The Spark Gap Podcast - Episode 41

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Show Synopsis

Karl and Corey are joined by Chris Gammell to talk about how to pick the right op-amp.  Part 1 of 2.

Part of the Podcast

Ad553x: Dual Output DAC

MAX7400: 8th-Order, Lowpass, Elliptic, Switched-Capacitor Filters

First Page of a Datasheet

We started off by talking about lies found on the first page of a datasheet.

Corey mentioned Mosfet datasheets with their fantastical rated Id current. We mentioned that those current ratings mean very little unless you understand the limitations imposed by the specified Safe Operating Area of the transistor.

Here is Bill Herd giving a great explanation of what SOA is:

Opamp Specifications

We talked about the various specifications of a typical opamp.
There are a multitude of pdfs and blogs discussing the various parameters in an opamp’s datasheet. So, I let you do the googling on it.

One example I liked was this short and simple pdf that discusses the LM741 opamp’s datasheet.

The link in that pdf leads to National Semiconductor which was acquired by TI.

So here is a working link to the LM741 if you are curious.

Note: Chris hates LM741s.

Also, I have mentioned this resource in past episodes but I will do it again.

Go download the Op Amp Applications Handbook from Analog Electronics:

Resistor Noise

I mentioned resistor thermal noise. It is more commonly referred to as Johnson Noise.
Here is your obligatory wikipedia link:

Grinds my Gears

I mentioned having a little bit of a hard time with the current range switching of the Keithley 2460.
Here is the piece of kit I was talking about:

Here is The Signal Path doing an excellent review of it:

Chris is helping to make finding parts a lot less painful with his job at
I use it personally and it has saved me a ton of time already.
In my humble opinion, it is a big step in the right direction and has continued to get better as I’ve been using it. Try it out at: just recently opened to the public..i.e no more need to signup to use it.

You can read a little more about it on’s blog:

Chris mentioned that there was a blog post discussing how they calculated risk.
Here is a direct link to that post in case you are short on time:

To Be Continued…

Tune in to the next episode for more exciting conversation with Chris Gammel!