[sdiy] NJM2068 gone bad

Tom Corbitt tom.corbitt at gmail.com
Thu Jun 25 00:23:33 CEST 2020


Just to clarify, was the system and/or part known good when it shipped out?

Assuming it was, you mention the protection ESD diode and reverse
protection but I wonder does the circuit have any other protection for
voltages below ESD levels but over the safe maximum for the chip?

 I see +/- 18V max listed on the datasheet I looked at.

That's just my first instinct, that someone plugged in something with too
great of a potential and it damaged one of the two channels.

It's easy enough to test and there are very simple fixes if it is an issue
(36V zener with a current limiting resistor in parallel with input is a
very basic old school way to do it, plenty of smarter folks here on the
list with better ideas and ways I'm sure)

Tom


On Wed, Jun 24, 2020 at 1:23 PM Frédéric (Opensource) <marzacdev at gmail.com>
wrote:

> Hi to everyone,
>
> In a client audio design, I used a NJM2068 dual op-amp
> as the input signal conditioner before the ADC circuit.
>
> The op-amp is powered with symmetrical supply rails (+12V, -12V)
> provided by the power bus of an eurorack system.
> Rails are protected by series shottky diodes therefore the
> case of a polarity reversal can be discarded I presume.
>
> Audio input has an ESD protection diode and the impedance
> between the + input of the amp and the input jack tip is about
> 20k (resistor). The input is specified for "eurorack level" signals.
>
> Unfortunately, after the field tests, we got back one module
> whose input op-amp had a defective channel. Input signal would
> be saturated while being far away from the rails.
>
> Had any of you a bad experience with this component?
>
> I am also open for all suggestions about what wrong could
> have happened?
>
> Best from Bonn,
> Frédéric
>
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