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destroyer X 24th October 2004 03:03 PM

I found this old "fellow" when surfing, a friend told me to change those parts.
2 Attachment(s)
What do you think?

Will those changes increase the amplifier "sonic" qualities?

Are there some mistake on it?

Do you think can change other parts?.... what parts?

regards diy guys


Eva 24th October 2004 03:07 PM

Removing the 150nF will make most amplifiers unstable
Replacing discrete transistor by integrated darlingtons may also make the circuit unstable

destroyer X 24th October 2004 03:21 PM

Thank you Eva, 150N will stay
Will not remove 150N

Thank you



Duo 24th October 2004 03:32 PM

Hmm, could anyone enlighten me on why the inverting input resistance is 10ohms reference to ground?

Wouldn't this result in a rather unbalanced current at the input from the source?

Also, the output stage is fused on either rail. What happens when one side blows and the other doesn't?

No time to observe what really happens, must go out for breakfast!

djQUAN 24th October 2004 03:52 PM

from what I remember, the 10R is used to eliminate groundloops by other equipment.

MikeB 24th October 2004 04:30 PM

The only changes i would make is as you said remove this strange
resistor in output, reduce coil to 2uH, reduce stopresistor to ~10ohm.
You should keep the bc639, as i remember it is identical to bd139,
only other case.
And you should replace the 2 output-bjt-pairs with something like
mjl21193/4 or mj15003/4 or mj15024. An keep the 0.22ohm ?
And you might replace d3 with a matched bc640, the "standard"way
for a currentmirror.


demons_wing 24th October 2004 05:10 PM

this is an australian design from the Silicon Chip magazine..i have the article somewhere... the 10R resistor is a ground loop terminator, and the resistor capacitor combination at the input is design similar to the rod elliot RF suppression technique..

Duo 24th October 2004 05:49 PM

So then this obviously isn't designed for balanced input is it?

destroyer X 24th October 2004 10:13 PM

I am collecting all your informs and ideas.

MIKE B, i was thinking if the small 1 ampere BC, will it work in the limit...... around 8 mA idle current... can it works near some limit?



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