Thursday, March 22, 2012

Evolution of the High End, Part 3

There is a fact in physics that states "Maximum power transfer between the source and destination occurs when the output impedance of the source matches the input impedance of the destination." This means that if your preamplifier has an output impedance of 100,000 ohms, then the input impedance of your amplifier should also be 100,000 ohms. Anything else creates problems.

Audiophiles love to swap this piece of gear and that piece of gear without a thought of this principle of physics. Changes heard usually describe "the sound is more mellow, or darker" and even "the sound is now quite bright compared to the other." While theree is no doubt that a great difference exists between various types of electronics, what is also heard is the audible effect of this impedance mismatch.

Unbalanced outputs and inputs are notorious for this mismatch. But despite the promise of better audio (and it does deliver on its own merits), this mismatch can still occur in balanced systems.

How can this be? Balanced connections were supposed to be the Holy Grail of audio...what's up with that?

It's the same issue: impedance mismatching causes problems. No one has settled on a standard and I doubt if we ever will. While some companies do in fact match impedance within their own product lines, impedance mismatches can and do occur regularly within the industry. Balanced cables are primarily quieter and do offer much better immunity to electrical noise, however, other issues can also occur in less than optimal designs.

For example, there is no standard for connecting the shield. I don't know about you, but to me, this is a pretty big OOPS. Ground loops are a huge source of coloration and time smearing and interconnect cables are one source of this problem.  When more a signal has the opportunity to take more than one path (even when the input and output impedance are matched), it will. Like a overflowing rain puddle, it will travel in whatever direction it can find and in many ways as it can to eventually get to the sea.

.It a balanced system better than a single ended system? Maybe, maybe not. If the engineers have done their homework, it will be far better; if not, it will be mediocre at best despite the effort put into the circuit design.

Another related issue is the characteristic impedance of the interconnect cable (this should also match whatever the input/output impedance is). This is why swapping brand X amplifier with brand Y preamplifier creates changes in sound but then changing cables again changes the sound.

Other issues are going on inside interconnect cables even when impedance is matched and no ground loops are inadvertently built into the electronics. Simple single-pulse tests reveal a myriad of issues with improperly designed cables from ringing to echoes to slew-rate limitations to...well you get the idea.  A well designed cable has a lot to consider and a lot to overcome.

So, the next time you swap a piece of gear in your system, think about where the change is really coming from. Is it the new piece of gear? Or is it a better matched input-output impedance? Or is it a better match to the interconnect cable design? Or is it two of these...or all of these...or other issues not mentioned herein?

The answer is in your ears. Trust what you hear and whenever possible compare it to the real thing. Forget the sales hype; it's always a search for new, complimentary adjectives to describe some ethereal property anyway.

Yours for higher fidelity,
Philip Rastocny

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

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