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Old 22nd August 2007, 03:27 AM   #1
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Default PCB layout for audio

Do we need to have a solid ground plane on the bottom layer for linear audio amp?
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Old 22nd August 2007, 03:38 AM   #2
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Tough question, and I can argue it either way. Given the low frequencies involved, you don't need a ground plane to insure return currents run parallel and close to their upper traces. You don't have the EMI and loop problems associated with higher frequencies. A ground plane will provide the lowest inductance ground, and helps tremendously with bypassing. OTOH, it can increase stray capacitance to ground through the only so-so dielectric quality of the pcb. It also makes it tougher to insure currents flow where you want them to and circuit blocks don't interact. Even a ground plane has finite resistance. I don't use 'em for audio 99% of the time, but if you tend towards high BW op-amps or unusually high BW discrete designs, there could be benefits. IMO, great amps can be built with or without.
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Old 22nd August 2007, 04:48 AM   #3
AKSA is offline AKSA  Australia
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Consistent with Conrad's comment, no. You don't need to.

If you want to, you can put in a ground plane, but be prepared to revisit compensation regimes because the parasitics can be considerable.

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Old 22nd August 2007, 05:28 AM   #4
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Thanks to ALL!

How about using top layer un-used area as ground plane?
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Old 22nd August 2007, 06:45 AM   #5
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Hi Panson_hk

I would not bother with either ground plane. It is better to direct exclusive ground returns to a specific "low noise" point. This way you can be sure there are no "stray" un-accounted current flows. If you want to; place a thin sheet of metal under the PCB (insulated from the soldered connections and the rest of the case) with a single connection from it to your star ground.

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Old 22nd August 2007, 08:32 AM   #6
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Quote:
Originally posted by panson_hk
Thanks to ALL!

How about using top layer un-used area as ground plane?
Save your money and go for a single sided PCB.

For audio use, I will agree with Quasi, Hugh and Conrad, you most likely don't need one, and I never put one on the first prototype run of a board. I might add one if I have problems, but they are normally not required, (however, read the component datasheets, some DAC or Class D circuits do require at least a limited GP on part of the board).
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Old 22nd August 2007, 09:11 AM   #7
banana is offline banana  Hong Kong
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Let me dare to say the opposite

If you're skillful enough, you might have good result with single side board. However, too good is never enough. It doesn't hurt to be better.

I always use double-side board, even for prototype board, it's way easier to layout.

But like others have said, stray cap at high impedance point have to be addressed.
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Old 22nd August 2007, 01:43 PM   #8
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Quote:
Originally posted by banana


But like others have said, stray cap at high impedance point have to be addressed.
Could you elaborate a bit and explain how one can address this problem?
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Old 22nd August 2007, 01:49 PM   #9
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Quote:
Originally posted by aparatusonitus
Could you elaborate a bit and explain how one can address this problem?
Don't use a ground plane unless you really need to is the best way of avoiding the problem!
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Old 22nd August 2007, 03:44 PM   #10
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But imagine that I have to use it ('cos my circuit is so complex, for e.g.)
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