[sdiy] input buffer question

[Scott Nordlund]

Clamping diodes may also offer the benefit of preventing the dreaded
"phase inversion" distortion that some op amps are susceptible to
in this configuration.  Not that it's likely to be a big issue if you're
powering it from +/- 15V.


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> Date: Mon, 8 Feb 2010 20:53:57 -0800
> From: dixon at interchange.ubc.ca
> Subject: RE: [sdiy] input buffer question
> To: dlmanley at sonic.net
> CC: synth-diy at dropmix.xs4all.nl
>
>> Curious why your ASR input need any different treatment than any other
>> modules?
>
> Dave, to be brutally honest, I was looking at some schematics from a
> "professional" module maker at a mate's the other day, and noticed that all
> off-board inputs to opamps were protected. I thought that perhaps I should
> do the same. Prior to that, I would have simply slapped the follower in
> there without a care in the world. Of course, most such inputs (at least,
> in my modules) are attenuated, and this gives a path to ground. However,
> not so with the follower. I'm sure it's overkill, but it makes me feel
> better, so what the hell?
>
>> BTW, the opamp may already have protection diodes to the rails. With
>> the series resistor on the input to limit current through the internal
>> diodes, are external diodes really necessary? I don't know, just asking.
>
> According to the schematic in the datasheet, TL07x does not have protection
> diodes on the inputs. It has output short circuit protection (and, hence,
> the 1k output resistor we typically put in there is not strictly necessary,
> but I still do it anyway), but the inputs are just bare JFET gates.
>
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