Mix and match impedance

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Popular audiophile lore has it that a mismatch in impedance between the preamp and amplifier will result in bass loss. Yup. If the amp's input impedance is too low weaker bass will be the result. That's true in the same way it's important to pump the car's accelerator before starting it. In the days of carburetors, a cold engine started easier when you primed the pump with a few squirts of gas. I remember a manual choke on cars that had to be pulled when they were first started. But no modern car has a carburetor just like no modern amp has impedance so low it would impact a preamp. But it was once true. Preamps of old, especially tube preamplifiers, were capacitor coupled (many still are). On preamplifiers where sound and performance mattered high-quality film capacitors were used at their output, which meant values were small. And, small capacitors result in rolled off bass in the presence of low impedances. This is because the preamp's output capacitor and amplifier's input resistor form a high pass filter (reducing low bass). But today we need not worry about such matters. Most power amplifiers have input impedances of at least 20kΩ and higher. Our own power amps, for example, have 30kΩ input impedance, high enough to never reduce bass levels of capacitor coupled preamplifiers, even if they are the vintage kind. So yes, matching impedances used to be a thing to worry about. Modern designs have obviated the need for hand-wringing. I put together a small video on the subject you can watch here.
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Paul McGowan

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