As many of you may have read previously in my blog, before Thanksgiving last year I moved to a new city. This meant that the AMZ lab had to be shut down and I have not been able to build a pedal or even turn on my soldering iron since then.

The good news is that the new AMZ lab is under construction and should be finished within two weeks! The recording studio is already complete and I have been working on getting it in operation.

Once the desks, shelves and lab equipment go in, I can get to work on some of the new projects that have been stacking up. The expansion also gives me room to work on video tutorials that are planned, and there will be kits for the AMZ boosters and several projects from the CD, like the SoS and Fuxx Face!

PC boards and transistors are available now, and the kits will be announced in this blog once they are ready. Thanks for your support!

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

Boosters are not buffers! While it is possible to make a booster that also provides a buffering action, the vast majority of the boosters commercially available ready-made or kits, do not have the proper design to be buffers.

Another part of these designs that prevents their use as buffers is that they have a volume control potentiometer on the output. The volume pot impacts the impedance of the circuit. If the volume pot is at the 50% position, represented above by R5 and R6, the output pot is acting as a voltage divider. Here we have the 100k pot in parallel with the output impedance of the LPB1 (10k) that is driving the cable to the amp or next pedal.

The cable capacitance (Cc) even on a good cable can be 800pF, as I measured in a previous test, and is shown on the schematic in light blue. The output impedance of the booster and the resistance of the pot are driving the cable and form a low pass filter with the cable capacitance. In this example, the high frequencies are rolled off starting at around 7.2kHz.  This is obviously not what we want from a buffer!

The same problem caused by the output volume control is present, even with an opamp output, as illustrated by the following schematic:

This is a typical opamp distortion pedal schematic fragment, and the high frequency limit is similar to the transistor booster example (7.5kHz corner frequency). You should note that as the volume is turned up, the frequency limit rises as well, letting more high frequencies through.

The shunt resistance of the pot, shown as R6 on the examples, is in parallel with the input impedance of the next stage. If that stage is a pedal with a high impedance, much of the advantages of the high Z input will be lost since the resistance of the pot is in parallel with the input and effectively reduces the impedance. This will change how a pedal responds or reacts to an input signal, and will vary with the setting of the volume pot.

It is obvious from these examples that an unbuffered volume pot on a pedal circuit output can be a problem, whether on a booster like the LPB or a distortion pedal like the Fuzzface (which has a 500k pot that makes the problem even more noticeable).

The AMZ Mosfet Booster is a good example of a booster design that does not have a volume control on its output, and its fairly low output Z makes it capable of driving cables with little difficulty – the 2.7k output Z will drive the 20 ft. cable in our example to over 73kHz!

Use the AMZ Filter Calculator to check some of the values of pots and cable capacitance. (0.8nF = 800pF = 0.0008uF)

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

http://www.empressplugins.com/

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

The Coyote-1 Open Stomp pedal has arrived! The picture above is my actual unit. I’ll have more to report once I run it through some tests.

The documentation included on the CD that comes with the pedal is quite thorough and also includes a full schematic with datasheets for the major components. A quick look at the schematic reveals it to be a solid design.

Coyote-1 Open Stomp

This is the Multi-Purpose pc board that can be used to build a variety of projects to use as boosters or buffers, including designs for circuits using bipolar silicon, germanium, jfet and mosfet transistors. Each board purchase includes a link to a page of example circuits (with parts lists) that may be used with this board.

Circuits that can be built on this pcb include:

• Silicon Transistor Booster
• AMZ Muffer
• AMZ Muffmaster
• AC128 Germanium Transistor Booster
• PNP Rangemaster-type Treble Booster
• Germanium Transistor Buffer
• Jfet Transistor Booster
• Jfet Transistor Buffer/Line Driver
• Mosfet Transistor Booster (not the AMZ Mosfet Booster)
• Mosfet Buffer
• Power Supply Filter
• and MORE!

Read more about this versatile circuit.

The OpenStomp™ Coyote-1 is an open source audio effects processor built for guitar players. With the Coyote-1 users can develop custom audio effects in software (like distortion, echo, chorus etc.), mix multiple effects to build “patches”, and exchange those effects and patches with the OpenStomp™ community.

Technical Specifications:
- Propeller Processor (eight independent 80MHz cores or “cogs”)
- 1MByte SRAM
- 44kHz 24-bit sampling (2 input channels and 2 output channels)
- 4 control knobs
- 16×2 LCD screen
- 2 stomp switches
- 2 stomp indicator LEDs
- 1 1/4 inch audio input
- 1 1/4 inch audio output
- 1 multipurpose 1/4 inch audio jack (can be used as either a second output (for stereo effects) or as an additional input (for modulation effects etc.))
- NTSC Video out
- Micro USB
- 9V DC Power in
- Headphone out (mini phono jack)
- RJ45 expansion port (for potentially adding things like external foot pedals)
- Steel chassis

Coming soon at OpenStomp.com

Just for fun, there is a page at HCFX with cartoon images of pedals that can be used to make a graphic representation of your pedalboard. Plenty of excellent user-submitted images are free for downloading. Make your own pedalboard graphic:

Cartoon Your Pedalboard

I got a mention again this month in Premiere Guitar

So, I’ve moved my large collection of books on effects pedals, amps and guitars to a new section.  Take a minute and have a look around in it:

AMZ Online Store

Bob Sweet, maker of the Mojo Vibe, Ultra Vibe and other excellent pedals, has been diagnosed with cancer. He has a tumor that is malignant and will need to be removed and treated with chemotherapy, and radiation. Bob does not have medical insurance and the treatments that he requires will be very expensive and have already taxed Bob and his wife financially.

I ask that you donate what you can to help our friend, so please send a Paypal contribution to his email address at b0bsweet@bellsouth.net. Every little bit helps with Bob’s medical bills as he continues his treatments.

I am sure that many of us have had family members and friends that have battled this disease.

Musictoyz has established a Bob Sweet Charity page for information and updates.

My contribution has been sent. Please help if you can. Many thanks in advance!