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Matching diodes
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LektroiD



Joined: Aug 23, 2008
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Location: Scottish Borders
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PostPosted: Fri Oct 11, 2013 2:06 am    Post subject: Matching diodes
Subject description: for the EMS Filter...
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What's the best (or easiest) way to match the diodes for the EMS filter?

Are diodes heat sensitive like transistors? Presuming it is a similar technique to transistor VBE matching...

I would also like to know how to set up the test gear and what to look for on the multimeter/scope?

If anyone has a schematic, or breadboard/stripboard layout to make a simple diode matcher that would be most helpful.

(OR)... can I just throw any diodes in there and expect a reasonable sounding filter - does it really affect the sound that much?

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analog_backlash



Joined: Sep 04, 2012
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Location: Aldershot, UK
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PostPosted: Fri Oct 11, 2013 3:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi LektroiD.

Most multimeters have a diode test setting (as part of the resistance range(s)), you just have to match the voltage drop across them. Alternatively, you can put a resistor in series with the diode, apply a voltage across the resistor/diode and measure the voltage across the diode, as in this previous posting:

http://electro-music.com/forum/post-188963.html

A "schematic" (for an entirely different end use) is shown at the bottom of this page:

http://www.qrp.pops.net/xmfr.asp

Yes, they are temperature sensitive (you can use them for making electronic thermometers) so you need to let the temperature stabilise before taking a reading.

I hope that this helps,

Gary

P.S. I think that I may have been a little ratty with you once before. Sorry, I was in one of my moods...
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LektroiD



Joined: Aug 23, 2008
Posts: 977
Location: Scottish Borders
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PostPosted: Mon Oct 14, 2013 11:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Gary, the only thing I'm not really sure about is 'voltage drop'. What's the difference between testing that and straight voltage? I have a diode setting on my tester, but not sure what I'm looking for exactly (it's all new to me).

*EDIT* I found a video on Youtube demonstrating what I need to know.

Don't worry about being ratty; I'm not one to hold grudges, which is probably why I don't remember the incident. Wink

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analog_backlash



Joined: Sep 04, 2012
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PostPosted: Tue Oct 15, 2013 4:12 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm glad that you've worked it out now LektroiD.

Any forward biased p-n junction (i.e. where the p is held more positive than the n), whether in a silicon signal/rectifier diode or a silicon transistor will show a voltage drop of (very approximately) 0.6V across it. The value is lower for germanium diodes/transistors and also for Schottky diodes. It is quite variable from one diode to another, so you need to match them as well as can (depending on the accuracy of your multimeter).

Thanks for not remembering my last post to you - it wasn't offensive, just a little bit condescending Laughing .

Gary
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