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Old 17th September 2006, 01:45 PM   #11
lineup is offline lineup  Sweden
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Location: the north
hi
I agree with Babowana.
Hum is the sound of remains of 50Hz ( 60Hz ) from MAINS AC.
Sometimes, Often! ... this is doubled to 100Hz ( 120 Hz ) after rectification and power supply filter.

Amplifier amplify.
So even quite low levels of this 100 Hertz
reaching input
will be possible to listen to, hear, in speakers.

When is a hum
we will try to see: in what improper way is Sound of TRAFO
getting into contact with INPUT transistor.

Sometimes, in small boxes,
and especially when you use NOT toroid trafos
it can simpy be Trafo being too close to amplifier board.
Or too close to some wire, that is connected to input.

Babowana is having a fair idea of the cause.
Based on what we can read in this forum,
9 times out of 10
-- this hum is is transported
via GROUND ( 0 volt ) wires or PCB tracks or Metalbox, amplifier case
from TRANSFORMER ....... to INPUT of amplifier.

Cutting and re-arranging 0 Volt / Ground wires
will fix these issue quickly in those 9 cases.

Case number 10 out of 10 is the more mysterious one.
But also this will be solved, if not by brain and experienced helpers,
so by trial-and-error method for fixing.

lineup - haikku haikku
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Old 17th September 2006, 04:33 PM   #12
r_jik45 is offline r_jik45  Japan
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Location: Jpn, Fr
Thanks to both of you for your suggestions/comments.

For the 0V - signal ground connection, it seems that they are also connected on the original board proposed by Tortello. I will try to see if I can 'cut' it somewhere... even if I do not really know how to make the difference between them

Regarding the position and possible interaction/interference between the 50Hz source and the inputs: I will try to isolate them better. The transfo is indeed close to the inputs... but there is not much space to do organize the parts another way.

And what about the fact that the input-ground is connected directly to the potentiometer? Is it normal that way?

Anyway thanks again
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Old 18th September 2006, 02:28 AM   #13
Formerly "jh6you". R.I.P.
 
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Quote:
Originally posted by r_jik45


... even if I do not really know how to make the difference between them

The attached sketch might help . . .
Whatever their sizes are, R is R and I is I . . .
And, AMP's role is amplfying the samll v=ir into bigger . . .
Attached Images
File Type: jpg grounding concept.jpg (67.7 KB, 199 views)
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Old 19th September 2006, 09:39 PM   #14
r_jik45 is offline r_jik45  Japan
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Location: Jpn, Fr
Hi Babowana,

I see: a star-ground has to be a real star.
I thought that something like what is presented on the right side would be ok

I will try to arrange the wiring as soon as I have some free time.

Thanks again!
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