Archive for December, 2007
Sunday, December 30th, 2007
Op-Amps 3: Between the Rails
Op-amp output hits the rails because op-amps are powerful amplifiers with gains in excess of 200,000. With a 9V single-supply, all it takes is an input voltage difference of 9V/200,000 = 45uV to hit the positive rail. Guitar outputs are around one thousand times that magnitude. So how do you keep the output of an op-amp between the rails? You use feedback.
Photo credit: Mike Malak on WikiMedia Commons
Saturday, December 29th, 2007
Input and Output Impedance
You have probably heard or seen it said that high input impedance and low output impedance are desirable properties for a circuit. Or at least something like that. 😉 Maybe it was the other way round, as in low input impedance and high output impedance? I found it hard to remember before I had some grasp on the concepts. This note describes the understanding that I have so far and a practical way to measure impedance. … more …
Tuesday, December 25th, 2007
Op-Amps 2: Hitting the Rails
A first step in understanding op-amps, and amplification generally, is to see that op-amps are like a water faucet that controls the water pressure in a garden hose. In the simplest setups, the faucet alternates between completely closed and wide open. As a result, the output of the op-amp is either the lowest or the highest available voltage, in analogy with no water pressure or maximum water pressure in the hose. … more …
Sunday, December 23rd, 2007
Op-Amps 1: Description
Appearance
Op-amps (operational amplifiers) come in an integrated circuit, or IC. The one pictured on the right is in a form called DIP-8, which is short for dual in-line package with 8 pins. “Dual in-line” refers to two lines of pins, in this case 4 on each side. Each pin has a special function and they are numbered from 1 to 8. Often, there is a circle on the top of the case to show the location of pin 1. Also the case is usually notched at the same end with half-circle cut-out. At least one of these two markings appear, but not necessarily both. … more …
Thursday, December 13th, 2007
Another PVC Amp Stand
I admit it–this isn’t specifically about stompboxes. But people who need stompboxes also need amp stands. 🙂 I needed several and it occurred to me that PVC pipe would be a good building material. Scouting around on the net, I found one example: PVC guitar amplifier stand. This gave me some good ideas but I decided to try something simpler. This figure above shows an exploded view of what I settled on. … more …
Saturday, December 8th, 2007
LTSpice AC Analysis with the BMP Tone Stack
One useful application of SPICE is to see how a tone stack behaves. Looking at tone stacks is so interesting that Duncan Munro (Duncan Amplification) wrote a now famous computer program, the Tone Stack Calculator (TSC), in 1999 that is still in wide use today. You can download the Windows application from the Duncan Amplification site. This tutorial shows how to use LTSpice to make the same calculations as the TSC for the tone stack of the Big Muff Pi (BMP). … more …
Thursday, December 6th, 2007
A View on DIY Stompboxes
Try to give due credit to others wherever and whenever you can. If you offer something to the public domain, then do so without expecting any compensation or credit. Everything that you receive in return is a gift. … more …