Succeeded! OB-8 has Multimode Filter now!

Haible_Juergen#Tel2743 HJ2743 at
Thu Feb 15 19:06:00 CET 1996


It works. If You like, I will put together a complete description of the Mod
for Music Machines.
On Tuesday, after work, I went to a local electronics dealer to buy the
required 4051's. As these are sensitive CMOS chips, and I intended to
do some weird pin bending on them, I wanted to buy 10 instead of the
8 that I needed. The guy in the shop laughed: "I can offer You three!"
I dropped my hope for an optimized pin layout, and asked for a 4053.
"I got five of these", was the answer. Already feeling some dispair,
I tried the 4052. "No", he said. "Eight is all I have." Well, eight was all
I needed, if I didn't kill one of them. I was quite happy. (They know
they have trouble with me, since I tried to buy a hundred TL074's
for my Vocoder!)
Tuesday evening my wife and I were invited by some friends. When
we came home, I started the surgery on my OB-8. Before I opened
it, I played some notes and asked myself: It sounds so smooth - do
you really want to risk loosing this one?
Believe me, I had trembling hands and a prayer on my lips, when I
took the little rotary grinder to cut the tiny pcb traces!
After some hours of work I had modified the whole upper voice board,
so I could play a "4-voice" in High Pass mode at 3'o clock in the morning.
I was very satisfied and very tired, and I decided to sleep and do the
lower voice board the next day. On wednesday morning I called
at work and asked to take a day off, and I completed the thing.
Oh, and Clive, I nearly broke my skull, when I bumped against a beam
in the loft, in search of this thin wire with an insulation that melts from
the soldering iron's heat (ideal wire for modifications, btw!). Remember:
OB-8's are dangerous for your head! (;->)
How it sounds? Well, if you know how a SEM sounds in HP mode ...
I couldn't do a cross-check with a real n-Voice, but at least it sounds
as good as my SEM-filter clone. All the famous HP filter tricks work.
Nice bass boost with low cutoff  and high resonance!
I often routed the OB-8 thru the SEM-filter clone before, but it makes
a gread difference to have the HP filters available polyphonic and
I still have to start and explore Dual patches with different filters on
Upper and Lower. It definetly works, but I don't get the Notch filter
effect with Upper=HP, Lower=LP and otherwise identical settings.
But then again, I have 4 VCO's per voice instead!
I'm really happy. Now I have almost an Obie 8-voice - fully programmable!
(Yes Gene, it looks like a Mad Max car now - but only on the inside!)

Thanks for listening,


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