Thursday, July 27, 2017

Viola Woes


So, here's a short bit of actual chords on the SS30-M.

No Alla Viola - Silenzio

(These heading puns are getting more convoluted by the week. Top marks if you can unpick that one)

Last time I fixed the missing clock to G3. Finally I was done with the SS-30 problems! Or was I? No.

After having missed the fact that I had an issue with G3 I went more carefully through each octave and found another problem. On the bottom octave (K1/G1) there was no output from the Viola.

Tracing this problem took me to a board I've not had any issues with so far - LF.

On LF there are a pair of analogue switch ICs.

4016 Analogue Switches on LF Board

The Old Switcharoo

These 4016 devices control the signals which get selected in and out by the Keyboard Switch control. Either the Cello is selected or the Viola/Violin voices. This is called the KYB. Split Gate.

KBD. Split Gate

In this case 16U from G1 was arriving at the switch gate but not being routed through. I could see that the voltage from the switch was working fine so the problem was really with the IC.

I've ordered the replacement so it should be another easy IC swap when it arrives. The main concern is to make sure no wires break loose whilst the boards are being moved around.

And then I can start on the full MIDI interface. I have a couple of posts in the works about that.

LF Board

The LF board hosts the vibrato, pitch control, sustain control and the oscillators for the Orchestra effect.

I guess the LF board is named Low Frequency because the Vibrato and Orchestra oscillators are essentially LFOs. 

F Board

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