[2599] Bodge wire

Date: August 1st, 2019 | Comments : [2] | Categories: DIY.

It looks like the pcb on this Daphon E20CM compressor was supposed to have a square cutout in the top left corner to match the one on the right side, in order to fit around the mounting post. When cutting the pcb, the board fractured and chipped off a small piece including a portion of a copper trace. Instead of trashing the damaged board, they added a bodge wire to replace the missing trace.


[2596] Mini Boards

Date: July 28th, 2019 | Comments : [1] | Categories: DIY.

I ordered a selection of prototype mini-boards from Oshpark, including tiny boosters, fuzz, and more.


[2594] Compressor Testing

Date: July 26th, 2019 | Comments : none | Categories: DIY.

I asked the manufacturer of my audio analyzer instrument to modify one of their plugins to be able to measure compression. They did so, and it works really great, so I am planning on doing some tests on various guitar compressors.

In my first trial run of the compressor test setup, I learned 3 things:

  1. My Empress Compressor seems to be broken;
  2. The LM3080 based compressor is not as noisy as I anticipated;
  3. Opto-coupler compressors do not react linearly.

I’ll have an article about the compression results in the near future.


[2583] Power Jack Ratings

Date: June 21st, 2019 | Comments : [4] | Categories: DIY.

Did you know that DC power jacks have a voltage and current rating, and they may not be as high as you would think?



[2579] Pickup Simulation

Date: May 16th, 2019 | Comments : none | Categories: DIY.

A popular article on my web site is the one about pickup simulation, and questions come up several times every year about the transformers recommended for this project. One technique that works well is to get a cheap guitar pickup and use it as the input inductor.

The black wire of the pickup goes to the input jack while the red wire connects to the input of the electronic circuit. If there is also a braided shield, it can be connected to ground. The 10k trimmer and the 330pF capacitor are simulating the cable connecting the guitar to the pedal.

Cheap pickups are readily available for $5 or $6 on Ebay, or from US suppliers of parts for cigar box guitars (cbg). The 3-pole pickups for the cbg projects will be physically smaller and there are even versions with a metal shield over the coil.

The pickup has the electrical characteristics of a guitar pickup (because it is one), and in this circuit it works quite well to modify the tone and response of a fuzz circuit or other project.


[2566] Inside Ge Transistors

Date: May 10th, 2019 | Comments : [1] | Categories: DIY.



[2562] Power Testing

Date: May 8th, 2019 | Comments : none | Categories: DIY.

This is a small test board that I made for my own use. It goes between a power source and a pedal being tested. The objective is to provide access to the voltage source terminals. A battery or unregulated power supply will often have voltage sag when loaded, so this lets me measure the actual voltage with the pedal connected without having to remove the back of the box.

The power jack was mounted on the back of the pcb to make sure that it is out of the way of the probes, but now that I have assembled it, that placement seems unnecessary.

There is not only easy access to the actual voltage being used, but also the yellow jumper block can be removed and a meter placed across the two pins so that a measurement of the current draw can be easily made.


[2551] Closeup of LEDs

Date: April 29th, 2019 | Comments : [1] | Categories: DIY.

This is a rectangular LED shot with a closeup lens. The plastic housing is so clear that the internal parts of the diode are easily visible.


[2546] Tube-like Harmonics

Date: April 9th, 2019 | Comments : none | Categories: DIY.

This graph illustrates why the Mini-Booster has a tube-like sound. The second harmonic (2HL) is much larger than the third (3HL). In fact, the total harmonic distortion (THD) is almost all second with only small amounts of third at lower levels. Only when the pedal begins to clip at higher input signals does the third harmonic begin to rise.

Mini-Booster pc boards and pre-assembled modules are available on the AMZ order page.


[2538] Changing Diode Vf

Date: March 15th, 2019 | Comments : [1] | Categories: DIY.

The forward voltage of a diode is not fixed, and this is easily seen on the datasheet for the 1N4148, for example. At 200ma, the 1N4148 diode Vf is over 1v but if the current is only 1ma then the Vf is less than 0.625v. As the current goes lower, so does the diode’s Vf.

This circuit will vary the peak clipping of the diodes, but only over a modest range. Also, the opamp driving it must be capable of sourcing enough current to make a difference, and you have to be careful that the power rating of the 47 ohm resistor is not exceeded.

The circuit is of limited practical use, but there it is for your experimentation anyway!



AMZ Home Page

Guitar FX PCBs