Electronic – Op Amp in buffer configuration is decreasing output voltage

As TEMLIB pointed out, a comparator is not an op-amp, even if it happens to be drawn as a triangle with with 2 inputs and one output.

A typical design for a comparator is an open drain comparator, which can be modeled like this:

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Here, OA1 is an ideal op-amp. If you connect Vout to V-, you won't get a voltage follower.

Additionally, even if you stick to the world of "true op-amps", there are some restrictions on what op-amps you can use and how you use it. For example, some op-amps are not unity gain stable. Since a voltage follower has by definition a gain of one, trying to build a voltage follower with one of these will always be unstable, and you won't get the desired voltage follower behavior.

You could start with an advertised unity gain stable op-amp and drive it unstable by what you connect the output to and what input waveform you give to the op-amp. It is also possible to do the reverse and add components to stabilize an unstable configuration. There's a wide variety of literature available online on op amp stability.

You'll never get am LM324 to do what you want so why not bite the bullet and use an LM386. It's minimum supply is 4 volts and at 5 volts can produce 4 volts peak to peak. It's intended for audio applications as well and can drive a 4 ohm load (or greater): -

Read the data sheet if you want more details and other application circuits.