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Old 13th May 2009, 01:30 PM   #1
flacer is offline flacer  Malaysia
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Default Amplifier circuit questions~

Hi~
Here is my questions:

Question1.
the variable resistance i cant find 220 Ohm , can i do like this? (see diagram).
Or what should i do?
Click the image to open in full size.

Question2.
why parallel two caps and dont just use one 13.6uf cap?( any audible difference? )
or can i parallel different value say 4.7uf + 8.9uf to get this 13.6uf? (i cant get the 6.8uf caps)
Click the image to open in full size.

I'm not sure with these in my school project
hope someone can help me.
thanks =)
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Old 13th May 2009, 02:11 PM   #2
jaycee is offline jaycee  United Kingdom
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In practice, 2x100 ohm resistors will be fine.
The main reason for the trimpot is to adjust DC offset - the way the circuit shows is not a good way to do it!

The reason for the parallel caps is because they are "MKP" types (metallised polypropylene). These are not usually available in large sizes, so two smaller ones in parallel are used instead.

You could probably get away with using a single 10uF electrolytic here.

If this is for a school project - dont build this. It's rather oddball. Also it's a high power amp and unless you really understand how it works, you're asking for sparks and smoke.

My recommendation for you would be to look up the "ST151" amp by sixtek on this forum. This is a good amp using a tried and tested circuit, with cheap and easy to get parts.
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Old 13th May 2009, 04:05 PM   #3
flacer is offline flacer  Malaysia
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Quote:
Originally posted by jaycee
In practice, 2x100 ohm resistors will be fine.
The main reason for the trimpot is to adjust DC offset - the way the circuit shows is not a good way to do it!

The reason for the parallel caps is because they are "MKP" types (metallised polypropylene). These are not usually available in large sizes, so two smaller ones in parallel are used instead.

You could probably get away with using a single 10uF electrolytic here.

If this is for a school project - dont build this. It's rather oddball. Also it's a high power amp and unless you really understand how it works, you're asking for sparks and smoke.

My recommendation for you would be to look up the "ST151" amp by sixtek on this forum. This is a good amp using a tried and tested circuit, with cheap and easy to get parts.
thanks jaycee
you clear all my questions.

And one sad thing is that i already bought all the component that needed and a transformer of +-32V 8A, and it's expensive.

thanks your suggestion , ST151 seems much easier to build~
Anyway i will try to build it first, until i cant control this monster =(

maybe i will have more question about this amp~
hehe

regard!

-flacer
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