[sdiy] JX-3P question

[synth at schmitzbits.de]

That. You see the buffers and S&H caps on the left, there is a DC under control of the processor.
With VR32 you even out the variations in amplitude of the noise transistor, by changing the control sensitivity.

Cheers,
 René
________________________________
Von: Synth-diy <synth-diy-bounces at synth-diy.org> im Auftrag von Adam (synthDIY) <synthdiy at adambaby.com>
Gesendet: Sonntag, 18. Januar 2026 22:52
An: Richie Burnett <rburnett at richieburnett.co.uk>
Cc: synth-diy mailing list <synth-diy at synth-diy.org>
Betreff: Re: [sdiy] JX-3P question

I wonder if it has something to do with the noise modulation option in the JX3P, rather than just the use of noise as part of the patch mix?

Noise modulation is available from the front panel but not from the PG-200

A

> On 19 Jan 2026, at 05:47, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>
> Thanks for the confirmation everyone.
>
> It just seemed like a strange thing to include what must have been an expensive BA662 OTA device at the time, instead of using yet another trim-pot to calibrate the noise level.
>
> Obviously the AGC approach would try to correct for long-term drift of the noise level and possible variation with temperature, but that can't account for that much amplitude variation, and the user can adjust the level of noise in the mix anyway!  I would have thought the AGC circuit would need to measure the RMS of the noise in order to accurately control its perceived loudness anyway?
>
> It's interesting that it's used in other synths of the era like the Juno 6 & 60 and a variant in the Jupiter 6, but the Juno 106 design went back to using a trim-pot again (VR32).  (See attached.)
>
> JX-8P and the Alpha Juno / MKS50 got the luxury of digital noise sources!
>
> -Richie,
>
>
>
> -----Original Message----- From: Florian Anwander via Synth-diy
> Sent: Sunday, January 18, 2026 6:15 PM
> To: synth-diy mailing list
> Subject: Re: [sdiy] JX-3P question
>
>
>
> Hello Richie
>
> Am 18.01.26 um 18:13 schrieb Richie Burnett:
> but on closer inspection it looks like the OTA is in some sort of local feedback loop, intended to keep the noise amplitude constant, maybe?
>
> I never investigated deeper on this circuit, but that is my impression too. Roland used that in the JX3P and in the Juno6/60. A similar circuit was used in the Jupiter6:
>
>
>
>
>
>
> I don't remember the JP8.
>
> Florian
>
>
>
>
>
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