Vintage Synth Repair

Indeed, current input is something very different, so I take back what I've wrote about substitution.

Jammie: 'bipolar' in my terminologi would be transistor input, which is the low impedance version. The other one would be FET input (in my vocabulary), sorry if it confused anyone.

Still, the current differential input is a completely different construction and it did not come through to me from the data sheet... Good thing you can order them and so cheap.

--- In vintagesynthrepair@yahoogroups.com, Tom Russell <russelltc@...> wrote:
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> Here's a tutorial I found on how the LM3900 is different from a "regular" opamp:
> http://mysite.du.edu/~etuttle/electron/elect21.htm
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> --- On Sun, 8/19/12, Doug Slocum <dougslocum@...> wrote:
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> From: Doug Slocum <dougslocum@...>
> Subject: [vintagesynthrepair] Re: ARP 2601 (2600) 4072 VCF problem...
> To: vintagesynthrepair@yahoogroups.com
> Date: Sunday, August 19, 2012, 11:49 AM
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>       Argh!  Nooooo!    The 3900 is a completely different type of “opamp”.  It’s VERY likely that it could NOT be replaced with a standard opamp.  It is good that the 3900 (LM3900) is still available because there are so many legacy designs that rely on them.  They are a very useful, yet “white elephant” opamp.  If you think it’s bad, order the real thing.  Substitution will not work.
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