This is a circuit designed for a classroom project whereby the instructions were to “improve” a differential amplifier circuit. The differential amplifier design is essentially an exercise in understanding the inner workings of an opamp, and it effectively works in the same way. The figure below is a schematic for the differential amplifier without the cathode follower output stage. In the LTspice simulation, the input signal is connected to the V+ terminal and the V- terminal is connected to ground. There is no feedback loop between the output and either input terminal making this a high-gain open-loop configuration. However, adding a resistor from V- to ground and one from the output terminal to V- would accomplish the same results as a non-inverting opamp.
I wouldn’t say that adding a cathode follower “improves” the output stage of the amp. It was more an experiment in comparing different solid-state output stages with a vacuum tube stage operating at very low voltages. However, I will say that this thing sounded amazing with the couple of guitars I tested through it. Putting a potentiometer in the feedback network allowed me to play with different gain settings. It’s a very bright sound overall giving lots of high-end sparkle, but the breakup was quite remarkable. I suspect this might be a very usable configuration for a tube mic preamp or a number of audio applications. Hopefully, I will get an opportunity to revisit this before too long.
For those of you interested in the ins and outs of this experiment, you can download our full report here.
“As we march along on our mission to create a diverse and expansive creative community, we reach a new milestone: 200 releases. To this end, we bring you ‘Document II’, a retrospective cassette that comes with a Golden Ticket good for downloads of our last 100 releases. This is a one-time limited edition of 200 golden cassettes with hand numbered gold fold j-cards and golden tickets.
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– Joshua Tabbia, Already Dead Tapes, 2016
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.
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-22.214.171.124 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.
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.