McIntosh power output
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Mc_Man
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Could be, as explained in the link. Say you use a speaker that is spec'd as "8 ohms" and "200W max" power. You purchase a Krell KSA-200 to mate with it, and you like to play Metallica at live concert levels. Now, say at 100Hz the impedance actually dips to 4 ohms ...Cool, yes, thanks for the link!!Does this mean though, that amps that put out extra power at lower resistances is a bad thing?
The amp puts out 400W and melts the woofer voice coil!
The other way to look at it is as others have explained. Buying a Krell KSA-200, you are paying for an 800W amp (into 2 ohms) as it must be designed to supply that power into that load.
If you use 8 ohm speakers that stay above 8 ohms, you will only get the benefit of a 200W amp, as it cannot deliver more than that into the 8 ohm load.
With the McIntosh autoformered amps, the design can be optimized for 400W or whatever, and will be 'comfortable' into any rated load. You get your 400W no matter what the speaker impedance happens to do at any frequency.
Yes, it's a different way of thinking about things, but makes sense once you understand it ...
If you use 8 ohm speakers that stay above 8 ohms, you will only get the benefit of a 200W amp, as it cannot deliver more than that into the 8 ohm load.
With the McIntosh autoformered amps, the design can be optimized for 400W or whatever, and will be 'comfortable' into any rated load. You get your 400W no matter what the speaker impedance happens to do at any frequency.
Yes, it's a different way of thinking about things, but makes sense once you understand it ...
Well, guess I was the one who DIDN'T understand it! :tears:
Could be, as explained in the link. Say you use a speaker that is spec'd as "8 ohms" and "200W max" power. You purchase a Krell KSA-200 to mate with it, and you like to play Metallica at live concert levels. Now, say at 100Hz the impedance actually dips to 4 ohms ...
The amp puts out 400W and melts the woofer voice coil!
I'm still learning some technical things here, so bear with me... :scratch2: If the speaker I'm using is rated at 8 ohms, how will it dip to 4 ohms? I thought everything would be playing at 8 ohms with 8 ohm speakers?
dshoaf
That high voltage buzz
The hints to what is happening when SS amps attempt to drive too low impedance speakers is in the first paragraph of Roger Russell's linked text. There he notes that excessive heat dissipation happens when you get a mis-match of the amp's impedance relative to the impedance of the speaker at any specific frequency.
Here's the first paragraph from the link:
"Transistor power output circuits can match 8-ohm loads directly. This eliminates the need for the output transformer for most manufacturers. However, output stages that are designed to operate into an optimum load of 8 ohms can double or quadruple heat dissipation when operating into 4 or 2 ohm loads. At some frequencies, speakers rated at 8 ohms can dip as low as 4 ohms. Some 4-ohm systems can dip even lower. This mismatch can cause the amplifier to exceed its thermal dissipation limits."
What this involves is efficiency in the transfer of power from the amp to the speaker. When there is not an efficient transfer of power, the excess power is converted to heat in the amp - mentioned by Roger above. The output autoformers are designed to ensure that the output stage of the amp 'sees' a relatively constant impedance and, therefore, can supply current to match that impedance. This why there are multiple taps on an autoformer for you to 'match' your speakers to the Mac amp. It also explains why trying to run a set of 3-4 ohm speakers on a solid state amp will likely send it into thermal shutdown, depending on how hard you run it.
Autoformers: Read more details here: http://www.answers.com/topic/autotransformer
From this link, the difference in an autoformer/autotransformer is that there is no electical isolation between the primary and secondary windings. In a transformer, the primary and secondary windings are fully isolated, electrically but are coupled with magnetic fields. This is why you will only find transformers on the output of tube amps in order to isolate the 300-600 vDC from frying your speakers - and yourself if you touched the terminals!
I hope that helps the clarification a bit.
Cheers,
David
Here's the first paragraph from the link:
"Transistor power output circuits can match 8-ohm loads directly. This eliminates the need for the output transformer for most manufacturers. However, output stages that are designed to operate into an optimum load of 8 ohms can double or quadruple heat dissipation when operating into 4 or 2 ohm loads. At some frequencies, speakers rated at 8 ohms can dip as low as 4 ohms. Some 4-ohm systems can dip even lower. This mismatch can cause the amplifier to exceed its thermal dissipation limits."
What this involves is efficiency in the transfer of power from the amp to the speaker. When there is not an efficient transfer of power, the excess power is converted to heat in the amp - mentioned by Roger above. The output autoformers are designed to ensure that the output stage of the amp 'sees' a relatively constant impedance and, therefore, can supply current to match that impedance. This why there are multiple taps on an autoformer for you to 'match' your speakers to the Mac amp. It also explains why trying to run a set of 3-4 ohm speakers on a solid state amp will likely send it into thermal shutdown, depending on how hard you run it.
Autoformers: Read more details here: http://www.answers.com/topic/autotransformer
From this link, the difference in an autoformer/autotransformer is that there is no electical isolation between the primary and secondary windings. In a transformer, the primary and secondary windings are fully isolated, electrically but are coupled with magnetic fields. This is why you will only find transformers on the output of tube amps in order to isolate the 300-600 vDC from frying your speakers - and yourself if you touched the terminals!
I hope that helps the clarification a bit.
Cheers,
David
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http://stereophile.com/floorloudspeakers/aerial_acoustics_20t_v2_loudspeaker/index5.html
or most of Stereophile's speaker reviews, shows impedance measurements vs. frequency.
This one is described as '4 ohm nominal' but goes >8 ohms in the mid to high treble. Seems like (at least high end) manufacturers are getting more accurate when describing impedance. There are probably still some '8 ohm' speakers that dip to 4 in the bass. This one could be described as a 6 or 8 ohm speaker, since the impedance is above that >1kHz. I think most manufacturers these days use an average of the minimum levels as the spec.
