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Old 8th October 2012, 10:35 PM   #11
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Originally Posted by Rundmaus View Post
This is the original PSU I did not use, actual schematic follows tomorrow! Now tired --> bed!
My wife always says www.go2bed.com
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Old 9th October 2012, 02:37 PM   #12
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Originally Posted by gootee View Post
Andreas,

You could try running the two signal grounds through wires, instead of through the chassis, back to the ground end of the last capacitor of the main power supply.
Hey there,

I took another look at the breadboard after a good night of sleep and found that in the line of 'solder iron enthusiasm' I slightly mixed up my star ground scheme, leading to the following:

Grounding scheme (current setup)

Click the image to open in full size.

Some connections do not feel right, I marked them with '!'. Any more comments on how to improve the grounding?

Andreas
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Old 10th October 2012, 04:42 PM   #13
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No one willing to comment on that grounding scheme?
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Old 10th October 2012, 06:44 PM   #14
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if the hum goes away with a cheater plug on the amp or preamp....this virtual cheater plug will work without posing a shock risk. it acts like a cheater plug for normal ground loop voltage levels but once the voltage goes above the diodes forward volts...the circut transistions into a ground preventing the shock hazard.
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Old 10th October 2012, 06:59 PM   #15
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if the hum goes away with a cheater plug on the amp or preamp....this virtual cheater plug will work without posing a shock risk. it acts like a cheater plug for normal ground loop voltage levels but once the voltage goes above the diodes forward volts...the circut transistions into a ground preventing the shock hazard.
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Old 11th October 2012, 02:20 AM   #16
gootee is offline gootee  United States
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Quote:
Originally Posted by Rundmaus View Post
Hey there,

I took another look at the breadboard after a good night of sleep and found that in the line of 'solder iron enthusiasm' I slightly mixed up my star ground scheme, leading to the following:

Grounding scheme (current setup)

<snipped image>

Some connections do not feel right, I marked them with '!'. Any more comments on how to improve the grounding?

Andreas
Yeah, I would definitely make _separate_ ground-return conductors all the way to the star ground point for all of the small-signal stuff.

Just as inportant as star grounding is to not make antennas by having enclosed loop area between conductor pairs. "Current flows in loops. Eliminate or minimize the area they encircle."
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Old 11th October 2012, 01:57 PM   #17
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Quote:
Originally Posted by gootee View Post
Yeah, I would definitely make _separate_ ground-return conductors all the way to the star ground point for all of the small-signal stuff.
Yes, I think I will try this. In the current grounding scheme, the ground connection from the EL34 cathode resistors with its high current (approx. 90mA) goes to the star with all the small signals and grids. I'll move this one to the middle star and report back!

Andreas
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Old 11th October 2012, 10:44 PM   #18
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A lot of very good advice here.
KISS works for me many times though.
Check your voltages.
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Old 12th October 2012, 03:02 AM   #19
ChrisA is offline ChrisA  United States
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Originally Posted by gootee View Post
Just as inportant as star grounding is to not make antennas by having enclosed loop area between conductor pairs. "Current flows in loops. Eliminate or minimize the area they encircle."
One way to do that, that works well on breadboards is the "star of stars" groiunding system. You can make local star ground for each sub circuit and then conect these to the central star.

The idea is to place the AC curent source (A power suply filter cap) physically near the load (such as a driver tube) and also place the local star ground physically close to both. This minimises the antenna effect described above. Then you conect the local stars to the central. Typically you have as many local stars as you have power suply filter caps.

the diagram on this page shows how to do this, it really does minimize the loop antenna effect The Valve Wizard
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Old 15th October 2012, 01:34 AM   #20
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That is a great link, ChrisA. Thanks for posting it.
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