Amp preamp impedance matching...can anyone explain?

@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.

Back in the days of tube audio gear in radio stations, almost everything was 600 ohm transformer coupled (inputs and outputs). Some professional broadcast solid state gear was even transformer coupled (not sure why, except for maybe RFI rejection). As you can see in my link above (600 ohm output transformer termination), there is still sometimes on-going discussion on the subject, as some highly sought after vintage pro processing gear has 600 ohm transformer outputs. AKG even made a K240 headphone that was rated at 600 ohms. I’ll have to dig back into some of my old broadcast magazines to refresh my memory on the subject, since it rarely concerns me anymore.