Will this amp need a star ground? - diyAudio
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Old 23rd August 2007, 11:03 PM   #1
ghetto is offline ghetto  United States
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Location: Oklahoma
Default Will this amp need a star ground?

This amp was inspired by BWRX - specifically the component choices have been lifted from him. It's basically a balanced, bridged chip amp. I do understand the rhyme and reason for a star ground, but I feel like this particular configuration really isn't going to suffer much without it. Your comments are welcomed (even if you just call me an idiot!)
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Old 24th August 2007, 03:59 AM   #2
BWRX is offline BWRX  United States
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Hi ghetto. Glad to see someone else pursuing this configuration! From a technical standpoint, it has a leg up on the more minimalist designs.

As you saw in the Instrumentation LM3875 thread, I chose to modularize the design so there is one complete inamp per pcb (with local regulation for the dual op amp). This makes it easy to use them as building blocks for bridged/parallel designs. To make a parallel amp you just wire the inputs in parallel and use a low value power resistor in series with each output. To make a bridged amp you just wire the inputs in parallel and out of phase. It's that easy. As always with a DC coupled amp, be careful of the DC offset from your source.

Your schematic differs because of the use of a global regulation scheme for the dual op amps. There is also a mistake in the schematic - you can't use two positive regulators to derive the +/-15V rails from the unregulated suppply with the windings connected to form a ground. You will need to use positive and negative regulators. You can use 3 terminal regs or simple emitter followers with zener references.

Anyway, you are correct that this particular configuration won't suffer much without star grounding because of the balanced/bridged configuration. Even so, I would still advocate using a star grounding technique when wiring up multiple modules. I would also recommend using local regulation for each dual op amp because it allows you to better implement the star grounding technique for the two supplies on each module.

If that doesn't make sense, I can try to rephrase that in a more understandable way.
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Old 24th August 2007, 10:50 PM   #3
ghetto is offline ghetto  United States
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Good catch - I'm not sure what I was thinking with the regulator setup.

I'll update and come back with corrected schematics and layout.
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Old 25th August 2007, 05:25 PM   #4
sexya is offline sexya  India
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hii there ... wow... some one cares for dyslexics.. i am one.. well ihave a desing for my bed side stereo.. can you have a look and let me know if its ok frm the grounding point of view.. i am a bit raw in that field..
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