[sdiy] JX-3P question

[Adam (synthDIY)]

It's an undocumented feature.
In the manual, it would appear that LFO modulation is restricted to sine, square or random (Edit group B, option 10, buttons A B or C). However, if you hit the fourth button "D" you get a noise source modulation that can affect both the oscillators and filter, depending of course how much mod you have dialled in for these areas.
(Side note: the LFO Delay function also works on this noise source, for those times where you want your delicate synth-brass sound to be slowly taken over by short-wave radio hash... erm..)

But, no, I don't know the actual source of that noise modulation....
I do know I'm gonna need another coffee before I open the service manual though...

A

> On 20 Jan 2026, at 07:31, rburnett at richieburnett.co.uk wrote:
> 
> 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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