[sdiy] JX-3P question

[Richie Burnett]

That sounds cool.  Thanks Adam.  I definitely need to give this a try when I 
get my JX-3P put back together :-)

-Richie,

-----Original Message----- 
From: Adam (synthDIY)
Sent: Monday, January 19, 2026 10:17 PM
To: rburnett at richieburnett.co.uk
Cc: synth-diy mailing list
Subject: Re: [sdiy] JX-3P question

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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