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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Soundlab Ultimate Calibration/Tuning problems
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htk



Joined: Aug 18, 2015
Posts: 2
Location: Helsinki

PostPosted: Tue Aug 18, 2015 4:56 am    Post subject: Soundlab Ultimate Calibration/Tuning problems Reply with quote  Mark this post and the followings unread

Hi,

I bought a used Soundlab Ultimate some years ago and have just used it on itself, without CV sequencing.
Now that I tried to use CV I see it is not calibrated correctly, so I tried correcting it. However it doesn't seem possible to calibrate the VCOs, I'll try to explain.

If I set VCO tuning at say 100 Hz at 0V, then send in 1V and try to adjust the scale adjust trimmer and high frequency compensation trimmer so that the VCO would reach 200 Hz at 1V, but it never does.

Adjusting the trimmer always moves the starting frequency at 0V upwards, and the frequency is always less than doubled with the move of +1V. This behaviour is same for all three VCOs.

My knowledge of electronics is pretty thin so troubleshooting own my own will be hit and miss, help/pointers what could be the cause is greatly appreciated!
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elmegil



Joined: Mar 20, 2012
Posts: 1681
Location: Chicago
Audio files: 14

PostPosted: Tue Aug 18, 2015 11:22 am    Post subject: Reply with quote  Mark this post and the followings unread

First: set the high frequency adjust all the way to one end .... unfortunately Ray uses a different type of HF Adjust than what I'm familiar with (e.g. Thomas Henry's circuits, he feeds the output back to the CV summer) so I can't say for certain which end. I'd try one end, and if it still seemed impossible to tune I'd turn it to the other end.

The only time the HF adjust should be needed is with higher input voltages, but if it's way out of whack you could have difficulty like you describe.

You should note that the direction the pitch moves when you adjust the trimmer doesn't necessarily follow the direction you need the interval to change. I built an Ultimate last year, but I can't remember now which way; many VCO implementations, when your octave is too wide, the adjustment you need to make will take the pitch sharp, and when it's too narrow it will take the pitch flat (flat octave == flat pitch shift, sharp octave == sharp pitch shift, which to me has always been counterintuitive).

As I re-read your post, I think maybe this last one is what's causing you grief, you think that you should be turning it to go sharper when the octave is flat? You're basically shrinking the interval as you do that, and you need it to grow.
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htk



Joined: Aug 18, 2015
Posts: 2
Location: Helsinki

PostPosted: Wed Aug 19, 2015 1:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

thank you for your reply elmegil.

I described quite badly as I was not around the synth and it was a couple of days ago when I tried to calibrate it. You're correct, if I adjust the trimmer so that the pitch of the oscillator goes higher, the octave will go narrower. I did adjust the pitch so that the octave gets as wide as possible.

I tried again tonight, and now I noticed something else in the behaviour. Actually if I start to measure the octave gap right after turning on the synthesizer I do get a sharp octave. Here are some measurements at t=0 to around 10 minutes later:

0V 3V
102 950
130 995
135 1001
136 999

After some time the oscillator stabilizes, and I have tried the calibration after ~1 hour, but at that point the trim pot can't reach a full octave anymore.

I set the high frequency adjustment according to Ray's calibration video: oscillator at around 2.0 kHz and then turn to the direction where it lowers the pitch. This way it should not contribute to pitch of the oscillator at this point.
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elmegil



Joined: Mar 20, 2012
Posts: 1681
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Audio files: 14

PostPosted: Wed Aug 19, 2015 4:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok...

There was one time with a Soundlab (not ultimate) where I had swapped a couple of resistors in the expo converter sections and one VCO would calibrate fine and the other behaved somewhat like you're describing. Have you double checked the resistors in that general section of the circuit?

I say this with the addition that when that happened to me I looked at the values of the resistors about 4 times before I recognized the problem Smile
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