[sdiy] IN your mind, what is .... LM3900

[Tim Parkhurst]

The most excellent Arptech site shows the following schematic for the 4072
VCF (found in the early 2600) using an LM3900

http://www.arptech.synth.net/pdf/4072.pdf


The 4075 VCF (found in the 2810-2823 Odyssey, 2310-2323 Axxe, Omni, Omni-2,
Pro DGX, Avatar, and Quadra) is here

http://www.arptech.synth.net/pdf/4075.pdf

The site also has the mod required to fix the 12KHz bandwidth limit in the
4072 and 4075. 

The earlier 4012, 4034 and 4035 VCFs (moog transistor ladder copy) do not
use the 3900


Tim Servo
"Imagination is more important than knowledge." - Albert Einstein




> -----Original Message-----
> From: Scott Gravenhorst [mailto:music.maker at gte.net]
> Sent: Wednesday, February 04, 2004 1:15 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] IN your mind, what is .... LM3900
> 
> Magnus Danielson <cfmd at bredband.net> wrote:
> >From: Scott Gravenhorst <music.maker at gte.net>
> >Subject: Re: [sdiy] IN your mind, what is .... LM3900
> >Date: Wed, 04 Feb 2004 12:19:43 -0700
> >Message-ID: <200402042019.i14KJhd24670 at linux6.lan>
> >
> >> Dare I bring this back to actual synth-DIY?
> >
> >Sure, confuse the hell out of us by bringing in the sexy chick of
Synth-DIY!
> >;O)
> >
> >> I had asked if anyone could describe what it is that the LM3900 was the
> >> best choice for in analog synth design.  Paul Perry answered that the
Serge
> >> Wave Multiplier uses it, but other than that, there were no other
> >> responses.  I'm assuming now that it isn't all that useful for analog
synth
> >> work other than the SWM module (which looks fun and simple).  This is
> >> probably because it's a current input device, and apparently, there
isn't
> >> much need for a current differencing amplifier in analog synth
electronics.
> >>  My poorly wired cerebrum doesn't seem to pop out anything
über-wonderful.
> >
> >But... didn't the ARP filter module use the LM3900? I seem to recall
that...
> >
> >I'm sure you find the schematic on the web somewhere... I've seen it, but
I
> >don't recall the details very clearly... and I *AM* ashamed for that
fact!
> 
> Thanks!
> 
> On this site is published a schematic of an ARP 4075  (Japanese text
tho.):
> 
> http://www.asahi-net.or.jp/~WZ4K-TNK/diy/arpvcf.html
> 
> and an EFM page with what appears to be an adaptation of a 4072:
> 
> http://www.ele4music.com/vcf7b/vcf7b.html
> 
> I must say, this is a structure that I am not at all familiar with.
> 
> =========================================================
> - Where merit is not rewarded, excellence fades.
> - Hydrogen is pointless without solar.
> - What good are laws that only lawyers understand?
> - The media's credibility should always be questioned.
> - Governments do nothing well, save collect taxes.
> 
> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
> -- Linux Rex         | RedWebMail by RedStarWare
> -- FatMan: home1.gte.net/res0658s/FatMan/
> -- NonFatMan: home1.gte.net/res0658s/electronics/
> -- Autodidactic Master of Arcane and Hidden Knowledge.



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