The monopoly actually has two post filer VCA's these are transistor VCAs. The first is to counter act the reduction in level when the resonance is turned up. the second is the VCA controlled by the amp envelope generator. These two stages add a little noise each and make the output of any monopoly a little more noise than some of it's contemporaries. Also as Florian mentioned there is lots of head room going in to the filter as you have four oscillators passing in to the same filter and these can all be sdtacked in hard sync which is pretty loud so your going to here the noise floor if running single oscillators at less than 100%.
To address this issue Lazlo who developed the midipoly kit MIDIpolis was also developing a new vca modification using an IC design. Maybe get in touch with him and see how that has come on.
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From: "freb101@yahoo.com [korg_mono-poly]" <korg_mono-poly@yahoogroups.com>
To: korg_mono-poly@yahoogroups.com
Sent: Monday, 13 April 2015, 17:35
Subject: Re: [korg_mono-poly] Noise problem when key is pressed [1 Attachment]
[Attachment(s) from freb101@yahoo.com [korg_mono-poly] included below]
Thank you for your answer Florian. You are right about the two noises, I didn't noticed the 50hz buzz.
I recorded a new file with VCOs vol at 100%. EG intensity is at 0.
At high cutoff settings the noise it's not so easy to distinguish but, at low and medium cutoff settings, it's imo very audible, especially listening to the recording with headphones.
Maybe it's a normal thing of all Mono/Polys, I don't know. The thing that made me think there's a problem with mine is that it's not a noise floor , which is always present even if no key is pressed, but it's something that pass thru the VCA and goes to the output, even with all VCOs at 0% volume.