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 :-(

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