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Oscillation in effect loop
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Old 7th November 2019, 05:09 PM   #21
razorrick1293 is offline razorrick1293  United Kingdom
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Ok, any pointers on good layout/wiring?
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Old 7th November 2019, 10:55 PM   #22
Gnobuddy is online now Gnobuddy  Canada
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Good layout is too big a topic to cover easily, and it's a bit of a "soft" skill, half art, half science. But here's a little write-up to get you started: How to Layout and Build a Guitar Amplifier Chassis - GuitarKitBuilder

That write-up is very incomplete - it only really talks about physical placement of the main components. It doesn't address wiring at all, and the wiring layout can make or break the build.

I'll see if I can find a good wiring layout write-up somewhere (there must be some!), but in the meantime, some general guidelines off the top of my head:

1) Keep wires as short as possible, within reason (i.e. don't fight to shave a millimetre off the length, but shave off an inch whenever you can.)

2) Don't run signal wires side-by-side and close together.

3) When possible, cross signal wires at right angles or nearly so.

4) Keep wires carrying low-level signals far away from wires carrying large signal voltages.

5) Keep output wires as far from input wires as possible - at every gain stage, as well as over the entire amplifier.

6) Route wires flat against the grounded metal chassis when possible; this reduces hum and noise pickup.

7) Use shielded cable (coaxial cable) for sensitive wiring carrying small signal voltages.

8) Distance is your friend in many cases - space wires further apart, keep outputs well separated from inputs, position gain stages a few inches apart. (Yes, this appears to contradict item #1, and you have to figure out a reasonable compromise.)

9) Grounding within the amp is critical. This is a whole topic by itself; the chapter on grounding schemes in Merlin Blencowe's Tube Preamp book is well worth reading.


-Gnobuddy
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Old 12th November 2019, 03:12 AM   #23
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by Gnobuddy View Post
Good layout is too big a topic to cover easily, and it's a bit of a "soft" skill, half art, half science.
The best advice I ever heard (I think first phrased this way by Lynn Olson) was
"think in loops"

Current flows in loops; voltage adds up to zero around loops and magnetic coupling happens in loops. A twisted pair is an anti-loop.

Capacitive coupling does take a little more visualisation but it's still in a loop. Shielding trys to block or cut loops. Static is probably the odd man out here but that's usually only a problem during construction

Last edited by thoglette; 12th November 2019 at 03:14 AM.
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