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

As human beings we're quite familiar with the idea of things wearing out with use. If you hang a piece of clothing up in a closet and seldom wear it, then unless something happens like moths eating it, you can take it out years later and it'll still be good - whereas if you're wearing it every single day and washing it frequently, it may show visible damage and no longer be as good after just a few weeks. Many things in our world are like that, and we naturally expect electronic equipment to be included. Many synth users have, consciously or unconsciously, the idea that for each module there's an hour meter ticking away somewhere, like a car's odometer, measuring the time until the module will die or need servicing, in terms of the number of hours power is applied. READ MORE

There's a lot of confusion and worry over the idea that modules wear out or age over time, and what can be done to prevent or deal with that process. It's a part of human life that many things including our own bodies do change with use and time; and if you've spent a lot of money on musical instruments, then it's reasonable you might be worried about wearing them out or hurting them. Electronic equipment and the physics behind it are mysterious to many people. We know that invisible things like "voltage" can possibly damage electronics; it's not obvious what those invisible things are, or where they come from or how to protect the equipment; we have some idea that things in general can wear out, but may be unsure of exactly how that applies to electronics; and so modular users, and especially beginners, end up with a lot of confusion, worry, and misconceptions about wear and aging of equipment. 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

If you plug a patch cable into an input jack on a module, the module receives the signal from that cable. What if you don't plug a cable into the input - what will the module do? Let's look into that in detail. READ MORE

Here's a little project I put together to solve a specific problem: checking power cables for shorts. I made it using the parts I had on hand, and if you build one yourself you may well end up wanting to make changes, so I'm not going to prepare a complete set of documentation or sell kits or anything. I don't think it's going to be popular enough for selling them to be profitable. But if, like me, you're in a position of needing to check a lot of power cables, you might find these notes useful in designing your own tester. READ MORE

There are a lot of counterfeit electronic parts in circulation. It's especially a problem with parts that are obsolete, hard to find, or expensive; sold privately in places like eBay or AliExpress at unusually low prices; and shipped from the People's Republic of China. However, just this week I had to deal with a batch of fake TL074 op amps from a well-known US distributor. Here are some notes that might help others avoid, or at least debug, similar problems. 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

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