<html aria-label="message body"><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><span style="font-family: Monaco;">oops, I sent that from the wrong email.</span><div><span style="font-family: Monaco;"><br></span></div><div><span style="font-family: Monaco;"><br></span></div><div><span style="font-family: Monaco;"><br></span></div><div><span style="font-family: Monaco;"><br></span></div><div><span style="font-family: Monaco;">Is this guy suggesting that the variation from ideal models and a real unit are all up to aging, not that the components had super wide tolerances, like 5 or 10% resistors and upwards of +/-20% capacitors? Then they aged 40 years. I mean, this article gives the impression that there is not variation unit to unit, or “good sounding” 909s, but all of them sound the same, just aged.</span><br style="font-family: Monaco;"><span style="font-family: Monaco;">I can tell you from experience that real units sound different from each other.</span><br style="font-family: Monaco;"><br style="font-family: Monaco;"><br style="font-family: Monaco;"><span style="font-family: Monaco;">Mark</span><br style="font-family: Monaco;"><br style="font-family: Monaco;"><br style="font-family: Monaco;"><br style="font-family: Monaco;"><br style="font-family: Monaco;"><br style="font-family: Monaco;"><blockquote type="cite" style="color: rgb(0, 0, 0); font-family: Monaco;">On Sep 1, 2026, at 03:59, cheater cheater via Synth-diy <<a href="mailto:synth-diy@synth-diy.org">synth-diy@synth-diy.org</a>> wrote:<br><br>Really interesting stuff:<br><br><a href="https://www.reddit.com/r/DSP/comments/1w2z13c/every_surviving_tr909_is_40_years_old_what_does/">https://www.reddit.com/r/DSP/comments/1w2z13c/every_surviving_tr909_is_40_years_old_what_does/</a><br><br>quoted below.<br><br>PS Some people say he might have used AI to write this. Best as I can<br>tell it's not AI written, but what do I know. It seems like the<br>research is legit. Maybe he used it for rephrasing his notes into a<br>post. Or maybe we're seeing a phenomenon where people who use AI a lot<br>just start talking like it. Historical linguists will have a field day<br>on this 100 years from now, in case we survive that long...<br><br>-----------<br><br>by BeatForge_Dev<br><br>Every surviving TR-909 is 40 years old. What does "authentic" even<br>mean when the schematic and every living unit disagree in the same<br>direction?<br><br>I'm modelling the TR-909 the way I modelled the 808 and 606 before it:<br>component by component from the service notes, with one hard rule - no<br>fitted or matching EQ anywhere. Every filter, every time constant,<br>every gain in the model has to trace back to a component that is drawn<br>on the schematic, or it doesn't ship. Validation is against recordings<br>of real units (multiple machines where I can get them), but the<br>recordings are the gate, never the source: when the drawing and a<br>recording disagree, I don't get to turn a knob until they agree. I<br>have to find out why.<br><br>That rule is what made the following visible, because without it I<br>would have EQ'd the discrepancies away in an afternoon and learned<br>nothing. As the model got close - close enough that the remaining<br>deviations were a dB here, a few percent of a time constant there -<br>the residuals stopped looking like noise. They grouped. Specifically,<br>they grouped by what the component that owns each parameter is made<br>of.<br><br>Time constants owned by tantalum capacitors read consistently long, by<br>14 to 19 percent, on every unit measured. The 909's tom body decay is<br>set by a tantalum; every reference unit decays 14-19% slower than the<br>drawn RC says it should, and they all miss in the same direction.<br><br>A recovery time owned by an aluminium electrolytic reads consistently<br>short. The hand clap has a roughly 228 ms recovery between hits set by<br>an electrolytic; on both units I could measure, the effective<br>capacitance comes out around 0.83 times the drawn value. Electrolytics<br>dry out and lose capacitance - this is the single best-documented<br>aging mechanism in the business, and it points exactly this way.<br><br>A clock frequency owned by a carbon-composition resistor reads<br>consistently high, by about 16 percent - on four different machines.<br>Carbon comps drift upward with age, heat and humidity; four units<br>agreeing on the direction and roughly the magnitude is not a lottery.<br><br>And the control that makes this believable: not everything drifts. The<br>kick's poles sit dead on the drawn values across units. Film caps and<br>metal film resistors holding their values while electrolytics sag,<br>tantalums stretch and carbon comps climb is exactly what a 40-year-old<br>PCB should look like. If every parameter had missed, I'd have<br>suspected my own readings of the schematic. The residuals sorting<br>cleanly by dielectric and resistor construction is what flipped my<br>interpretation: these aren't model errors. The model was measuring the<br>age of the reference units.<br><br>Which lands you somewhere genuinely strange for validation. The<br>schematic describes the machine Roland built in 1984. Every recording<br>anyone can make today describes a machine that has been drifting away<br>from that schematic for four decades - and drifting coherently,<br>because the same chemistry is running in every unit. So a model that<br>is exactly right by the drawing will sit at a small, systematic,<br>same-signed offset from every reference you can buy or record. If you<br>validate purely by fitting to samples - which is the industry default<br>- the fit will happily absorb one particular elderly unit's drift,<br>your metrics will reward you for it, and you will ship "authentic<br>1984" with today's electrolyte chemistry baked in.<br><br>Edit:<br><br>After listening more and more, i prefer the old values, Toms and Kick<br>have more sustain, it just sounds more alive and less stiff.<br><br>Question for the room: has anyone treated component aging as a<br>first-class model parameter rather than a nuisance? Tape emulations<br>have had "worn" controls for years, but those are usually designed<br>sounds, not chemistry-driven parameter drift. And if anyone has good<br>literature on solid tantalum capacitance drift over multi-decade<br>timescales, I'd genuinely like to read it - the electrolytic and<br>carbon-comp stories are textbook, but the tantalum shelf is thinner,<br>and right now my 14-19% is a measurement in search of its chemistry<br>paper.<br><br>Disclosure: I make a commercial drum plugin, this work is in it.<br>________________________________________________________<br>This is the Synth-diy mailing list<br>Submit email to: <a href="mailto:Synth-diy@synth-diy.org">Synth-diy@synth-diy.org</a><br>View archive at: <a href="https://synth-diy.org/pipermail/synth-diy/">https://synth-diy.org/pipermail/synth-diy/</a><br>Check your settings at: <a href="https://synth-diy.org/mailman/listinfo/synth-diy">https://synth-diy.org/mailman/listinfo/synth-diy</a><br>Selling or trading? Use <a href="mailto:marketplace@synth-diy.org">marketplace@synth-diy.org</a></blockquote></div></body></html>