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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
Calibrating 1V per Octave Keyboard
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pico.farad



Joined: Feb 27, 2013
Posts: 16
Location: New Zealand

PostPosted: Thu Jun 27, 2013 3:37 am    Post subject: Calibrating 1V per Octave Keyboard
Subject description: Can't see any voltage
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Hi, I have started trying to calibrate the 1v per octave circuit, but I am seeing no voltage over R5.

Here are some details:
+ Power supply is working
+ Checked the voltages on the chip sockets
+ Haven't connected the glide pot
+ Haven't connected LEDs
+ Using TL074 instead of LF444
+ Haven't been pressing keys when testing voltage
+ Diodes seem OK
+ Electrolytic caps in the right way
+ Chips in the right way
+ Switched TL071 once
+ Trimpot works

I don't know exactly where I should be looking for the problem, or whether I am doing something wrong so far.
Thanks
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brock



Joined: May 26, 2011
Posts: 96
Location: Canada

PostPosted: Fri Jun 28, 2013 9:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you are just looking for voltage on R5 you don't need to look much beyond U1 and the components around it that make up the constant current source.

I'd check the following things:
Q1 is a 2N3906, or at least a pnp and it's installed correctly.
The keyboard resistor ladder is connected and the low end grounded.
Input voltages on U1 are roughly 8V.
There is an output voltage on U1 and it is the same at Q1 base and it's not at the + or - rail.

If any of these things look wrong check component values and connections for opens or shorts.

Good luck.

Brock
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pico.farad



Joined: Feb 27, 2013
Posts: 16
Location: New Zealand

PostPosted: Sun Jun 30, 2013 12:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Ha, I forgot to ground the keyboard, whoops.

Thanks for your help
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