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Electronics

Component level · Audio · Signal

Industrial work stops at the terminal block. Electronics is what happens on the other side of it — and for twelve years it wasn't a sideline, it was a second trade with customers waiting on it.

A second trade
2005 – 2017

Self-employed guitar and amp technician, running alongside the automation work and straight through the years I was home with the twins. Setups and fret leveling, custom guitar electronics, tube and solid-state amplifier repair, effects design and modification. Twelve years of other people's equipment on my bench, which is a very different education from twelve years of my own.

Why this page exists

Automation lets you get a very long way treating components as boxes with datasheets. Put 24V here, get a contact there. That works, and for a lot of the job it's the correct level of abstraction.

But the intuition for why a signal is noisy, why a ground loop hums, why a long motor cable does something unpleasant to a drive — that doesn't come from panel work. It comes from building circuits small enough to hold in your head, getting them wrong, and chasing the fault down to a component.

So: guitar amplifiers, attenuators, MIDI interfaces, cab simulators. Audio is a beautifully unforgiving test bench, because the failure mode is something you can hear rather than a number that's slightly off.

SENSOR SIGNALCONDITION CONTROLLERscan · decide DRIVER ACTUATOR feedback — the half everybody forgets until it oscillates
Component-level layout. Same instincts as a panel, three orders of magnitude smaller and far less forgiving of a lazy ground.
01Component-level layout. Same instincts as a panel, three orders of magnitude smaller and far less forgiving of a lazy ground.
Where the two disciplines meet — a drive is a power electronics problem wearing an industrial enclosure.
02Where the two disciplines meet — a drive is a power electronics problem wearing an industrial enclosure.
Build — distortion pedal

A dirt pedal is a near-perfect teaching circuit. Small enough to hold entirely in your head, cheap enough that killing one costs an afternoon, and the output is a sound — so you find out immediately and unambiguously whether you were right.

Perfboard, top down. Point-to-point on a grid — no PCB, nowhere to hide a bad joint.
03Perfboard, top down. Point-to-point on a grid — no PCB, nowhere to hide a bad joint.
Under construction. Pots landed, chassis strip alongside for the jacks.
04Under construction. Pots landed, chassis strip alongside for the jacks.
Chassis drilled, jacks mounted. The metalwork decides whether the finished thing looks built or looks bodged.
05Chassis drilled, jacks mounted. The metalwork decides whether the finished thing looks built or looks bodged.
On the bench next to a factory pedal. Having a known-good reference in reach settles arguments the meter can't.
06On the bench next to a factory pedal. Having a known-good reference in reach settles arguments the meter can't.
The schematic it was built from. Everything above is this, made of metal.
07The schematic it was built from. Everything above is this, made of metal.
Build — MIDI controller

The MIDI controller was the crossover project — analog front end, microcontroller in the middle, a protocol at the end. Rotary pots reading into a micro, an LCD for state, and a panel that a human has to actually use.

Which is where it stops being a hobby circuit and starts being the same problem as an HMI: somebody has to reach for the right knob without looking.

Microcontroller, LCD and perfboard mid-development. Breadboard wire everywhere, which is the correct amount.
08Microcontroller, LCD and perfboard mid-development. Breadboard wire everywhere, which is the correct amount.
Bench state — meter in one hand, half the harness in the other.
09Bench state — meter in one hand, half the harness in the other.
Panel with the pots mounted. From here on it's an interface design problem wearing a soldering iron.
10Panel with the pots mounted. From here on it's an interface design problem wearing a soldering iron.
On the bench

Ninety seconds of the actual loop. A circuit on perfboard with test leads into it, wired through to the amp, and then the rig running — because the whole reason audio is a good teacher is that the result arrives through your ears before any meter tells you anything.

11Bench test. Perfboard and test leads on the left, the chassis it feeds, and a Mesa head and cab doing the reporting. Shot on a camera that thought 640×480 was generous.
Where it came from
<em>Electronic Projects for Musicians.</em> A lot of this page traces back to that cover.
12Electronic Projects for Musicians. A lot of this page traces back to that cover.
The wheel. Power, volts, amps, ohms — four quantities, twelve ways to get from any two to any other. Everything else on this page is elaboration.
13The wheel. Power, volts, amps, ohms — four quantities, twelve ways to get from any two to any other. Everything else on this page is elaboration.
Where it happens
The bench. Amps, monitors, keyboard, and a computer doing three jobs badly.
14The bench. Amps, monitors, keyboard, and a computer doing three jobs badly.
The reason any of this exists. Every circuit on this page was ultimately in service of something plugged into it.
15The reason any of this exists. Every circuit on this page was ultimately in service of something plugged into it.
Body and neck, pre-assembly. Building the instrument and building what it plugs into are the same hobby wearing different hats.
16Body and neck, pre-assembly. Building the instrument and building what it plugs into are the same hobby wearing different hats.
On paper first
Schematic capture. Stages laid out left to right, which is the only arrangement that stays readable once there are enough of them.
17Schematic capture. Stages laid out left to right, which is the only arrangement that stays readable once there are enough of them.
A simpler signal path. Small enough to hold entirely in your head, which is the point of working at this scale.
18A simpler signal path. Small enough to hold entirely in your head, which is the point of working at this scale.
The MIDI controller, on paper
What the bench photos above actually are. 8051-family MCU, I²C EEPROM for patch storage, regulated supply, LCD and the header breakouts that became those rows of pots — with analog and digital grounds run as separate nets and tied at one point.
19What the bench photos above actually are. 8051-family MCU, I²C EEPROM for patch storage, regulated supply, LCD and the header breakouts that became those rows of pots — with analog and digital grounds run as separate nets and tied at one point.

That single-point ground tie is the whole grounding note below, drawn. Two ground nets, kept apart everywhere they could pick up each other's noise, joined at exactly one place so there is no loop for anything to circulate around. Get it wrong and the symptom is a hum you will chase through the analog section for a week.

What crosses over

Grounding is a topology, not a wire

The single most transferable lesson. A ground is a network with impedance and opinions, not a place where electricity goes to be forgiven.

Everything is a filter

Cable capacitance, input impedance, an unintended RC you didn't draw. Once you see it in audio you can't unsee it in a plant.

Measure, don't infer

A scope on the actual pin has ended more arguments than any amount of reasoning from the schematic — including my own reasoning, repeatedly.

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