[sdiy] Prophet 5 noise sources

[Dave Manley]

Anybody have the rev2 schematics?

On 3/14/2011 5:54 AM, Harry Bissell wrote:
> I'd have to check the REV3 layout, but its possible that they used two noise sources to eliminate having to route
> the noise signal all over the PCB...
>
> H^) harry
>
>
>
> ----- Original Message -----
> From: Tom Wiltshire<tom at electricdruid.net>
> To: Rutger Vlek<rutgervlek at gmail.com>
> Cc: synthdiy diy<synth-diy at dropmix.xs4all.nl>
> Sent: Sun, 13 Mar 2011 13:39:32 -0400 (EDT)
> Subject: Re: [sdiy] Prophet 5 noise sources
>
>
> On 13 Mar 2011, at 12:28, Rutger Vlek wrote:
>
>>> So there you go! Between Rev 2 and Rev 3, Sequential decided it'd be a good idea to have independent noise sources for modulation and audio. God only knows why!
>>
>> Perhaps they wanted to avoid modulation of an audio noise source with a predictable copy of itself (which might lead to strange effects).
>>
>> Rutger
>
> Perhaps. I suppose you could feed the noise source to the filter, and then modulate the filter cutoff with the same noise source from the wheel.
> This is asking for another Pro-One experiment....one moment...
> <short while later>
> Yes, it looks like you might be right. If I use an external noise source to modulate the filter with the internal noise source fed through it, I get a hissy, noisy sound. If I also plug the external noise source into the audio input (so that the same source is used for audio and modulation) then the sound gets noticeably more "splattery". It's not a huge difference though.
> Still, that's about the only situation I can see that the problem could arise, and I'm surprised they added a chip to improve one probably fairly littel-used sound. (Or are you all modulating your filters with noise sources all the time, and I'm just weird using envelopes?)
>
> T.
>
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