I set up a breadboard in order to conduct tests on diodes to compare clipping harmonics. The idea is to see if there is really a difference between different types of silicon diodes when used as clippers.
I adjusted the test rig to drive the diodes to 10% distortion to make the comparison. While adjusting the setup, I noticed that after 5 to 10 seconds, the percentage of distortion would slowly go down. The change was very slow but noticeable. I repeated the adjustments several times with the same results. It then struck me that maybe the diodes were heating up and the forward voltage was changing ever so slightly as they warmed.
I started the oscillator and waited for the diodes to begin the slow change. Once the steady decline started, I blew on the diodes to cool then off. Sure enough, the distortion change stopped then slowly reversed! Once I stopped blowing on them, the slow decline began again.
The change I was looking at was very slight but easily seen since I was looking at the distortion percentage down to 3 decimal places. I doubt the change would be audible but it is interesting to note that the effect is definitely there.
In the end, I got around it by sending a short burst of the test signal and measuring the distortion before the diodes had a chance to heat up.
I have been working on an updated version of the gyrator bandpass filter calculator that has a chart with instant updating!
After more than 16 revisions, I am getting closer to something that I like, and which I think will be useful. Just for readers of this blog, you can try out the beta version at:
This probably a temporary link so don’t bookmark it yet. The intro paragraph with schematic is not on the page yet but I will put it back once I get to the final release.
I am working on a new issue of Analog Music Projects. The last one came out 24 years ago, so it is time for another one. Actually I had it all completed but when compiling the table of contents, it did not look like there was enough good information. So I have gone back into writing and will add a few more sections.
The good news is that the third issue (v1.3) already has some articles ready so maybe I can get out a follow-up in less than 24 years!!!
Update: This edition is finished but not yet formatted for final output. I am terribly slow, but there is a good reason for it that I will explain in the near future.
TL;DR: The pedal is not working correctly. I suspect it is a wiring error on my part and I am looking for it.
Full Story: I went to test the new pcb for the SSM2166 compressor pedal. The laptop on my test bench had not been used in several months, and Windows had updated. It now was forcing me to log into a Microsoft account and use OneDrive. I don’t need OneDrive and I don’t need a Microsoft account for this computer that is only used for testing and audio recording. Not only that, I did not remember the password for that laptop’s account. But, I had written it down, and after a lengthy search, I found the password and got in.
Next came a succession of errors on my part related to cables and jacks that were not labeled. Once I got that sorted, and all the cables plugged in correctly, I could run a few tests. The pedal did not work correctly. It worked in bypass but not when compressing. That sounds like a wiring error but this is a buffered bypass pedal so I would not expect it to work if the bypass wiring was wrong. But it did.
I looked closely at the switch wiring. It was correct. I suspected the battery but it was lighting the LED to full brightness. I tested 2 other pedals that were on the bench and they worked as expected (on the same battery).
Back to looking more closely at the inside of the comp pedal. Then it struck me… the 3pdt switch was oriented correctly for true bypass, but turned 90 degrees for a buffered bypass. Doh!
I pulled all the wires off the switch and turned it around. All of the switch lugs were plugged with solder so the wires would not go back in without a fight. Blah, blah, blah… I finally got it wired up.
So after some tests, it passes a signal on bypass but not a good one. It is losing some volume. At this point, I have to take a break. It is hot in that room and I am sweating, and I have looked at the wiring too long. Later, after resting my eyes, I’ll have another look at it. I may have damaged the op amp when moving cables and wires.
4/27 Update: I was right in that fresh eyes would be able to spot the problem. It only took me about 2 minutes to find the misplaced wire in the prototype’s ratsnest. The good news is that voltages are perfect and the buffered bypass is clean and stable. The bad news is that it does not compress properly. I was afraid of that because I went WAY off the datasheet’s basic design on this version and it looks like that was a bad idea because the internals of the chip were not doing what I thought they did. I still have to test the ssm2166 chip to make sure it is functioning properly but I expect it to be okay.
A lot of people have written to me about the Q&D 2 compressor that uses the SSM2166 chip. I looked at the revised pcb a few times in the last couple of days and made some revisions. I plan on looking at it again tomorrow. and if I am satisfied with the layout, I will order the new boards.
The revised version will fit in a 125b box with top jacks, and has several other changes but it is the same compressor at its core. I will post an update later this week.
Edit: PC boards have been ordered.
Update: Boards have arrived and I need to work on building the prototype and writing the documentation.
I had to open up the new MXR Rockman X100 to move the output switch over to stereo, so I took a picture of the pcb while I had it open.
It looks to be very well done, with only a couple of minor glitches. The switch pcb on my pedal is quite crooked, and the soldering on the MN3007 delay chip is not the best. It also looks like someone has taken a cotton bud with some alcohol, and removed the ink from all of the chips. It makes it hard to read the numbers but not impossible. I could see a pair of TL074 quad op amps, a TL072, the MN3007 and an LM317L voltage regulator. There are more but I did not take the time to try to identify them all
Thumbs up to MXR for making this classic design available again!
I logged in today to my main Instagram channel and got the type of warning popup from the administration that I had started to get on my a.i. artwork channel before it was deleted. Was it just coincidence that this warning came soon after I posted the picture of the Octa-Psi with the heavy metal attachments? Was it because I modified that picture with AI? It started as a photo but I modded it with Midjourney. In any case, no more pix on the main channel that have any A.I. connection whatsoever.
Diecast boxes are typically made from Aluminum Alloy 380 (also known as A380). This is a common alloy used in diecasting due to its good balance of strength, corrosion resistance, thermal conductivity, and workability. Alloy 380 also has good resistance to environmental corrosion, which makes it ideal for enclosures protecting electronics in various conditions.
The typical composition of Aluminum Alloy 380 includes:
These elements contribute to its strength, machinability, and corrosion resistance, making it an ideal material for diecast enclosures and housings, especially in electronics and automotive applications.
