Guest Brian_D Posted March 31, 2004 Report Share Posted March 31, 2004 I've been reading the AR9 manual I downloaded from this site, mainly the comments regarding the design and room placement of these rather unweildy cabinets, when I ran across the hookup section and found something I thought was interesting...When the manual talks about hooking up the speakers (which it does at length) Every mention of an amplifier attachement references the "8 ohm tap" of the amplifier.The nominal impedance of the speaker (4 ohm) not withstanding, for what purpose would a seperate terminal for a diferent impedance exist? None of the amplifiers I've ever used had a specific 4ohm output, as opposed to an 8ohm. I've seen multi-output amps where impedances have to be right when attaching more than one pair of speakers, but again, no single speaker output is specified with a "target" or intended impedance. And of course there's P.A. amps with different voltage taps, but that's something completely different...In fact, if a speaker terminal were labled 8ohms, I would certainly be double-checking the manual to make sure that a lower impedance is appropriate. Was it common for amps in the past to have taps labled with seperate impedances?-Brian Link to comment Share on other sites More sharing options...
rrcrain Posted March 31, 2004 Report Share Posted March 31, 2004 Yes, many amps did have multiple outputs on them. Some had 2, 4, and 8 ohm outputs; others just 4 and 8 ohm. And many current tube amps such as those made by Rogue Audio and Jolida have 4 and 8 ohm outputs. Link to comment Share on other sites More sharing options...
Guest Nigel Posted March 31, 2004 Report Share Posted March 31, 2004 Amplifiers with transformer output (tubes and some very expensive transistor amps (Mc's)) had multiple output taps on the transformer for impedance matching. Impedance matching maximizes the power transfer from the source (amplifier in this case) to the load (speaker), this was important 30 and more years ago because of the very limited power available. Link to comment Share on other sites More sharing options...
rrcrain Posted March 31, 2004 Report Share Posted March 31, 2004 The output transformers were commonly called 'autotransformers". No clue why though. Link to comment Share on other sites More sharing options...
Guest Brian_D Posted March 31, 2004 Report Share Posted March 31, 2004 Thanks guys. The only McIntosh Amp I ever owned only had one output (stereo) and I've never delved into the world of tubes...Thanks again! Link to comment Share on other sites More sharing options...
Guest Brian_D Posted April 2, 2004 Report Share Posted April 2, 2004 Ok, so this begs the question; why would AR suggest connecting a 4-ohm speaker to an 8-ohm tap if a 4-ohm output would be available?If they specify an output, wouldn't they specify the output that is "optimized" for the speaker/amplifier combination?I'm just imagining some bewildered about-to-be audiophile reading the manual of his brand new McIntosh amplifier, which tells him to connect 4-ohm loudspeakers to the 4-ohm tap, while is AR9 manual tells him to attach them to the 8-ohm tap.Obviously a moot point with modern amplifiers, but it makes me wonder about AR's reasoning... Link to comment Share on other sites More sharing options...
soundminded Posted April 2, 2004 Report Share Posted April 2, 2004 Just as a point of information, the difference between an autotransformer and other transformers is that in an autotransformer, some of the windings are shared between the primary and secondary circuits. In other transformers, they do not and are completely isolated. For an output transformer in most vacuum tube amplifiers, this isolation is valuable because it blocks the DC between the power supply and the output tube plates from getting into the loudspeaker. Only the AC component appears on the secondary winding. For some solid state amplifiers such as those which are DC coupled, this is not necessary. Although I am not familiar with McIntosh's solid state circuits, their decision to use an autotransformer in their output circuits especially in their early solid state designs reflected a design philosophy that was different from most other manufacturers. IMO, the limitations of the output transformer is what most contributes to the so called tube sound of vacuum tube amplifiers and may make a solid state amplifier sound more like a tube amplifier.In non audio applications, autotransformers are commonly used as buck/boost transformers to slighly alter the voltage applied to a circuit when the power available is marginally too low or too high. Sometimes the primary and secondary circuits of an ordinary transformer each have one winding connected to the same point, usually a ground reference. This does however not make it an autotransformer. Link to comment Share on other sites More sharing options...
ar_pro Posted April 2, 2004 Report Share Posted April 2, 2004 Many McIntosh enthusiasts have reached the same conclusion as soundminded - their solid-state amplifierss sound a lot like tube amps. Even in the early days of hard-sounding transistor amplifiers (I'm thinking of the Dyna 120, and some of the early Japanese amps), the McIntosh solid-state amplifiers with output autoformers made for a much more tube-like listening experience. Sam Tellig in "Stereophile" has also compared some of the current McIntosh tube & solid-state amplifiers, and has stated that they sound very similar. The (I think) unique McIntosh autoformer circuit seems to be the difference. Link to comment Share on other sites More sharing options...
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