Having finished my master’s degree over a year ago now, I’ve started to see my thesis show up on various academic web sites. I decided I should probably link it on this site in the event that anyone is interested in building and/or designing their own QRP mono-band radio. Additionally, I’ve been doing some more experiments with QRP setups and like using this rig as a qualification vehicle. Being a mono-bander with a very narrow receive bandwidth, I just find it more sensitive to picking up weak signals, and it’s very easy to listen to when operating in less noisy environments. I’ve done a lot of comparisons with the KX3 (thanks to KK7B), and sometimes it’s just easier to copy signals closer to the noise floor on the DCT.
With that being said, any later posts that utilize this transceiver will point back here for reference. A full text PDF of the design is listed here:
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.
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.
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.
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-126.96.36.199 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.
an experimental EQ circuit based of the TL082 datasheet. i modified it to use a 9V battery, but could probably still use some work in terms of efficiency… as most things. nothing is ever finished really. the mid portion has a pretty high quiescence. fine tuning, of course, can be done with the resistor values and more dramatic differences by adjusting the cap values. if you happen to build it, shoot me an email and let me know what you changed or decided to change.
also keep in mind that the TL082 is a little noisy, so 6dB of highs will add in some noise. i kind of like it myself, but the TL072 is a better choice from what i understand.
i’ve been experimenting with this PT2399 chip and using various schematics to create a digital delay circuit. the delay time seems to be directly attached to the sample rate since lengthening the delay time gives a nice decrease in pitch. i’m toying with the idea of dropping a time constant in around the controlling delay time circuit to see about achieving a “tape warble” sort of effect. we’ll see what works.
here’s the schematic i’ve been working with though the values i’m using are hardly similar.
here’s a small battery-powered guitar amp that i’ve constructed from reused parts. the housing is a busted computer power supply (some of which is in the No. 5) as well. i’ve got several options for this little fellow in mind, but, for now, it’s a tiny amp with a mean distortion. lo-fi enthusiasts should contact me if you’d like one custom built.
This little guy is currently on eBay. I always thought that this tremolo wasn’t bad, but the volume drop was insatiable and drove me nuts sometimes. I thought I would try modding this one by cutting out the C4 cap (a 0.1uF bypass cap) which is the alleged cause of the gain loss. It is, but not without good reason. It does keep the effect sounding smooth and really clean. Removing the cap also opens up those capped frequencies which some people report a more warm and/or harsh tremolo tone. I enjoyed the more dramatic effect of the pedal myself, and decided to make it even more so by substituting the 10k ohm resistor before the non-inverting terminal of the first opamp for a 4.7k. This added a nice volume boost which gives the tremolo more cut especially when combined with heavy reverb or a washy delay. We’ll see if anyone decides to buy it. I think it’s a huge upgrade from the original sound.