Monday, May 21, 2018

Thanks For Your Input!

Putting in the input

Some things are just too easy and you wonder why you didn't just do them earlier. Attaching an external input to the Orchestra effect is one such job.

Referring back to the modification I did to the switches and depth control to have individual wet/dry mix controls for each voice...

I simply added a wire to the Violin voice's input to the mixing amp and switched off the Violin voices for good measure. I haven't replaced the Violin switches yet and I just wanted to isolate the external input as much as possible.

And, hey presto, I have a chorus effects unit!

Because the PSS-580 sounds relatively poor and because I had it to hand I filmed a demo of it with a few different presets to show how useful the effect is.
 This film is a multi-camera wonder! You can see me playing the'580 and adjusting the effects-send at one and the same time! I also downloaded Lightworks so I could superimpose them together.

The channel on the right is the PSS-580. The one on the left is the SS-30. By using the mixer I can also feed the SS-30 back into itself. This creates an even deeper effect. As you get closer to the point of howl-around you get some interesting artifacts around the attack portion of sounds too. A couple of times I push it too far.

Now that this is tested I need to decide how to implement it.
  • Input connector on the front or back panel?
  • Is it worth having an input level control?
  • Should I add a feedback control for the SS-30 so that the deeper effect can be obtained without any external mixing? 
  • Should the external input be routed in with the SS-30 voices or should it just go into the Mixing Amp with it's own channel and 22K resistor?
That was an hour's work on Sunday afternoon so in the evening I decided to try something else with the Orchestra.   

The indications are good

The Orchestra has two LFOs. One fixed at 0.6Hz and the other variable. It occurred to me recently, whilst having deep think about the user interface (of which a blog post is forthcoming), that I could have a blinking light to indicate the rate of the variable LFO. At least now that it's fully variable and not just two fixed speeds it's useful.

The LFO is generated by the IG00150 VCO. This device has two outputs, a sine wave is used for the Orchestra effect and there's an unused sawtooth which I can use to control an LED. 

With a simple transistor driver circuit and borrowing a 15V supply rail I quickly got this demo working.

I would need a small board to hold the components but this is a nice addition to the SS-30M.

Thursday, May 17, 2018

Switching Controls

Earlier this week I sepnt a bit more time fiddling with the front-panel controls.

The first job was to remove the switches I wanted to use from the donor Organ. More on that in a later post.

I also replaced the two Cello voice switches (1 and 2) with faders.

As you can see I hacked them onto my laser-cut temporaray panel. they oinly fitted the gap sideways asnd needed a bit of accommodation. The temp panel's going to be abused a bit whilst I work through this phase of the project.

The faders are from an old mixer (Starsound Dynamix 260) I got from my old high school. I binned it years ago but kept the faders. These are 10Kohm log audio 'A' type and worked perfectly!


Here's an old post I put together when I was looking for the perfect knobs to use. I have a solution now, I think but here's the research I did...

Alright! Settle down!
 Yes, we're looking at knobs.

CS/SK style slider knobs 

Where can you get these nowadays?

These exact slider caps are available from http://www.synthparts.com -

"Yamaha CS50/60/80 Slide Pot $12 (larger quadrant type $14)"

That's quite a lot of dosh for some knobs if I get 10 or more, but would be absolutely pukka. I also might feel bad depriving CS owners of precious spares though..

There is a spare part for Numark mixers NS6/NS7 and AKAI APC - PT11106163-  which looks similar, but is possibly a bit bigger and flatter on top.They are definitely textured and matt and not smooth and silky like the original ones.

In context :


And then there's the mix slider - PT11106178 - for the 'Numark
NS6 :

This looks rounder but a bit short.



CS style lever switch caps


The switch are caps not so available - except they may be the same as some of the Electone Organs some of which can be bought very cheap, although getting enough of the same colour would be an issue and that's a lot of wastage...
EDIT : I know have a bunch of these lever knobs from the B-75 organ I bought. They aren't quite right for faders though. The sliders have a curved travel.

SK/CS30 style knobs

Right - SK /CS knobs

Perfect Circuit sell SK knobs but they don't seem right at all.  Not U shaped knurls and strange lip on the cap. These are in fact from the Korg MonoPoly - Syntaur sell them too.

Wrong - Korg MonoPoly

Where can I find the right ones? I don't think I will. I've searched high and low and whilst there may be a plastic bin with a dozen sat in a surplus shop in Japan or the States, I can't find them.

Syntaur are our of stock

Here's something with the nearly the right knurling - U shape -  but the base is wrong. I quite like it anyway. I think I have something similar on the back of some speakers I made when I was a lad. There are more sturdy than beautiful.


Mammoth do them too - in different colours - but manufatuer is not mentioned


On ebay

CS 15 smaller sliders

Part number CB811290.
These guys seem to do a similar part http://www.shokaifareast.com/Products/Pots/Slide/slide_knobs.htm



Large range - no exact matches though.


Many and varied


Large range of knobs - sliders fairly standard mixer and eq types.


Standard range


Standard range.


 Huge range




Coolor Caps

Fancy, candy coloured and novelty knobs - single stripe fader knobs, sold in packs too.

 Even do hydrodip printed ones

Specialised synth shops' knobs

Perfect Circuit


https://www.perfectcircuitaudio.com/juno-106-slider-cap.html <- similar to CS/SK slider cap but not rounded.


Have a large number of parts inclusing some real synth classics, not nothing at all for classic Yamaha analogues :-(


Single design - Rogan?

http://www.synthparts.com/ <- Have CS50 slider caps
 http://www.vintageplanet.nl/ (Closed)

Organ shops

http://www.mcnsystems.com/parts.htm <-No lists but lots of stuff.

Small Electronics shops

https://www.tubesandmore.com/products/knobs  <- Guitar stuff mostly
https://www.westfloridacomponents.com/Knobs.html <- not much stuff
http://www.mzentertainment.com/store_dr_zee_workshop_parts_knobs.html - <- Loads but nothing 'right'
http://www.electronicsurplus.com <-quite a bit - bad site though



General Electronics Shops


Overall though I want these and I can't get them.

Monday, May 14, 2018

Orchestra Manoeuvres

I did do most of them in the hours of darkness, yes.

I’ve been thinking about and planning the power supply a good deal this week, but it’s turning into a mini project of its own and I wanted to keep the momentum up on the rest of the SS-30M.

As the weather is good and I now have an electric heater for when the evening temperature starts to drop, I was out in the garage again tonight with the aim of trying out the redesign of the Orchestra section.

You may recall that the SS-30 Orchestra effect section has four controls.

Depth - Which is actually a form of dry/wet mixer knob which goes from mostly dry to mostly wet
Speed - A switch with a fast or slow setting for one of the LFOs
Cello - A switch to route the  Cello voice to the Orchestra, or bypass it.
Violin - A switch to route the  Violin voice to the Orchestra, or bypass it.

When I wrote the Orchestration blog post I came up with a more versatile scheme with three controls.

Speed - A knob which controls the speed of one of the LFOs
Cello Depth - A knob which controls a wet/dry mix for the Cello voice
Violin Depth - A knob which controls a wet/dry mix for the Violin voice

The advantages of this scheme are that with fewer controls I get greater control. Yamaha’s designers would probably argue that the benefits of controlling the speed are minimal but for such a small cost I simply say ‘why not?’. As for having a depth control for each voice, again it’s questionable when you consider that it’s mostly an on/off choice, but I think having the greater freedom allows for more possibilities - even if you don’t always want to take advantage them.

This evening I got the new scheme working with some linear rotary potentiometers. The old controls are gone.
This was the rough sketch I did before and it’s what I ended up doing.

It leaves the dry mix of Violin and Cello from ‘Mixing Amp’ unused. Previously, some of this would have made it into the mix even when the Depth setting was full on. The depth pot was 50K so not much would have got in, but some would. Now the balance of wet/dry is done before the mixing of the voices, but a little of each will get through even when the setting is at the extremes.
I used 100K for the Violin voice but I only had a 47K left so used that for the Cello.
I’m not sure how much difference this makes, if any. I could eliminate this slight bleed through at one end if I use a pot with a switch. Perhaps so the dry mix is totally dry.

The other thing, which I didn’t consider before, is that even when little or no signal is going into the Orchestra effect there is still some noise coming out. In the original design the switches ensured that this would never reach the output. I need to do some listeing tests and think about this.  The effect is not totally clean but I didn’t hear anything untoward this evening.

Tuesday, May 08, 2018

Current Affairs & Power Couples

Current Account

A critical issue for the SS-30M has always been where the extra power for the MIDI interface would come from. If it needs to have it's own supply then there would have to be an elegant way to incorporate that. I mean, I don't want two different power inputs.

Now that the interface is working I have been able to measure the current drawn in the worst case situation of all 49 keys being pressed at once. This isn't a realistic use case but it could be a failure mode of the interface or an accidental occurrence

There's only one positive rail in the SS-30 power-supply, 15V, and that's just right for the CMOS MIDI interface so that's what I tried to use. The +15V rail has a 500mA fuse, so as long as the total current  draw does not exceed 500mA - with some headroom - I can use it to power the interface as well.
Firstly, the supply to the MIDI interface is (ahem) currently coming from my bench power supply. This tells me how much current it's supplying and when all the keys are down that's 144mA, DC. Ideally then, the draw on the 15V rail of the SS30 will be well under 350mA DC.

To measure the current there are two options. Interrupt the DC rail coming into the SS30 and place my multimeter in series there, or simply remove the fuse and measure there. There is difference though. The fuse is on the AC side of the power-supply - before DC regulation. I measured at the fuse and got around 570mA when both the interface and SS-30 are powered and all keys are on. At first I thought thatat was it and the current was too high. Then I recalled that the fuse is rated to the RMS value. The RMS value for a sinusoidal signal - which is what we get from the mains transformer - is I/1.44 (where 1.44 is an approximate value for the square root of 2). I measured 570mA so the RMS current is 570mA/1.44  = 396mA.

To be sure, I replaced the 500mA fuse and tested again. The fuse held and I have my answer: I can power the MIDI interface from the SS-30 power supply.

Power Couple

The second problem with power is that the SS30 power supply won't fit into the space left in the 19" rack enclosure. I need a case just for the PSU and then to get the power rails into the SS-30M I need a connector and cable arrangement with enough conductors.  Carrying a single rail is easy but I  need 6 conductors.
2x 0V

They also need to be rated up-to 500mA. I don't want to lose voltage through the resistance much either.

I found these connectors.


And there's a ready made 1.5m cable assembly


The length is important because the SS-30M could be mounted relatively high up and the supply would likely be on the floor.

This is what Cliffcon say:

CliffCon® Miniature ZC Series

Our ZC series, miniature, locking, multi-pole, shielded connectors are available in a range of 2 to 8 pole plugs and sockets. These are primarily intended for low voltage and signal applications. Contacts are tin plated and other metal parts are nickel plated brass or Mazac. There are also 90° versions of the plug available to order.

Specification: Rated 1A / Pin - 48V max.

I'd like the 90 degree angled plug but Farnell only stock the other kind. Otherwise it's perfect! All I need now is an enclosure for the power-supply.

Monday, May 07, 2018

Now with MIDI!

Last September I may have mentioned that the SS-30M is now functional. That's to say, the MIDI interface is fully wired up and it works. Mission accomplished! Err, well, the MIDI part is.

Shortly after that milestone the nights closed in and all work ceased. But I did say there would be a video of it all working. Well, I'm pleased to say that this May Day bank holiday weekend the weather has been as sweet and warm as a the sound of an analogue synthesiser. With my usual trepidation I powered up the old monster and was glad to hear it was all working as before. Well, almost. The highest A sharp was pulsing on and off because a transistor had been pushed over and was shorting. And the Violin section only works if the Orchestra section is on, but that's just a bit of a bother with the switch.

Here then is a short bit of unrehearsed and barely thought through keyboard playing. The Yamaha PSS-580 is the MIDI keyboard.

Wow, eh?

Well, I will think of some more interesting things to play on it, but you get the idea. It works!

I also had time to measure the current on the +15V rail. It seems that I will be able to use the existing supply for the MIDI interface too! Hooray! I have another post in the draft folder all about how to have the power supply in a desperate unit. Hang on to your hats!

Wednesday, April 11, 2018


I just wanted to draw attention to the incredible muzines site which is archiving old music technology magazines.


I haven't found a review of the SS-30 there yet - and most magazines seem to to be early 80s - but there's plenty to enjoy.

I found this quote from Rusty Egan talking to Electronic Soundmaker - Aug/Sep 1984 - about the first Visage album.

"We used everything on that album. We had a GS2, two Yamaha grands, two ARP Odysseys about three Yamaha string synths, a CS80 and a Minimoog. We used a Fairlight on that album, we had the first one that came over from Australia. Before The Steps it's Peter Gabriel going 'Waugggh, wauggh!' 


 And this round-up of stringers, also from Electronic Soundmaker in 1984 :


Tuesday, January 02, 2018

Attack Formation

When I wrote this post about the concept art  I said "I've assumed I can replace all switches with potentiometers".  That assumption was wrong in the case of the Attack control though. In the last post I mentioned that "it's more of a re-design job than a modification".I shall now try to explain briefly, why that is.

The SS-30 Attack control is a switch and according to the user manual :

With this tablet switch on, the rise of the sounds of the Violin system will be softened.
 Softened is the adjective because although it is slower with the switch on the change is subtle. The normal attack is not particularly hard, but the Slow setting is only slightly longer. As we'll see below when I calculate the the rise time, it's not the typical attack range setting that you get on a synthesizer.

Another bow to the string?

Billy Currie put his finger on the reason for this choice in the interview he did with GForce Software. "You were able to create the feeling of a bow" he states. I had a bit of a look around at the synthesis of bowed strings but all I could really come up with was that you need a bit of attack to stop it sounding like an organ. Fair enough, but Curie's point is a bit more subtle than that. The Slow setting provides a softer attack option which his Elka Rhapsody 610 could not. In any case, an even slower attack is not typical of a bowed string. You cannot, for example, slowly increase the volume of each string. Therefore, an even slower attack wasn't needed, because that would stop it sounding like a bowed string (or bowed strings), and a shorter attack would have the same problem.

That's the design choice Yamaha made dealt with, but what about redesigning the attack circuit? Can it be done?

Not easily, no. I had a stab at analysing this circuit before, in the post A Switch To Variable Controls. I wasn't quite correct* in the description there, but I was right that no control could easily be added. Let's see why.


Charging into attack

Keying Drive circuit
 In the diagram above I've highlighted in red the part which controls the attack setting. Tr24 is a transistor which controls the current that charges the 6.8uF capacitor when the key is pressed. The same capacitor discharges through Tr23 when the key is released - this is the sustain control.

The key to the attack time is the charging time of the capacitor. Capacitor charging time is constant for a fixed voltage and is the product of resistance and capacitance. As the capacitance will not change the charging time is controlled by altering the resistance.

The collector of Tr24 is common across all the keys. This node is either open-circuit or grounded depending on the Attack switch.

Attack Switch - BL is the BLack ground wire, which is fed from VR3.
 The base of Tr24 is connected to the key switch. It's normally -7V (via the supply rail and the diode D12) and then switches to 0V when the key is pressed.

The emitter of Tr24 is normally at -7V (again via the supply rail and) so, as this matches the base voltage, normally there's no current flowing through the transistor. When the key is pressed and the base is set to 0V the base-emitter junction acts as a diode and current flows across it and thus the capacitor is charged . What about the collector though?

Let's start with the collector open-circuit. In this case we can treat the base-emitter as a diode and simplify the circuit somewhat. In this case the resistance is circuit with the capacitor is 12K Ohm and 2K2 Ohm,  in series, which give 14.K Ohm in total.

Now what happens if the collector is grounded? In this case we have provided a path from ground to the capacitor directly through the transistor Tr24. When the key is pressed the base switches to 0V as before and a small current is produced across the base-emitter, but now the transistor is switch 'on' and current runs through from the collector. In terms of the resistance to ground the 12K resistor has been bypassed and the total resistance is now just 2K2 Ohm. As the resistance is lower this will produce a shorter charging time, so the normal attack setting is grounded - as you can see in the diagram above.

We can now calculate the attack time for both the normal and Slow settings.

Normal  - R = 2K2 C = 6.8 uF RC = 1.496e-2 = 14.96ms
Slow - R = 14K4 C = 6.8 uF RC = 9.792e-2 = 97.92ms

Note that I haven't accounted for the Vce voltage drop of 0.2V. With that the normal attack time is slightly longer at around 15.3ms.That assumes that the supply rail is exactly -7V and to be more accurate will require some actual measurements. The important thing is that the attack time changes from approximately 15ms to roughly 100ms for the Slow setting.

The long and short of it

Now we know how it works, what about making the attack time more controllable? Can it be adjusted to be shorter or longer? The answer is that the circuit can be modified only to make it adjustable between 15 and 100ms. The RC constant of the circuit is limited by the 12K and 2K2 resistors and no matter what you do with the collector voltage those two impedances will still be there. The attack cannot cannot be shorter or longer than the setting already obtainable, without completely changing components on all the 49 switch circuits.

With 2K2 after the emitter the minimum attack time will always be 2200x6.8e-6=14.96ms. The resistance can't be set any lower so the CR time constant of the capacitor charging will never be lower than that  If I remove the 2K2 resistor from every key circuit, and replace it it with a short-circuit, I could replace the attack switch with a 2K2 variable resistor and vary the resistance from 0 to 2K2 Ohm, giving an attack time of 1-15ms - or thereabouts.
Similarly the 12K resistor into the base of Tr24 sets the maximum attack time. Increasing the resistance between the collector and ground will initially provide an increase in the time constant from15ms upwards, but the higher it gets, the more the total resistance is being determined by the two impedanaces in parallel. In practise the total resistance will never get back to the same value as when the collector is open-circuit and the maximum attack time will always be just a bit lower than the 100ms.
The only way to make the attack time fully controllable, via the collector would be to replace the 12K resistor with much higher value - like 1M - and replace the 2K2 resistor with 0 Ohm link. Then the collector resistance would be in complete control of the CR charging constant.

I don't think I'm going to do that. It would probably take several hours, and that could still be be worth my while, however the risk of damaging a PCB track when there's 4x49=196 joints to de-solder is, well, it's not good odds.

In conclusion, where there's a will there's a way but there's no will to do this one. The attack control will remain as a switch.

Organ Donor

Which brings me to a confession. I bought an entire organ to get hold of two switches.

I may have gone too far this time. It's quite something to discard the wooden case of the SS-30 only to later by a dual-manual organ because I need a couple of switches.

Not just any switches, of course...

These Yamaha switches are just the right sort  - being black and tablet, not too large and the right vintage - to go into my front panel. There will be more about this, and the organ, later.