double densed uncounthest hour of allbleakest age with a bad of wind and a barrel of rain
double densed uncounthest hour of allbleakest age with a bad of wind and a barrel of rain is an in-progress piece for resonators and brass. I’m keeping a composition log here as I work on it.
As of March 2025, I’m writing about other things here too.
Wednesday April 15th
Someone had a good idea.
Sunday April 12th
Today I’m going to try to fix the amplifer module in the contraption.
There are two stereo amplifier boards stacked on standoffs behind the module panel. They are each connected to a gain pot, an audio breakout and the lead to the power supply.
The bottom board produces a significantly weaker signal than the top. I’m hoping for something simple like a loose connection or weak solder joint, but if I need to replace the board altogether I’ve got a backup, too.
It’s a good opportunity to practice debugging with the scope and the multimeter, which I have rarely done!
First, I’m going to probe every connection to see if I can find anything loose or broken.
testing connections
The first multimeter I bought didn’t have a continuity feature at all. This one optionally beeps, which is nice when you’re probing something like a row of header pins one right after the other.
For those like me who had never probed a circuit, worry not: the process is easy to learn when your multimeter has a continuity testing function. I think I used this guide but it’s worth finding the operating manual for your multimeter to see how to put it into the right mode. (And it’s worth checking on this before buying one!)
After that, just put one of the probes at one end of the connection you’d like to test, and then touch the other probe to the other end and listen for a beep. This is also the way to find accidental solder slop creating bridges between connections that shouldn’t be there.
Your multimeter might come with different kinds of probes to connect. Sometimes it’s difficult to probe successfully with a standard tip and using a version that has a little hook you can use to temporarily affix a probe to something is nice.
In this case, probing every connection – eight audio lines, six gain pot lines, four power lines – didn’t turn up any problems. Ruling out a bad connection is kind of a bummer, since that would be the easiest thing to fix!
Next I’m going to try sending test tones through the amps while they are powered and connected to a scope, and see if I can reproduce the problem I’ve been having with the lower amp board. Fingers crossed I don’t need to replace it since I made the questionable choice to solder most connections directy to the board itself (rather than use terminals) and it’ll be a bit annoying to redo. :-p
I’ve got one of the battery power supplies I’m using in the contraption in a standalone enclosure (well sandwiched between two boards) that will be handy for testing (if I can rule everything else out, I can try a different power source and see if that fixes it – but I really hope that’s not the problem!) and I’ve connected one channel from each board to the scope probes, so I can compare the amplified signals coming from both in the scope.
As a test tone, the easiest thing is to just put a WAV file on my mp3 player, I think, with a stereo test tone. The amplifer boards have 1/8” TRS audio connectors, which is the way I’m feeding the inputs in the contraption itself, so it’ll be easy to feed the test tones into both through the same cables.
(pictured displaying the test tone in ASCII graphics is harry by mathr)
This makes the test setup, hopefully essentially identical to the way it is when it’s being problematic inside the contraption, except I can probe at it.
It’s hard to communicate just how confusing and fiddly it is to probe for signals on a contraption like this haha. I managed to get things arranged to be able to check both board outputs, but looking at the amplified signal was weird. The boards are D-class, which means they try to be off as often as they can, and actually construct the signal with pulses, so just comparing the two outputs visually on the scope didn’t help me very much.
Maybe if I knew the scope better I’d be able to suss out the normal noise from problematic noise by looking?
I didn’t get anywhere with the scope. :-/
Instead I hooked the amps up to two exciters (which they’re normally hooked up to) to debug by ear. I hear the same weak & crackly signal from the bottom board.
At this point I think it’s worth swapping out the board – the one on the bottom is an older design, which shouldn’t matter at all, but it’s older so maybe I managed to damage it at some point without realizing it.
Yep, I had a bad amplifier board! The replacement is working well, and the contraption is back to four channels again.
My mp3 player died (hopefully not for good?) so I used a CD (just arrived from Commune Disc though nearly 20 years old now!) of Hidenobu Ito’s reimagining of Systemisch as a test tone, instead.
Wednesday April 1st
I just started reading W. Ross Ashby’s An Introduction to
Cybernetics last month. I’m amazed to find that the
operand, operator, transform and
transformation concepts introduced right away in the book
seem to encompass functional programming, relational database design and
other fundamental concepts embedded deep into programming languages and
systems, including machine learning.
I guess it makes sense! My understanding is that information theory and cybernetics drove a lot of early applied theory in computing, but I’m curious to learn more…
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