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Old 2nd June 2013, 04:09 PM   #341
Zen Mod is offline Zen Mod  Serbia
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try like this :

twisted triple of wires ( +,-,gnd) from PSU to (each) output pcb , shortest possible route , not going from coast to coast);

RCAs isolated from chassis ; their GND tabs connected with one wire bridge ; from exact mid point of that bridge - one wire to main GND point of PSU ( which ic connected to chassis/safety gnd via NTC)

then shielded ( or twisted pair ) from each RCA to correspondent channel pcb , where gnd (shield ) wire connected just on RCA side

if needed - fat , shortest possible , wire as bridge connecting two pcbs main GND points
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Last edited by Zen Mod; 2nd June 2013 at 04:11 PM.
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Old 2nd June 2013, 04:10 PM   #342
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Quote:
Originally Posted by Mr. dB View Post
Well if you look at Nelson's amps with balanced inputs, he uses a balanced audio line from the rear panel to the circuit board, and then for unbalanced operation just sticks a jumper in the XLR connector. I imagine the resistance of that arrangement would be more than the short length of small-gauge jumper wire that 6L6 has used?
I know, just suggesting a possible issue. Hook scope up to it with inputs grounded and then plug in amp. Lets see what's happening
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Old 2nd June 2013, 04:15 PM   #343
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Quote:
Originally Posted by Zen Mod View Post
try like this :

twisted triple of wires ( +,-,gnd) from PSU to (each) output pcb , shortest possible route , not going from coast to coast);

RCAs isolated from chassis ; their GND tabs connected with one wire bridge ; from exact mid point of that bridge - one wire to main GND point of PSU ( which ic connected to chassis/safety gnd via NTC)

then shielded ( or twisted pair ) from each RCA to correspondent channel pcb , where gnd (shield ) wire connected just on RCA side

if needed - fat , shortest possible , wire as bridge connecting two pcbs main GND points
Yes Choky. My assumption was that his RCA's are isolated completely from the chassis. If not, it may cause some major problems, but I am sure he knows better.
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Old 2nd June 2013, 04:18 PM   #344
6L6 is offline 6L6  United States
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Quote:
Originally Posted by Zen Mod View Post
twisted triple of wires ( +,-,gnd) from PSU to (each) output pcb , shortest possible route , not going from coast to coast)
Ok, I was going to try that next anyway...

Quote:
RCAs isolated from chassis
They already are, so that's easy!

Quote:
their GND tabs connected with one wire bridge ; from exact mid point of that bridge - one wire to main GND point of PSU
Ok, I like it! Is this different from equal length wires connecting to same point on PSU?


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(which is connected to chassis/safety gnd via NTC)
Yep.

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then shielded ( or twisted pair ) from each RCA to correspondent channel pcb , where gnd (shield ) wire connected just on RCA side
So the shield will be at same potential as GND... Very good!!

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if needed - fat , shortest possible , wire as bridge connecting two pcbs main GND points
Will try that last to see if it helps.
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Old 2nd June 2013, 04:22 PM   #345
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Not sure what's going on there with your hum situation, will be interesting to see what finally solves that. Looking at those pics, just wanted to make an observation. In building that amp, I would have swapped positions of the power transformer and the PS board. The way the Firstwatt (and many others) are done.
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Old 2nd June 2013, 04:32 PM   #346
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Quote:
Originally Posted by william2001 View Post
just wanted to make an observation. In building that amp, I would have swapped positions of the power transformer and the PS board.
Sounds interesting... Why?

Is there any connection that could be made shorter that way? I'm asking because a second set of eyes is always helpful and maybe you are seeing something I'm not...


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The way the Firstwatt (and many others) are done.
I bet you a beer that it's done that way to get the balance of the amp in the center of the chassis more than anything else...
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Old 2nd June 2013, 04:34 PM   #347
Zen Mod is offline Zen Mod  Serbia
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FW amps aren't exactly center weight balanced
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Old 2nd June 2013, 05:04 PM   #348
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Just seems like a better way to do it. Not so much to do with stray radiation / weight or anything. I would just rather have my "Main Audio Ground" point near the rear of the case instead of the front. Only an opinion...
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Old 2nd June 2013, 05:13 PM   #349
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good thinking
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Old 2nd June 2013, 05:49 PM   #350
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Originally Posted by william2001 View Post
I would just rather have my "Main Audio Ground" point near the rear of the case instead of the front.
Duh! Of course! That makes perfect sense.
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