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Old 22nd March 2008, 12:07 PM   #1
dome406 is offline dome406  United Kingdom
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Default Velleman K4700

I am building this speaker protection circuit and just wondered the purpose of R23, R24, R25 and R26 (see attached diagram) and weather i need to include them.

In the instruction manual (see instructions1) it says to include them if:

If the amplifier to which the module is to be connected has a simple power supply (asymmetrical supply) i.e. an amplifier with output elcos, the following resistances has to be mounted...
My amplifier is a non inverting lm3875 with a regulated 18V 0 -18V power supply so i am guessing it doesnt need these resistors since the supply is symmetrical ?

What confuses me is what elcos mean i thought it might mean electrolytic capacitors? but am unsure. Also my amplifier has 2.2uF non polarised capacitors if this makes any difference.

Hope someone can explain

Thanks very much
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Old 22nd March 2008, 12:12 PM   #2
dome406 is offline dome406  United Kingdom
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Heres the other image.
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Old 22nd March 2008, 09:16 PM   #3
Thago is offline Thago  Belgium
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I used the same Velleman K4700 kits in Pass Aleph 2 monoblocs, which have a symmetrical +45V - 0 - 45V power supply, thus meaning that both + and - are 'hot' (see attachment).
I did'nt use the resistors you mentioned, the K4700 works fine.
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Old 23rd March 2008, 11:38 PM   #4
dome406 is offline dome406  United Kingdom
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thank you Im still not quite sure what they are needed for but will try without the resistors.
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Old 24th March 2008, 12:14 AM   #5
Zen Mod is online now Zen Mod  Serbia
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these resistors are needed for bleeding output caps , which are certainly used if amp is made with non-symmetrical PSU ;

better to charge/discharge them through resistors , than through speaker coils, don't you think?
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