Amp preamp impedance matching...can anyone explain?

Bifwynne, that is a common problem if you are trying to use a balanced preamp with a subwoofer. Many subs only have SE inputs.

Another solution is that Jensen transformers makes a transformer that is optimized for subwoofers. It has a fairly high impedance input that can be run balanced or SE, and has bandwidth to less than 2 Hz so it does not mess up the bass.

But I think you are lucky you ran into Tom Tutay. He does good work :)

I don't know if this thread is still active (if not I'll have to find another forum).

I'm driving a Quad 303 power amp from the headphone socket of my Yamaha Amp.

From the published specs:

The Quad Power Amp i/p is 0.5V @ 22K ohms impedance

The Yamaha Headphones o/p is 0.51V @ 330 ohms

It looks like the impedance match is ok, but I had to attenuate the signal with 1MΩ resistors which I soldered into the DIN plug (Quad i/p).

What I want to do now is connect to the aux i/p of a Cambridge amp; the impedance is 47KΩ (the signal requirements aren't mentioned in the specs, but I would think it'll be around 15omV). From what I read here this will be a mismatch one option is to solder 47KΩ resistors across the i/p's (sig to scr) in the phono/rca plug; I don't really want to go inside the amp and change the resistors to lower values.

I'll also need to attenuate the signals perhaps with higher values than 1MΩ.

I wonder what the experts think.

Regards:
-Pete

Sorry for reviving this important thread.

In the posts above, we see conversation about output impedance of (tube) preamps that have a coupling capacitor (the fact that, most likely, the output impedance shall be highest at 20Hz).

What about impedance matching for tube preamps like the VAC Renaissance Mk V that have transformer coupled output (and input) stages?

Transformer coupled output is an excellent approach, especially for tube preamps which otherwise contend with the noted issues of output caps and rising impedance. The Ren V claims an even 150 ohms or less over the entire music bandwidth, and so should have no problem driving any SS or tube amp. Using transformer coupling for both inputs and outputs also frees up the preamp circuit to use “only” 2 tubes, and handles SE to balanced (and the reverse) conversions “for free”. 

@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