{"id":10410,"date":"2022-02-24T13:20:41","date_gmt":"2022-02-24T18:20:41","guid":{"rendered":"https:\/\/glyphpress.com\/talk\/?p=10410"},"modified":"2022-02-24T14:05:58","modified_gmt":"2022-02-24T19:05:58","slug":"restoring-an-arp-2600-synthesizer","status":"publish","type":"post","link":"https:\/\/glyphpress.com\/talk\/2022\/restoring-an-arp-2600-synthesizer","title":{"rendered":"Restoring an ARP 2600 Synthesizer"},"content":{"rendered":"\n

I recently received a truly resplendent gift from my friend Kate: an ARP 2600 synthesizer, owned by their dad, who died recently. It\u2019s in OK shape, but parts of it don\u2019t work, and I\u2019m doing some research to figure out when it was built and what has happened to it since!<\/p>\n\n\n\n

And I\u2019m going to get it back in working condition so I can make R2-D2 say whatever I want.<\/p>\n\n\n\n\n\n\n\n

\"\"
Yes, my workshop is churning chaos. But I also really, really love it there.<\/figcaption><\/figure>\n\n\n\n

First, I had to answer some fundamental mysteries. I knew that it came from Kate\u2019s dad, who I\u2019d had a great time talking about science fiction and sound with. But I didn\u2019t know just when it was built or even what condition it was in.<\/p>\n\n\n\n

Initial with-screwing showed that the sliders were more \u201coff-road adventures\u201d than \u201csliders\u201d. Their response was very sketchy and I couldn\u2019t get the filter to do anything at all. All I could do was bypass it to get sound out.<\/p>\n\n\n\n

So it was time to open it up!<\/p>\n\n\n\n

If you know the ARP 2600, you\u2019ll see that it has grommeted screws down the sides of the control panel. These had all been removed, so obviously someone had been in here already. Initial searches on Teh Interwebs told me that the panel is held in place by the screws in the handle, so<\/p>\n\n\n\n

\"\"
Let\u2019s goooo!<\/figcaption><\/figure>\n\n\n\n

So, I took the faceplate down. Let\u2019s take a look at it!<\/p>\n\n\n\n

\"\"
The back of the control panel. Just LOOK at those gorgeous traces. Arnold Perlmutter wasn\u2019t a hip guy. He was an electrical engineer who realized he could build a good synthesizer for musicians and music teachers. So those traces\u2019 amazing shapes serve a function and aren\u2019t there just to be beautiful. But they also came about during the height of psychedelic rock and I think he was influenced by the aesthetics around him, too.<\/figcaption><\/figure>\n\n\n\n

Let\u2019s look at each of those modules, potted in black epoxy to ironically maintain trade secrets. And you\u2019ll note that one of them lacks a black block.<\/p>\n\n\n\n

\"\"
The 4017 voltage-controlled oscillator, the first model oscillator they used, incorporating Perlmutter\u2019s design that allowed it to stay in tune. The company replaced this design after a while with a more reliable one, but since these are still working, it looks like we\u2019ve got a keeper!<\/figcaption><\/figure>\n\n\n\n
\"\"
Sample & Hold is also working fine! I love S&H just faintly desynched from a regular oscillator, like an LFO used to control multiple modules. That way, it puts out multiple evolving sequences that keep a relationship to each other over time, even if they never quite repeat.<\/figcaption><\/figure>\n\n\n\n
\"\"
The Ring Modulator. This is where R2-D2\u2019s voice comes from. I\u2019ve been really enjoying this effect. <\/figcaption><\/figure>\n\n\n\n

And finally, the filter. Before 1976 or so, it\u2019s a filter that was close enough to Bob Moog\u2019s legendary transistor ladder design that Moog wrote them a letter and told them to cut it out. After that, it\u2019s their own design which I\u2019m told is inferior, losing high frequency harmonics.<\/p>\n\n\n\n

\"\"
Ah. Definitely not the answer I wanted.<\/figcaption><\/figure>\n\n\n\n

OK, so it\u2019s the later ARP filter design. And yet, we can see by the Tonus logo, the model of oscillator, and rectangular grill pattern on the front, that the synthesizer is one of the earliest models from 1971!<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

OK, so, let\u2019s talk about that floppy disk.<\/p>\n\n\n\n

\"\"
As I found the floppy<\/figcaption><\/figure>\n\n\n\n

This disk was just rattling around in there.<\/p>\n\n\n\n

\"\"
400k Mac floppy.<\/figcaption><\/figure>\n\n\n\n

StuffIt came into existence in 1987, toward the end of the 400k floppy era. So the last time someone was in here, they had 400k floppies in good condition and were expecting to use them for the foreseeable future. In fact, this would have been readable on a stock Mac for at least a decade, so good call. Kate confirms that it\u2019s her dad\u2019s handwriting.<\/p>\n\n\n\n

MacPaint was published from 1984 until 1988, but we don\u2019t know what version it is.<\/p>\n\n\n\n

It\u2019s the \u201cetc\u201d that intrigues me, particularly given that this disk seems to have been hidden in here. Even with StuffIt\u2019s incredible compression algorithm (it felt like cheating at the time), getting MacPaint onto a floppy with enough room for \u201cetc\u201d means that the cetera can\u2019t be THAT much bitmapped porn. But the disk label might be a lie, and it\u2019s Kate\u2019s dad\u2019s history as a 1980s hacker blowing up the crimes of the Reagan administration.<\/p>\n\n\n\n

Hey, if you like weird science fiction art, you should definitely support my Patreon <\/a>because I make a lot of it.<\/p><\/blockquote><\/figure>\n\n\n\n

Or it could have fallen off the desk while he was putting it back together.<\/p>\n\n\n\n

Apparently, he opened it enough that putting the screws back on the face plate was a pain. So it could have just fallen in there. Until we find a working Mac with a floppy drive running MacOS 5 or so, we won\u2019t know.<\/p>\n\n\n\n

\"\"
The power supply with replacement power capacitors.<\/figcaption><\/figure>\n\n\n\n

More to the point, I couldn\u2019t get a picture of the bottom of the caps, but I found the date code on the replacement power supply capacitors: 1988<\/em>. So we know that the repair happened no earlier than 1988.<\/strong><\/p>\n\n\n\n

The repair in question was not only the power supply (used only on the very first \u201cmid-1971\u201d models, with examples from November, 1971 using one that\u2019s easier to repair), but also to the filter.<\/p>\n\n\n\n

This model, since we know it\u2019s from 1971, originally shipped with the Moog Violator filter. The later one may have been installed in the original broke in some way, or perhaps it was a misdiagnosis, or perhaps Kate\u2019s dad wanted to \u201cupdate\u201d it.<\/p>\n\n\n\n

Here\u2019s what he did:<\/p>\n\n\n\n

\"\"
The modification to the board<\/figcaption><\/figure>\n\n\n\n

There are traces carefully cut, then bridged, with a resistor soldered in. Thanks to some fellow vintage synthesizer nerds I tracked down across online synth scenes, this is a mod for making the replacement filter work.<\/p>\n\n\n\n

You\u2019ll also note that there\u2019s flux all over the place. The original boards had no apparent flux. This is definitely an amateur repair, though definitely has some craft to it.<\/p>\n\n\n\n

However, someone \u2014 almost certainly Kate\u2019s dad in 1988 \u2014 apparently gave up troubleshooting and desoldered the resistor, severing the filter from the rest of the circuit. At first, I thought it was a cold joint that had broken by accident, but the rest of the soldering seems quite competent and I don\u2019t see the rough edge on the solder that you see when it breaks.<\/p>\n\n\n\n

\"\"
This looks like evidence of 34-year-old frustration.<\/figcaption><\/figure>\n\n\n\n

I resoldered the resitor when I thought it had just broken loose\u2026<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

\u2026but the filter still doesn\u2019t do anything.<\/p>\n\n\n\n

At this point, I decided to redesolder the resistor and, since I\u2019d found a dude in Wales<\/a> who sells kits for the original one anyway, I decided to order one. I\u2019m told that it\u2019s arrived at my mailbox, but I\u2019m in the wrong state right now to check.<\/p>\n\n\n\n

That means I get to cut out the old one and look for damage!<\/p>\n\n\n\n

\"\"
The bottom side of the filter module<\/figcaption><\/figure>\n\n\n\n

\u2026and I sure don\u2019t see any, which is concerning. If one of the two op-amps was popped, I\u2019d have guessed that something had been hooked up backward, or perhaps it was defective. But this all looks fine.<\/p>\n\n\n\n

So that\u2019s where I leave this first exploration: the machine was built between \u201cmid-1971\u201d and November, 1971. The power supply is like the Grey Meanie short-run prototype that preceded it, but unlike all later models, the earliest of which I\u2019ve found is from November. Sometime not long after 1988, someone \u2014 probably Kate\u2019s dad \u2014 either tried to modify or repair the filter by replacing the module with the newer, non-patent-threatening one, then got frustrated that it didn\u2019t work, a desoldered the resistor that connected it to the rest of the synth.<\/p>\n\n\n\n

This project is an incredible opportunity and some deep fun.<\/p>\n\n\n\n

\"\"
Modular systems are a function of industrial society. But do people of The Fifth World still know how to agree to standards? With their acute interest in efficiency, I think they might have carried that lesson forward!<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"

I recently received a truly resplendent gift from my friend Kate: an ARP 2600 synthesizer, owned by their dad, who died recently. It\u2019s in OK shape, but parts of it don\u2019t work, and I\u2019m doing some research to figure out when it was built and what has happened to it since! And I\u2019m going to … Continue reading “Restoring an ARP 2600 Synthesizer”<\/span><\/a><\/p>\n","protected":false},"author":35,"featured_media":10433,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[254,172],"class_list":["post-10410","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-set-of-all-sets-that-do-not-include-themselves","tag-arp-2600-restoration","tag-shrieky-little-machines"],"_links":{"self":[{"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/posts\/10410","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/users\/35"}],"replies":[{"embeddable":true,"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/comments?post=10410"}],"version-history":[{"count":3,"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/posts\/10410\/revisions"}],"predecessor-version":[{"id":10435,"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/posts\/10410\/revisions\/10435"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/media\/10433"}],"wp:attachment":[{"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/media?parent=10410"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/categories?post=10410"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/glyphpress.com\/talk\/wp-json\/wp\/v2\/tags?post=10410"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}