[sdiy] Guy researches and talks about how aging components change the sound of a synth

[cheater cheater]

now we have your secret email

On Tue, Sep 1, 2026 at 10:44 AM mark verbos <markverbos at gmail.com> wrote:
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> oops, I sent that from the wrong email.
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> 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.
> I can tell you from experience that real units sound different from each other.
>
>
> Mark
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> On Sep 1, 2026, at 03:59, cheater cheater via Synth-diy <synth-diy at synth-diy.org> wrote:
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> Really interesting stuff:
>
> https://www.reddit.com/r/DSP/comments/1w2z13c/every_surviving_tr909_is_40_years_old_what_does/
>
> quoted below.
>
> PS Some people say he might have used AI to write this. Best as I can
> tell it's not AI written, but what do I know. It seems like the
> research is legit. Maybe he used it for rephrasing his notes into a
> post. Or maybe we're seeing a phenomenon where people who use AI a lot
> just start talking like it. Historical linguists will have a field day
> on this 100 years from now, in case we survive that long...
>
> -----------
>
> by BeatForge_Dev
>
> Every surviving TR-909 is 40 years old. What does "authentic" even
> mean    when the schematic and every living unit disagree in the same
> direction?
>
> I'm modelling the TR-909 the way I modelled the 808 and 606 before it:
> component by component from the service notes, with one hard rule - no
> fitted or matching EQ anywhere. Every filter, every time constant,
> every gain in the model has to trace back to a component that is drawn
> on the schematic, or it doesn't ship. Validation is against recordings
> of real units (multiple machines where I can get them), but the
> recordings are the gate, never the source: when the drawing and a
> recording disagree, I don't get to turn a knob until they agree. I
> have to find out why.
>
> That rule is what made the following visible, because without it I
> would have EQ'd the discrepancies away in an afternoon and learned
> nothing. As the model got close - close enough that the remaining
> deviations were a dB here, a few percent of a time constant there -
> the residuals stopped looking like noise. They grouped. Specifically,
> they grouped by what the component that owns each parameter is made
> of.
>
> Time constants owned by tantalum capacitors read consistently long, by
> 14 to 19 percent, on every unit measured. The 909's tom body decay is
> set by a tantalum; every reference unit decays 14-19% slower than the
> drawn RC says it should, and they all miss in the same direction.
>
> A recovery time owned by an aluminium electrolytic reads consistently
> short. The hand clap has a roughly 228 ms recovery between hits set by
> an electrolytic; on both units I could measure, the effective
> capacitance comes out around 0.83 times the drawn value. Electrolytics
> dry out and lose capacitance - this is the single best-documented
> aging mechanism in the business, and it points exactly this way.
>
> A clock frequency owned by a carbon-composition resistor reads
> consistently high, by about 16 percent - on four different machines.
> Carbon comps drift upward with age, heat and humidity; four units
> agreeing on the direction and roughly the magnitude is not a lottery.
>
> And the control that makes this believable: not everything drifts. The
> kick's poles sit dead on the drawn values across units. Film caps and
> metal film resistors holding their values while electrolytics sag,
> tantalums stretch and carbon comps climb is exactly what a 40-year-old
> PCB should look like. If every parameter had missed, I'd have
> suspected my own readings of the schematic. The residuals sorting
> cleanly by dielectric and resistor construction is what flipped my
> interpretation: these aren't model errors. The model was measuring the
> age of the reference units.
>
> Which lands you somewhere genuinely strange for validation. The
> schematic describes the machine Roland built in 1984. Every recording
> anyone can make today describes a machine that has been drifting away
> from that schematic for four decades - and drifting coherently,
> because the same chemistry is running in every unit. So a model that
> is exactly right by the drawing will sit at a small, systematic,
> same-signed offset from every reference you can buy or record. If you
> validate purely by fitting to samples - which is the industry default
> - the fit will happily absorb one particular elderly unit's drift,
> your metrics will reward you for it, and you will ship "authentic
> 1984" with today's electrolyte chemistry baked in.
>
> Edit:
>
> After listening more and more, i prefer the old values, Toms and Kick
> have more sustain, it just sounds more alive and less stiff.
>
> Question for the room: has anyone treated component aging as a
> first-class model parameter rather than a nuisance? Tape emulations
> have had "worn" controls for years, but those are usually designed
> sounds, not chemistry-driven parameter drift. And if anyone has good
> literature on solid tantalum capacitance drift over multi-decade
> timescales, I'd genuinely like to read it - the electrolytic and
> carbon-comp stories are textbook, but the tantalum shelf is thinner,
> and right now my 14-19% is a measurement in search of its chemistry
> paper.
>
> Disclosure: I make a commercial drum plugin, this work is in it.
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