[sdiy] JX-3P question

[rburnett at richieburnett.co.uk]

That's interesting Adam. I didn't know the JX-3P could do that!

I don't see a modulation path from the analogue noise source to the DCOs 
though, so I guess the noise modulation you mention must be done 
digitally by the micro?

-Richie,


On 2026-01-18 21:52, Adam (synthDIY) wrote:
> 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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