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Old 19th June 2003, 04:35 PM   #31
ukram is offline ukram  Finland
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http://www.national.com/ds.cgi/LM/LM3875.pdf

The single point ground principle is explained in the chip data sheet. Basically you should not have big currents flowing in the signal ground, because ground wire has some small resistance that causes small voltage that is seen as an input signal. U=RI.

It is also good practice to separate speaker and power supply ground the same way.
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Old 19th June 2003, 04:53 PM   #32
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here is my attempt,

any wire will have resistance, capacitance, etc. so think of a wire as a resistor in its simplest form.

If different sections of the amp are grounded differently and linked with those wire/resistors, as current flows through those wires, it will produce little voltage that can be picked up by, for example, the input stage and amplified later one, causing obiviously problems.

To ground all sections of the amp together will eliminate that problem. alternatively, you can use really large wires (small resistors) to link those grounding points together.
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Old 19th June 2003, 05:35 PM   #33
Nuuk is offline Nuuk  United Kingdom
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I have now uploaded the corrections for the Gainclone beginner's guide. I have also added a bit more based on some questions on the forum and others received through DD.

The parts list now includes the part number and price for the insulating pads from Farnell.
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Old 19th June 2003, 09:50 PM   #34
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Thanks for the explanation for the separate star grounds... It does make more sense now!

Nuuk I noticed the new diagram but did you correct the step-by-step guide as well (part #9) that says to point to pin 7?
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Old 20th June 2003, 08:01 AM   #35
Nuuk is offline Nuuk  United Kingdom
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Quote:
Nuuk I noticed the new diagram but did you correct the step-by-step guide as well (part #9) that says to point to pin 7?
No I didn't It will be done today. Thanks again for pointing out these mistakes; both from me and those who come along after you.
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Old 20th June 2003, 08:59 AM   #36
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Thumbs up good attempt

Quote:
Originally posted by millwood
here is my attempt,

any wire will have resistance, capacitance, etc. so think of a wire as a resistor in its simplest form.

If different sections of the amp are grounded differently and linked with those wire/resistors, as current flows through those wires, it will produce little voltage that can be picked up by, for example, the input stage and amplified later one, causing obiviously problems.

To ground all sections of the amp together will eliminate that problem. alternatively, you can use really large wires (small resistors) to link those grounding points together.

Absolutely correct.
You should not have differences in potential.
Ground wires should be thick, for the grounds to flow fast.
Less noise.
That's why on some PCBs you see large tracks for the ground, almost all the empty spaces of the PCB are occupied with the ground tracks.
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Old 22nd June 2003, 06:23 PM   #37
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loading any page on www.decdun.fsnet.co.uk/
crashes Safari
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Old 22nd June 2003, 07:59 PM   #38
Nuuk is offline Nuuk  United Kingdom
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Quote:
loading any page on www.decdun.fsnet.co.uk/ crashes safari
What is safari? If it's a browser, I'm not sure why DD would cause any crashes. Apart from a little javascript code, it is just CSS/HTML!
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Old 22nd June 2003, 08:18 PM   #39
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its a browser. i sent in a bug report to Apple cos no javascript should be able to crash a browser. you know?
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Old 22nd June 2003, 09:00 PM   #40
Nuuk is offline Nuuk  United Kingdom
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its a browser. i sent in a bug report to Apple cos no javascript should be able to crash a browser. you know?
I agree. FYI I have had no other reports of my site crashing a browser. I'd be interested to hear what Apple have to say.
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