@atmasphere
Ralph, could you clarify a point regarding impedance matching between tube amps and speakers with roller coaster impedance and phase angles numbers.
I think you mentioned that the function of an output transformer is to step down the high voltage from the output tubes to the amps output taps. In addition, the output tranny will step up a speaker's impedance presented to the output power tubes at the primary windings of the tranny.
Maybe a simple example will help further clarify my understanding. My amp is an ARC Ref 150SE which uses KT-150 tubes in push-pull fashion. I recall that the output impedance of KT-150s is 3000 ohms. In a theoretically perfect world, if I had a speaker with a perfectly flat 4 ohm impedance function, plugging the speakers into the amps' 4 ohm taps would result in a stepped up impedance of 3000 ohms presented off the primary windings of the output tranny. That would be a perfect match with the power tube's output impedance.
We all know that in the real world, most speakers have roller coater impedance functions. As a result, the impedance off the primary windings of the output transformer will vary from the optimal 3000 ohm target. ARC says, just use the taps that sound the best.
So here is my question. What is happening electrically if there is an impedance mismatch? Is the amp producing distortion if there is an impedance deviation from 3000 ohms? If so, does having larger wattage and power supply capabilities ameliorate distortion effects?
How about negative feedback? In my case, I understand that the Ref 150 uses 14db of negative feedback and as a result, performs like a voltage source amp. Does that feature help to reduce distortion effects?
I have not touched on phase angle or sonic coloration issues caused by impedance mismatches between the amp's output taps (nominally, the 4, 8 or 16 ohm taps) and the speaker's actual impedance at a particular frequency.
As to sonic coloration, I recall that the output impedance of the ARC Ref 150 off the 8 ohm taps is around 1 ohm or less. This results in some sonic coloration, ... but not a lot. In a Stereophile review of the ARC Ref 150, John Atkinson measured the Ref 150's voltage output variation off the 8 ohm taps to be (+) or (-) .8 db when presented with a synthetic speaker load.
Btw, are similar issues presented with OTL tube amps?
Thanks for the education.
BIF
Ralph, could you clarify a point regarding impedance matching between tube amps and speakers with roller coaster impedance and phase angles numbers.
I think you mentioned that the function of an output transformer is to step down the high voltage from the output tubes to the amps output taps. In addition, the output tranny will step up a speaker's impedance presented to the output power tubes at the primary windings of the tranny.
Maybe a simple example will help further clarify my understanding. My amp is an ARC Ref 150SE which uses KT-150 tubes in push-pull fashion. I recall that the output impedance of KT-150s is 3000 ohms. In a theoretically perfect world, if I had a speaker with a perfectly flat 4 ohm impedance function, plugging the speakers into the amps' 4 ohm taps would result in a stepped up impedance of 3000 ohms presented off the primary windings of the output tranny. That would be a perfect match with the power tube's output impedance.
We all know that in the real world, most speakers have roller coater impedance functions. As a result, the impedance off the primary windings of the output transformer will vary from the optimal 3000 ohm target. ARC says, just use the taps that sound the best.
So here is my question. What is happening electrically if there is an impedance mismatch? Is the amp producing distortion if there is an impedance deviation from 3000 ohms? If so, does having larger wattage and power supply capabilities ameliorate distortion effects?
How about negative feedback? In my case, I understand that the Ref 150 uses 14db of negative feedback and as a result, performs like a voltage source amp. Does that feature help to reduce distortion effects?
I have not touched on phase angle or sonic coloration issues caused by impedance mismatches between the amp's output taps (nominally, the 4, 8 or 16 ohm taps) and the speaker's actual impedance at a particular frequency.
As to sonic coloration, I recall that the output impedance of the ARC Ref 150 off the 8 ohm taps is around 1 ohm or less. This results in some sonic coloration, ... but not a lot. In a Stereophile review of the ARC Ref 150, John Atkinson measured the Ref 150's voltage output variation off the 8 ohm taps to be (+) or (-) .8 db when presented with a synthetic speaker load.
Btw, are similar issues presented with OTL tube amps?
Thanks for the education.
BIF