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Old 25th June 2003, 07:57 AM   #1
jarthel is offline jarthel  Australia
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Default comments please on star grounding points for tube headphone amp

I'll be making the optimized MJ amp designed (http://home.swbell.net/acavalli/imag...dphone_Amp.gif) by Alex Cavelli. I will also be using the tube rectifier power supply (http://home.swbell.net/acavalli/imag...r_Supply_2.gif) also designed by Alex.

I just need comments/feedback/suggestions on the points of the main "star"

1. from ground from plate supply (tap from negative lead of first capacitor)
2. from ground from heater supply (tap from negative lead of first and only capacitor)
3. from ground loop breaker
4. from ground of left channel
5. from ground of right channel
6. from ground of input female RCA
7. from ground of the volume control

Ground point for the individual circuits will be going to a single point. for example, the ground connection for the 2nd and 3rd capacitors in the plate supply will be connected to the negative lead of the 1st capacitor.

I also plan to connect input female RCA ground to the volume control ground directly. I will be using a twisted pair with 1 wire carrying signal from input female RCA to volume control and the other line is ground

Thanks for the replies.

Jayel
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Old 25th June 2003, 12:10 PM   #2
Joel is offline Joel  United States
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Jayel,

Lift one of the bolts underneath the power transformer and put a ground lug there. Solder all ground leads to that. Done.

Leave the Mystical grounding schemes to someone else.

Joel
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Old 25th June 2003, 12:21 PM   #3
jarthel is offline jarthel  Australia
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I am assuming that the mains ground is connected to chassis. I'm also assuming that with your suggestion, this ground lug will have contact with the chassis.

so with your suggestion, will there be a ground loop?

and the grounding scheme I just stated has nothing mystical in it I think. Well as far as I know there's nothing 'snake oil" about it.

Thanks for the replies.

jayel
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Old 25th June 2003, 12:52 PM   #4
EC8010 is offline EC8010  United Kingdom
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Default Star earth.

I'm not quite sure what you mean by your question. If you're going to star earth (definitely a good idea) then the physical location of the star is largely down to mechanical convenience. I would suggest that you put it somewhere in the middle of the audio circuitry. I am assuming that you are going to do a true star earth here, and that there will be one wire per component coming to the star - with no components sharing a wire.

Bonding your star down to the chassis is a separate issue, but if the star is in the middle of the audio circuitry, it's an easy matter to bond it to the chassis. Whether, or not, you bond your star to the chassis, make sure the chassis (and transformer E/S screen, if fitted) is properly bonded to mains earth.

Does that answer your question?
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Old 25th June 2003, 12:56 PM   #5
Morse is offline Morse  United States
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Hi Jarthel;

Since I use nonconductive chassis on my homebrew amps, I have to run discrete ground lines for everything. That said, I usually just use 3 substars and a single main star. The substars are for the PS filters and heaters (same star), the output valves, and the signal valves. If there is a separate driver it gets it's own substar. The main star connects directly to the safety ground on the IEC. All the metal fittings and trafo cases are just daisy chained by ground shackles directly to the main star.

It's probably more work than it needs to be but my amps have all been very quiet thus far (*knocking on wood for luck to avoid jinxing myself after typing that!!*).

By the way, I've built the MJ headphone amp, albeit to the circuit over at headwize.com (using a fixed feedback loop and with a different PS) and it's really a good little amp, particularly in the optimised form! I think you'll be most pleased with it.....

Good luck with your amp!
All the best,
Morse
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Old 25th June 2003, 01:32 PM   #6
jarthel is offline jarthel  Australia
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does connecting mains ground with circuit ground create a ground loop?

I've seen a lots of circuits albeit they are for headphone amps and they use ground loop breaker. I used a ground loop breaker too in my solid state amp.

Maybe connecting circuit ground to mains ground is okay?
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Old 25th June 2003, 01:35 PM   #7
jarthel is offline jarthel  Australia
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Default Re: Star earth.

Quote:
Originally posted by EC8010
and that there will be one wire per component coming to the star - with no components sharing a wire.

I'm not sure if if the definition of component in your message is every component in the circuit like individual resistors and capacitors.

but my idea is to use sub-stars and a main star just like what morse said.
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Old 25th June 2003, 01:37 PM   #8
jarthel is offline jarthel  Australia
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I'm using a Hammond 369GX and according to the datasheet, there should be a grey wire that needs to be connected to ground. Well this grey wire is absent in the transformer that I have.

Should I scrape some paint in the mounting holes in the xformer and use that to connect the xformer to ground? Is it mains ground or circuit ground?
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Old 25th June 2003, 01:41 PM   #9
jarthel is offline jarthel  Australia
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Quote:
Originally posted by Morse
Hi Jarthel;

Since I use nonconductive chassis on my homebrew amps, I have to run discrete ground lines for everything. That said, I usually just use 3 substars and a single main star.
where do you connect the ground for the output? to the respective ground of it's channel? like right channel output's ground is connected to the right channe's circuit ground.

Thanks

jayel
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Old 25th June 2003, 02:17 PM   #10
Joel is offline Joel  United States
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Jayel,

Ground is ground - many will argue with me on that, but it's true. "Ground loops" occur between COMPONENTS, not within a single circuit - provided you don't do anything weird. Use a single point. How you get each component to that point is up to you - use a bus or individual lines - it doesn't matter as long as the connections are as short as you can make them, and use decent size wire.

Yes - bolt the transformers to the chassis. And "circuit ground" is the same as "chassis ground" to me at least - and in most commercial amplifiers.
Make sense?

Joel
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