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Old 30th July 2009, 08:23 PM   #11
vince76 is offline vince76  Italy
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grazie Piero Thank you Piero
I checked the grounding.
The fact is that the amp is dead quiet when no source is connected. I start thinking I have a bad source cable. Two bad cable actually.
V.
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Old 30th July 2009, 11:44 PM   #12
piero7 is offline piero7  Italy
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Old 31st July 2009, 03:35 AM   #13
chrish is offline chrish  Australia
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Have you tied the grounds of the two inputs together and from there to ground?

Chris
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Old 31st July 2009, 06:48 AM   #14
vince76 is offline vince76  Italy
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I have four input, two per source, and a selector.
I tied the four grounds together with the potentiometer ground and grounded all at preamp grounding point

V
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Old 31st July 2009, 05:12 PM   #15
vince76 is offline vince76  Italy
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Default war to the hum

dear boys,
I'm in a dead point.
I need your advice.
My amp, when no source is connected is super silent.
if I connect one channel of the CD source to the amp using shielded or unshielded wire than the hum starts. The same happens with an Ipod. same if I connect both channels. Volume doesn't affect hum.
don't know what to search for since I don't understand where it comes from (50Hz hum, a loop....?)
thank you,
Vincenzo
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Old 31st July 2009, 09:27 PM   #16
Brit01 is offline Brit01  United Kingdom
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Just one thing.

Did you put grid stoppers in? I don't see them in the schematics.
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Old 31st July 2009, 09:36 PM   #17
vince76 is offline vince76  Italy
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I followed the schem... other builders report no hum problem.
Do you think grid stoppers would help? I think it's power related or ground loop.
Thank you
V
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Old 31st July 2009, 09:41 PM   #18
Brit01 is offline Brit01  United Kingdom
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Probably not due to the absence of grid stoppers but I've always understood it's good practice to put in grid stoppers. Good quality resistors though.

Your RCA chassis connectors are isolated well yes (if you have a metal chassis)?
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Old 31st July 2009, 10:14 PM   #19
vince76 is offline vince76  Italy
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rca connectors are well insulated (the hot is well insulated) checked today, the grounds go all to preamp ground point.

V.
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Old 31st July 2009, 11:07 PM   #20
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Quote:
Originally posted by Brit01
Just one thing.

Did you put grid stoppers in? I don't see them in the schematics.

It is good practice, I have 1k on mine.
I don't think this is the hum issue though (as previously mentioned)
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