Analog Output on Rich Holmes

Website move

Mon, 11 Aug 2025 11:28:25 -0400

Due to problems with the .xyz TLD, I’ve moved my website to https://richardsholmes.com. The old domain name is supposed to redirect there, though so far that isn’t working.

Kosmo gets rungled

Tue, 18 Feb 2025 16:28:22 -0500

After some breadboarding, I went ahead and designed a rungler in Kosmo format.

Rungler module

I included the loop offset switch and knob discussed in the previous post. Also on the front panel is a feedback switch. This enables or disables sending the output of the last stage of the shift register to be XORed with the input to determine the next bit to be loaded in. Feedback on is the “normal” configuration, hard wired in the Benjolin, but you may find it useful to turn it off sometimes.

LMNC 4051 Plexquencer

Sun, 16 Feb 2025 19:03:08 -0500

The Look Mum No Computer 4051 Plexquencer (description, purchase) is an interesting new module. It’s kind of like your basic eight stage Baby-8 style analog sequencer, except that instead of taking a clock signal, it takes three gate inputs (A through C). Those three gates, interpreted as a binary number, tell the module which of the stages to activate. If the inputs count in binary from 0 up to 7 and back to 0, it’ll go through the stages in order (though they’re numbered 1 to 8, which has already caused me some confusion), like a typical sequencer, but if they form a different binary sequence it’ll do different things.

The winter of our discontent

Fri, 10 Jan 2025 17:28:51 -0500

December through early January was not my greatest time building.

I have two Kosmo modules under construction. One is an FM Drum, built around a circuit board from Barton Musical Circuits. It needed two SPDT toggle switches, and I had a ton of them in my stash… right? Turns out, no, I didn’t; I had two. So no problem? Except they had no nuts and washers on them, but I have toggle switch nuts and washers lying around loose or in their own little bags all over. Except they don’t work. Apparently these switches have a different diameter or thread than the usual.

Barton JFET Phaser

Tue, 10 Dec 2024 11:57:22 -0500

I have a new module. This is just a Kosmo format adaptation of the Barton JFET Phaser.

Front view

And yes, once again JLCPCB failed to honor my request to put the order number in my specified location.

I assembled the PCBs following Barton’s instructions, except I omitted the board mounted pots and jacks. (And, as I usually do with Barton designs, I used 100 nF for the bypass caps, and 1N5817 Schottky diodes rather than 10Ω resistors on the power rails.) Instead I used panel mounted components and wired them to the PCB footprints. I mounted the PCBs to the panel with a sheet aluminum bracket clamped between the panel and the bottom two pots.

Rungler? I barely...

Sun, 01 Dec 2024 08:56:12 -0500

I’ve been breadboarding a rungler. “Cool,” you say. You take another bite of leftover turkey. You chew. You swallow. Finally you say, “So what’s…”

Rungler

Rob Hordijk was a Dutch engineer and synth designer. One of his creations was the Benjolin, a quirky little synthesizer featuring two oscillators, a filter, and a… rungler.

The rungler is a control voltage sequencer based around a digital shift register. In that, it somewhat resembles the well known Turing Machine module. Unlike the Turing machine, the rungler is deterministic, not random, though it is unpredictable enough to render the distinction somewhat, though not entirely, moot.

Kosmodrome's new instar

Thu, 05 Sep 2024 12:18:29 -0400

I’ve been working the past several weeks on my traditional summer activity, expanding my synth cases (too cold in the garage workshop for woodworking in winter), and reassembing Kosmodrome. I’ve added two rows to the bottom of the second case.

Kosmodrome case extension

Kosmodrome case with extension mounted at bottom

The woodworking is, erm, imprecise, and the finish is positively slapdash, but good enough.

Weirdness

Tue, 16 Apr 2024 07:12:24 -0400

Here, have some Weirdness.

Weirdness

Weirdness is a Kosmo format synth module based on the Music From Outer Space Weird Sound Generator by Ray Wilson.

Pulses and gates

Sun, 14 Apr 2024 10:11:58 -0400

The Halting Problem, based on the Music Thing Modular Turing Machine, has pin headers for connections to expansion modules like the HP Potentials and HP Gates. One of these headers is marked GATES1 and the other is PULSES1. Normally expansion modules connect to one or the other, but what if you want to switch between both?

The GATES1 header is connected directly to the shift register output pins. As long as a particular shift register entry contains a 1 bit, the corresponding GATES1 level will be high.

Nuclear Decay video

Thu, 14 Mar 2024 13:06:50 -0400

previous:	Wave Displacer
next:	Pulses and gates

Wave Displacer

Mon, 04 Mar 2024 19:48:47 -0500

I call this a Wave Displacer:

It’s a wave shaping module that will work on low or audio frequency waveforms. The idea is simple: Any part of the waveform that is above a threshold gets displaced upward or downward. Any part that’s below a second threshold also gets displaced upward or downward. With low frequency waveforms this gives more complex wave shapes for interesting modulation possibilities. With audio waveforms it adds harmonic content. The result depends on five parameters: The two thresholds, the two displacement amounts, and the amplitude of the original signal. All five parameters are voltage controllable.

Three new ones

Mon, 04 Mar 2024 17:39:34 -0500

I finished up three modules recently:

Nuclear Decay and Bong0

On the left is Nuclear Decay, which I’ve written up. All that’s new is the fabbed front panel — and the piece of clear acetate film I glued behind the window, to protect the Geiger tube and the user from one another.

DSO138 Oscilloscope video

Mon, 19 Feb 2024 19:03:29 -0500

previous:	Fumbling with SMD
next:	Three new ones

Fumbling with SMD

Sun, 18 Feb 2024 07:47:31 -0500

Back in 2020 I built two modules using mostly SMD components — one was problematic and I needed outside help with it, the other went OK. Then I got into Kosmo, and there aren’t many SMD Kosmo modules out there and I was designing my on PCBs through hole for the most part. I did build a VCO using the MFOS PCB with one SMD part, and my output module used an SMD amplifier you can’t get as through hole, but that was it.

Nuclear Decay meets autunite

Sat, 20 Jan 2024 22:11:29 -0500

So I did a little followup research and found this site:

geigercheck.com

and… well, today I got a package in the mail:

Just a harmless package

Inside was a little rock:

Autunite piece in visible light

and a small UV light that makes the rock do this:

Autunite piece in UV light

And if I put the little rock close to the Nuclear Decay module’s Geiger tube, it does this:

Ringer video

Sat, 20 Jan 2024 18:25:12 -0500

Ringer video!

https://diode.zone/w/tqo7v2pCiqN2RwK6AWg6YT

(I’ll be posting new videos first at diode.zone, an ActivityPub federated PeerTube instance, then later at YouTube.)

previous:	Nuclear Decay meets autunite
next:	Fumbling with SMD

LMNC builds AO

Sun, 14 Jan 2024 16:07:02 -0500

A new video from Look Mum No Computer includes a brief glimpse of my Gate Grinder module, followed about 10 seconds later by footage of building two Dual Quantizers. You can see them in use afterward as he makes music with his synth.

AO Dual Quantizers (left) in LMNC’s PortaKosmo synth

previous:	AND video
next:	Nuclear Decay meets autunite

AND video

Sun, 14 Jan 2024 15:15:41 -0500

Add Noise Drum video!

https://diode.zone/w/5uob3TnU9R7dDQK4VKM25v

(I’ll be posting new videos first at diode.zone, an ActivityPub federated PeerTube instance, then later at YouTube.)

previous:	Nuclear decay
next:	LMNC builds AO

Nuclear decay

Thu, 11 Jan 2024 21:54:25 -0500

About three years ago, TimMJN of the LMNC Discourse made a module out of a cheap Geiger counter. Whenever the counter detects a particle the module produces a time-decaying control voltage. Nuclear decay, get it? Kind of a poor man’s version of Nervous Squirrel’s uranium-driven Random Voltage Generator.

Recently I decided I wanted to build a module like Tim’s too. I mean, I used to work in nuclear and particle physics research, I felt like I kind of really should.

Ringer

Mon, 08 Jan 2024 22:02:29 -0500

This is Ringer:

Ringer module

It’s a Kosmo format four quadrant multiplier, basically. That means it can take two voltages as input and multiply them together for the output. A VCA does that, sort of, but it takes a bipolar signal and multiplies it by a control voltage that has to be non negative — if you give it a negative CV it’ll just treat it as zero. That means it’s a two quadrant multiplier. A four quadrant multiplier can multiply one bipolar signal by another: Both signals can be either positive or negative, and it will multiply them.

Add Noise Drum

Wed, 03 Jan 2024 11:05:04 -0500

I had a bit of a problem with my last PCB/panel fabrication order:

Not how I designed it

It looked fine in both the KiCad Gerber viewer and the fabricator’s web-based Gerber viewer. Turns out there was a bug in their engineers’ software. They’re redoing the panels.

But that’s why this post ~~contains~~ contained no photos of my new module. [Update: Now it does.]

A theremin for Christmas

Sun, 31 Dec 2023 08:13:42 -0500

I got a theremin for Christmas! Okay, I got it from me. Also, two days after Christmas. Still, it’s the thought that counts.

It’s the OpenTheremin V4.5 from GaudiLabs.

It’s not for theremin purists: It produces its sound digitally, not the old fashioned way. But it’s still controlled by capacitive sensing with two antennas, like the 1919 original. Output jacks give you not only sound, but two control voltages and a gate, so you can use it as a synth controller.

Attenuverters two

Tue, 19 Dec 2023 19:50:55 -0500

Here’s an attenuverter:

Simple attenuverter

You find this design in lots of places. When the wiper is fully counterclockwise, it’s equivalent to this:

Equivalent circuit with wiper CCW

R3 doesn’t matter, it doesn’t change the input voltage, so we can ignore it (aside from the fact it draws a little current, but it doesn’t change the output). So it’s just an inverting amplifier with gain equal to -1 times the ratio of R2 to R1, which is -1: The output voltage is minus the input voltage. Which is one thing you (normally) want from an attenuverter.

Analog Drum breadboard notes

Sun, 05 Nov 2023 08:33:59 -0400

I made a Barton Analog Drum in Eurorack a few years ago, and I currently have one on breadboard. I’ve found a few things I want to change.

I noticed in my Eurorack module if I tried triggering with a gate it sometimes would trigger on both the rising and falling edges. I never chased down the reason but I suspect it was that there was some ringing on the falling edge, taking it up above the comparator threshold again. That threshold is pretty low, about 120 mV from a 100k/1k voltage divider on +12 V. Changing that to a less extreme ratio might help, or better yet changing it to a pot for an adjustable threshold.

Whistle while you noise

Sat, 04 Nov 2023 00:11:19 -0400

[Revised 2023-11-17]

A couple years or so ago I built a Kosmo version of the MFOS Noise Cornucopia. Now I’m designing a module that needs white noise so I thought I’d just drop in the Noise Cornucopia source. I breadboarded it:

Noise source from Noise Cornucopia Rev. 1

And… it didn’t work. I mean it did generate noise, but it also output a faint tone, up very very roughly around 1 kHz I’d say. Almost a whistle. I’d never heard that from the module I built.

Display and Slope

Mon, 30 Oct 2023 16:02:48 -0400

My summer building break is over (late, but it started late too). I’ve built, technically, two new modules, though one is hardly enough to merit the title.

Power Display

I’ve built one power display module (just a couple LEDs and test points) for each of my bus boards, but I decided to do a new version to replace at least one of them. This one adds a power header on the front panel — to make it easier to power modules that are being tested or undergoing troubleshooting.

Less droopy YASH

Tue, 24 Oct 2023 20:17:21 -0400

I finally got around to modifying my YASH: 10 nF instead of 1 nF for the integration cap and 4.7 nF instead of 470 pF for the gate width cap. The former change makes the droop rate about 10x slower and the latter makes the integration gate 30 µs instead of 3 µs to compensate for the longer charging time. Originally, with a 1 V input signal, the output was drooping by about 150 mV over 10 seconds. With the new capacitor values I can still see a little droop on that time scale but it’s a big improvement over what it was. I updated the design files and docs at https://gitlab.com/rsholmes/yash.

Kosmodrome Phase 3

Tue, 24 Oct 2023 09:56:05 -0400

Kosmodrome Phase 2 is done. What about Phase 3?

There isn’t really so much of a need to formally define Kosmodrome Phase 3. Phase 1 was all about putting a basic synth together and Phase 2 was extending it in some fundamental ways. At this point, further expansion is mostly a matter of “this seems like an interesting module” or “hm, I need more of xxx”. More “these are things I want to do” than “this is an aspect that needs to be included”.

AC coupled square waves are less than obvious

Thu, 19 Oct 2023 23:41:30 -0400

Okay, this is about nothing of any practical importance I can think of, but I got interested in the subject, and arguably it’d be better posted at Mathematrec, but then I’d have to explain things like what a high pass filter is and so on, so it goes here.

This is about AC coupling. That’s when you use a capacitor in series after a signal source to remove its DC component, leaving only the oscillatory behavior around zero. Or rather, not just a capacitor. Think about it. If you connect a signal source on the left side of a cap, how does the right side know how to remove DC? Voltage, after all, is relative — it’s always measured relative to some other point, usually ground. The DC component is a constant voltage relative to ground. But how does that cap, which isn’t connected to ground, know what ground is? It doesn’t. So it can’t know how much DC to subtract.

Here we go again

Fri, 08 Sep 2023 08:00:16 -0400

For reasons, I took a break from synth building for a few months. Some design work but no building. With (meteoroligical) fall here, it’s time to get back into it. So what’s up?

One of my top priorities: Modifying YASH. This sample and hold works okay, but the droop rate is pretty high. From the LF398 datasheet, it should improve more or less proportionally to the size of the integrating capacitor, so bumping that up from 1 nF to 10 nF should make it a lot better. But that also means it will take ten times as long to charge. So the cap in the trigger processor also needs to go up a factor of ten. The charging gate as it stands is only 3 µs; making that 30 µs should be fine, still too short to be audible.

Hub to Lab

Sat, 02 Sep 2023 23:43:06 -0400

I’m absolutely not a fan of the hype, inappropriate uses, bad designs, questionable ethics, and poor implementations characteristic of the recent surge in AI or LMM or whatever initials you want to call it by. I don’t want AI writing my blog (so I left Wordpress) or doing my web searching for me (so I’m very concerned about Google and Bing), and I certainly don’t want AI doing my coding — to the extent I do any coding anyway. Point is, when GitHub opens an account on the Fedi, where (at least in my home feed) I see all sorts of skepticism, antagonism, and hostility toward the AI fad, and proudly puts in their profile that they’re “AI powered”, I find that both sad and amusing, and it also brings home the idea that, yes, it really is time to abandon that platform too.

An index for MFOS

Mon, 17 Jul 2023 21:42:35 -0400

If you’re into synth DIY you have to know about Music From Outer Space. Ray Wilson ran that site for many years, posting his circuit designs and PCB layouts with BOMs and copious explanations, everything you need to know to build your own synth, freely available — you could buy PCBs from him but you could also just etch your own from the graphics he supplied. Wilson unfortunately died around 2016, I think, and since then the site’s been kept up by SynthCube. But they haven’t really changed anything; it’s pretty much the way Wilson left it.

I like big knobs and I cannot lie

Tue, 11 Jul 2023 14:11:34 -0400

2HP Eurorack modules with knobless pots you need tweezers to work? Puhlease.

Gimme some mil spec knobs.

(From here: https://www.product-lifecycle-management.com/download/MIL-STD-1472F.pdf.)

… Okay, fine, a modular synth is not a nuclear submarine. Still, to my mind, a synth knob isn’t a setup parameter; it’s a performance control. You don’t just set up a patch to get some particular sound, press record, play some notes on the keyboard, and stop recording. You use those knobs as part of playing the synth, morphing and evolving and mutating the sound as you go. But you can’t do that well unless you have a knob per function, one you can find easily and grab onto easily and turn smoothly and continuously, maybe with one hand while turning the next knob over with the other hand, without bumping into other knobs or your other hand or anything else that’ll prevent that smooth and continuous motion.

Here we are again

Fri, 07 Jul 2023 16:39:46 -0400

Well. I’m trying something else for my blogs, again.

I found some faults with WriteFreely and write.as. For one thing I could not get ActivityPub federation to work properly — that is, it worked more or less correctly on the writing.exchange Mastodon server, but on vmst.io and mastodon.social I could follow my blogs but new content simply did not appear in my Home feed. For another thing, I use MathJax, especially on my Mathematrec blog, but in WriteFreely it’s basically impossible to proofread MathJax — because it doesn’t render it until you publish.

Bitty boards

Sat, 17 Jun 2023 01:09:03 +0000

I got some new PCBs yesterday:

They’re kinda tiny. I’ve been thinking I should break my long SMD hiatus and do some surface mount projects. But for breadboarding, what do you do? Through-hole equivalents where they exist, breakout boards that carry SMD part pins to 2.54 mm pin headers where they don’t. These boards are for SOIC-8, SOT-23, and SOT-363 parts. The SOT-23 ones would have a single right angle 3-pin header, the other two would have pairs of straight headers.

Here we are

Wed, 14 Jun 2023 23:28:30 +0000

Having reached the breaking point with wordpress.com (the straw being their introduction of an AI garbage content generator), I’ve moved my blogs here, including Analog Output.

It’s powered by WriteFreely. That means it can publish via ActivityPub and be followed from other Fediverse platforms, such as Mastodon. At least in theory. I haven’t seen that working yet but it’s early days.

I’ve set it up with a custom domain, [richholmes.xyz](https://richholmes.xyz “Rich’s website"o), and there’s intended to be an actual though minimal website at that URL. That’s not quite on the road yet, though.