Category Archives: notes

Class AB amplifier test


this was an attempt at designing a simple transformer-less class AB amplifier using two BJT power transistors. i setup the USB fan to protect against thermal runaway and cool off the transistors during operation. it took me looking over several schematics to realize that the the emitters of both the PNP and NPN transistors were tied together. the collector of the PNP (TIP32C) is grounded which is obvious! the synapses just weren’t seeing the PNP symbol as upside down. it’s definitely something i’ll have to work on. i’d like at some point to have a nice 40W amp based on a similar configuration.

initial PCB milling test…


here’s an initial PCB test for the Triode tube overdrive on the SMBA site. this picture is pre-sanding. it was milled using LinuxCNC on a Xubuntu 14.04 LTS running the Xenomai- kernel version 3.5.7. it’s taken some time to get the configuration working and compiled since i didn’t want to use the live CD. the CNC machine is a Chinese 3020T that i got off eBay. the board layout was done in EagleCAD using the PCB-GCODE ULP script.

pcb milling test from abram on Vimeo.

LFO modulated simple VCF


this is a rough draft of a circuit i’ve been working on based of the Simple VCF circuit floating out there. a big thanks to the original author for that. i’m sure there are some mistakes in here. it’s an odd one for sure, but it works on the breadboard. the opamp is a TL072. square-wave input from the generator comes out pretty sine-wave like which is what is desired. the output is a little noisy, but i will work that out with time.

DOD FX69B Grunge insanity mod…


this “insanity” mod makes this pedal sound much more insane that the original version. i dropped in a couple of germanium clipping diodes between gain stages for a warmer, beefier tone and decided to mess with the active filters that control the two-band EQ. the filters now allow each band to be driven into cutoff to make more PWM type wave forms when in the lower positions. if the player doesn’t want 8-bit computer sounds, he or she can bring the filters up to the horizon level (about 90 degrees on the left side of the straight up postition) to acheive cutoff when no signal is present from the instrument. i also maxed out the gain for a ferociously loud effect. the “loud” knob under the halfway mark about 7dB over the clean signal. both audio samples are recorded direct with no effects whatsoever.

original sound:

modded sound(s):

this item is for sale on eBay.