Op-amp matching simulation vs expectations

Hello,

I had just a question about matching op-amps to 50 ohm devices/ circuits, and a quick follow up concerning some results I saw in LT-spice

I created a non-inverting amp and filter.

As per suggested by a previous solution, when i want to cascade the filter and amp, I need a 50 ohm termination at the input of the amp.

When i reverse the situation and have the amp drive the filter, I used series 50 ohm resistor. Perhaps the answer is obvious, but is the voltage difference at the output, compared to the amp alone, is due to dissipating power in BOTH the series 50 ohm and 50 ohm load?

When I remove the series 50 Ohm resistor, i expected the frequency response of the filter to change, but it didn't? And i was able to recover the power dissipated in the series 50 Ohm. Is this OK to do in reality?

Thanks for the help

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Those pictures couldn't have turned out worse, here is a larger version

View attachment Presentation1.pdf

It's unnecessarily wasteful to drive loads 50 ohms between stages. Redesign component values so the filters draw low current, and keep your desired rolloff curves.

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Conserve Amperes until you run them through your final output stage 50 ohms.

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Anyway most op amps are not intended to drive 50 ohms, unless it's designated a power op amp.

You may need to install a discrete half-bridge, to drive the final output.

General purpose OPs like OP07 aren't suited to drive 50 ohm load with higher signal level. You don't see output current limitations in your small signal simulation. A LC filter designed for OP interface should better use a higher characteristic impedance. It's also possible to design the filter for asymmetric termination, e.g. high load impedance.

The frequency response of LC filters is generally affected by source and load impedance, but the difference is apparently not so strong in this case.

50 ohms is only for transmission line connections of
that characteristic impedance. You may need it at the
front, if that's how the signal come in and you may
need it at the back, if that's where it's going. But on
a short-haul PCB at frequencies an IC op amp can
work properly at, there's no reason to burden the
signal and its source otherwise.

There are line drivers (like LH0063, hen's teeth but
a solid performer) which are made to drive 50 ohm
loads from megohm input impedance and up to
100MHz. Looks like an op amp, only with oomph.