[sdiy] Need one of two things....

[Paul Perry]

The most incomprehensible thing about the LM3900 is the pinout.

------ Original Message ------
From: "Pete Hartman" <pete.hartman at gmail.com<mailto:pete.hartman at gmail.com>>
To: "Oren Leavitt" <obl64 at ix.netcom.com<mailto:obl64 at ix.netcom.com>>
Cc: "synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org> DIY" <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>>
Sent: 31/10/2020 2:53:12 PM
Subject: Re: [sdiy] Need one of two things....

A bit of an extreme approach when troubleshooting a different circuit, but sure :D

Pete

On Fri, Oct 30, 2020 at 9:10 PM Oren Leavitt <obl64 at ix.netcom.com<mailto:obl64 at ix.netcom.com>> wrote:


On 10/30/20 8:42 PM, Pete Hartman wrote:
Thanks Neil!

Currently trying to absorb it.... :)

Pete


Clone a PAiA Gnome - It'll give you a feel for how Norton op-amps work.


On Fri, Oct 30, 2020 at 7:52 PM Neil Johnson <neil.johnson71 at gmail.com<mailto:neil.johnson71 at gmail.com>> wrote:
Hi Pete,

TI's AN-72 is a pretty good read on how Norton op-amps work and many
applications, including all the "standard" circuit blocks:
https://www.ti.com/lit/pdf/snoa653

Neil

On Sat, 31 Oct 2020 at 00:09, Pete Hartman <pete.hartman at gmail.com<mailto:pete.hartman at gmail.com>> wrote:
>
> 1) Is there anyone with experience or a pointer to a description of how the Serge '73 R7 envelope generator works?  Basic googling gets me various summaries of Ken Stone's page where "a little on how it works" is just the schematic.  Got that, don't grok it in the slightest...
>
> ...Because I don't really "get" Norton Amplifiers.  (I have been able to repair VCS' in the past but leaned very heavily on Tim Stinchcombe's description of how it worked).  I mean yes, I understand logically "current differencing" but in practical uses I can't look at a topology and say "oh yes, this is an inverter/summer with gain X" the way I can with a standard Op Amp.
>
> So
>
> 2) out of all of the various circuit simulation tools that have been discussed, which one or ones has a decent Norton Amp simulation?  Simulation is usually my go to with circuits that don't follow "standard" often used topologies (standard like an expo converter, or integrator/differentiator, etc).  I'm one of those who has long leaned on the Falstad javascript simulator, and they do NOT have a Norton Amp (at least not as far as I could tell, no promises that I didn't miss something).
>
>
> I've got one of ZThee's 73-75 panels and none of the three EGs will cycle in the usual way.  Power looks good, components have not been 100% verified but everything I've checked directly against the circuit appears to be correct.  Nothing is hot.  Soldering is solid (I resoldered a few joints here and there, but mostly out of an abundance of caution).  None of the usual first step troubleshooting methods has borne fruit so I'm now into "ok I have to understand the circuit well enough to know what each bit of it SHOULD be doing when I have end connected to start or cycle."
>
> Thanks!
>
> Pete
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