Pixie: 40m QRP CW transceiver

pixie_cw_qrp

first post of 2015. it’s a small pocket size 40m CW transceiver that i got off of eBay for a mere $8. i’ve mainly used this while i’m at school to flex my cognitive abilities and decode the communications of extra class morse pros. the transceiver has a tuning range of 7.023-7.026MHz (maybe) which puts it in that tiny 250kHz portion of the 40m band reserved for amateur extras. at 5:30pm PST, it’s virtually an endless cacophony of signals. however, i was able make out a signal 565 miles south this afternoon from KI6JD using only the support railing as an dipole antenna. i don’t think he heard my response, but i would expect that considering my total radiating output is somewhere around 0.25 watts. also, my morse skills are lackluster at the moment, so i might have just sent gibberish out on the air. who knows.

DOD FX55B SupraDistortion – BigBuff Mod

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Here’s another in a line now of DOD pedal mods. For this FX55B, I decided to go for more of a BigMuff sound. Playing around with this pedal initially, I found it to be like most mass-produced distortion/fuzz effects. It had a very thin sound and that notorious volume drop that you may have heard on a high-school band’s first album. The lows were almost non-existent when the effect was engaged. I found the following schematic and, with a few simple changes, came out with a distortion pedal with considerable gain, massive lows, and a smoother, more rounded square wave.

dodfx55b_bigbuff_mod

Overall, the idea here was to get more from the pedal by employing some germanium to smooth out the harshness and to increase the overall output. The output is now considerably higher as long as the tone knob is set closer to 10 o’clock. At noon, the mixing is practically useless. At the 4 o’clock position, you get more of a thin, trash punk type of sound with an excessive noise floor. The sound sample demonstrates the effect with the tone set at about 10:30-11 and first contrasts the distortion setting. The third set shows off the tone below 10 o’clock. The last set shows what the tone does when you sweep through it.

Class AB amplifier test

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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…

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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-2.6.2.1 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

lfo_vcf_rev_aa001

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.