In the Pedal Power post I briefly outlined how the Volume Foot Controller worked. Here's a more thorough description. If I am to use it as a control voltage input I will need a special cable.
I don't like this schematic in the main Service Manual page
TRRS??
There's a better view in the Block Diagram
TRS... I think?
It's easier to see the contacts in this diagram and it's clearer that pins 2 and 7 both connect to the Tip of the TRS jack. The Ring connects to pin 4, carrying the FC signal back to the SS-30. Note that 2 and 3 are unused.
This is the original connector
TRS! And two connections to the Tip.
For the SS-30M I used a new connector, a Switchcraft 114BPCX
Switchcraft 6.35 mm Chassis Mount PCB Mount Jack Socket 114BPCX
The Tip Spring and Tip Shunt are equivalent to pins 7 and 6 on the original, with the shunt disconnecting the +15V supply from the Ring Spring when the jack in inserted.
To recap, the TRS connector is wired like this.
T - Tip - +15V
R - Ring - FC signal
S - Sleeve - Ground.
When using a foot pedal, the Tip and Sleeve are connected to either end of a variable resistor with the FC signal coming from the wiper. Thus the FC signal is swept between 0 and 15V.
Therefore, to drive this input from a control voltage only the Ring and Sleeve are needed and as the Tip is normally used to carry the signal a normal cable isn't going to work.
To use this input with a control voltage a convertor cable will be need to only connect the FC signal and ground. Perhaps a diode would good to block negative voltages too.
This cable will be a 6.35mm TRS at one end and 3.5mm TR at the other for connection to Eurorack. The RS of the TRS will be connected to the TR at the other end.
Note, I have tried this CV input by simply holding some wires on to a jack plug and it does work.
Also, when I was playing around with different Eurorack LFO inputs I noticed that the sound was similar to a recording by a band with a close relationship with the SS-30. I may come back to that and possibly solve a 40 year old mystery.
Edit
Instead of making a cable I decided to go a slightly different way. As soon as anything is plugged into the Volume Foot Control the connection between +15V and FC is broken, so it must be made again to get any sound out of the SS-30. As this connectiion is on the back panel and largely inaccessible leaving anything plugged in is going to be a problem - even more so if I've removed the +15V.
I need to be able to a) keep a cable connected b) default to the +15V connected to FC and c) occasionaly connect FC to a control voltage from elsewhere. d) still connect an actual foot controller if required.
Right now d) is low priority, but I have a plan for a,b, and c.
Firstly, this is going to be connected to the SS-30
Hosa YPP-117
As this splits the signal in two I can either connect just the FC to a control voltage or connect both together and regain the +15Vto FC link.
My plan is to run two TR-TR cables from this adaptor to the back of my patch-panel - A Behringer PX1000.
This panel is configured such that if two cables are connected to both A and B sockets of the same port on the back and nothing is inserted on the front, they are shorted together.
This doesn't quite work though, because only inserting two connections at the front will not disconnect this pair.
Trying to use the patch panel to manage the situation will only work if I use two different ports' connections (not two connections on the same port) on the back and manually patch them together at the front. Not as neat but will work.
There's one more thing though. The +15V to FC connection is normally current limited by a 2.7K resistor. If I bypass this what will happen?
To avoid the potential problem a special cable incorporating the resistor could be made to link the to two connections back together.
Then pulling this cable will be required to access the FC connection
i.e.
At the back:
Port X - +15V connected to rear A
Port Y - FC connected to rear A
At the front, either:
PortXA patched to PortYA to short the connection and keep Volume at a maximum - requires special cable?
OR
PORT YA patched to input from modular, or whatever source of CV
Also:
Port X' and Y's rear B sockets are both shorted to the front connectors. These should never be connected to anything. The +15V is only for looping back and FC can only take one input. I have ordered some caps to block the B sockets on the front of the patchbay and prevent any accidents.
Edit II
I receieved the splitter cable and by patching it's two ends back togethr the volume level was restored. I then set about cabling the patch bay. Unfortunately I immediately found that the +15' supply line from this circuit had gone and there was no sound.
Power Supply (for Foot Controller)
I made a guess that TR7 was the fault and, sure enough, swapping it out restored the supply.
I assume that the line was shorted to ground at some point in the wiring and that was what did for it. Quite why though is less clear. What is certain, is that I had been running the supply line back to the FC input without the 2.7K resistor I mentioned above. My best guess is that I must ensure this resistor is in line with the power-supply at all times, but also ensure that it is not shorted. I will need a special cable for this.
This is an old post which I wrote a couple of years ago and never finished... till now
Short summary: The Volume controller can be connected to a potentiomer in voltage-divider configuration via TRS jack or a control voltage can be applied via a TR jack. The Sustain pedal is a switch connected via TR jack, but this is not easy to control from other equipment due to the same negative voltage problem as the keys. An opto-isolator will be needed to make this work with a standard S-Trig input. The Expression output of the MTP-8 MIDI interface is of limited use but helpful so a CV output has been added to the rear-panel and could be scaled up and converted to drive the Volume pedal.
Foot Use
The SS-30 has quarter-inch jack sockets on the rear panel for two foot-pedal controllers. So far I have never investigated or used either. This is rather remiss of me and before the SS-30M comes together I need to look further into these optional extras.
And whilst I'm here I will also take the oppotunity to test the Expression output from the MTP-8 MIDI converter.
Volume Control
The first foot controller is labelled ‘FOOT. CONT (VOLUME)’ and the User Manual suggests connecting a volume pedal, such as the Yamaha FC-3
Metal from the pedal
The connection from the pedal is via a TRS jack with the following signals
Tip - Volume signal
Ring - +15 volts supply
Sleeve - Ground
And this is the schematic:
Note that there is a 2.7K resistor between the +15V suppy (pin 6 and 7/ring) and the FC (foot controller) signal (pin 4/tip). With no jack plug in the socket I measured 12.7V on pin 4.
After connecting a jack plug, this droppped to 0V. That's because pin 7 is disconnected from pin 6 when the plug is in. Hence, with no plug the 15V supply feeds into the volume control circuit via the 2.7K resistor and when the jack is inserted the resistor is disconnected and the foot controller's internal resistance sets the level of the signal.
Thus, the volume foot controller is just an audio log potentiometer wired as a voltage divider. The voltage being divided between the +15V and ground.
Volme Control Voltage Control
The Volume Control socket is designed for a foot controller / potentiometer, however there is no reason not to simply insert a voltage from somewhere else. The good news is that you can safely use a TR jack which shorts the +15V 'ring' to ground, because ground is not actually shorted to ground. There is a resistor there.
The voltage would ideally to be up-to and above 12V. It also needs logarithmic scaling. That can be tricky though, as we'll see.
This input opens up the possibility for external global envelope control or tremelo effects.
Expression
The off-the-shelf MIDI decoder I'm using has a output called Expression. This is mapped to the velocity of the last note event recieved and is limited to just 4 bits, or 16 steps, of resolution.
MIDI velocity has a resolution of 128 steps (0-127) so the Expression output reduces this to just 16, like so.
MIDI note velocity
MTP-8 step
MTP-8 voltage (V)
0
to
7
=
1
0.000
8
to
15
=
2
0.208
16
to
23
=
3
0.417
24
to
31
=
4
0.625
32
to
39
=
5
0.833
40
to
47
=
6
1.042
48
to
55
=
7
1.250
56
to
63
=
8
1.458
64
to
71
=
9
1.667
72
to
79
=
10
1.875
80
to
87
=
11
2.083
88
to
95
=
12
2.292
96
to
103
=
13
2.500
104
to
111
=
14
2.708
112
to
119
=
15
2.917
120
to
127
=
16
3.125
Those steps would be of no use for swells or gradual fades, without filtering, but there are some tricks that can be used here.
Velocity Sensitivity
It would be possible to build a sample-and-hold circuit for each note and build in velocity sensitivity per note. I'm not keen on building and wiring another set of boards to do this though. Tempted, but not keen!
The output could be useful for setting a global level though.
Another suggestion from the MTP-8 guide is to smooth out the steps and the changes for each new note on event and then use the voltage to control a power amplifier which in turn drives the 'output common voltage' which sets the level to each note output.
Referring back to the opto-coupler interface design you may recall that the output for each note from the MTP-8 is this +15V, common voltage and this switches on the opto-coupler which in turn shorts the input of the keying circuit to ground.
Things start to get complicated with the optocoupler though. What is the effect on this device if the voltage is less than +15V and consequently reduced current to the internal LED? Is it linear? honestly it's hard to tell! I was aiming for around 1mA for each note but I can't find the actual current in my notes. If it was 2mA maxmum then it seems to be outside of the non-linear region, but I could only tell if I tried this.
Another consideration here is that the keying circuit doesn't expect anything but -7V or 0V. In theory, anything between -7V and up to 0V would result in a lower in amplitude for that particular note. However, because of the way the attack time capacitor charging works it isn't quite so simple. For a start, the transistor would change from being in saturation mode to active mode. This would have consequences not only for the output voltage of this circuit, but most imediately the collector-emiiter current and therefore the charging time/attack time of the circuit.
On the whole, I'm almost sure this approach won't work without affecting the attack time in ways that would make the attack time proportional to the velocity. in which case it's mostly unusable and not worth the effort.
Velocity Switch
Just saying that I did though...
As a minimum, there would have to be a switch to enable this feature, as leaving always on just wouldn't be, err, on. Why is that important? It doesn't have any effect if the MIDI input device only has fixed velocity - such as the PSS-580 - but when there is a velocity sensitive keyboard there still needs to be an option to only use the SS-30M as designed.
Our Velocity
Whilst applying the voltage from the Expression output at the keying circuit is flawed, it seems obvious that wiring this control voltage to the overall volume control
should at least be an option.
The MTP-8 Expression
output is not scaled for 0-15V, alas. Instead, it only goes up to 3.125
volts. Therefore, to achieve the full range of volume this will have to
be scaled up by a factor of (15/3.125) 4.8. This is simple with an op
amp and two resistors. However, this is still a linear scale. Can it also
be converted to a logarithmic scale easily?
No. Not really. It's realtively easy - compared to some problems - but would call for a lot of components. It is a bit of a rabitt hole to go down.
Scaling up - brief notes
A constant-gain amplifier or scale changer is a basic op-amp circuit. In this case it must be non-inverting - and as we're not as worried about the frequncy response this is fine.
In this configuration, the non-inverting input is used with the inverting input in the feedback path, which is formed as a voltage divider.
In simple terms the the feedback resistor should be a multiple of the input resistor. That multiple defines the scaling where Gain = Rf/Ri
There is another problem though. This control voltage must be logarithmic. This video makes it clear what this all about.
Changing the scale from a linear to logarithmic range is a little more challenging. I've made some headway with a design but that idea's been shelved for now.
Expression Yourself
In summary then, the Expression output could be of some use but I'm not in the mood to divert time and effort to it when I'm so close to finishing the whole thing. I could go back to it, but only if I really feel the lack and can make a case for using it, no matter how limited.
I have included a rear-panel output for this CV signal, just in case I want to use it, but I'm just as likely to externally create a control voltage from MIDI and send that into the Volume Control input.
Sustain Switch
The other pedal input is labelled ‘FOOT SW. ( SUSTAIN)’.
For this the User Manual suggests the use of the optional accessory FC-3, a Sustain Pedal.
This one is simply a TR socket, so it's not a voltage divider like the volume control.
The tip is measured at the familiar -7V and the ring is grounded.
The -7V, when shorted to ground cuts the sustain off. I haven't analysed the sustain circuit much before so, here goes...
Sustain is set independently for the Cello and Violin voices. The sustain controls on the front-panel are linear 100K variable resistors which form a voltage divider between 0V and -7V. In addition to the 100K potentiometer there is between it and -7V at one end a 1.5K resistor and 18K in series with ground at the other end. These additional resistors are important.
The voltage difference is sent through a 47K resistor to a tranistor and then through a 22K resistor on to the keying circuits. This is repeated for the Violin and Cello.
The footpedal switch also has an 18K resistor in series, and is fed through diode into the base of the transistors.
A concern for this external control is positive going trigger inputs being added accidently, but that's easily blocked by this protection diode.
So, when the foot switch grounds, any current from either Sustain control is carried away from the transistor and the K boards.
In practice this is a very sharp cut in the sustain and creates a rather unnatural and abrupt stop. Obvioulsy it can be a case of adding sustain back in. A resistor as well as a switch could provide for more than one level of sustain.
Switching things up
For extenal control of the Sustain circuit that -7V level creates a problem, again. Not an issue if a foot-switch is used, with a physical switch, but if a synth gate control will not play nice with -7V. Synth type gates ae either S-Trig or V-Trigger. Neither will work with this input though.
A V-Trig (Voltage Trigger) output wouldn't work, because there is no way a postive voltage will do anything to this circuit. As noted above, it would do no harm either, which is good to know because setting up a gate output can sometimes be a matter of trial and error.
Normally such an input, requiring a switch to ground, can be controlled by a gate output in S-Trig (Switch Trigger) output. Those gates are switching postive voltages to ground though, and this is a negative voltage. Where have we encountered this problem before?
Trigger Happy
Avid readers of this blog will know that the whole story of the MIDI inteface for the SS-30 was complicated by this switching of -7V to 0V. The positive gate signals for each note from the MTP-8 had to be used to switch opto-isolators with the -7V keying circuits on the other side.
Thus, the obvious solution for the sustain switch is to use the same idea. Connect 15V through a current limiting resistor to the anode of the LED input side of the opto-isolator, and connect the cathode to the Sustain input. An S-Trig connection into the input will then switch the LED on when the S-Trig is switched to ground. As with the key triggers, the sustain circuit -7V is then connected to the photo-transistor of the opto with ground on the other pin.
I can add an extra opto-isolator to the key trigger boards and the rest is just wiring. More wiring...
I've found a review of the SS-30. It has long bothered me that I've never seen a contemporary review of the SS-30 so when I espied just such a thing on eBay I snapped it up.
This article is from the November 1978 issue of, umm, not sure. It took a bit of digging, but the 'Keyboardcheck' column was active in International Musician and Recording World back in 1975. So, I guess that is the one. I found that the author Robin Lumley was also writing for Sound On Sound in their early days and they were using the same photo.
Here's the review and further below my comments...
Lumley
Robin Lumley lucked into being, as you may have read above, briefly keyboardist in Ziggy Stardust's Spiders band. That was his calling card and got him session work and eventually producer credits. He formed Brand X, a jazz-fusion band, with, amongst others, Phil Colins. So he's a first rank keyboard player at the heart of the British music scene, recording and touring. I think he's worth listening to. And he's Joanna Lumley's cousin, too!
Well, the first joke didn't age well, so let's move swiftly on to surveying the market.
Competitive Edge
Roland RS-202
This is the first string synth since the Arp Solina (1974) and Roland RS 202 (1976) worth bothering with. That's the competition. Forget the rest, this is a three horse race.
Which is best though? Lumley wisely notes that this is matter of taste and that some will never be parted from their Solina. This debate still trundles through the ages and whilst you might prefer one over another there has never been an objectively best sounding string synth when you narrow the field down to these top three. Other synths should not even be on the market, in the view of our reviewer! So, the SS-30 Cellos are "warmer" than the Solina "at the lower end" but "edgier" than the Roland". In summary he says the SS-30 sound is "rich and warm". You decide!
ARP Solina
Swimming in sound
Moving on to the chorus effect, and, after underlining the importance of that "swimming sound", Lumley wryly observes that enobling what he refers to as "modulation" to Orchestra is probably "somewhat optimistic" for some. Throughout this review he is careful to dampen down any scoffing about how realistic string synths can be. Nevertheless, he says that set up with "detuning the instrument slightly on the tuning pot, and then setting the slow orchestra tab with about half depth gives you, finally, one of the best pre-set synthesizer string section sounds available". With reverb "the illusion is almost perfect".
That mention of 'pre-set' sounds, is something else that's stressed in this review and later on he compares the sounds available from string machines to what can be achived with a serious synth such as the Yamaha CS-80. His view is that with time and careful adjustment you can expect "super realism quality" from a really programmable synth. This is 1978, remember, he's only referring to analogue polysynths. I am going to take issue with "super realism" there and I sense a slight wink to those scoffers again, but he has a point. The CS-80 strings are sweet. And yet, isnt the string synth pre-set to sound as good as a well programmed synth? If it could be better, why not make the preset be just the same? The main reason I can think of is the way the tones are generated in the first place. The oscillators. Stringers all use a divide down architecture which means there's perfect agreement between each note's tuning. The advantage is you can play as many notes as you wish and with overlapping sustains - no note stealing. The disadvanage of that approach is that this agreement in tuning is not natural. A polysynth like the CS-80 has 8 voices each tuned on a well maintained machine to be as close as possible but all naturally just ever-so slightly off from each other. Just like the instruments in an orchestra. If you want a realistic string section you need as many independently tuned oscillators as instruments in the section. Stringers get around this with chorus, but the underlying oscillators tend to give the game away.
None of that is really news and is covered elsewhere or is well known to synthesists. What he then says is that string synths arent there to be all that realistic anyway. Their job is to "provide orchestral sounding thickening and sustained notes". Ah. So, it's about articulation and the way you play it too. He ends by stating that the string synth's real raison d'etre is to supplant the huge and weighty Mellotron - a practical issue for professional live musicians in the seventies when facing the task of replicating studio recordings on stage.
"Sounding right"
What is a bit more interesting and less commented on when talking about string synthesizers is the actual notes you play and how that affects the realism. Here Lumley gives some real insight and takes a shot at those who sniffily dimiss them as "not sounding right". His advice is to look at actual string section scores, forget triads and other common keyboard chords and add 7th or 9th notes to much simpler harmonies. This is good advice, which I admit I was sort of aware of, but have never really followed. One day I plan to get some MIDI files and try this out. Perhaps even multitrack each tone from Cello 1 & 2, Viola and Violins 1 & 2, or, as I now have the feature, a different mix of the two.
"That little bit more"
In conclusion Lumley is enthusiastic about the SS-30. He likes the keyboard split option and notes how useful this is for "live and recording". He's generous in his praise for the overall sound, albeit whilst hedging against those who might look down on a mere preset machine. He admits it will cost more than it's only real competition from the RS-202 and Solina but balances that against the additional features and faultless Yamaha execution of the design.
I enjoyed this review. Lumley know's his stuff and this authoratitive view is useful in getting a better picture of how the SS-30 fitted in to the market place. When the Solina came out there was no polysynth market. The Polymoog arrived a year after but was another divide down solution to the polyphony problem. The RS-202 was still needed, but by 1978 there was choice and the CS-80 in particular was equal to the task of making string sounds. Nonetheless these synths were pricey. Yamaha evidently saw a continuing demand for string machines but made their move relatively late, but with a bit extra to set it apart.
There was still something to be said for mere preset machines, but the tenor of this review makes it clear that by late 1978 you had to make that case or be seen as blind to the future.
The advice on what notes to play and mimicing string sections is sesnsible, but also shows that Lumley knows his readership and their misconceptions as well respecting their views.
There was never any doubt in my mind that the Solina and RS-202 were well thought of. That it was a simple choice of these three was less obvious. I suppose cost is always a good measure of quality and the SS-30 was a bit pricier. It's a Yamaha though, and that is mark of quality, but the extra keyboard split feature is what makes it worth it though.
