Zoebel & RFI
Hi Christer,
I think it's certainly not trivial. Perhaps boring, because output coils were ad nausea discussed in a dedicated thread:
http://www.diyaudio.com/forums/showthread.php?postid=1202201#post1202201
Anyhow, a Zoebel filter is a good idea, for two reasons:
1. To block RFI from outside.
2. To avoid instabilities in amps with (high) NFB from the output stage.
One problem is that some people claim they can hear the (detrimental) effect of a coil, that is, if larger than say 1uH.
Another problem with Zoebel networks is that the de facto standard configuration, blindly copied by almost everyone, is seldom optimal. See: E.M. Cherry, "Ironing out distortion", EW+WW, Jan. 1995, pp.19-20, fig. 9a and 9b.
Cheers,
Edmond.
Christer said:
Hi Christer,
I think it's certainly not trivial. Perhaps boring, because output coils were ad nausea discussed in a dedicated thread:
http://www.diyaudio.com/forums/showthread.php?postid=1202201#post1202201
Anyhow, a Zoebel filter is a good idea, for two reasons:
1. To block RFI from outside.
2. To avoid instabilities in amps with (high) NFB from the output stage.
One problem is that some people claim they can hear the (detrimental) effect of a coil, that is, if larger than say 1uH.
Another problem with Zoebel networks is that the de facto standard configuration, blindly copied by almost everyone, is seldom optimal. See: E.M. Cherry, "Ironing out distortion", EW+WW, Jan. 1995, pp.19-20, fig. 9a and 9b.
Cheers,
Edmond.
Re: Zoebel & RFI
Yes, power amps usually have a Zobel filter for stability reasons, but that one is usually placed before the coil, although Leach recommends placing it at the output connector (although for entirely different reasons). For RFI reasons, it seems better to have it att the connector for the same reason as we discussed for inputs. However, does that work as well for stability? Perhaps there should be two Zobels, one before the coild and one at the connector?
Then of course, I was not only considering power amps, but also line level amps etc. where we usually do not have a coil or Zobel filter. There it seem reasonable to add a Zobel at the connector.
Yes, and some don't like the sound of Zobels and burn their amps instead. At least serious designers who avoid coils and/or Zobels usually care about coping with stability in other ways.
What about my other question, whether it matters if the input connector filter is a voltage divider type or a shunt type (ie. a Zobel)? My thinking was that since the input impedance of the amp is usually at least many kOhms, it shouldn't matter for HF termination which method we use. However, then I realised that maybe the wires from connector to PCB should also be considered as transmission lines so the actual amp input impedance matters too, in which case the voltage divider is probably better. (Maybe this is more of a theoretical question, since an extra 50 Ohm series input impedande usually doesn't matter).
Edmond Stuart said:
Yes, power amps usually have a Zobel filter for stability reasons, but that one is usually placed before the coil, although Leach recommends placing it at the output connector (although for entirely different reasons). For RFI reasons, it seems better to have it att the connector for the same reason as we discussed for inputs. However, does that work as well for stability? Perhaps there should be two Zobels, one before the coild and one at the connector?
Then of course, I was not only considering power amps, but also line level amps etc. where we usually do not have a coil or Zobel filter. There it seem reasonable to add a Zobel at the connector.
Yes, and some don't like the sound of Zobels and burn their amps instead. At least serious designers who avoid coils and/or Zobels usually care about coping with stability in other ways.
What about my other question, whether it matters if the input connector filter is a voltage divider type or a shunt type (ie. a Zobel)? My thinking was that since the input impedance of the amp is usually at least many kOhms, it shouldn't matter for HF termination which method we use. However, then I realised that maybe the wires from connector to PCB should also be considered as transmission lines so the actual amp input impedance matters too, in which case the voltage divider is probably better. (Maybe this is more of a theoretical question, since an extra 50 Ohm series input impedande usually doesn't matter).
mlloyd1 said:
Tell this to E Stuart, PMA, jcx etc. etc. the list is loooong ....
There are a whole bunch of others here is doing more spice works than me.
I have not heard anyone complain about that. To them.
And we are getting more and more day by day, using this wonderful tool.
Even Nelson Pass uses spice. But he avoids to mention it.
John Curl wishes he knew more how to use spice!
Spice is a great tool for explorations, man
It has also been witnessed by those guys,
that the real thing is not too far from a good analyse.
Figures will not be at same level.
But the tendencies we can see in a good spice circuit
will more than often be exactly the same in a real amplifier.
-----------------------------------------------------------------------------
No offense, but
I am more interested to hear John Curl / Scott Wurcer / Bob Cordell comments on my issue brought up.
They would know, very well ,what I am addressing.
About complementary JFET input stages & the adjustment of
regars to mlloyd1
Lineup
Fellow engineers, let's get real. If Spice works for your needs, and you have 'mastered' it, OK. Then use it and be productive.
Spice is not absolutely important for audio design. We have done without it for decades. However, the future is yours. IF you find a new way to do something better with Spice, that will be very good. Let us see what comes out, but please remember what has already been done without Spice, before announcing a new 'breakthrough'.
Spice is not absolutely important for audio design. We have done without it for decades. However, the future is yours. IF you find a new way to do something better with Spice, that will be very good. Let us see what comes out, but please remember what has already been done without Spice, before announcing a new 'breakthrough'.
Re: Zoebel & RFI
previous posting on this topic.
http://www.diyaudio.com/forums/showthread.php?postid=1475396#post1475396
and the excel spreadsheet based on Dr Cherry's formulae.
http://www.diyaudio.com/forums/attachment.php?s=&postid=1475396&stamp=1207315043
Sorry this is off the pre topic
Edmond Stuart said:
previous posting on this topic.
http://www.diyaudio.com/forums/showthread.php?postid=1475396#post1475396
and the excel spreadsheet based on Dr Cherry's formulae.
http://www.diyaudio.com/forums/attachment.php?s=&postid=1475396&stamp=1207315043
Sorry this is off the pre topic
Zoebel coils
Hi Folks,
Speaking of coils, I still stick with the one as shown here:
http://www.diyaudio.com/forums/showthread.php?postid=1285241#post1285241
It has only one minor drawback: lots of oxygen inside.
Cheers.
Hi Folks,
Speaking of coils, I still stick with the one as shown here:
http://www.diyaudio.com/forums/showthread.php?postid=1285241#post1285241
It has only one minor drawback: lots of oxygen inside.
Cheers.
output coils
Hi John,
I don't like coils either, but as long as you don't know what kind of 'rogue' speakers some people will use, I prefer to stay on the safe side.
Moreover, are there other (or better) means to keep outside RFI away (picked up from the speaker cables) without a coil and a capacitor?
Cheers,
Edmond
john curl said:
Hi John,
I don't like coils either, but as long as you don't know what kind of 'rogue' speakers some people will use, I prefer to stay on the safe side.
Moreover, are there other (or better) means to keep outside RFI away (picked up from the speaker cables) without a coil and a capacitor?
Cheers,
Edmond
Sigurd Ruschkow said:
Epoxied?
An externally hosted image should be here but it was not working when we last tested it.
What's the point of using unbleached cotton if you're just going to slather a bunch of nasty epoxy all over it?
se
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