -7V is not low enopugh and some positiev current is getting through. On the other hand, if the diode is really blocking the noise it must be coming though from the capcitors via ground. But how does it get there? On the input side of the diode is the keyting cictcuit. The offset signal is heading straihgt back to the K boards. Is it entering ground there? The K boards down't even have a 0V connection until the key is pressed down and connected to earth. The attack and sustain controls do feed in some voltage but what that is I'm not sure. They could easily be disconnected to check.

Capacitors are supposed to pass some signals to earth but the issue seems to be that whereas the earth is supposed to absorb this unwanted signal, it is instead passing it on. Maybe the earth being used is not grounded properly.

Next time I hope to have some answers.