Prophet 5 Noise Circuit

[tomorrowstops]

I hadn't really played around too much with the noise function of my P5 (rev 3.2) until now.

When utilizing the white noise circuit by itself, I'm getting a pulsing signal with it, almost like if the LFO section was leaking voltage. However, no matter what knob I twist, I cannot manipulate the rate of this pulse, nor make it go away.

Is this a problem, or the nature of the beast? My Voyager OS has a nice, pulse free noise circuit.

[snod_donkey]

Well i have just tried my 3.2 with only noise and no modulation and it does have a sort of constant lfo with it... sort of a tick in the sound a bit faster than every second

Never noticed that before so thanks!! Gonna bug me now!

[tomorrowstops]

damn, sorry mang!

at least these two are the same....

anyone else?

[rhino]

Poking my $0.02 in where I have no business. IIRC, many vintage synths generated noise using a shift register - randon 1's and 0's are clocked in a loop, with feedback to keep things stirred up. But, there IS a periodic repeat of sorts that will sound like a pulse.

[snod_donkey]

Yep i was thinking its sounding rather digital - most likely based around a MM5837 ic which goes in a loop so that would explain it.

[adhmzaiusz]

Poking my $0.02 in where I have no business. IIRC, many vintage synths generated noise using a shift register - randon 1's and 0's are clocked in a loop, with feedback to keep things stirred up. But, there IS a periodic repeat of sorts that will sound like a pulse.

I also read this and indeed it is true with the P5, you are hearing the loop

[snod_donkey]

Just checked the circuit and yes there is a 5387 in the noise circuit... that being the case i would say your sound is ok

[EdGs]

This might be of help

http://dsiforum.org/viewtopic.php?t=912

[tomorrowstops]

Sweet, very helpful post indeed, EdGs!

A little beyond my capabilities, but once my techie pal gets my Linndrum all ship shape, I'll see what he can do with this circuit!

[snod_donkey]

Sweet, very helpful post indeed, EdGs!

A little beyond my capabilities, but once my techie pal gets my Linndrum all ship shape, I'll see what he can do with this circuit!

Nice.. have a p5 and also got a Linndrum last week. Just rebuilt and serviced it too

[EdGs]

You're welcome! It seems to be a neat mod to do. However, the noise chips in my P5 are not marked MM5837, instead 8119DB. I'm not quite sure what the deal is there. Possibly an upgraded chip or different manufacturer's # for an eqivalent part? Mine's a rev. 3.3 s/n 4992.

[snod_donkey]

Noise ic should be U366 and in the service manual is shown as a 5837 but this was a rev 2 i was looking at so it may well have changed later


Just found a later rev manual and it says u427 5837

[EdGs]

Yeah, the rev.3 tech manual says 5837. But that pic is U427 in my machine. The other noise chip on board 3 (U375)is the same. I could not locate a datasheet for this one either. Definately strange.

[tomorrowstops]

Sweet, very helpful post indeed, EdGs!

A little beyond my capabilities, but once my techie pal gets my Linndrum all ship shape, I'll see what he can do with this circuit!

Nice.. have a p5 and also got a Linndrum last week. Just rebuilt and serviced it too

shooooot - meaning you are now playing with it? I bought mine non-functioning over a month ago. Turn it on, no lights, no sound (except for the humming xformer). Batteries exploded all over the power supply board. Cleaned it up, replaced the batteries, recapped the power supply, still nothin'. Currently reading about replacing the xformer....

*sigh*

[bhrama]

Yeah, the rev.3 tech manual says 5837. But that pic is U427 in my machine. The other noise chip on board 3 (U375)is the same. I could not locate a datasheet for this one either. Definately strange.

I have a rev 3.0 and mine says the same thing...

Also did the whole sound check and its quite similar, if not identical to what you all describe as "digital" sounding, in that it seems to have a a pattern.