Amp preamp impedance matching...can anyone explain?

@mulveling  @river251 

The Ren V claims an even 150 ohms or less over the entire music bandwidth

That looks to be true, but if you look at the pre-amp specs, the Ren V wants to see a recommended output load of 300 ohms. Most solid state pre-amp's have input ranges of 10K to 47K (using those figures as general examples), which will not provide this load. As the radio broadcast industry segued from transformer outputs, to op amp inputs/outputs, many transformer devices (audio gear) incorporated selectable 600 ohm terminating resistors, so that you could load the transformer output (a perfect example was 600 ohm transformer outputs) if feeding a high impedance input. I think many tube pre-amp owners need to be aware of transformer output loading when feeding a solid state high impedance input. 

Renaissance Mk V Pre Amplifier technical specifications 

@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?

@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.

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.

@mulveling 

You might find this article interesting:

THE 600 OHM AUDIO STANDARD, WHERE DID IT GO?

@mulveling 

Yeah, I guess I drove it off the rails a bit, but no one else seemed to be paying any attention to the original part of the discussion, so I figured no big deal.