[sdiy] LM3900 Sub ( more info then you'd ever wanted! )

[Scott Gravenhorst]

In one of those email exchanges discussing the LM3900, someone else also
pointed out, and I just looked to confirm that the pinout is one of the
stupidest for a 4 amplifier package ever.  I cannot imagine what it was they
were drinking (sterno?) or smoking (road tar?) when the designer did that. 
It's just deplorable.


xyzzy at sysabend.org wrote:
>Because I'm bored, I scrapped my 40k email mailbox for LM3900 emails.
>TI is still making the LM3900
>Jameco.com ( and I'm sure others ) still stock the LM3900.
>NTE has a cross reference that is probably from TI's "maginally defective"
>pile.
>
>And here are the comment cream of the crop :
>( I also need to note that LM3900's seem to come up about every 6 months
>amusingly enough! )
>
>From: "Steve Ridley" <spr at spridley.freeserve.co.uk>
>Date: Sat, 2 Mar 2002 14:43:52 -0000
>
>You could try the LM2900, or the MC3301 or MC3302.                    
>
>
>From: Ian Fritz <ijfritz at earthlink.net>                         
>Date: Sat, 02 Mar 2002 10:19:45 -0700                                  
>
>An upgraded Norton amplifier is the LM359. It is much faster than the 3900,
>which it is intended to replace. DigiKey has them. The downside is that
>they are duals rather than quads, and they are a bit pricey. Has anyone
>tried these for DIY?
>
>
>From: "John Loffink" <jloffink at austin.rr.com>
>Date: Sat, 2 Mar 2002 13:06:49 -0600                                        
>
>Note that some of these equivalents have a more limited supply voltage
>range, 5-18V, not 4-32V like the LM3900s.   Also, I bought some RCA
>3401s from a discount supplier (All Electronics) and the matching of the
>current mirror appears to exceed the specification, causing some
>circuits to fail unless you tweak them.  One clue about these parts was
>that RCA hasn't badged ICs in 10 or 15 years, having gone through a
>series of buyouts by GE, Harris and Intersil. 
>
>
>From: "Paul Schreiber" <synth1 at airmail.net>
>Subject: [sdiy] LM3900 slamming
>Date: Sun, 8 Feb 2004 12:40:48 -0600 
>
>The *original* intent of the device was to control variable-delay windshield
>wipers in cars.
>
>
>From: Grant Richter <grichter at asapnet.net>
>Date: Sun, 08 Feb 2004 13:20:09 -0600
>Subject: [sdiy] LM3900
>
>The LM3900 is not the first choice for audio, because the slew rate is no
>better than a 741. Unless you are using it for a waveshaper where the slow
>slew is good for smoothing diode transients or other glitches with high
>frequency content.
>
>There's four useful circuit topologies that come to mind that, as far as I
>know, can only be done with a CDA.
>
>The first is a full wave rectifier that uses only a single op-amp stage.
>Shown in the ap-notes as a frequency doubling tachometer, it forms the basis
>for the Serge Waveshaper and NTO waveshaper.
>
>The second is a current controlled integrator. Current into the negative
>terminal makes it ramp down, current into the positive terminal makes it
>ramp up. With no control current and proper trimming, it holds the output
>voltage, ramp and hold. Hit either input with a fixed width pulse, and the
>output "steps" up or down. Works great for a linear envelope generator. The
>step generator makes a useable voltage controlled frequency divider.
>
>The third is minimizing parts count for voltage comparators. They eliminate
>several resistors, while providing a robust interface. Bernie Hutchins used
>them as input comparators for the Electronotes ADSRs. One thing he didn't
>explore was the use of a single LM3900 for latching the trigger pulse and
>acting as it's own voltage peak comparator for reseting the latch. Works
>good.
>
>And if you want to make an analog neuron, they are essential:
>http://www.musicsynthesizer.com/Neurons/Neurons1.html
>
>It's an amazingly versatile chip for those who genuinely enjoy the challenge
>of getting the absolute most from the fewest number of parts.
>
>Of course, the advantage to low parts count is low noise, as every active
>device adds some noise to a circuit.
>
>
>
>
>-- 
> -----------------------------------------------------------------
> - Tom Arnold       -  Free Synth DIY webspace http://www.sdiy.org 
> - SynthGeek        -
> - BBD Fanatic      -  "...is it a virus, a drug, or a religion?" 
> - echo evho wjxo   -    Juanita Shrugs. "What's the difference?" 
> --------------------  
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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