Current amp vs Voltage amp

Unsound,

If the output impedance of the amplifier is a good match for the particular speaker, the output of the amplifier WILL adapt appropriately.

Think of the amplifier as an amplifier having zero output impedance in series with a resistor whose value corresponds to the actual output impedance. If the impedance of the speaker varies significantly as a function of frequency, and if the amplifier's output impedance is significantly greater than zero (e.g., 1 or 2 or 3 ohms or so, as in the case of most tube amps), the voltage divider effect resulting from the interaction of that output impedance (corresponding to Z1 in the first figure of the reference) and the impedance of the speaker (corresponding to Z2 in the first figure of the reference) will result in the voltage at the amplifier output/speaker input varying as a function of frequency. If the amplifier's output impedance is a good match for the design of the particular speaker, that variation in amplifier output will result in minimal variation of the output of the speaker, as a function of frequency.

Audiolabyrinth,

I didn't say that amps operate in a current mode and a voltage mode. Actually, I don't know what that would mean, if anything. What I said is that amplifiers amplify both current and voltage. In other words, the voltage at their output is greater than the voltage at their input, and the current supplied by their output is greater than the current going into their input.

You are probably referring to Krell's CAST concept, as described here. Note the statement in the first paragraph that "A Krell system connected in CAST transfers the signal in the current domain, throughout the signal path to the amplifier output stage where only one current to voltage conversion (I-to-V) takes place."

Following that current to voltage conversion, at the output of the amplifier, both voltage and current would certainly be greater than at the input of the amplifier, or it wouldn't be able to drive the speakers to anything approaching reasonable volume.

I see in the manual for the 700CX that its gain is spec'd at 26.4 db. That corresponds to an increase in voltage of about 20 times. And its 700 watt capability into 8 ohms certainly represents vastly more output current (actually, about 9.4 amperes, when the full 700 watts is being delivered into 8 ohms) than any preamp could ever supply to the amplifier's input.

Best regards,
-- Al

Al,
As always I appreciate your patient and clear explanations. What you eloquently describe is born out with simply listening. Either tube or SS amplifiers will be the best choice depending on the particular driven speaker's design characteristics. Just listen. There's no universal one fits all amplifier design that exists. It all begins with the intentions of the speaker designer.
Best Regards,

@ Almarg,, Thankyou so much!, That was very good of you to put an explanation in a very good context!your educated facts is an asset to us all!, you are absolutly correct!,,Happy listening!

Frequency response flatness at the amplifier output/speaker input has no direct relevance. Speakers whose impedance varies significantly as a function of frequency, and that match most optimally with tube amps, can be presumed to require a non-flat frequency response at their input terminals to produce an acoustic output whose frequency response is flat. If such a speaker is mated with a solid state amplifier having near zero output impedance, frequency response flatness will have been optimized at the output of the amplifier, but it will be wrong at the output of the speaker.

hi Al, often it seems that a speaker manuf tries to find an amplifier that has an approximate H^-1(f) transfer function of that manuf's speaker so that the amplifier input-to-speaker output (which is sound) transfer function is more or less flat over the audio bandwidth.
As you would agree this is a very limiting way to design a speaker - change the amp (or another variable) & the performance falls off the cliff....

Hi Bombaywalla,

Yes, agreed.

As you certainly realize, any design involves a zillion or so tradeoffs and competing considerations, but it's still striking how some speakers can perform well with very diverse kinds of amplifiers, while other speakers cause the choice of amplifier to be very critical.

One of the reasons I chose the Daedalus speakers I have is that their combination of a pretty much flat impedance curve, high efficiency, and high power handling capability makes them suitable for use with just about any amplifier out there, except for the really flea-powered types. The Coincidents that Charles uses are similar in that respect.

Charles & Audiolabyrinth, thank you most kindly for the nice words.

Best regards,
-- Al