Amp preamp impedance matching...can anyone explain?

@dpop it specifies a recommended load impedance of greater than 300 ohms. That includes loads like 10K, 50K, 500K, etc. This is not like matching taps on power amp transformers, where maximum power transfer is the goal. Here we are only concerned with transferring voltage signal, where Ohm’s law dictates a good transfer. That means you want as low an impedance on the source side (150 ohms being very low for a preamp, especially at 20 Hz), and a “sufficiently high” impedance on the amp side (300 ohms being far lower than typical). It is reasonable to aim for a load impedance 20x (or more) greater than the source impedance to minimize losses caused by voltage division.

@mulveling

it specifies a recommended load impedance of greater than 300 ohms

I totally understand the concept of solid state low impedance op amp output feeding a solid state op amp high impedance input. No questions there, but these transformer outputs (if that’s what the Ren MK V has) have confused me in the past. There’s no doubt in my mind about terminating 600 ohm transformer outputs before feeding them to solid state op amp inputs. That’s definitely necessary, but I’m not 100% sure in this situation if a 300 ohm termination is needed. I suppose Renaissance technical support could answer that question.

600 ohm output transformer termination?

It’s absolutely not needed here. In fact, I think it would be a very bad idea to feed a Ren V into 300 ohms - that’s the lowest impedance that it will work “ok” with. I’ve used the Ren V into 100K ohm tube amps no problem. I now use the VAC Master, same circuit, same specs, same deal (just better sound quality from premium parts and PSU). Also works great into a SS amp. The “> 300 ohms” spec is intended as a flexibility boast, not a requirement or limitation. Many tube preamps will require a minimum load of 10K or higher, which can become a restriction with some SS amps.

@mulveling

OK, that sounds good to me. Maybe you can explain (in better terms) the need for the 600 ohm terminating resistors with older transformer 600 ohm output gear?

Many tube preamps will require a minimum load of 10K or higher, which can become a restriction with some SS amps.

Interesting. I don’t think I’ve ever seen a solid state audio impedance input rating lower than 10K.

I can’t, because I don’t know what gear that is or its intended use (you mentioned radio broadcast). A 600 ohm load requirement doesn’t sound like anything related to high end home audio, honestly. I can speak to the VAC Renaissance V because I owned one and know its intended application. It is designed to work well with as wide a range of 2ch SS and tube power amps as possible.