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Old 20th April 2012, 02:47 PM   #1
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Default Pre-amplifier grounding compendium?

Hey Diy'ers,

I'm in the process of making a preamplifier and wonder if any of you knows of a thread here in DIYaudio - or elsewhere - that can be considered a "compendium" on the best routing & grounding strategies for pre-amplifiers?

I know of this article by Guido Tent of Tentlabs:

http://tentlabs.com/Components/Shunt...decoupling.pdf

- which is about supply decoupling and tracing in that respect, but is it e.g. wisest to place the common ground close to the input or close to the output? And what would be the reasoning for either choice?

So if any of you knows of a short, easy-to-read, yet valid "compendium" on grounding I'd appreciate hearing about it.

Spring greetings from Denmark,

Jesper
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Old 20th April 2012, 05:19 PM   #2
Mooly is offline Mooly  United Kingdom
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I don't know of or indeed haven't seen a compendium on this.

Every design is unique and every design MUST follow basic principles. It helps to think of it all as a DC problem sometimes. Ask yourself, "if any current were to flow in this line or that track etc, then will it alter the output of the circuit in way".

To just follow the "star ground" and connect everything to that approach doesn't work in practice... there are just to many ifs and buts.

If you can read all of this then it might give you a little insight into the problems.
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Old 20th April 2012, 07:08 PM   #3
hags is offline hags  United States
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If working on a preamp with a 2 layer pcb why not dedicate one layer for power/decoupling traces and grounds and the other for signal routing and signal ground.

Use a ground plane on each layer and then have them connect at one point/via on the board for connction to the PSU.

I have seen Borbely use this approach, although he did not use ground planes but simple traces due to the single layer.
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Old 20th April 2012, 07:28 PM   #4
jcx is offline jcx  United States
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I won't even try to do 16+ bit resolution instrumentation circuit designs for anybody not willing to spring for 4 layer PCB - at low production volumes it is a waste of time and money trying to squeeze the performance into 2 -layer layouts - requires more design time, often more pcb layout/prototype passes

for pre-amp level signals a single gnd plane is likely OK, possible slots/necking down to constrain power supply/return current paths

the bigger issue can be deciding what to do with source signal gnd, chassis, safety gnd, gnd loops from PS leakage currents

Whitlock's papers at the Jensen site is good for the system interconnect issues - even if he keeps ending up recommending signal isolation transformers http://www.jensen-transformers.com/apps_wp.html


there is also an article here at diyAudio: Audio Component Grounding and Interconnection

Last edited by jcx; 20th April 2012 at 07:32 PM.
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Old 20th April 2012, 07:39 PM   #5
hags is offline hags  United States
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Quote:
Originally Posted by jcx View Post
I won't even try to do 16+ bit resolution instrumentation circuit designs for anybody not willing to spring for 4 layer PCB - at low production volumes it is a waste of time and money trying to squeeze the performance into 2 -layer layouts - requires more design time, often more pcb layout/prototype passes

for pre-amp level signals a single gnd plane is likely OK, possible slots/necking down to constrain power supply/return current paths

the bigger issue can be deciding what to do with source signal gnd, chassis, safety gnd, gnd loops from PS leakage currents

Whitlock's papers at the Jensen site is good for the system interconnect issues - even if he keeps ending up recommending signal isolation transformers JENSEN TRANSFORMERS, INC. - APPLICATION PAPERS AND SCHEMATICS


there is also an article here at diyAudio: Audio Component Grounding and Interconnection
Right, so it's more difficult, but possible, but at the same time not important b/c it's likely ok.

At low, DIY volume, say one or two boards for personal use, 4 layer boards are cost prohibitive for a hobbyist such as myself.

I don't see anything wrong with a 2 layer, 2 ground plane approach for diy. No iso. transformers please.
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Old 20th April 2012, 08:15 PM   #6
jcx is offline jcx  United States
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if you don't insist on "professional" look - all signals routed on board, no jumpers, no bus bars, no aux boards then you don't have to go 4-layer if you don't have mixed signal MHz DSP, uC, ADC, DAC on board

imaginative use of jumpers, twisted pair pwr distribution, all Class A, low current circuitry you can do OK on a nominally 2-layer board - too many diyers try to make their board layout look "pro"/mass producable not understanding the effort, compromises that went into those layouts

in fact you can do really well on gnd plane perf board for one-off circuits if you let actual electrical performance demands guide your build instead of tyring for a "pro look"

read everything Jim Williams has written on prototyping, layout - Pease was OK for audio frequency signals

Last edited by jcx; 20th April 2012 at 08:19 PM.
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Old 20th April 2012, 08:37 PM   #7
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Kent English of Passlabs has an article entitled "Ground loops" which helps.
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Old 20th April 2012, 09:10 PM   #8
hags is offline hags  United States
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Quote:
Originally Posted by jcx View Post
if you don't insist on "professional" look - all signals routed on board, no jumpers, no bus bars, no aux boards then you don't have to go 4-layer if you don't have mixed signal MHz DSP, uC, ADC, DAC on board

imaginative use of jumpers, twisted pair pwr distribution, all Class A, low current circuitry you can do OK on a nominally 2-layer board - too many diyers try to make their board layout look "pro"/mass producable not understanding the effort, compromises that went into those layouts

in fact you can do really well on gnd plane perf board for one-off circuits if you let actual electrical performance demands guide your build instead of tyring for a "pro look"

read everything Jim Williams has written on prototyping, layout - Pease was OK for audio frequency signals
I'll have to look up your recommendations.

Ha, no more perf-board please! I've used them for years with great success but have recently started using layout software, Eagle and ExpressPCB. Much nicer IMO.
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Old 21st April 2012, 06:03 PM   #9
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Hey All,

& thanks so much for your replies

I've taken a look at your comments and your links and I can see that there's a bit of reading to do - and things to ponder - so will say thanks for now, and start reading/pondering

'Best for your day (evening it is here in Denmark),

Jesper
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Old 21st April 2012, 08:52 PM   #10
djoffe is offline djoffe  United States
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Doug Self has lots of good things to say about this in his books.

Here's an article I wrote for my web-site:

http://www.updatemydynaco.com/docume...lemsRev1p4.pdf

All the best...

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