The value depends upon the load tolerance of your amp. You have to work this out for yourself, really, sorry.caesar148 said:
There are a couple of subtle issues with inductors. An air-core coli will not saturate like a ferrite cored one but it will produce a wider magnetic field, a function of the instantaneous current.
The extra inductance creates more potential for resonances.
You are generally correct that low or no NFB designs are more load tolerant so are less needy of inductors. This is not the case in all designs; it depends upon the output stage design.
Speaker cable is inductive. So you don't necessarily need a discrete inductor if you choose a sufficient length of cable.
john curl said:
The value I have seen used of these air inductors in amplifiers, are usually 0.5 uH - 2 uH.
1 uH is a very common value.
This confirms the above statement of professor Curl.
My conclusion:
If 1 uH is enough to stabilisate most amplifiers (DIY or Commercial)
- there is no need to use more than this.
Further,
Nelson Pass has told here in forum, he uses Zobel (to protect for INDUCTIVE LOADS),
but he has found usually no need for any Output Inductor (protecting for CAPACITIVE loads).
It appears, to me, most modern Loudspeakers + Crossovers + Speaker Cables
are to be regarded as RESISTIVE or slightly INDUCTIVE LOAD Impedances.
Lineup
john curl said:
lineup said:
Ah!, I am beginning to see the light now. Now I know why matching amplifiers to speakers is important to get the right sound. The complex output impedence of the amplifier from the output inductor and Zobel circuit causes a change in the performance characteristics of speakers. That is why some high end expensive amplifier driving some high end expensive speaker may sound crappy. They are are all good components but they just don't like each other.
This brings out the question of designing the ideal amplifier - the proverbial "Staight wire with gain" amplfier. There should some agreed upon standard as to the component value for the reactive components at the amplifier output. In that way speaker designers can design speakers to match a wider range of amplifiers. Am I asking too much? I do admit amplifer transfer characteristics are more complex than this, but could be a start.
Not really. It's the other way around. The complex output impedence of the output inductor and Zobel circuit (and cables and speakers) causes a change in the performance characteristics of the amplifier.caesar148 said:
The output reistance of the amp over the audible band will affect the speaker's damping, but usually this is not the primary issue.
john curl said:
Hi John,
If an output coil affects the sound WITH a loudspeaker, are you saying that the same coil may not produce a measurable difference with, say, a 4-ohm resistive load?
If this is the case, what kind of loudspeaker was it that you had this effect demonstrated to you on, and what kind of an inpedance characteristic did it have?
Did you measure the in-situ frequency response at the speaker terminals in the course of this experiment to see if there was any measurable frequency response change caused by the presence of the coil?
I'm thinking that 2 uH has an impedance of 0.25 ohms at 20 kHz, so it certainly does reduce the damping factor of any amplifier down to on the order of 32 at 20 kHz. Do we think that a reduction in DF to 32 at 20 kHz is audible, or do we think it is something else that has nothing to do with damping factor?
Obviously, tube amplifiers don't even have a DF of 32 to begin with. I also believe that they have more than 2 uH of leakage inductance at their outputs. If so, why do some people think THEY sound so good?
Cheers,
Bob
Could anybody explain how 2uH of added ideal air-core inductance (or 5uH for that matter) can change the performance below 20Khz of a tweeter which already has 50uH or more of series non-linear inductance in it?
Speakers are not ideal black boxes.
BTW: Tweeter inductance is not constant, it's frequency dependent too!!
Speakers are not ideal black boxes.
BTW: Tweeter inductance is not constant, it's frequency dependent too!!
Eva said:
A little Maxwell calculation shows that:
A 0.3" twin lead cable (as in the speaker cable) with 0.1" dia. wire diameter in a medium relative permitivity of 4 has an inductance of about 1uH/ft.
A simple 0.1" dia. wire in air (as in the speaker enclosure) has an inductance of about 1uH/ft.
Now, could somebody explain how a 0.5uH lumped inductance is audible if only the typical speaker wiring inductance is at least 10uH?
Ok, 0.5uH is 5% out of 10uH so perhaps a golden ear, in a fully controlled setup, can hear that. But how on earth can you extrapolate the results and declare "0.5uH is good, 2uH is bad" if the rest of 95% is a customer's site wiring setup variable you can't control or influence?
Or is this another example about the high end audio environment having little to do with the fundamental physics laws?
Yes, you are correct, Mooly, but Julian found the inductor audible, BEFORE exotic wire was introduced, so he was caught up with a problem. He presumed, mostly rightly, that the normal zip cord almost universally used in the early 70's, would make up for the coil, as far as stability.
More modern designs often do not need a coil, because of improved output devices and circuit design. It is NOT absolutely necessary to have an output coil for a feedback amplifier in EVERY CASE, and doing without actually seems to sound better. I didn't believe it at first either, but I kept an open mind about it, 20 years ago when it was first shown to me to be audible. That makes me flexible and more able to improve my designs.
More modern designs often do not need a coil, because of improved output devices and circuit design. It is NOT absolutely necessary to have an output coil for a feedback amplifier in EVERY CASE, and doing without actually seems to sound better. I didn't believe it at first either, but I kept an open mind about it, 20 years ago when it was first shown to me to be audible. That makes me flexible and more able to improve my designs.
That's interesting. I might investigate reducing the value or at least reducing it in my design at some point. I played safe-- too safe probably. I must admit I use a low value resistor 0.22 ohm in series with the output and this probably gives all the "isolation" that is needed in my case.
Thanks for that
Karl
Thanks for that
Karl
my input .....
simple and nice made P3 from rod never wanted any inductor .....
connecting an inductor had negative audible effect destroyed the high sonics and made the all amp sound kind of dark .....( keep in mind that i try with quiet many of them and results were more or less the same )
on the contrary adding inductor to a DR Bora's legend 4 or nelson pass citation 12 mosfet ( choose any name you like the circuit is the same ) made a hell of a lot of diference and also prooved that was a huge diference first between inductor or not ...and then quiet a lot of diference between coils ....i end up with 14 windings of 1.2mm wire to a 12 mm diameter and 3.3R resistor in parallel ....
this had a result making the amp more detailed in high frequency before that sound was kinda messy ...not crystal clear ....
thats from listening point ....inductors provide aditional safety to the amplifier which i have no knowledge to analyze.....
all the best sakis
simple and nice made P3 from rod never wanted any inductor .....
connecting an inductor had negative audible effect destroyed the high sonics and made the all amp sound kind of dark .....( keep in mind that i try with quiet many of them and results were more or less the same )
on the contrary adding inductor to a DR Bora's legend 4 or nelson pass citation 12 mosfet ( choose any name you like the circuit is the same ) made a hell of a lot of diference and also prooved that was a huge diference first between inductor or not ...and then quiet a lot of diference between coils ....i end up with 14 windings of 1.2mm wire to a 12 mm diameter and 3.3R resistor in parallel ....
this had a result making the amp more detailed in high frequency before that sound was kinda messy ...not crystal clear ....
thats from listening point ....inductors provide aditional safety to the amplifier which i have no knowledge to analyze.....
all the best sakis
I'm curious about the magnetic field effect of the inductor.
Obviously, the inductance itself may be aletering the amplifer and causing the audible degradation, but I wonder how significant the field is?
If the experiment were done with the inductor outside the amp case, at the speaker terminals, it might give a different delta.
Obviously, the inductance itself may be aletering the amplifer and causing the audible degradation, but I wonder how significant the field is?
If the experiment were done with the inductor outside the amp case, at the speaker terminals, it might give a different delta.
I wouldn't care about linear crosstalk, it's mostly harmless. Then again, in practice you can't get much better acoustic crosstalk than -6dB with a pair of speakers in a room.
How about the mains transformer? It can produce much stronger fields than any 2uH coil. I have just measured 600uH !!! of leakage inductance from the primary side of a 470VA toroid with shorted secondaries. Mains Chopped-sine current pulses, whose amplitude and width is signal dependent (actually speaker current dependent), are flowing through this inductance, and all the signal wiring and amplifier PCB tracks are picking the field up. This is a real disaster, particularly with non-toroid transformers having 5 times more (or so) leakage inductance. In comparison, a good SMPS can in no way leak such strong magnetic fielts right in the audio band.
And what about supply rail wiring? Positive speaker current pulses flow through a particular wire and supply capacitor thus producing a particular magnetic field spatial pattern. Negative pulses flow through a different path (since nobody twists the wires) resulting in another spatial pattern. As a result, positive and negative pulses are picked up with a different strength by small signal wiring and PCB tracks.
We are ignoring physics and the real amplifier problems and inventing new non-existent ones...
I gathered most of my knowledge about parasitics by doing high power switching mode power supplies and class D amplifiers. These applications are really demanding, unlike linear amplifiers (almost anybody can get one to work!) I would have never learnt all this by doing class AB amplifiers and listening, that's a dead end for anybody willing to know in detail what's going on inside circuits.
How about the mains transformer? It can produce much stronger fields than any 2uH coil. I have just measured 600uH !!! of leakage inductance from the primary side of a 470VA toroid with shorted secondaries. Mains Chopped-sine current pulses, whose amplitude and width is signal dependent (actually speaker current dependent), are flowing through this inductance, and all the signal wiring and amplifier PCB tracks are picking the field up. This is a real disaster, particularly with non-toroid transformers having 5 times more (or so) leakage inductance. In comparison, a good SMPS can in no way leak such strong magnetic fielts right in the audio band.
And what about supply rail wiring? Positive speaker current pulses flow through a particular wire and supply capacitor thus producing a particular magnetic field spatial pattern. Negative pulses flow through a different path (since nobody twists the wires) resulting in another spatial pattern. As a result, positive and negative pulses are picked up with a different strength by small signal wiring and PCB tracks.
We are ignoring physics and the real amplifier problems and inventing new non-existent ones...
I gathered most of my knowledge about parasitics by doing high power switching mode power supplies and class D amplifiers. These applications are really demanding, unlike linear amplifiers (almost anybody can get one to work!) I would have never learnt all this by doing class AB amplifiers and listening, that's a dead end for anybody willing to know in detail what's going on inside circuits.
Do not make sense to me too... cannot disturb sound
But i have made many tests... and even not believing what i was listening, i have to accept what i have listened.... was clear, perceived that coils disturbs sound quality.
Even beeing so small inductance compared to speakers, wires, crossovers and having not a phisic law support.... i had to accept that thing sounds.
I do use coils to some amplifiers, in special when i do not know the use the builder will give to the amplifier, for protection purposes...but in my home, my own amplifiers have no output coil.
I do believe in theories, but if they go against my ear... i decide by my ears.... music is to listened....by humans, not by meters.
I do not believe this small inductor can make difference... even no believing i know they make difference... and this do not make any sense to me..but sounds!... and worse with them.... well... almost everything inside the audio chain worsens the sound quality.
"Yo no creo en brujas, pero que existen, existen."
" I do not believe in bewitches or if they exist, but, they for sure exist" (because of the effects we feel, we know, we suffer, we perceive)
regards,
Carlos
But i have made many tests... and even not believing what i was listening, i have to accept what i have listened.... was clear, perceived that coils disturbs sound quality.
Even beeing so small inductance compared to speakers, wires, crossovers and having not a phisic law support.... i had to accept that thing sounds.
I do use coils to some amplifiers, in special when i do not know the use the builder will give to the amplifier, for protection purposes...but in my home, my own amplifiers have no output coil.
I do believe in theories, but if they go against my ear... i decide by my ears.... music is to listened....by humans, not by meters.
I do not believe this small inductor can make difference... even no believing i know they make difference... and this do not make any sense to me..but sounds!... and worse with them.... well... almost everything inside the audio chain worsens the sound quality.
"Yo no creo en brujas, pero que existen, existen."
" I do not believe in bewitches or if they exist, but, they for sure exist" (because of the effects we feel, we know, we suffer, we perceive)
regards,
Carlos
