Soldering mistakes are by far the most common thing to go wrong in do-it-yourself electronics. It seems like I spend most of my tech-support time gently urging customers with failed kit builds to re-check their soldering, and when I have problems in my own builds, those also usually turn out to be soldering-related. Everybody, myself included, tends to think of failed components as a likely cause of problems, and we spend a lot of time doing differential diagnosis to figure out which components might have failed; but then once the problem is narrowed down to a single component, the actual issue usually turns out to be a bad solder joint on that component, not the component itself. The real point of the debugging is often just to figure out which solder joints to look at more closely. READ MORE

Operational amplifiers ("op amps") are popular analog building blocks, especially in synthesizer electronics, because it's easy to analyse what they do to voltages. The first rule of op amp analysis is that (in negative feedback configurations, and when this is possible) the amplifier moves its output voltage in order to make its input voltages equal. That is useful in building circuits to manipulate DC voltages. READ MORE

There are some special considerations relevant to electrolytic capacitors in AC coupling applications, and that's the topic of this second part of the series on AC and DC coupling. Low impedances and low cutoff frequencies require high capacitance values, and electrolytic capacitors may be the only practical way, or at least a very appealing way, to achieve those values. READ MORE

I overheard somebody asking about the plusses and minuses of DC coupling, and AC coupling capacitors, and being told to read the detailed explanation of such things I'd written on this Web site. I was flattered to think the speaker found my article helpful, especially because I'd never actually written one about that! READ MORE

There's a lot of confusion in the modular synth world about signal levels. We often don't have a clear idea of what can plug into what, even within the modular rack; let alone when it comes to interfacing with other equipment. I've been working on guitar pedal designs recently and connections between those and modular often raise level-conversion issues. A whole lot of unnecessary "external input" and "external output" modules are sold to newbie wigglers who've been told that modular and other-equipment levels are fundamentally different and need to be converted - but although usually unnecessary in most modular racks, such modules do also serve useful purposes in certain contexts. What is really going on with signal levels? In this article I'll go through some of the concepts used for describing signal levels accurately, then talk about some of the levels commonly seen in audio work. READ MORE

Thinking in terms of equivalent circuits is one of the basic mental skills needed for understanding electronics. I use the concept of an equivalent circuit implicitly in a lot of my writing about other things, but it's probably worth stepping back and learning about equivalent circuits in themselves. READ MORE

Electronic design is sometimes imagined to begin and end with the schematic. Whoever drew the schematic gets the "designer" credit; hobbyists search the Web for "free schematics" and just assume they will encounter no issues getting from there to a working build; and technical documentation for modules (including my own) focuses on displaying and explaining a clear schematic rather than giving much or any coverage to the PCB design. READ MORE

So, you want a simple digital logic function in a synthesizer. Maybe it's an AND gate, or a couple of XORs, maybe as much as a shift register. How will you build it? READ MORE

There are a lot of bad synthesizer schematics on the Web, and it doesn't hurt their popularity. As a designer who tries to get everything right, it's somewhat disheartening to see designs with obvious, simple flaws get built commercially and cited as positive examples - and it's even worse when someone has trouble with one of my modules because they tried to connect it to the latest popular whiz-bang box which has bad levels or whatever and does not play nicely with others. In this article I'm going to talk about some of the problems I see time and time again both in free schematics published for DIY hobbyists, and in commercial modules. READ MORE

In the last several weeks I've been working on development for my next product, which I'm ready to announce will be called the MSK 013 Middle Path VCO. It's planned to be a "complex" VCO design with two independent triangle cores that can be synced, and a special waveshaping section based on the Barrie Gilbert sine shaper modified to produce quadrature output; that makes it capable of some through-zero phase modulation effects even though the cores themselves are not through-zero. I've been posting pictures from my development process in other places, and this posting gathers some of those together. READ MORE

Alternate title: "This Dad put -10V into a TL074 and here's what happened to his liver!" READ MORE

Q: The analog synth circuit I'm building calls in the schematic for ferrite beads on the power rails, but it doesn't give any further information. What kind of beads should I use? READ MORE

Testing and adjustment are often underestimated in DIY circuit design. It's all very well to choose exactly the right topology and component values for a circuit; but even with a perfect design on paper or in the simulator, how does one get from there to a physical construction that correctly realizes that design? READ MORE

When I draw the first draft of a new circuit design, I'll usually work out the topology of the circuit first, and leave out any component values unless it's instantly obvious what they need to be. The topology means which components exist and how they connect to each other, and it's a separate step from deciding their values. I'll come back and fill in the missing values later. There's interaction between these two steps, and I may well modify the topology in later drafts of the schematic as the requirements become clearer, but there's still a definite progression from working on the topology to specifying the component values. READ MORE

In the last entry I described the electrical requirements of LEDs and how to drive them in the context of analog circuitry. When you want to indicate information with the brightness level of a single LED, as in my Transistor ADSR where the LED directly shows the progress of the envelope, it's appropriate to use an analog driver which provides current proportional to the desired light output. But another common use of LEDs is many of them at once, to display information like the shift direction in an octave switch, or even numeric digits in a 7-segment display. For those kinds of applications, it's appropriate to use a digital style of driver circuit. READ MORE