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Old 20th May 2010, 11:40 AM   #7891
AndrewT is offline AndrewT  Scotland
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with RCA1 return wire disconnected at the input, how does RCA1 circuit flow and return?
How close are the flow and return routes?
How much loop area is in that route?
Will that loop area result in greater hum at the speaker output terminals?
Will the hum be the same for both stereo channels?

If the Hum is zero for both channels, then you have done something else.

Help.
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Last edited by AndrewT; 20th May 2010 at 11:50 AM.
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Old 20th May 2010, 12:39 PM   #7892
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I do not use this trick in F5s as they are double monos.
I have built several stereo (not double mono) amps which are silent without this trick.
I had to use this trick in a 4 channels amp.
Typically: one get hum when both RCA input (from source) are connected, the hum disappear when one is disconnected
The trick works then.

Q\ with RCA1 return wire disconnected at the input, how does RCA1 circuit flow and return?

"Return" i prefer "shielding" is made
-Outside the amp : the shields are joined into the source.
-Inside the amp: the shields are joined at the star ground.

Generally, I do not connect the audio ground to chassis. It may help, i do not know.

Last edited by bobodioulasso; 20th May 2010 at 12:46 PM.
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Old 20th May 2010, 12:53 PM   #7893
AndrewT is offline AndrewT  Scotland
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Default 2+ channel amplifiers

alright, you shield your input.

Where does the signal flow and return if the shield does not provide the necessary return route?
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Old 20th May 2010, 01:12 PM   #7894
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Is it "hum" or "hiss" -- if the amplifier isn't connected to a low impedance source then you have the 100k plus its connecting cable sitting out there as a little antenna -- and your transformer is radiating energy.

The F5's noise is spec'd at some tens of microvolts -- if you are using the power supply setup which NP had recommended.
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Old 20th May 2010, 01:50 PM   #7895
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Quote:
Originally Posted by AndrewT View Post
alright, you shield your input.

Where does the signal flow and return if the shield does not provide the necessary return route?
There is a unique ground into the source connected to the unique amp ground. I suppose it is sufficient.
Pr Leach himself tells this (scroll down to penultimate paragraph)
The Leach Amp - Part 2

I insist, i do not use this with F5.

Last edited by bobodioulasso; 20th May 2010 at 02:05 PM.
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Old 20th May 2010, 02:17 PM   #7896
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I prefer a drawing to a long speach.
Do you see the return path?
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Old 20th May 2010, 02:49 PM   #7897
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If you prefer symetry:
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Old 20th May 2010, 04:16 PM   #7898
lae2 is offline lae2  United States
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Quote:
Originally Posted by bobodioulasso View Post
If you prefer symetry:
What about the case where you have a chassis earth isolated from a signal ground. What about running those shields to the chassis earth? That way the length of the return path can be equated to the signal path for even more symmetry. I have done it that way in electrophysiological recording hardware then is extremely sensitive to input noise (30 meg input Z). I just hacked at it though not really understanding what I was doing. Seems to work.

Last edited by lae2; 20th May 2010 at 04:19 PM.
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Old 20th May 2010, 05:17 PM   #7899
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Do you mean two wires + shielding, such as microphone wire?
The two wires used as signal and return, the shielding connected to earth only?
Interesting!
Though, it works only if ground and earth are not connected into the source.


Anyway, as Jackinnj said, the F5 is not concerned; it is easy to get it silent and it does not need special care for grounding. Only respect of the common rule.
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Old 20th May 2010, 05:27 PM   #7900
lae2 is offline lae2  United States
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Quote:
Originally Posted by bobodioulasso View Post
Do you mean two wires + shielding, such as microphone wire?
The two wires used as signal and return, the shielding connected to earth only?
Interesting!
Though, it works only if ground and earth are not connected into the source.


Anyway, as Jackinnj said, the F5 is not concerned; it is easy to get it silent and it does not need special care for grounding. Only respect of the common rule.
Yes, that is what I meant. Two conductor with a shield, a signal conductor, a return conductor, and a shield to earth. I have wrestled with this kind of thing for years in recording equipment. Then there is a driven ground and my head starts to swim. What works one day does not work the next day. I have never waded through an academic understanding. I do know that inadvertent pathways between signal ground and chassis earth generally spell trouble for low noise high Z amplification. At least, this is true in my hands.
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