To go back to the original question about whether there is a model ratio for component costs, I would suggest that the speakers should determine the amplifier chosen. Rather than cost, the key issue is the power required to properly reproduce the kind of music you like at the volume you like, in the room in which you listen. Simplistically, highly efficient speakers require less power than less efficient speakers. Large listening rooms generally require more power than smaller ones. More power is a safer bet than not enough.
And let’s not forget the impedance of the speakers. Speakers rated at 4 ohms need amps that can deliver the required power at that impedance, not at 8 ohms. Furthermore, some speakers function at an impedance as low as 2 ohms at some frequencies. Inexpensive amps may well noticeably distort at such a low impedance. So try to match the speakers you like (and can afford) with an amp that can drive them and bring out the best in those speakers.
With respect to those suggesting that $500 is all you need to spend for an amp or that an iPhone will suffice as a source, perhaps they would benefit from auditioning somewhat better equipment. Or maybe they listen primarily to rock at high volumes and can’t differentiate between the distortion of the electronic instruments used in the recording vs. that generated by their audio equipment. Listen to an acoustic guitar through an iPhone vs. a modestly priced DAC like a Dragonfly and I am reasonably confident they will hear more lifelike and otherwise improved sound.
And let’s not forget the impedance of the speakers. Speakers rated at 4 ohms need amps that can deliver the required power at that impedance, not at 8 ohms. Furthermore, some speakers function at an impedance as low as 2 ohms at some frequencies. Inexpensive amps may well noticeably distort at such a low impedance. So try to match the speakers you like (and can afford) with an amp that can drive them and bring out the best in those speakers.
With respect to those suggesting that $500 is all you need to spend for an amp or that an iPhone will suffice as a source, perhaps they would benefit from auditioning somewhat better equipment. Or maybe they listen primarily to rock at high volumes and can’t differentiate between the distortion of the electronic instruments used in the recording vs. that generated by their audio equipment. Listen to an acoustic guitar through an iPhone vs. a modestly priced DAC like a Dragonfly and I am reasonably confident they will hear more lifelike and otherwise improved sound.