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.
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.
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.
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When I was unloading some boxes that were in my garage after moving, I discovered this unit.
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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.
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
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.
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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!
If you are looking for a guitar signal booster that is not entirely clean and can add some grit to the sound, then you should consider the new Dirty Boost, which can be built on the AMZ Multi-Purpose pcb.
The circuit adds low level harmonics (predominantly even) to the boosted guitar signal. If you drive the booster hard enough, it will produce a mild overdrive effect with a range of harmonics.
Anyone who has already purchased the Multi-Purpose pcb can review the instructions page for the latest update with this new circuit.
