I’ll say it up front, in case you missed it like I did, the power supplies on the Analog Discovery 3 cannot do current limitng, which is a huge bummer. No constant current limiting for you sir! Also, just go ahead and set the power limit to 5.5W please…
Failed Calibration Coefficients For some reason, going through the calibration wizard in Waveforms (as of June 2023) introduced offsets and gain errors which were different for both scope channels. This doesn’t make sense, as both scope channels are calibrated with the waveform generator channel 1, after that has itself been calibrated, of course. My failed calibration attempts were done with a calibrated Keithley DMM7510, so basically with the best multimeter in the world save for the insane 8....
When I got my Analog Discovery 3, I made the decision to also purchase the BNC adapter board. Trying it out with some OWON scope probes I got from Amazon, it unfortunately didn’t cut the mustard. This was the most square I could get by twiddling with the compensation adjustment. To prove that I haven’t goofed it somehow, this is at the opposite end of the compensation range: This waveform ain’t even square at this point....
The Analog Discovery 3 is a great debugging tool, but as I discovered here in a note on using it with 10x scope probes, the input capacitance was too high for the probes to be compensated correctly. Custom LNA design To combat this, I decided to design an amplifier that would have a low input capacitance so that we fall within the 5-35pF compensation which is typical of these 10x scope probes....
Why I bought it in the first place The Analog Discovery 3 seemed like a band-aid solution to an ongoing problem I have been facing here at Cambridge: how do I get my own oscilloscope so that I can get back in to doing electronics without having to rely on the few shared scopes at the Dyson Center (the Dyson Center is sort of like a makerspace for engineering students, it isn’t great though…)...
This is an attempt to try to get more signal out of dynamic microphones, as I literally have to max out the gain on my Presonus AudioBox iTwo to barely get a usable signal level, and that is with me speaking right on top of the microphone. This design is based on Project 66 by Eliott Sound Products , with some minor modifications, mostly me just playing around to see what are the effects of changing stuff around....
So here’s the situation, I accidentally ordered the parts for the Inline Microphone Preamp Project … to Malaysia. One month and a trip to Portugal later, I finally got the chance to use the electronics lab here in Cambridge for the first time to asesemble this thing (thanks Elena for bringing the stuff over for me!), and in good old DIY analog electronics fashion, it didn’t work first time. Turns out, the SOT-89 footprint in KiCad has it’s pins in the opposite order from those in the NXP datasheet for the PBSS4540X and PBSS5540X transistors I was using....
I recently picked up a Behringer BA85A (yes, yet another Behringer clone…) dynamic microphone, and have thoroughly enjoyed the sound that comes out of it. However, it does require me to crank the gain on my PreSonus AudioBox iTwo audio interface all the way to the maximum, and even then, I either have to speak quite loudly or be right on top of the microphone to get a signal that I don’t have to apply any post amplification, which is kinda annoying because I use it quite a lot for video calls, and sometimes adjusting the levels for ASIO devices can be tricky....
This is my attempt to try building this power amplifier from Elliott Sound Products , which was specifically designed to be a practice amplifier, in the sense that it allows electronics enthusiasts like us to practice our building and bug-tracking skills, and also to try modifying the circuit to learn some analog electronics. I had a lot of fun building this amplifier and attempting to do some measurements on it, and I hope you will enjoy this slightly more lab-notes style post....
Being on a little analog synth nerd-out lately, I chose to kick things off by designing the sawtooth generator that will ultimately determine the switching frequency of the boost converter. The sawtooth wave generated is used to derive the PWM signal that drives the gate of the FET. By connecting it and a control voltage to a comparator, a PWM signal with a duty cycle directly proportional to the control voltage will be generated....