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Old 19th August 2003, 03:14 PM   #1
Buhl is offline Buhl  Denmark
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Default Tricky little problem with Z4 component

Hi there !

This is a little embarressing, but when i ordered the parts for my dual bridged Z4, i couldent get fixed value 5 pF capacitors, so i ordered variable 5-15 pF. Fine enough, but how do I check i witch of the outer positions (the lowest 5 pF one) those trimmers has to be in ?

I have no scope to measure the square wave as mentioned by
nelson in the article, only a "standard multimeter that can measure volts, amps, resistance and diode function.

Can I do this without a capacitance-meter ?


Cheers !

Hans Houmøller
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Old 19th August 2003, 03:39 PM   #2
Netlist is offline Netlist  Belgium
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Hans
You should definitely try to buy a scope.
As for the cap, only with a scope it will be possible to trim a square wave up to it's nicest shape.
You could also buy 2 10pf caps and solder them in series.
If you get some decent caps (silver mica) it will improve the sound as well. I'm not claiming I would hear the difference but a trimming cap is probably not the best sounding device to put in a feedback loop.
Without a scope, my guess is that it will be difficult to measure
the trimming position with such low values.
Maybe others know how to do this...

Greetings

/Hugo
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Old 19th August 2003, 08:58 PM   #3
Buhl is offline Buhl  Denmark
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Quote:
Originally posted by Netlist
Hans
You should definitely try to buy a scope.
As for the cap, only with a scope it will be possible to trim a square wave up to it's nicest shape.
You could also buy 2 10pf caps and solder them in series.
If you get some decent caps (silver mica) it will improve the sound as well. I'm not claiming I would hear the difference but a trimming cap is probably not the best sounding device to put in a feedback loop.
Without a scope, my guess is that it will be difficult to measure
the trimming position with such low values.
Maybe others know how to do this...

Greetings

/Hugo


Thnx for the advice Hugo - Ill try and persuade someone with a scope to measure a squarewave for me. No harm will come to the amp or speaker though if operating for a short while in the 15 pF mode instead of 5 pF - just in the power-up period ?

Cheers !

Hans Houmøller
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Old 20th August 2003, 07:37 PM   #4
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This is not a critical thing. When I want 5 pF, I twist 2
pieces of wire wrap wire (the teflon insulated kind) together
for about an inch.
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Old 21st August 2003, 01:15 AM   #5
eLarson is offline eLarson  United States
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A teflon trimmer capacitor that anyone could afford! How cool is that?

Erik
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Old 21st August 2003, 03:10 PM   #6
Buhl is offline Buhl  Denmark
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Thanx for the replys, but I actually came across 4 pcs. of 5 pF at my local electronics shop, that normally have everything but the partsI need, but in this case - they had what I couldnt find on the web......

Another thing, I very soon about to fire up my Z4 - can i run two boards supply from the unregulated supply in parallel ? Simply connecting board two to the same supply + and - as board one ?



/cheers !

Hans Houmøller
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