MPS Noise Problem

bubzy · Posted: Fri Apr 01, 2011 4:18 am Post subject: MPS Noise Problem

have just completed the awesome MPS and while playing with it have noticed that the noise is hardly noticeable, this makes any sort of "snare" sound difficult to acheive. any help would be greatly appreciated.

jordroid · Joined: Jan 17, 2010 Posts: 193 Location: ithaca, new york

If i'm not mistaken Q1 (schematic page 1) is the "noise" transistor, you might try auditioning different NPNs in that spot till you find the best sounding one. A socket here might be a good idea.

The noise goes through a voltage divider before being fed into the state variable filter, so you could mess with R11 as well. Bigger R11 means more noise, smaller R11 means less noise. You have to be a bit careful here because LM13700s don't like a large voltage input, 20mV peak to peak max is usually recommended in most designs i'm familiar with.

Oooh, i just thought to check out Scott Stites MPS page, and Thomas pretty much says the same thing, here http://www.birthofasynth.com/Thomas_Henry/Pages/MPS_project.html about halfway down the page in blue right after this "Here's a description of Sheet 1 in Thomas Henry's own words:"

cheers

jordan Smile