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-   -   Audibility of output coils (http://www.diyaudio.com/forums/solid-state/101468-audibility-output-coils.html)

john curl 6th May 2007 04:55 PM

Folks, I am trying to teach aspiring audio designers something hard learned over the decades. We don't use output coils anymore, because they are audible.
Even when we did, most people did not go beyond 2uH. Think what happens to your precious high frequency damping factor when you use a 2uH or higher output coil. Better yet, put a 2-10 uF cap as a load, and see what happens.
It used to be that output coils were considered necessary, but that is not true any longer.
There may be special cases, such as class D design or making a very powerful amp for woofers only drive operation.

Edmond Stuart 6th May 2007 05:36 PM

Quote:

Originally posted by john curl
Folks, I am trying to teach aspiring audio designers something hard learned over the decades. We don't use output coils anymore, because they are audible.
Even when we did, most people did not go beyond 2uH. Think what happens to your precious high frequency damping factor when you use a 2uH or higher output coil. Better yet, put a 2-10 uF cap as a load, and see what happens.
It used to be that output coils were considered necessary, but that is not true any longer.
There may be special cases, such as class D design or making a very powerful amp for woofers only drive operation.
Hi John,

We don't use output coils anymore? Wouldn't it more appropriate to say: YOU don't use output coils anymore. Besides, there are more (and larger) inductances to worry about: loudspeaker cables, cross-over filters and voice coils.
Loading an amp with a 2-10 uF cap? With a lot of global NFB and no Zobel network, probably disastrous.

Cheers, Edmond.

Christer 6th May 2007 05:47 PM

Perhaps the interesting question is how many other serious amp designers, except for John, skip the coil? Are we to assume that has become normal practice in state-of-the-art design, or is it only John and maybe a few others?

Netlist 6th May 2007 05:56 PM

An equally interesting question would be to know more reasons the coil has become 'démodée' apart from audibility. I could easily think of more parts that are audible.

/Hugo

Edmond Stuart 6th May 2007 06:35 PM

Quote:

Originally posted by Netlist
An equally interesting question would be to know more reasons the coil has become 'démodée' apart from audibility. I could easily think of more parts that are audible.
/Hugo
Hi Hugo.

Please, tell us more about the other evil parts you're suspecting, maybe.......... oxygen-rich copper perhaps? :rolleyes:

Cheers,

forr 6th May 2007 06:42 PM

After reading Cyril Bateman's "RF effects on AF" article (Electronics World, june 1997), one may think that everything able to diminish RF returns via the speaker cables is wellcome. Albeit far from being perfect, the output coil could be, from an electronic point of view, more beneficial than none.

Edmond Stuart 6th May 2007 06:45 PM

Quote:

Originally posted by forr
After reading Cyril Bateman's "RF effects on AF" article (Electronics World, june 1997), one may think that everything able to diminish RF returns via the speaker cables is wellcome. Albeit far from being perfect, the output coil could be, from an electronic point of view, more beneficial than none.
:yes:

Netlist 6th May 2007 06:52 PM

Electrolytes in the signal path? :)

/Hugo

Edmond Stuart 6th May 2007 07:02 PM

Quote:

Originally posted by Netlist
Electrolytes in the signal path? :)
/Hugo

:yes:

See articles by Cyril Bateman: "Capacitor sound?", EW 2002/2003.

Cheers,

Christer 6th May 2007 07:03 PM

Quote:

Originally posted by Netlist
Electrolytes in the signal path? :)

/Hugo

But surely anyone who worries about the sound of the coil has got rid of the electrolytes in the signal path long ago? Even Self accepts that they distort.


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