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 Forum index » DIY Hardware and Software
Diods for DIY?
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Per



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PostPosted: Wed Jun 07, 2006 2:36 pm    Post subject: Diods for DIY? Reply with quote  Mark this post and the followings unread

I have some spare space in my modular. I am extremely bad at soldering, but:
I have the idea of using one single diode as sort of wave shaper, reducing the frequency of a sine wave to the half. Four diodes in a bridge should work as a passive recifier, and change ramp waves to triangle.

Have anyone tried it? Will it work?

Per
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bugbrand



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PostPosted: Thu Jun 08, 2006 1:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Slightly wierdy idea...

Take a look at the Ken Stone CGS module:::
http://www.cgs.synth.net/modules/cgsrr.html

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Blue Hell
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PostPosted: Thu Jun 08, 2006 6:04 am    Post subject: Reply with quote  Mark this post and the followings unread

re. the single diode : Depending on the input impedance of the circuit following the diode it might turn out to be a bit slow. Probably this will be cured by adding something like 4k7 to ground after the diode.

The diode bridge will not work as expected when the ground references on input and output are simply connected (which they are in a modular synth environment). You'd need an isolating transformer then, it would be even better to build an active rectifier (using one or more op amps) I guess.

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zipzap



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PostPosted: Mon Jun 12, 2006 12:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

[/quote]The diode bridge will not work as expected when the ground references on input and output are simply connected
Quote:

why? got some more info/link on that?
I think the problem with diodes is always the turn on step at 0,7v with normal silicon. There is no such thing as an ideal diode, but luckily the active rectifier behaves like one.
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Blue Hell
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PostPosted: Mon Jun 12, 2006 12:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

zipzap wrote:
why? got some more info/link on that?


I'll try.

I can't do so myself right now, but just make a drawing of the diode bridge, and label the points in the usual way, that is one point with +, another with - and two with ~ (the 'transformer' side so to say).

Connect one of the points labeled ~ to the output of something and the other point labeled ~ to ground. Then connect the + of the bridge to some input and the point labeld - to ground.

When you then look at it you'll see one diode being bridged/paralleled by a wire causing negative input voltage to be short circuited to ground by a second diode. Te third diode making a single phase positive rectifier and the fourth diode doing absolutely nothing.

So it's not a problem with the diodes being non-ideal, but it just can't work when both the input and output of the bridge use the same ground reference. Just draw it, and you'll see.

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zipzap



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PostPosted: Mon Jun 12, 2006 12:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for trying, i think you succeeded.
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PostPosted: Mon Jun 12, 2006 12:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

See Very Happy
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