AW: Re: external input (again)

[Matt Haines]

>   Right? So would a couple of 1w 16v zeners do?
>
>Ummm, no, that's not what I meant.  What you've drawn is a circuit
>intended to protect the opamp from overvoltage and reverse polarity
>power supplies, but it won't really work.
>
>You never mentioned how you were going to power this thing; I assumed
>it was to be hard wired to the power supply of your synth, but I guess
>I have no idea what you're doing in this respect.  If your unit is
>going to be connected to random sources of power at random times, then
>yes, power supply protection is important.  Otherwise it's not.
>
>I meant input proection like this: Input jack to 1.0k resistor, other
>side of that resistor goes to the anode of a diode to +15v, and to the
>cathode of a diode to -15v, and to the actual input (I guess that
>would be the pot in this case).
>

OK, I get it. The PS will be hardwired to the synth, nothing unusual. I
just interpreted what you said wrong.

>   Like a 30pF cap in parallel with the feedback resistor?
>
>Yes, depending on the specific feedback resistor.  Make it roll off at
>a time constant of 40KHz or so.
>

OK, cool.

>   >It's important... at the very least it will give you the warm fuzzies
>   >about how these things work.
>
>   Hey, I've got the Radio Shack Engineer's Mini-Notebook, the op-amps volume!
>   That's a start. :)
>
>Maybe good, maybe not.  I don't know this publication, so I can't say.
>I suggested Walt Jung because he has a reputation for doing things
>correctly.

I was being funny. :) The Mini Notebooks are these little 50-page booklets
on recycled paper, with sketches on graph paper of op amp circuits. Not
exactly an in-depth publication! I'll look for the Jung book sometime this
week. Thanks again!


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Matt Haines  haines at apc.net         .       .       .       .
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Moonlight, Muzak, Knick-Knack, Paddywack