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Old 5th November 2007, 07:35 PM   #1
stein2 is offline stein2  Serbia
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Question tube buffered LM3886T grounding

Hi, this is my first post here. I tried to read all written about this subject but I'm still not sure about at least one thing. The basic design is described on JLTI and I built a couple of GC amps but all non-inverted with more or less luck (did manage to send one of my Tannoys to heaven) and since I had much more luck with tubes than with solid state stuff, I decided to give it a go. I understand most of the issues I'm facing here, so I'll skip the idiotic questions. What I'm not quite sure of is the way of grounding it with three transformers but with them being separated from the box with the tube and chipamp. The question #1 is should I make a star ground and ground all the 0V in the power supply box and only ground the 0V from the filtering capacitors in the amp box or there is something I am missing ? (I have a single 300VA toroid for the chipamp supply)

The other question is regarding the LM3886 being used instead of LM3875. Should I fit the resistor-capacitor to do the mute or can I skip these as I did before (without any noticeable problems) Is there a good reason why I should order the LM3875 and use that instead of LM3886?

That would be it for my first post. For now.
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Old 6th November 2007, 10:17 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
do not take all your audio ground connections to the smoothing cap zero volt link.
Instead take a short thick wire from the zero volt of the smoothing caps to a nearby location and bring all the other grounds to this audio ground. These are the RCA input ground or signal ground from the PCB, the power ground from the PCB, the speaker return (ground), the smoothing cap zero volt, the Safety Earth disconnecting network (or a direct link), any relay or control circuit grounds. This audio ground or star ground can be very close to the amplifier PCB, some even fit it on the PCB.
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Old 6th November 2007, 10:38 AM   #3
stein2 is offline stein2  Serbia
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I thought so, or at least something like you explained. I will try this way and let you know the results, with a couple of images added. At this moment, I'm still waiting for the small toroid to arrive and when I get it, I'll finish up the power supply, connect everything and give it a try. So far the main (amp) PS and the heater works fine...

Thanks a lot!
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Old 12th November 2007, 09:21 PM   #4
stein2 is offline stein2  Serbia
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It worked fine, actually more than fine. All started up without problems (I did build a couple of VT amps some years back) and now I'm all in listening to possible hidden problems, so far, no reason to worry. Thanks Andrew!
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Old 12th November 2007, 09:24 PM   #5
stein2 is offline stein2  Serbia
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... and here's one more, showing the point I chose to act as a star ground, grounding point, call it whatever you think is correct, it works.
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Old 30th January 2012, 07:40 AM   #6
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Quote:
Originally Posted by stein2 View Post
... and here's one more, showing the point I chose to act as a star ground, grounding point, call it whatever you think is correct, it works.
If this schematic can be stepped up?
Thanks
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Old 30th January 2012, 02:58 PM   #7
GloBug is offline GloBug  Canada
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Nice amp.
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