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Old 31st December 2009, 08:44 PM   #21
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Location: Ireland
Exactly.... and if you do need to add the diodes plain ones will do ask, just make sure they can take the full mains voltage.

Fran
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Old 31st December 2009, 08:55 PM   #22
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Quote:
Originally Posted by alazira View Post
Hi Bigbillc,
I would not use the resistor by itself. In fact, if you do not have ground hum with the circuit ground wire direct to the chassis, then you do not really have to do anything else.
Alazira, why are you saying to not just use the resistor to isolate the
chassis ground from signal ground? BigBill now has a safe chassis ground,
or so he says, assuming he has not misunderstood what others are writing.
That's all he needs from a safety point of view.

But I agree Bill, go ahead and just connect the signal ground to the chassis
ground and if you've got no hum you're good.

Actually before that.... How this all started is you saying you were getting
shocked by the chassis. Is that still happening?

Also. That CL60 you've got - I can't tell from the photo - is that connecting
hot from the IEC socket to a fuse holder? If so, that's a diabolical piece
of kit..... there is about an inch, times 2, of hot exposed inside the chassis !!!



You should unplug the unit, desolder the CL60, put some heatshrink tubing
or some wire insulation over those exposed leads, then solder it back in.

One more thing. The wire that was connecting the signal ground to the chassis
is too thin. I can see all sorts of thick power wires in the pictures and the wire
that should be the thickest is instead the thinnest. If you don't have like 16
guage wire, you can just bulk up 2 or 3 or 4 pieces of thinner wire to connect
the IEC socket ground to the chassis, but it should be able to conduct a fair
bit of current without melting.

Clearly whoever built your amp wanted to lift the ground and of that he did a
good job. Given what I think I see in the pictures I would question why did the
person bother to connect signal ground to the chassis - it didn't help anything
and would only serve to transfer static shocks directly into the audio circuit.

Cheers all and happy new year.

Last edited by wayne325; 31st December 2009 at 09:03 PM.
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Old 1st January 2010, 12:10 AM   #23
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So thats hum!!! Its loud...I'll try putting something in between the circuit ground and the chassis later. Its time for NYE!!

I think that the builder was trying to prevent hum when he did it the way he did. In any case I did not touch he case b/c I turned it off as soon as I heard the hum.

Happy New Year to all.
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Old 1st January 2010, 12:39 AM   #24
alazira is offline alazira  United States
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Quote:
Originally Posted by wayne325 View Post
Alazira, why are you saying to not just use the resistor to isolate the
chassis ground from signal ground?
Hi wayne325,

Although using the resistor would eliminate hum, it's not as safe a setup. Using a CL60 here is preferred.

Time to go home and watch fireworks from a safe distance (est. 350K crazy people wandering Las Vegas Blvd tonight)

Happy New Year!
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Old 1st January 2010, 08:09 PM   #25
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Quote:
Originally Posted by bigbillc View Post
So thats hum!!! Its loud...I'll try putting something in between the circuit ground and the chassis later. Its time for NYE!!

I think that the builder was trying to prevent hum when he did it the way he did. In any case I did not touch he case b/c I turned it off as soon as I heard the hum.

Happy New Year to all.
Bill,

I think something is shorted to the chassis. Since you have a resistor to
use, I'd start wtih that. If the hum is gone you're good and think about
replacing the resistor with another CL60. I agree with alazira it is the better
solution.

W.
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Old 2nd January 2010, 01:00 AM   #26
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You know what? This happened me one time before on a preamp build. Exactly those problems, and also the V between chassis and neutral. Turned out to be a bad transformer. I can't remember exactly what the Tx problem was, but a buddy of mine copped it right away, said try a different transformer and problem magically dissappeared.

Grasping at straws I know, check for shorts first.

Fran
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