Sound generation - SS30 Lives! Part 2

On Friday night I made some more wiring fixes and played around with the pitch, detune and vibrato controls.

More on the oscillators and pitch control later.

Sound generation - SS30 Lives!

Last night I proved that all the key switches on the K boards are working and that G boards are generating tones on all of those notes. In fact I got some sound out of the SS30!

I had to fix one wire on K2 

Then I hooked the scope to the keying circuit of C2, the first note on K1 and the 8L output of G1. 

The voltage on the key circuit rose when I connected it to earth (-7V up to 0V) and then fell back gradually when I disconnected it, showing that the sustain was working well. 

The output from the generator showed something like what I was expecting, although not exactly. It seemed to have a lot more going on that I was led to believe that it would by the circuit diagrams. It looked like a mix of notes.

G1 8U output

I tried the rest of the keys and got the same result. So far so good.

Then I moved to K2 and G2. I got the same result but this time it was unexpected. The G2 8L output should only have C#3 to F#3. On G2 the octaves are divided as part of the keyboard split option. So, keys on the upper half of the octave should not be generating output on the lower half of the generator board. 

 

G2 Outputs

My assumption had been that I would need to check each output from the G boards. This was my thinking because not only do the same key switches drive both the 8' and 16' outputs on each board, but also those outputs then get routed and mixed together in different combinations. Even if I got something audible at the final output for every key there might still be some missing components to the sound. 

I also assumed that because the switching controls, such as keyboard split and the mixing switches were disconnected there wouldn't be any signal making it's way to the output. 

Now that I am seeing what appears to be a mixed signal at every output I needed to check more carefully.

However rather than do that I decided instead to cut to the chase and see if there was any sound coming from the main output. And there was! 

Every key produced a tone and I could play more than one at once (no reason why it shouldn't, but.. y'know, it was nice to confirm). It sounded awful though. Partly because I just grabbed my Korg Monotron and used that as the amplifier. Also, I suspect there is a lot of noise being generated by the number of loose wires and the proximity of the audio output cabling to the power supply. However after looking at the circuit diagrams again I'm convinced that no sound should be reaching the output at all! With no keyboard split switch connected the bottom two G boards outputs should go nowhere and none of the outputs should get through if the mixing switches (Cello 1, Cello 2, Viola, Vioin 1, Violin 2) are disconnected. I can only guess that what I heard was somehow leaking through. All electrical signals create electro-magnetic radiation which can be picked up in wires, so it's possible.  I've seen stranger things happen. 

My next step will be to methodically trace the signals from the G boards through the circuit. Hopefully I will work out where the signal is getting through as expected and is not getting through .  I will also try reconnecting the switches to see if I can get some more consistent behaviour.

  

Owners Manual and other scans

After finding the Yamaha IC guide on the Internet Archive, mentioned here, I started to think I should share the owners manual and service manual. Actually, I was thinking it would be useful for me to have scans of them anyway. And of course if I was gong to share them they would need to be in pdf format. However, one of the things that irks me about .pdfs is when there are no links or searchable text in them. Most (all) synth manuals I've ever downloaded are just plain scans of the original printed documents and no active content. Fair enough, but I wanted to do better. So, I embarked on the task of creating scans and converting them to .pdf using Acrobat.

There are actually four documents

Owners Manual - User guide, in other words. "STRINGS SS-30 is a keyed instrument to let you enjoy rich tones peculiar to the strings with this instrument."

Service Manual - The circuit and wiring diagrams. This is, obviously, the really useful bit for the project.

Parts List - Including spectacular exploded 3D diagram

 Block Diagram & Overall Circuit Diagram - No scans yet.


 The service manual folder also contains the parts list and the block diagrams, which are printed on either side of a huge poster sized piece of paper.  I've scanned everything apart from that as I was having problems with the scanner I was using and wanted get on with the rest. It will need stitching together.


I made a start on the service manual and I'm about 80% done.

Work in progress

 It's been a huge job to add all the text though and I got tired of it and decided to knock off the owners manual quickly to show some progress.

So, here it is!


In the pdf all of the text is searchable, the contents section contains links to the relevant pages and the 'How To Use SS30' section has links for the numbered references on the diagram.