AMZ-FX Guitar Effects Blog

Musical Instrument Recalls

admin — Thu, 18 Feb 2010 17:19:56 +0000

I was scanning consumer product recalls for my day job when I noticed several musical instrument related recalls in the listings. There were more – audio amplifiers and such – and I’ve only linked a few here that caught my eye that are instrument related.

Ibanez Bass recall

Casio® Inc. Announces Recall of Electronic Keyboards

Bass Amplifiers Recalled by Fender Musical Instruments

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.

Super Buffer Update

admin — Sun, 14 Feb 2010 10:25:08 +0000

The AMZ Super Buffer was never meant to be used with a footswitch, but was intended as a line driver that was always left on and therefore did not need the pulldown resistor on the output. The R7 output pulldown resistor was left off the original pcb layout but it has been requested numerous times, so I finally got around to revising the layout to provide a place for it on the etched board.

The links in the article now have the revised artwork. The old pcb etch and parts placement are still available for those who need them.

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.

LED Resistor Calculator

admin — Thu, 17 Dec 2009 00:34:06 +0000

I have revised the page with the LED resistor calculator by adding a chart below the calculator with forward voltage measurements of selected LEDs. You will see on the chart that the red, green and yellow voltage drops are all similar while the other LEDs have a higher Vf.

I was surprised that the pink’s voltage was so high as I thought it was a modified red, but it turns out that it is apparently more closely related to the blue and white devices.

The UV is also a modified blue, as would be expected. I did not have an infrared pair to test but if I find some I will add them to the chart.

Update: I have modified the calculator so that it is more versatile. Enter the current at which the LED is to operate and the calculator will find the resistor value. Alternately, you can leave the LED current field empty and the calculator will report the milliamps being used by the LED. The Voltage Supply and LED forward voltage values must always be entered into the form.

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.

Revised Filter Calculator

admin — Fri, 04 Dec 2009 19:51:06 +0000

I have revised the R-C filter calculator in the Lab Notebook so that it can work out the value of any of the 3 parameters if you input the other two. For example, enter the resistor and capacitor values and it will tell you the cutoff frequency, or put in the resistor value and the frequency that you want, and it will calculate what capacitor to use.

This is a high pass filter and you will probably recognize it as being similar to the input of the mini-booster or a jfet amplifier. Frequencies below the cutoff are rejected and those hgher will be passed on to the circuit. If you input the values from the mini-booster, 1000000 ohms and 0.05uF, the calculator will tell you the lowest frequency that can get through.

Try the values from the AMZ Mosfet Boost to see its low end response.

The low pass filter rejects frequencies above the cutoff corner and passes those below. An example of this type of filter in a guitar pedal is the R-C combination that follows the clipping stage of the Tube Screamer. The values of 1000 ohms and 0.22uF will tell you the highest frequency that is passed unattenuated, and might surprise you.

The low pass removes high frequencies that can contribute harshness to the sound. Try the values from the Proco Rat tone control in the calculator to find out its range.

Remember that one of the data fields in the calculator must be empty. Use the “Clear Form” button to start a fresh calculation, or erase one field manually before recalculating.

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.

Son of Screamer

admin — Tue, 01 Dec 2009 00:20:00 +0000

When I was unloading some boxes that were in my garage after moving, I discovered this unit.

It is the prototype of the Son of Screamer overdrive that is featured on the AMZ CD. It was not originally mounted in this enclosure but instead was on a rack panel with the Fuxx Face. I removed the pcb from the panel and put it in this box so that I could test different mods for the circuit.

As I remembered, the chip is an RC4559 which worked quite well. The pcb is not exactly the same as on the cd so I must have refined the layout after I made this prototype.

My initial plans were to reuse this prototype box, with its power jacks, input/output jacks and mounted pots as a base unit to test other designs that I was developing. Obviously that never came to pass and the SoS was left in place.

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.

Transistor Applications

admin — Mon, 30 Nov 2009 14:08:47 +0000

Here are links to some old transistor application notes that I ran across recently. There should be some interesting reading in these publications for everyone involved with DIY electronics. Thanks to Brian Page, the original scanner of these items, for making them available.

28 Uses for Junction Transistors

Raytheon Transistor Applications, More than 50 Practical Circuits using Raytheon CK722 Transistors

Raytheon Transistor Applications Volume II

Point-Contact and Junction Transistors

Tunnel Diodes

Crystal Diode Circuit Kinks: More New Uses for Germanium Diodes

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.

Direct Box PCB

admin — Fri, 23 Oct 2009 01:06:28 +0000

This is a pair of completed pc boards (opamp multi-purpose) that are configured for use as direct boxes. The sockets are empty as I have not yet decided what opamp chip to use. I may experiment with several different parts before putting the boxes into regular use in the studio.

If you have purchased the Opamp Multi-Purpose pcb, you should check the construction page again since I have changed a few values on some of the projects. The link was emailed to you after you bought the board.

Voltage Doubler

admin — Mon, 19 Oct 2009 04:23:48 +0000

This is the assembled V-Dub pc board with all parts in place. A quick test revealed it was providing 16.7 volts at 8.7 milliamps. There is always some loss because of the series diodes, so the voltage cannot quite reach 18v.

A test of the negative voltage output gave -9.0v when driving an LED with about 5ma. There is no diode drop on the negative output so it gives the full voltage.

More info

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.

Stabilized Thermionic Amplifier

admin — Fri, 16 Oct 2009 07:04:31 +0000

This is one of the designs in a vacuum tube amplifier patent filed in 1949. The first gain stage (V1 & V2) forms a type of mu-follower.

You can download and read the entire patent to find out more about this circuit.

The circuit can be converted to work with jfets, as shown here. Use 1M for R1 and R3, 1k for R2 and a 5k trimpot for R4.

The trimmer should be adjusted until the dc voltage at the source connection of Q2 is 5.0v (+/-0.5v). Start with it set for about 1k between the wiper and Q2’s source.

The circuit has a lot of gain, so it may not be a totally clean boost, as it can run out of headroom rapidly when powered by a 9v battery. If you try this design, let me know your results.

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.

CFL bulbs

admin — Fri, 16 Oct 2009 01:44:16 +0000

You may remember my previous article about salvaging parts from compact fluorescent bulbs that no longer function. Today a bulb blew out in my office so naturally I pulled it apart to see what was inside. The parts in this lamp base appear to be better quality than in the previous units that I disassembled.

I’m sure I can find a use for some of these components. Salvage those parts and recycle!

Copr. 2008 by Jack Orman Visit my site to learn more about guitar effects, download free projects or buy pc boards and germanium transistors.