How do autoformers affect sound?
- Thread starter Burke
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Lefty
Super Member
Burke said:
Well there are three ways to couple an amplifier to it's load (speakers), capacitance coupled, transformer coupled and direct coupled. Each has advantages and disadvantages. Which is best is too simple a question to real analyze. What sounds best is up to the listener.
Lefty
Autoformers are a trademark of McIntosh, in so far as I know, and are output coupling transformers with roughly unity turns ratios - neither stepup nor stepdown supposedly.
However, since they have different taps for different load impedances, they have to have different secondary turns.
A big advantage is they block direct (unvarying) current. DC does not pass through the magnetic coupling of a transformer. Capacitors also block DC.
Direct coupled amps either have a set bias (DC voltage) or in more fancy designs, have active biasing. They also need protection circuits to remove power if things get out of hand.
As to sound, engineering is the art of tradeoffs. If autoformers were cheaper and lighter, more manufacturers would use them. McIntosh charges more for their products and are renowned for the quality of their house sound. Some significant segment of the market seems to be saying that the sound quality from autoformers is worth the premium.
I agree.
However, since they have different taps for different load impedances, they have to have different secondary turns.
A big advantage is they block direct (unvarying) current. DC does not pass through the magnetic coupling of a transformer. Capacitors also block DC.
Direct coupled amps either have a set bias (DC voltage) or in more fancy designs, have active biasing. They also need protection circuits to remove power if things get out of hand.
As to sound, engineering is the art of tradeoffs. If autoformers were cheaper and lighter, more manufacturers would use them. McIntosh charges more for their products and are renowned for the quality of their house sound. Some significant segment of the market seems to be saying that the sound quality from autoformers is worth the premium.
I agree.
macaltec
Metal Master
Thanks Burke. I was gonna say last time we talked that I thought it had something to do with how the output is coupled to the speakers but I was really unsure. So, delving further into it there is no physical connection between the power output and the load??????? The power out is passed through one side of the tranformer and inducted into the "load" side???????????? Am I close?
Autoformers
An autoformer has only one coil,the reason for using them is to raise the impedence seen by the amp,ie if you are a 4 ohm speaker and your amp wants to see an 8 ohm load the autoformer will increase the impedence by whatever the turns ratio is.If you look at the schematic printed on top of the Mac autoformers you will see the different windings and how the taps are arranged to reflect the impedence back to the amp,either up or down depending on which tap you use.Don't confuse an output transformer with an autoformer,the autoformer will pass DC to your speakers as there is only one winding and one side of it is grounded so no DC must be present.
An autoformer has only one coil,the reason for using them is to raise the impedence seen by the amp,ie if you are a 4 ohm speaker and your amp wants to see an 8 ohm load the autoformer will increase the impedence by whatever the turns ratio is.If you look at the schematic printed on top of the Mac autoformers you will see the different windings and how the taps are arranged to reflect the impedence back to the amp,either up or down depending on which tap you use.Don't confuse an output transformer with an autoformer,the autoformer will pass DC to your speakers as there is only one winding and one side of it is grounded so no DC must be present.
Learning curve
This is a great place to learn, really:yes: I'm assuming that if the primary winding of a transformer is connected across the amplifier's speaker output, whatever is fed into it will excite a similar output from the secondary. Would any transformer with equal primary and secondary windings act as a safety device and protect speakers from DC? Is there a trade off, such as reduced frequency response or anything? What about resistance; how could I make sure the amplifier was loaded the same as it would be with a speaker?
This is a great place to learn, really:yes: I'm assuming that if the primary winding of a transformer is connected across the amplifier's speaker output, whatever is fed into it will excite a similar output from the secondary. Would any transformer with equal primary and secondary windings act as a safety device and protect speakers from DC? Is there a trade off, such as reduced frequency response or anything? What about resistance; how could I make sure the amplifier was loaded the same as it would be with a speaker?
Lefty
Super Member
Whitehall said:
I don't believe that 'autotransformer' is a trademark of Mac as even a varac is a autotransformer with a variable tap rather then fixed tapes. As in:
http://en.wikipedia.org/wiki/Autotransformer
Lefty
shocley
Well-Known Member
From what I've come across, McIntosh may have kept the output transformers on solid state amps to intentionally keep the damping factor low, just like tube amps. A low damping factor means interaction with varying speaker impedance across the audio spectrum. Speaker designers in the tube era designed their speakers to take account of this kind of interaction, so if you remove it, the speaker might sound strange.
Anything to this?
Anything to this?
