North Coast News

Logic, before ICs
2020 Jun 19th

Logic, before ICs

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? Today it often makes sense to just throw in a microcontroller chip. They're…

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Design mistakes in synth schematics
2020 Feb 28th

Design mistakes in synth schematics

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 cite…

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What's the deal with phase reversal?
2019 Nov 18th

What's the deal with phase reversal?

Alternate title: "This Dad put -10V into a TL074 and here's what happened to his liver!" Most everybody knows that it's a bad idea to bring the inputs of the common TL074 op amp to a voltage more negative than about 4V above the negative power…

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The Truth About Ferrite Beads Will Shock You
2019 Sep 22nd

The Truth About Ferrite Beads Will Shock You

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? A: Pick some that will look nice on the board, maybe in a colo…

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Designing for adjustment
2019 Sep 15th

Designing for adjustment

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 t…

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How to choose component values
2019 Jul 28th

How to choose component values

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 a…

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Driving LEDs digitally
2019 Apr 15th

Driving LEDs digitally

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 dir…

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LEDs and analog drivers for them
2019 Apr 8th

LEDs and analog drivers for them

Light-emitting diodes! They're all over our electronic equipment; but what are they all about, really? The underlying concepts are simple, but there are a lot of frequently-asked questions that show there's confusion among hobbyists about how LE…

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Building a telephone ring booster
2019 Mar 22nd

Building a telephone ring booster

I recently switched to a new cable Internet modem, because the cable company (which provides my home Internet service) assured me that the package that came with the new modem would be cheaper for the same service compared to what I'd been paying…

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Exponential converters and how they work
2018 Oct 12th

Exponential converters and how they work

Exponential converters are basic building blocks used in many synth circuits, but for many of us, they are incomprehensible black boxes.  The basic concept of how an exponential converter works is very simple; but the simplest possible circuit f…

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Level up on circuit simplification
2018 Sep 22nd

Level up on circuit simplification

In my last entry I talked about the rules for simplifying series and parallel circuits. Two resistors in series can be replaced by one with a value equivalent to the pair of them; two in parallel can similarly be replaced; there are other rules in…

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