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.
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.
john curl said:
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.
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.
Originally posted by Netlist
---Electrolytes in the signal path?---
Above some frequencies, the parasitic inductance of electrolytics is the dominating element of the impedance. Maybe not so bad against the instrusion of RF.
The parasitic series resistance avoids a high Q resonance of the LC elements. Sometimes, a desirable feature.
---Electrolytes in the signal path?---
Above some frequencies, the parasitic inductance of electrolytics is the dominating element of the impedance. Maybe not so bad against the instrusion of RF.
The parasitic series resistance avoids a high Q resonance of the LC elements. Sometimes, a desirable feature.
You people make me laugh! This is just like high school. Maybe junior college. Please think about the problem and WHY successful audio designers, who used output coils for decades, MIGHT be inclined to not use them, when the coils potentially can add to circuit stability? Are they ugly? Are they expensive? Are they hard to make?
I am still curious how many others, apart from John, share his opinion that the coil affects the sound and takes the consequences of it? Until John told this a while back in another thread, I don't think I had ever heard of anyone before claiming that the coil affects the sound. That is actually surprising, considering that people discuss the sound of the most absurd things (not suggesting coils should necessarily be classified as absurd). I am not intending to give any opinion here. I am just curious since Johns earliser posts seems to suggest that he is far from alone in this venture.
I didn't believe it at first either. I had to be shown with an A-B test. However, I NEVER used more than 2uH, and I was using less that 1uH, before I gave them up completely. However, Naim didn't use them 30 years ago, I'm pretty sure, but Naim amps were also sensitive to cable capacitance, and this could be a problem, sometimes.
Faster output devices appear to reduce the need for output coils, BUT can't you folks conceive of a 2-10uF cap load and what happens? What would the coil do with that kind of load?
This reminds me of an auto design parallel:
Many years ago there was this auto designer and reviewer named Smokey Y. who even wrote books about cars and engine tuning. He could not understand why auto designers wanted to use 4 valves per cylinder, rather than the traditional 2. He really criticized the concept. What do you think about Smokey's opinion today? Was he right on? Was he right for his needs? Would 4 valves per cylinder just be a waste of effort in a '55 GM auto? Quiz on Monday. ;-)
Faster output devices appear to reduce the need for output coils, BUT can't you folks conceive of a 2-10uF cap load and what happens? What would the coil do with that kind of load?
This reminds me of an auto design parallel:
Many years ago there was this auto designer and reviewer named Smokey Y. who even wrote books about cars and engine tuning. He could not understand why auto designers wanted to use 4 valves per cylinder, rather than the traditional 2. He really criticized the concept. What do you think about Smokey's opinion today? Was he right on? Was he right for his needs? Would 4 valves per cylinder just be a waste of effort in a '55 GM auto? Quiz on Monday. ;-)
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