[sdiy] Prophet 5 noise sources

[Tom Wiltshire]

Try this Dave:

http://www.sendspace.com/file/syipi2

(Rev 2 technical manual)

On 14 Mar 2011, at 15:03, Dave Manley wrote:

> 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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