I have had several people ask about the actual modifications I performed on
my OMNI-VI+ (Option 3 Upgrade). I really did not do anything
extraordinary. I basically followed the suggestions listed by Piotr
Tomczak in his posts about the OMNI synthesizer noise. This board lacks
sufficient de-coupling caps, and the POWER (+5V) and GROUND connections to
the IC's are made with SIGNAL size traces are what I consider to be a
problem. The second part of the last sentence is what I feel causes the ~5
Ohm resistance between pin 26 and pin 57 of the DSP chip. I added
de-coupling caps between the POWER (+5V) and GROUND pins on all the digital
IC's. The value of these caps is NOT critical you can use .1uF, .01uF or
.001uF 50V CERAMIC caps. I did not have enough of any one value, so I used
some of each of the previous values. I also soldered a piece of 24ga.
Teflon wire between pin 26 and pin 57 of the DSP, this eliminated the ~5
Ohm resistance. I did NOT add any ferrite beads to any of the
interconnecting cables other then the incoming +12V line, for that I used a
small snap on ferrite I had handy wrapping the +12V wire twice through this
ferrite. As I said in my previous post, I CANNOT say for sure which mod
made the difference, but I have a SIGNIFICANT reduction in birdies across
the bands
73
Warren Walsh - K2BM
==================================================================
Warren J. Walsh (warrenw@pentek.com) Pentek, Inc.
Design Engineer One Park Way
Phone: (201) 818-5900 x 251 Upper Saddle River, NJ 07458
Fax: (201) 818-5941 http://www.pentek.com/
==================================================================
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