A couple mockups for an audio preamp display using dirt cheap character LCDs and the BigCrystal library for Arduino.
Category: Progress
GitLab acquires Gitorious
This post says it all. So much for having to choose between libre options.
This is also a case where reading the comments is worth it. There’s a very lively debate on the relative merits and pitfalls of “restrictive” and “permissive” open source licenses.
KiCad workaround for mounting hole too close to pad
Here’s a workaround I used in a KiCad layout that involved a DRC error with a module’s (non-conducting) mounting pin. The mounting pin is physically close enough to an electrical pin that it makes the DRC clearance test fail. The proximity isn’t actually a problem because the offending pin is just so much mounting foo for the part, but KiCad doesn’t know the difference.
The workaround is to edit the pad for the mounting pin and assign it the same pad number as the pad the DRC thinks it’s too close to. (See the two pads numbered 3 in the above image). Kludgey, but it silences the (not really an) error. I made this change in the PCB layout rather than in the library module as it won’t be a problem on boards with smaller copper clearance.
BTW, the module is for a Keystone 970 RCA jack and is available in my Bitbucket repo.
Audio module progress
Pictured here is a prototype of a miniaturized version of the audio module I’ve been working with for the last few months. A high-end audio manufacturer is currently evaluating the module for use in a new line of products. More as it develops.
Engineer meets Bugera V22 reverb – Parts 7 and 8
Circuit board removal and modification.
Engineer meets Bugera V22 reverb – Parts 5 and 6
Some sound samples using a different reverb algorithm on the effects chip and an exploration of noise modulation.
Engineer meets Bugera V22 reverb – Part 4
Gain scaling exploration.
Engineer meets Bugera V22 reverb – Parts 2 and 3
Quick and dirty dynamic range testing and tracing out the reverb board to find the configuration parts.
Engineer meets Bugera V22 reverb – Part 1
The Bugera V22 guitar amp is just too good to leave alone. Yes, it’s had its share of teething problems—the worst of which I believe have been sorted. Yes, it’s made in China. Yes the tube quality seems to be a crapshoot. But the build quality is better than what I’d expect at the price, and the sound is unique and just lovely. It’s a great buy.
One thing I’m not super jazzed about though is the amp’s reverb. I begin documenting my gripes below and start off in search of a solution.
It develops …
Picking up from earlier, what we’re looking at here is an audio DAC reconstruction filter built around a prototype discrete opamp-like differential gain cell I’ve had in the works for quite a while. I finally chased out the last engineering details and have been listening to the final setup for about a month. I am still astonished at how good it sounds.
I designed the gain cell from the ground-up as a dedicated high-performance audio device. It uses some novel topological and other features that I’ll probably go into in a future post. For now all I want to say that the thing is wicked fast for a discrete device and has been rock-solid stable.
But why bother? Aren’t there already tons of reasonably decent, some even cheap, audio IC opamps out there? Yes, there are. But I’ve never been totally happy with any of them. Some have too much LF bloat, some are too strident—none to my ears do everything right (which is to say, do as little as possible apart from making the signal bigger and stronger).
Designing a discrete device let me optimize the gain structure specifically for audio, minimize and more effectively manage the number of parasitic interactions throughout, thermally couple and, more importantly, decouple elements as necessary, and a few other things. It started as a “Gee, let’s see…” exercise, and I have been rather shocked by the results.
Now I’m contemplating where to take things next. I’ve designed a couple small-footprint packages for the gain cell. I’m implementing a few other ideas with it too. I suspect this surprising little circuit will see some commercial application soon.
Right then. Back to listening. 😀