I have not heard of these worst case scenarios happening often, but it's possible it just gets missed most of the time. A fried zobel will stink but the amp will probably continue to work. If a tweeter stops working the user might just decide the speaker broke and not think anything about the amp or source. I have heard that clipping amps can destroy tweeters.
Tweeters are rarely very powerful anyways, you could fry a tweeter with a 10KHz sine at full power. We can't just cut off everything above 1KHz because we want to protect the tweeter from the worst case scenario.
So I think the best way to go would be to monitor output power in the tweeter range and ultrasonics and cut power when the zobel or the tweeter is at risk to be fried. Oscillation protectors like this already exist, although I haven't seen many of them.
Tweeters are rarely very powerful anyways, you could fry a tweeter with a 10KHz sine at full power. We can't just cut off everything above 1KHz because we want to protect the tweeter from the worst case scenario.
So I think the best way to go would be to monitor output power in the tweeter range and ultrasonics and cut power when the zobel or the tweeter is at risk to be fried. Oscillation protectors like this already exist, although I haven't seen many of them.
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When the distortion gets to 10 ppm, a coil remote from the output stage is a very good idea. Even then, inductive distortion can be a real problem.
Aluminium won't have much effect on magnetic fields. Coil orientation is also a tricky business- see APAD6.
Output inductor is like a rail gun with it's field (field "shoots" out the ends) 
.
If it's parallel with a trace under/beside it , that trace becomes a "pickup".
Wow ! (below) An extreme example of a inductor field !
PS - would not want your input stage (or any other stage) in front of that !
OS
.If it's parallel with a trace under/beside it , that trace becomes a "pickup".
Wow ! (below) An extreme example of a inductor field !
PS - would not want your input stage (or any other stage) in front of that !
OS
Attachments
Hmmmm ... Just looked at actual physical diagrams and on my two OEM's.
They always have the inductors pointing straight up and separated by a healthy
distance from the amp circuit (or any other circuit).
NEVER parallel to the PCB or close to the output devices unless the PCB went
under the main heatsink , where they put the relays and coils on the other side.
Just an observation , wonder if this was "researched" in the H/K or sony lab ?
OS
They always have the inductors pointing straight up and separated by a healthy
distance from the amp circuit (or any other circuit).
NEVER parallel to the PCB or close to the output devices unless the PCB went
under the main heatsink , where they put the relays and coils on the other side.
Just an observation , wonder if this was "researched" in the H/K or sony lab ?
OS
Any amp with thd below -100dB is going to be tricky with the layout. I can see changes (thd instrument monitoring thd in real-time) just moving the test setup wires..... grounds and spkr and input wires.
Here is 50W thd (1KHz/8 Ohm): .00038%
With short, well placed wires from/to PS and I/O wires, a true minimum thd may be found... but that requires a chassis, heat sinks PTransformer, caps/rect. I/O ports... in other words a prototype finished amp. That takes me a lot longer.
THx-RNmarsh
Here is 50W thd (1KHz/8 Ohm): .00038%
With short, well placed wires from/to PS and I/O wires, a true minimum thd may be found... but that requires a chassis, heat sinks PTransformer, caps/rect. I/O ports... in other words a prototype finished amp. That takes me a lot longer.
THx-RNmarsh
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you can wind a air core toroid on a insulating former without any mag material - the numbers can be found in many online calculators
https://www.google.com/#q=toroidal+inductor+calculator
just enter u_r = 1
still some fringing field close in - but much reduced at distance vs cylindrical solenoid
https://www.google.com/#q=toroidal+inductor+calculator
just enter u_r = 1
still some fringing field close in - but much reduced at distance vs cylindrical solenoid
Cool idea , JCX. Much more confined field. according to this - https://www.easycalculation.com/engineering/electrical/toroid-inductance-calculator.php
I could just take my standard straight16-18 turn coil , bend it to a toroid and still
have my <2uH inductance. Wonder if a toroidal air core would adversely
affect SQ ? Why is nobody doing it ?
OS
Now we are getting closer to the simulation results. I am really impressed how god are new VDMOS ksubthres models from Cordell.
Damir
Just found a calc for that ! SRF is usually >100mhz for a 2uH .
Cool , two downloadable .exe standalone calcs. - Inductor Calculators
The toroid one just calculates for a ferrite core.
wiki says SRF for the toroid is just a tad lower than for a standard inductor.
The first calc is verbose (calculates the SRF).
Too expensive ... what ??? (below) I just made a 1uH in 10 seconds.
OS
Attachments
Do you end up with the same number of turns or do you need to increase the turns to get the same inductance? What if you reduce the diameter of the turns with the toroidal winding, would it really make any measurable difference? I don't think we would have to worry about saturation in an open air core coil winding like that would we with so few windings?
Room Interface Profile
With 'normal' speakers, you have to get them nearly touching before you measure a difference. I've tested this with DBLTs and I wouldn't bother taking the speaker out of the room ... but see below.
Our room was specifically designed to cater for this with 2 entrances and a black curtain between. He spends half a day setting it up, the exact position is marked so it can be replicated and then the curtain is drawn. The R&D crew cart speakers in and out when he requests a change ... trying not to give clues on the size of the speaker being brought in or out behind the curtain.
Proper DBLTs on speakers are much more expensive than buying the latest AP.[1]
And BTW, the guys who ask for this rigmarole were all deaf. The true golden pinnae don't need this rigmarole to reliably pick up differences. The true golden pinnae also can't tell if a speaker is disconnected but left in the room. Neither do they need the speaker in the exact position to reliably identify them and their faults.
YES, positioning & rooms make a huge difference to the sound of a speaker but each speaker has a Room Interface Profile which seems independent of the room and position. It is this which we object to or like.
Absolute Listening Tests-Further Progress
_________________________
Of course for the deaf HiFi Reviewers, you had to work on your "Hand Carved from solid Unobtainium by Virgins" too ... and tell it to them VERY LOUDLY AND REPEATEDLY.
Today, you can hardly find a shop which lets you listen to anything so the "Hand Carved .. bla bla" becomes paramount.
_________________________
People think DBLTs (especially on amps) only come up with NULL results. This isn't true at all. But the results are heretical to both the Objective and the Audiophool crowd.
I posted in this huge thread somewhere what Design Features would result if DBLTs were the MOST important tests on an amp. If someone finds it, please post it so I can write it down somewhere.
_________________________
[1] Loadsa caveats on DBLTs, curtains etc .. some of which were discussed by Fryer, Lee, Russell, Floyd & Olive ... but many which aren't. I'm also conscious of skimming over very important points.
You can test this proposition and it HAS been tested, notably by James Moir who IIRC published in either WW or HFN & RR.
With 'normal' speakers, you have to get them nearly touching before you measure a difference. I've tested this with DBLTs and I wouldn't bother taking the speaker out of the room ... but see below.
On a number of occasions, a reviewer (surprise surprise) has insisted we include his favourite speaker in a DBLT series and that he personally sets it up in our Listening Room.
Our room was specifically designed to cater for this with 2 entrances and a black curtain between. He spends half a day setting it up, the exact position is marked so it can be replicated and then the curtain is drawn. The R&D crew cart speakers in and out when he requests a change ... trying not to give clues on the size of the speaker being brought in or out behind the curtain.
Proper DBLTs on speakers are much more expensive than buying the latest AP.[1]
And BTW, the guys who ask for this rigmarole were all deaf. The true golden pinnae don't need this rigmarole to reliably pick up differences. The true golden pinnae also can't tell if a speaker is disconnected but left in the room. Neither do they need the speaker in the exact position to reliably identify them and their faults.
YES, positioning & rooms make a huge difference to the sound of a speaker but each speaker has a Room Interface Profile which seems independent of the room and position. It is this which we object to or like.
Absolute Listening Tests-Further Progress
_________________________
In da old days when you could walk into a shop with your CDs and ask to listen to speakers, I truly believed that making your speaker sound better helped sales. We were very successful with this philosophy for many years.
Of course for the deaf HiFi Reviewers, you had to work on your "Hand Carved from solid Unobtainium by Virgins" too ... and tell it to them VERY LOUDLY AND REPEATEDLY.
Today, you can hardly find a shop which lets you listen to anything so the "Hand Carved .. bla bla" becomes paramount.
_________________________
People think DBLTs (especially on amps) only come up with NULL results. This isn't true at all. But the results are heretical to both the Objective and the Audiophool crowd.
I posted in this huge thread somewhere what Design Features would result if DBLTs were the MOST important tests on an amp. If someone finds it, please post it so I can write it down somewhere.
_________________________
[1] Loadsa caveats on DBLTs, curtains etc .. some of which were discussed by Fryer, Lee, Russell, Floyd & Olive ... but many which aren't. I'm also conscious of skimming over very important points.
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