Amp preamp impedance matching...can anyone explain?

Al, thanks so much for your explanation - I get it now, although coupling capacitors and such are still beyond the scope of understanding for me :)

The only regrettable part in all this is that it seems impossible to determine good impedance matches based on the nominal output impedance spec that the preamp manufacturer will show. Everyone would have to rely on magazines like Stereophile or audio websites to actually review a certain product and show readers the detailed impedance measurements across the whole spectrum in order to do the correct calculation. This is not a problem for popular brands like ARC or Cary, but the lesser known brands might not get a review, and then we audiophiles are taking an educated guess as to whether a preamp is a good match impedance-wise with a power amp.

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”.