[sdiy] JX-3P question

[Richie Burnett]

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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