Output coil on power amp...

Skorpio · 4th August 2006, 09:27 AM

If i try to remove the output coil on my NAD3020 power amplifier, could it means that the amp will blow?

I know that is is there to secure stability in a NFB amp, but what does it actually do? Is it for extreame cases and special speaker cables? All speakers do have a coil af input for the woofer.

Some amplifiers does not have this coil....Pass, Hiraga Class A, etc.....why?

jaycee · 4th August 2006, 12:53 PM

It is mainly to damp the effects of a capacitive run of speaker cable, ie long cable runs, to prevent oscillation. In most cases leaving it out will do no harm.

Why remove it though?

AndrewT · 4th August 2006, 06:56 PM

Hi,
just follow me for a moment.

NAD sell very competitively priced amps.

The designer decided his amp did not need a Thiel network on the output.
The sales department said the amp would sell better if a Thiel network was added and would leave more margin for profit by allowing NAD to sell the amp at a higher price.

I think not.

jaycee · 4th August 2006, 07:17 PM

The way I see it, in a consumer market amp, they have to cater for all kinds of events, such as the user having 10 metre cables and such nonsense.

DIY or enthusiast amps such as Pass's amps know that the user is going to be (fairly) sensible and not do such things.

Whether there's any audible difference between the two is another matter. I usually add them "just in case".

destroyer X · 4th August 2006, 08:34 PM

miss this output filter....that coils with paralell resistance.

Maybe simulators are crazy, but i am afraid that it really does some effect in performance.

regards,

Carlos

mikeks · 4th August 2006, 09:09 PM

Quote:

Originally posted by destroyer X
......... i am afraid that it really does some effect in performance.

Carlos

Depends on construction of coil...and choice of values, of course.

CBS240 · 4th August 2006, 09:24 PM

In the real world, this coil rejects the extra phase shifting caused by adding components to the output such as complex reactive loads and long strands of wire. Having said this I digress to Mike B in post 35 of this thread: Amp distortion

and also rt7085 for post 46.

Christer · 4th August 2006, 09:30 PM

Coils are expensive components. If the manufacturer of an amp was absolutely certain that the amp couldn't oscillate under any imaginable load condition, it would skip the coil. Serious manufacturers are probably cautious, though, so the cases where the coil is really needed may be rare, but on the other hand, they may not. It depends on the particular amp.

destroyer X · 4th August 2006, 09:38 PM

Thank you all by the informs..they are always usefull.

regards,

Carlos

poobah · 4th August 2006, 09:39 PM

Sometimes people ask me if I have an extra cigarette. I examine the pack carefully pretending to count. I then say, "No, there are no extras".

4th August 2006, 09:27 AM	#1
Skorpio diyAudio Member Join Date: Mar 2004 Location: Denmark	Output coil on power amp... If i try to remove the output coil on my NAD3020 power amplifier, could it means that the amp will blow? I know that is is there to secure stability in a NFB amp, but what does it actually do? Is it for extreame cases and special speaker cables? All speakers do have a coil af input for the woofer. Some amplifiers does not have this coil....Pass, Hiraga Class A, etc.....why?

4th August 2006, 06:56 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, just follow me for a moment. NAD sell very competitively priced amps. The designer decided his amp did not need a Thiel network on the output. The sales department said the amp would sell better if a Thiel network was added and would leave more margin for profit by allowing NAD to sell the amp at a higher price. I think not. __________________ regards Andrew T.

4th August 2006, 08:34 PM	#5
destroyer X diyAudio Member Join Date: Feb 2004 Location: Recife - Brasil Northeast	Using simulators, a big damaged in the amplifier performance can be perceived when we miss this output filter....that coils with paralell resistance. Maybe simulators are crazy, but i am afraid that it really does some effect in performance. regards, Carlos __________________ Try to build an amplifier folks ... it is pure adrenaline!.. when not work first time, then becomes a nice challenge...and we usually overcome the trouble... and we feel very well to be mastering the machine.

4th August 2006, 09:24 PM	#7
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	In the real world, this coil rejects the extra phase shifting caused by adding components to the output such as complex reactive loads and long strands of wire. Having said this I digress to Mike B in post 35 of this thread: Amp distortion and also rt7085 for post 46. __________________ All the trouble I've ever been in started out as fun......

4th August 2006, 09:38 PM	#9
destroyer X diyAudio Member Join Date: Feb 2004 Location: Recife - Brasil Northeast	That is it folks...really we need them. Thank you all by the informs..they are always usefull. regards, Carlos __________________ Try to build an amplifier folks ... it is pure adrenaline!.. when not work first time, then becomes a nice challenge...and we usually overcome the trouble... and we feel very well to be mastering the machine.


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4th August 2006, 12:53 PM	#2
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	It is mainly to damp the effects of a capacitive run of speaker cable, ie long cable runs, to prevent oscillation. In most cases leaving it out will do no harm. Why remove it though?

4th August 2006, 07:17 PM	#4
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	The way I see it, in a consumer market amp, they have to cater for all kinds of events, such as the user having 10 metre cables and such nonsense. DIY or enthusiast amps such as Pass's amps know that the user is going to be (fairly) sensible and not do such things. Whether there's any audible difference between the two is another matter. I usually add them "just in case".

4th August 2006, 09:30 PM	#8
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	Coils are expensive components. If the manufacturer of an amp was absolutely certain that the amp couldn't oscillate under any imaginable load condition, it would skip the coil. Serious manufacturers are probably cautious, though, so the cases where the coil is really needed may be rare, but on the other hand, they may not. It depends on the particular amp.

4th August 2006, 09:39 PM	#10
poobah diyAudio Member Join Date: Nov 2005	Sometimes people ask me if I have an extra cigarette. I examine the pack carefully pretending to count. I then say, "No, there are no extras".

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