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PCB layout guidelines for audio
#1
Hi Guys

There are a few basic guidelines for laying out audio circuits on PCBs (printed circuit boards):

SAVE a lot - every few operations press SAVE so you do not lose hours of work if the program crashes.

NEVER use the AUTO-ROUTER. The auto-routing function is "a big deal" according to the designers of PCB CAD software, but it is entirely useless when laying out audio circuits as it will destroy the proper order of grounding. Galactic Grounding can be applied to PCBs as well as to hand-wired circuits, and is key to achieving a low-noise assembly. Just as with hand-wiring, the ground and power paths on a PCB must be made manually, or "forced" to go where we want them to. It is often easiest to NOT use the GND symbol to achieve this.

Lay out the schematic with normal orientations for the parts, circuits and symbols:
Positive voltage up
Negative voltages down
Ground symbols (if used) pointing down
Signal coming IN from left
NPN transistors with E pointing down*
N-mosfet with S pointing down*
N-jfet with S down*
PNP transistors with E pointing up*
P-mosfet with S pointing up*
P-jfet with S up*
*sometimes these must be rotated horizontal

Keep the signal path as straight as possible inasmuch as signal flow moves from left to right on both the schematic and the board.

Use proper voltage spacing especially for tube circuits. There are conservative and aggressive guides for this and it is better to err on the side of conservative. a good guideline is:
0.00012 x V
V=volts
measurement is in inches
solder mask applied
0.001" = 1-mil (milli-inch). The above equation can be done in mils as 0.12 x V = mils. It is easier to refer to a trace width or space as 16-mil, 40-mil, etc.
Without a solder mask (which is pretty unusual today) the equation becomes V / 0.001
When checking the board, turn on the GRID and set it to a small increment and count the divisions between traces, then divide by 0.12 for a spacing in V. For example, a spacing of 40-mil provides 40 / 0.12 = 333V. If you know the voltage spacing you need, multiply V x 0.12 for mils. For example, 500V needs 500 x 0.12 = 60-mils.

Use appropriate track WIDTH. You can select the track WIDTH on the fly, before you lay the trace, or change it afterwards. Track WIDTH determines current capacity and it is surprising how much current a narrow trace will handle.

More to follow.
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Messages In This Thread
PCB layout guidelines for audio - by K O'Connor - 09-13-2018, 11:36 AM
RE: PCB layout guidelines for audio - by jmcd - 09-13-2018, 05:17 PM
RE: PCB layout guidelines for audio - by jmcd - 09-30-2018, 11:16 PM
RE: PCB layout guidelines for audio - by jmcd - 07-16-2020, 01:43 PM
RE: PCB layout guidelines for audio - by jmcd - 07-17-2020, 02:30 PM

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