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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS58 saw/tri mod question
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Dave Kendall



Joined: May 26, 2007
Posts: 410
Location: England
Audio files: 3

PostPosted: Fri Oct 17, 2008 5:30 am    Post subject: CGS58 saw/tri mod question
Subject description: positive only?
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Hi All

Anyone know a way to get the triangle/saw wave outputs to be positive only, specifically 0V to +5V - without using separate op-amps wired as offset scalers?

I'm not so interested in the square wave outputs - it's a positive triangle I'm after.

Any ideas welcome Smile. (I've hit a block, and can't seem to work it out.....)

cheers,
Dave


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andrewF



Joined: Dec 29, 2006
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PostPosted: Fri Oct 17, 2008 6:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is pre-coffee and is probably crap
What if you power the circuit between just 0V and +15V.
leave off the -15V connection and link the -15V rail to 0V.

you need to isolate (cut the tracks) the op-amp inputs that go to 0V
pins 13,3,10 on one chip, 10, 5, 12 on the other.
Next get two 10k resistors, connect them in series between 15V and 0V. From the node between the two 10K resistors run jumpers to the above mentioned pins. This is your new virtual ground.

I haven't checked but I don't think the TL074 can swing to ground meaning the output will always be 'on', so you may be better off with an LM324, which can

You might also want to cut the tracks to the bases of the BC547 transistors and put a capacitor across the track, say 10n. otherwise the leds will be on 95% of the time and not indicate much.

Probably I have forgotten something or this idea is completely stupid or there is a much easier way to mod this cct.....anybody else got some suggestions Question
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Dave Kendall



Joined: May 26, 2007
Posts: 410
Location: England
Audio files: 3

PostPosted: Thu Oct 23, 2008 12:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the reply - have suddenly got a glut of work on, so no time for a couple of weeks to try it out. Will have a go then...

Your idea sounds interesting.....
Food for thought indeed. Smile

cheers,
Dave
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