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Two layer versus four layer PCBs
Two layer versus four layer PCBs
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Old 27th June 2020, 12:58 AM   #41
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by MarcelvdG View Post
For the same reason why audio op-amps always have gain-bandwidth products in the megahertz range.
My headphone amps generally sit around 50-200 MHz GBP...

Tom
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Old 27th June 2020, 04:57 AM   #42
MarcelvdG is online now MarcelvdG  Netherlands
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Quote:
Originally Posted by ohdsp View Post
It's not just the components, it's how they interact with the PCB traces and layout in general. Small SMD parts have some funky behaviour at high frequencies (like 4G and WiFi frequencies which are abundant these days) - resistors can become inductive and capacitors have low impedance, it can have unexpected interactions with a circuit when the parts don't work as expected. Assume with something like an audio amp that will result in more output noise - you can get that by placing your mobile next to some equipment.
True, but the same holds for through-hole components. In general, the bigger the component, the lower the frequency at which it doesn't behave as an ideal lumped component anymore.
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Old 29th June 2020, 05:09 PM   #43
ohdsp is online now ohdsp
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As I said in a previous post, would be interesting to see the difference by measuring comparable amplifier designs. 2 layer vs 4 layer (with ground plane), SMD vs through hole.

I've not seen through hole resistor designs in an EMC chamber, I have seen SMD parts. Given the larger size of through hole parts I would be interested to see if they are affected in the 2GHz+ region the same way SMD parts are. Given the abundance of that type of interference around now, it must have an impact on noise in some way. Maybe it's at such low level you would never notice it.
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Old 29th June 2020, 05:15 PM   #44
rayma is offline rayma  United States
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Originally Posted by ohdsp View Post
Given the larger size of through hole parts I would be interested to see if they
are affected in the 2GHz+ region the same way SMD parts are.
At GHz frequencies, everything matters.
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Old 29th June 2020, 05:53 PM   #45
ohdsp is online now ohdsp
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But, when looking at something like an audio application where it is an output signal you listen to, to what level and extent, and how is it affect by something simple like a ground plane and 2 layer vs 4 layer.

Unlikely to be a simple answer, and a power amplifier running off +/-50V will likely differ from something like my DSP boards with analogue stages working at <1Vrms with lots of digital signals.

If you have something like an audio power amplifier with limit bandwidth (say 100khz), then I thought the noise it picks up can "fold down" into it's working range, as it can't do anything else with it, so more output noise? Would it benefit from a 4 layer ground plane on the input sections, what is the real difference from through hole to SMD...
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Old 29th June 2020, 06:22 PM   #46
rayma is offline rayma  United States
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Quote:
Originally Posted by ohdsp View Post
If you have something like an audio power amplifier with limit bandwidth (say 100khz), then I thought the noise it picks up can "fold down" into it's working range, as it can't do anything else with it, so more output noise? Would it benefit from a 4 layer ground plane on the input sections, what is the real difference from through hole to SMD...
Yes, IMD, rectification, etc. These implementation differences are easily measurable with the proper tools.
The amplifier can have wider bandwidth but use input/output filters, which only addresses some problems.
https://www.edn.com/connect-signals-...nimize-errors/

Last edited by rayma; 29th June 2020 at 06:42 PM.
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Old 29th June 2020, 08:55 PM   #47
Mark Johnson is offline Mark Johnson  United States
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Two layer versus four layer PCBs
Quote:
Originally Posted by ohdsp View Post
... interesting to see the difference by measuring comparable amplifier designs. 2 layer vs 4 layer (with ground plane), SMD vs through hole.
Please feel free to perform the experiment and report the results! Lay out two PCBs from the same amplifier schematic; build them out into identical chassis with identical power supplies, and then measure their performance. I'm sure that (a) you'd have a lot of fun; (b) other diyAudio members would be delighted to peruse your data.
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Old 29th June 2020, 09:30 PM   #48
ohdsp is online now ohdsp
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I'm busy washing my hair....

and building other stuff.

Maybe one day, choose something simple like ESP P3A design, should have SMD and through hole versions of devices that would work, could probably do all 4 layouts on one PCB for testing
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Old 29th June 2020, 10:02 PM   #49
Mark Johnson is offline Mark Johnson  United States
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Two layer versus four layer PCBs
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Old 29th June 2020, 10:51 PM   #50
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by ohdsp View Post
If you have something like an audio power amplifier with limit bandwidth (say 100khz), then I thought the noise it picks up can "fold down" into it's working range, as it can't do anything else with it, so more output noise?
Sure. Have a look at page 12 here: https://www.ti.com/lit/an/snoa497b/snoa497b.pdf

Quote:
Originally Posted by ohdsp View Post
Would it benefit from a 4 layer ground plane on the input sections, what is the real difference from through hole to SMD...
If those changes made less RF energy reach the inputs of the opamp, definitely.

In case of the EMI-hardened opamps from National (now TI), the benefit is from a filter on die.

Tom
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