diyAudio Forums Archive - Function of Output Inductor

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Function of Output Inductor - Click HERE for Original Thread

caesar148

I am new to amplifier circuit design so please excuse my ignorance.

I noticed that some amplifier circuit have an output inductor parallel with a 8 to 10 ohm resistor. Could someone educate me as to the function of the inductor? What is the benefit of this part? For a high current amplifier driving a low impedence load, this part would seem to contribute considerable amout of DC resistance or cause the inductor to go into saturation. I may be mistaken about this saturation stuff since it is an air core inductor.

lochness

air core inductors cant saturate. Thats why they are used in passive Xovers (and a few other kinds of circuits). I don't do much in the way of SS amps outside of gainclones so I cant tell you what the circuit does or what it is for.

Eva

The inductor is there to isolate the internal feedback loop of the amplifier from external RF signals picked up by speaker wiring, crossover coils, driver voice coils, etc.. and from the own RF resonances of these elements.

Above audio frequencies, the internal RC dummy load should always dominate against external loads.

audiohead

Inductor isolates the capacitive loads from the feedback loop.

There goes to show that opinion is like an A** hole, everybody have one!

caesar148

Thanks to all who replied. Okay, I am beginning to understand better now. The inductor is to prevent amplifier oscillation when driving "difficult" loads that have high capacitance.

I would conclude that amplifiers with small or no feedback would be less susceptable to such speaker load and could do away with it.

Anyone know what a recommended value of inductance it should be?

fotios

quote:

Originally posted by caesar148
Thanks to all who replied. Okay, I am beginning to understand better now. The inductor is to prevent amplifier oscillation when driving "difficult" loads that have high capacitance.

I would conclude that amplifiers with small or no feedback would be less susceptable to such speaker load and could do away with it.

Anyone know what a recommended value of inductance it should be?

In the quoted graph bellow, appears the ringing caused from a resistive 8Ù dummy load paralleled with a 2ìF capacitor connected and damped via a 8ìH inductor in parallel with a 4,7Ù resistor in the output of amplifier. The test signal is a square wave.

nigelwright7557

quote:

Originally posted by Eva
The inductor is there to isolate the internal feedback loop of the amplifier from external RF signals picked up by speaker wiring, crossover coils, driver voice coils, etc.. and from the own RF resonances of these elements.

Above audio frequencies, the internal RC dummy load should always dominate against external loads.

RF picked up by the speaker wiring ?
How on earth is a 4 ohm impedance going to pick up RF ?

Yes have an RF filter on the high impedance input but never on the output.

You can get oscilation on the output due to capacitance and inductors ringing hence adding an inductor to decouple it from the feedback loop.

kevinkr

Actually RF very frequently couples effectively into the low impedance speaker wiring, your amplifier output may not look like a low impedance (and your speakers don't either) at a couple of MHz and above where even a few inches of wire may have an effect. Often rf picked up on the output wiring will couple through the feedback network particularly if there is a cap across the feedback resistor right back into the input stage which in most cases will rectify it, resulting in unwanted interference with the audio signal at the output.

Jfet based inputs generally don't exhibit this problem to the same degree as bipolar inputs. (no intrinsic diode junctions and higher slew rates, etc.)

This was an all too common problem at the large mid-fi manufacturer I spent most of the last decade at. Extensive testing was done in RF shielded chambers to mitigate this problem.

The inductor is there primarily to isolate capacitance from the output and feedback loop, but it may stop some rf from getting back to the input stage of the amplifier.

CBS240

I agree.

For a typical amp, 100Wrms, I just wrap some 22WGA magnet wire around a 10 Ohm 1/2W resistor and solder it at the ends. Use a 1/2W metal film resistor in series with the 100nF cap for the Zobel before the inductor. Don't think AC current can't flow through the 100nF cap because its value is small. I used a cheap 1/4W 11 Ohm carbon resistor in series with 100nF at the output of a test amp I built. I was fiddling with it once while it was on and it broke out into full RF oscillation and the 1/4W resistor suddenly burst into flames and burned up.:bigeyes: :flame:. Once the funky smoke cleared, I replaced it with a more suitable component.:smash:

kevinkr

quote:

Originally posted by CBS240
I agree.

<snip>

Don't think AC current can't flow through the 100nF cap because its value is small. I used a cheap 1/4W 11 Ohm carbon resistor in series with 100nF at the output of a test amp I built. I was fiddling with it once while it was on and it broke out into full RF oscillation and the 1/4W resistor suddenly burst into flames and burned up.:bigeyes: :flame:. Once the funky smoke cleared, I replaced it with a more suitable component.:smash:

Me too! (and more than once) Quite exciting... :smash:
Don't use fusible metal oxide resistors either... You could loose your zobel network at an inopportune time.. :whazzat:

Eva

quote:

Originally posted by nigelwright7557

RF picked up by the speaker wiring ?
How on earth is a 4 ohm impedance going to pick up RF ?

Yes have an RF filter on the high impedance input but never on the output.

You can get oscilation on the output due to capacitance and inductors ringing hence adding an inductor to decouple it from the feedback loop.

Load impedance is no longer 4 ohms at RF, and it's not purely inductive or capacitive either at these frequencies.

Parasitic capacitances and inductances due to wirings and crossover coils, capacitors and resistors produce a complex load impedance that may exhibit a few high-impedance and low-impedance resonant modes at various RF frequencies. This may easily force an amplifier to oscillate at these modes if some load isolation at RF is not provided.

RF behaviour of speaker wires, crossover coils and capacitors and speaker voice coils is obviously behind the understanding of the average forum member, but it can't be just simplified to "4 ohm" or to a plain "load capacitance".

nigelwright7557

quote:

Originally posted by Eva

Load impedance is no longer 4 ohms at RF, and it's not purely inductive or capacitive either at these frequencies.

The load impedance might not be 4 ohms but the output transistors will be a very low impedance.

Also the Zobel network will be a low impedance at RF.

Eva

Have you ever tried to measure amplifier output impedance at, say, 4Mhz? The R component from the RC network will dominate, but if you remove it, the output stage itself will behave much like an inductor (>50 ohms) with output transistor parasitic capacitances in parallel (thus becoming a resonator/oscillator with a high impedance peak at some frequency!). Fortunately the RC network masks this behaviour.

BTW: Note that parasitic capacitances increase when the output gets closer to the rails, where oscillation is more likely to happen.

boricuaso

could the output inductor be placed in series with the 8ohms or 10ohms resistor that is usually placed in parallel with that coil, an still keep its functionality as an RF filter?.
reason is, im looking for a cheap way to protect the output from speaker shorting out or simply human error of briefly shorting out the output.
that way that 8ohm or 10ohm resistor would serve as a load to the amp shorted output, and keep the output transistors or fets/mosfets from burning up, at least till the amp is turned off, and fixed. its to be used on an amp that doesn't have any form of output protection. sure, the resistor its going to have to be rated higher then 1/2w or what ever is usually rated at, to keep it from going up in smoke.
just not sure if it would change the functionality of the coil, if its set in series rather then the normal parallel to the resistor.
any other advise would be greatly appreciated.
thanks in advance.

laters

caesar148

How much effect does the output inductor have on the sound quality? Has anyone noticed a difference in sonic quality when the inductor is present or absent?

I would prefer not to have the output inductor and resistor if possible. Adding a reactive load to the output will cause a non-linear phase shift to the sound.

To do this, I believe the following needs to be applied:

1. Bandwidth limit the amplifier to within the audio frequency. High bandwidth amplifier that go to 100KHz and more serves no purpose except to become an RF amplifier.

2. Limit the amount of feedback.

nigelwright7557

quote:

Originally posted by caesar148
How much effect does the output inductor have on the sound quality? Has anyone noticed a difference in sonic quality when the inductor is present or absent?

I would prefer not to have the output inductor and resistor if possible. Adding a reactive load to the output will cause a non-linear phase shift to the sound.

To do this, I believe the following needs to be applied:

1. Bandwidth limit the amplifier to within the audio frequency. High bandwidth amplifier that go to 100KHz and more serves no purpose except to become an RF amplifier.

2. Limit the amount of feedback.

I never use the inductor on the output of my amps but I dont use crossovers. There is clearly going to be a small amount of loss across the inductor. I do include a Zobel network.

I use tweeters that dont require a crossover along with mid range speakers.

Christer

quote:

Originally posted by boricuaso
could the output inductor be placed in series with the 8ohms or 10ohms resistor that is usually placed in parallel with that coil, an still keep its functionality as an RF filter?.
reason is, im looking for a cheap way to protect the output from speaker shorting out or simply human error of briefly shorting out the output.

It is a very bad idea for other reasons. At audio frequencies you can ignore the inductor, so in this case you get an 8 Ohm resistor in series with an 8 Ohm speaker. This means two things.

1) The amp output stage suddenly sees a 16 Ohm load instead of an 8 Ohm load, so you get only half the maximum power out compared to the normal approach.

2) The output voltage is split between the resistor and the speaker, so they each get half of the output power.

Say your amp outputs 100 W in 8 Ohms. If you you now put the resistor in series with the coil instead of parallel, you only get half och half the power, that is 25 W, in the speaker. Furthermore, the resistor must now be rated for 25 W.

Eva

quote:

Originally posted by nigelwright7557

I never use the inductor on the output of my amps but I dont use crossovers. There is clearly going to be a small amount of loss across the inductor. I do include a Zobel network.

I use tweeters that dont require a crossover along with mid range speakers.

The resistances and inductances of speaker voice coils and crossover components are always in the signal path.

Even the voice coil of a tweeter is 10 to 100 times more inductive than our little inductor, and a woofer may be 200 to 2000 times more inductive (ignoring RF resonances). Furthermore, voice coil DC resistance is huge in comparison with the output impedance of the usual solid state amplifiers, and even in comparison with the resistance of any other element in the circuit (including the RF coil). This almost always limits effective damping factor to 2.

To make it more ironic, the resistances of speaker voice coils are modulated by signal level and they may easily increase by 15% during loud passages due to self heating.

Now you can continue blaming the little RF-filter coil for nothing. I wish everything was as harmless as this coil.

EDIT: Oh, I forgot to mention that voice coil inductance may easily change by another +/-15% with cone or dome excursion. Nowadays sound quality is something about speakers most of the time...

fotios

quote:

I suggest you to include the output inductor. In this link you can find ready calculators for any type of inductor and much more:
http://www.pronine.ca/links.htm

john curl

Output coil can effect the sound output WITH a loudspeaker. I have had it demonstrated to me in my own lab, by others. IF the inductance of the output coil is MORE than 2uH, you are in trouble. IF 1uH, maybe OK, and .5uH is probably essentially inaudible. This has been shown by experience of a number of audio designers. Arguing from mere measurement or first principles avails you little in this case.

traderbam

quote:

The value depends upon the load tolerance of your amp. You have to work this out for yourself, really, sorry.
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.

lineup

quote:

Originally posted by john curl
Output coil can effect the sound output WITH a loudspeaker. I have had it demonstrated to me in my own lab, by others. IF the inductance of the output coil is MORE than 2uH, you are in trouble. IF 1uH, maybe OK, and .5uH is probably essentially inaudible. This has been shown by experience of a number of audio designers. Arguing from mere measurement or first principles avails you little in this case.

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

caesar148

quote:

Originally posted by lineup

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

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.

traderbam

quote:

Originally posted by caesar148
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.

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.
The output reistance of the amp over the audible band will affect the speaker's damping, but usually this is not the primary issue.

Bob Cordell

quote:

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

Eva

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!!

john curl

Listening really helps in this situation.

syn08

quote:

Originally posted by Eva
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!!

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?

Mooly

Wasn't the lack of an output inductor the cause of problems for Naim Audio when "exotic" re low inductance speaker leads became fashionable. Customers were told to use Naim cables to avoid oscillation/destruction of the amp.

john curl

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.

traderbam

John,
Where, physically, in the setup was the inductor located...near the amp pcb, outside by the speaker terminals, at the speaker end?

Mooly

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

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

john curl

Traderbam, inside the amp body, so that super capacitive cable doesn't effect the amp.

traderbam

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.

lumanauw

quote:

Hi, Traderbam,

In DougSelf book 3rd edition, in chapter 7 (page203) there is a chapter about "crosstalk in amplifier output inductor" for stereo amp (2channel). The 2 inductors have to be spaced and aligned (90deg to each other) so their radiation don't affect each other.

traderbam

quote:

Originally posted by lumanauw

Hi, Traderbam,

In DougSelf book 3rd edition, in chapter 7 (page203) there is a chapter about "crosstalk in amplifier output inductor" for stereo amp (2channel). The 2 inductors have to be spaced and aligned (90deg to each other) so their radiation don't affect each other.

Better put the speakers in different rooms too. :clown:

I'm talking about the field impact on small-signal circuitry.

Eva

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.

destroyer X

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

traderbam

"When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth. " - Sherlock Holmes :magnify:

jcx

There is a threshold curve for statistically significant audibly detectable frequency response differences, this plot has the advantage of being on the web:
http://www.provide.net/~djcarlst/abx_crit.htm

from that set of curves it is pssible to argue that some speaker impedance curves would give response variations above the audible thershold difference for some speakers and 2uH added series inductance (some speaker impedance curves are measured in Stereophile equipment reports also on the web)

john curl

That is not the reason.

Eva

Was there ever a reason? ;)

Bonsai

Let s not get into a long discusion on this subject - we already covered it on another thread. To summarize:-

1. Unless you know a few tricks like JC does, its unlikley that you will be able to design an amp that will operate under all speaker load conditions without an output inductor

2. The output inductor (1-3uH typicallywith parallel a 2-4 Ohm resistor) is designed to isolate capacitive loads from the output stage where such loads cause excessive phase shift resulting on oscillation. It canm also help to reduce the ingress of RF picked up by the speaker cable.

3. If you are using your circuit with a well defined load (e.g. active speaker) you can getaway with it.

4. Don't forget that a typical speaker load along with the associated cable has many times the inductance of a typical output inductor of 1-3uH i.e. it is completly swamped by the wire and speaker load inductances

5. Conclusion: Mortals should use an output coil of 1-3uH in parallel with a resistor of between 2-4 Ohms.

lumanauw

quote:

4. Don't forget that a typical speaker load along with the associated cable has many times the inductance of a typical output inductor of 1-3uH i.e. it is completly swamped by the wire and speaker load inductances

Once I made a marginally stable amp. At the output binding post, if I put 2.2uF cap across +/-, the whole amp oscillates. But when I put a 30cm cheap speaker cable (ordinary twin cable), it doesn't oscillate when the 2.2uF cap is placed after this 30cm cable.
Seems the inductance of 30cm cheap cable is enough to prevent that amp from oscillating, but I don't know what is the inductance value of 30cm speaker cable.

Mooly

Usually smaller values of capacitance are the problem -- try 10nf to 0.47mfd as well.
Regards Karl

Bonsai

Lumanauw, I thinks 10nH per cm is the rule of thumb for a straight wire - maybe one of the other guys can confirm.

fotios

quote:

Originally posted by Bonsai
Let s not get into a long discusion on this subject - we already covered it on another thread. To summarize:-

1. Unless you know a few tricks like JC does, its unlikley that you will be able to design an amp that will operate under all speaker load conditions without an output inductor

2. The output inductor (1-3uH typicallywith parallel a 2-4 Ohm resistor) is designed to isolate capacitive loads from the output stage where such loads cause excessive phase shift resulting on oscillation. It canm also help to reduce the ingress of RF picked up by the speaker cable.

3. If you are using your circuit with a well defined load (e.g. active speaker) you can getaway with it.

4. Don't forget that a typical speaker load along with the associated cable has many times the inductance of a typical output inductor of 1-3uH i.e. it is completly swamped by the wire and speaker load inductances

5. Conclusion: Mortals should use an output coil of 1-3uH in parallel with a resistor of between 2-4 Ohms.

I agree absolutelly with you. For the 5 reasons that you mentioned above exactly, especially the nr. 5. We haven't the luxury of testing our projects with a big variety of expensive hi-end loudspeakers. The only that we are in place to do are simulations with dummy loads. I use the method of the 8Ù resistive dummy load paralleled with a 2ìF cap, because the same practice used from Bascom H. King in "Audio" magazine. In practice now, in the graph of my previous post nr. 6, it appears the damping of oscillation from an inductor of 0,8ìÇ. As for the coil i preffer always thick wire of 2mm diameter - it has realy enormous dimensions - for lowering as much as possible the resistive part ( a common practice that i know from Crest Audio and Peavey amplifiers - the 0,8ìH value used in Peavey amplifiers) and usually for lowering the length of coil i modify it in multilayer and i place it in vertical direction on the seperate output protection PCB just before the output relay ( far away from the main amplifier PCB, exactly as in Crest amplifiers ). Finally from measurements with or without the coil in output by injecting squares in input from my Hameg function generator of 10MHz i haven't seen - from my own eyes by looking at the screen of my Hameg DSO of 50MHz - any difference in the shape of output waveform at least in the audible spectrum. Maybe my Hameg instruments are not so accurate in comparisson with HP instruments or Tektronix - the latter are of course of China origin today.

Fotios

PMA

quote:

Originally posted by caesar148
I am new to amplifier circuit design so please excuse my ignorance.

I noticed that some amplifier circuit have an output inductor parallel with a 8 to 10 ohm resistor. Could someone educate me as to the function of the inductor? What is the benefit of this part? For a high current amplifier driving a low impedence load, this part would seem to contribute considerable amout of DC resistance or cause the inductor to go into saturation. I may be mistaken about this saturation stuff since it is an air core inductor.

The output inductor helps compromised designs, whose parameters are achieved by high amount of global negative feedback, to stay stable when output connected to complex load. It is a necessary bandaid to keep such circuits working, not oscillating.

G.Kleinschmidt

quote:

Originally posted by PMA

The output inductor helps compromised designs, whose parameters are achieved by high amount of global negative feedback, to stay stable when output connected to complex load. It is a necessary bandaid to keep such circuits working, not oscillating.

:yawn: You've got that the wrong way round: It's the compromised designs that generally achieve a high degree of capacitive load stability without a load isolating inductor.

Bonsai

:D

Well Said.

traderbam

quote:

Pretty much. But there is one factor you didn't mention. Speaker cable is a mis-matched transmission line. This means that at certain very high frequencies (MHz) it can look quite inductive and at others it can look quite capacitive. IOW it is not quite right to treat a speaker cable as if it is a pure inductance between amp and speaker.

I agree that it is prudent to use an inductor unless you know what you are doing. Designing an amp, especially a high feedback amp, to be adequately stable in to real loads is extremely difficult.

PS: I've measured straight wire to have an inductance of about 5nH/cm.
PPS: A loop of wire, a circuit, has additional inductance related to the size of the enclosed area of that circuit.

Christer

While I have no opinion whether coils are audible or not, I try to keep a bit of open mind in such issues and I don't mind exercises of hypothetical reasoning. So, if we assume the ouput coil is audible, can we imagine an explanation that might explain it? So let's speculate a bit instead of just dismissing it by adding inductances etc. If for no other reason, so at least just for the fun of it. :)

Tradebarm has already brought up the things that came to my mind too:

1. The coil and the speaker wire have different physical locations, so the explanation might lie there rather than in the inductance per se. As Traderbam said, what about the magnetic field of the coil affecting the small signal circuitry? Since the current dependes on the speaker impedance, the output current may have quite a different spectrum than the output voltage, so if the current induces a voltage in the feedback loop, for instance, perhaps that might distort at least the frequecy response of the amp? What happens if we add the coil just at the output connector instead of on the PCB, for instance? Would John still hear it?

Then, what about the other way around, ie. the coil picking up a field? In a class AB amp, the supply currents are heavily distored. We already know this can affect the circuit by inductive coupling with a bad PCB layout. Well, a coil is much better at picking up magnetic fields than a PCB track is. On the other hand, if this is the case, I suppose it should show up clearly already when testing with a single sine wave.

2. Assume it has something to do with high frequencies, like RFI, slight damped oscillation tendencies of the amp under certain load conditions or maybe back EMF from the speakers can cause fast rising edges with a HF spectrum? Whatever the reason for the HF, maybe we have to think transmission lines here, so we have to consider impedance matching of inner wiring, connectors speaker cable etc. Then perhaps the coil could make thing worse sometimes?

Yes, I know this is mostly very speculative, but if a phenomenon possibly exists, it usually requires quite a bit of speculation and creativity to figure out if it actually exists and why.

Edmond Stuart

quote:

Originally posted by G.Kleinschmidt

:yawn: You've got that the wrong way round: It's the compromised designs that generally achieve a high degree of capacitive load stability without a load isolating inductor.

Well put, Glen.

PS: When people say they hear a difference between a coil and no coil, I wonder what kind of difference. Maybe an amp without coil is perceived as "crystal clear" because it is just ringing. :D

Eva

Any output stage will tend to act as a current source with 90 degree lag at RF. This is because the gains of active devices start to roll-off and parasitic capacitances become no longer negligible. A proper RF load is required in order to achieve predictable RF gain/phase and load-independent stability.

A 2.2uF film capacitor (crossover type) is no longer a capacitor above 500Khz or so, which is the typical resonant frequency for a part having 30mm to 40mm lead spacing. It exhibits a very low impedance dip at that frequency and then becomes inductive. Most amplifiers won't oscillate with that load. That's why physically smaller capacitors can become very handy for testing (but never parallel them, as this causes new resonant modes, apart from self resonance, to appear). Internal (and external) amplifier wiring will also contribute to lower the effective resonant frequency of the load (to 100Khz or below), and a LR output network (2uH, 4ohm) will add considerable damping to that resonance, particularly above 250Khz (where it's mostly required).

A piece of speaker wire (like two 2.5mm^2 wires running parallel and close together) exhibits less than 1uH per meter.

This is not vodoo, it's just modelling everything as the L, R and C that it contains. It's a very healthy practice that helps to produce very reliable circuits without doing a million of empirical tests (what you usually do when you don't actually understand what's going on).

G.Kleinschmidt

quote:

Originally posted by Eva
Any output stage will tend to act as a current source with 90 degree lag at RF.

:rolleyes:

An audio power output stage with a single pole response at "RF" is an object of fantasy.

Christer

I think nobody disputes the basic circuit theory. However, alla models have assumptions that must hold for them to be valid. The questions we should ask are thus rather if we are perhaps failing to see that som assumption does not hold. That is most probably the case if there is something to explain at all here.

Eva

quote:

Originally posted by G.Kleinschmidt

:rolleyes:

An audio power output stage with a single pole response at "RF" is an object of fantasy.

I meant 90 degree or worse :D:D:D (for those claiming unconditional stability without specific RF loads and RF isolation).

Anyway, with some effort and the right Sanken LAPT and Toshiba parts (or a pair of IRF540 for that matter) you can shift the second and further poles quite high. An unity-gain bandwidth product above 10Mhz is not an object of fantasy (maybe an object of luxury? ;) ) My first output stage made with Toshiba 2SC4793/2SA1837 and Sanken 2SC3624/2SA1295 was happily self-oscillating at 30Mhz... Things have changed a lot since 2N3055 :D:D:D

john curl

PMA has it right, high speed output devices and improved compensation as allowed removing coils from being absolutely necessary. The only real compromise can be a little bit of slew rate limiting from the fastest that the amp can produce. Still, 100V/us or more is enough for me, at least, I have done up to 700V/us with coil and a similar circuit however. That was in the 'old days' about 25 years ago.

G.Kleinschmidt

quote:

Originally posted by john curl
PMA has it right, high speed output devices and improved compensation as allowed removing coils from being absolutely necessary. The only real compromise can be a little bit of slew rate limiting from the fastest that the amp can produce. Still, 100V/us or more is enough for me, at least, I have done up to 700V/us with coil and a similar circuit however. That was in the 'old days' about 25 years ago.

LOL!
Compromised bandaid, err..... *cough*...... "improved" compensation can make an amp built with 4MHz fT transistors stable into highly capacitive loads without an inductor.

john curl

Show Bob Cordell how, Glen. You don't have to convince me.

sakis

a simple question becoms a titan fight ......

which i think that bring us to the final conclusion which that many of the amplifiers presented in the forum have oytstanding performance but will not stand any abuse .....

then again the diference between comercial amps and diy amps is the protection methods like zobel, inductor, VI limmiters and so on ....

then the truth is somewhere in the midle ....you canot have everything .....

i wonder how most of these amps will perform with abuse .....

but thats me

Edmond Stuart

quote:

Originally posted by PMA
The output inductor helps compromised designs, whose parameters are achieved by high amount of global negative feedback, to stay stable when output connected to complex load. It is a necessary bandaid to keep such circuits working, not oscillating.

First, high-end solid state amps without NFB (no matter local, global or both) simply don't exist.
But even an amp with only error correction in the OP stage (like HEC) and no global NFB at all, needs a coil if loaded with a low ESR cap.

One more thing: please stop bashing "high amount of global negative feedback", by calling it a band aid. Such nonsense hurts your credibility.

lineup

quote:

Originally posted by sakis
a simple question becoms a titan fight ......

The more they know, the less they know about them selves & their own egos. At least at times looks so, in my 'humble' opinion.
-----------------------------

The Lab Workers/Designers at National Semiconductors, with the simple tools they posses
may not know and understand as much of amplifiers as we do.
But anyway, each time some great audio designer or whoever at our forum critizise these employees writing all them datasheets for us, It makes me doubt some of the things posted here.

My own opinion on this is clear:
If left with the choice
1. --- to believe in some Official Published data by those that made them amplifiers
and
2. --- some stuff posted by a 'moniker' or even 'guru' telling me otherwise in this forum
:) I have often no problems to make up my mind who to trust.
At least in the FIRST Place.

For example,
When Scott Wurcer gives a good piece of info on AD797,
I will listen carefully.
At least I would be reluctant to argue very much with him.
He was around when the chip was designed, tested and the datasheet public information written.

========================
=============================================

LM3875.
What do they recommend for such an output.
No doubt Overture series of 'gainclones chips' are among the most used ever Power Amplifiers of all times.
Why?
Because they please the users.
If not, they would not be such a sucess.
... there are others making such power amps .. with less sold units.

It might be interesting to see what The National Technical Staff
consider a fair typical Output for speakers.
And compare to what 'our' best & most qualified forum posters say.

See my attachment from LM3875 datasheet

Regards Lineup

quote:

LM3875 Overture™ Audio Power Amplifier Series
High-Performance 56W Audio Power Amplifier

14. *L ( 0.7uH )
Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce the
Q of the series resonant circuit due to capacitive load. Also provides a low impedance at low frequencies to
short out R and pass audio signals to the load.

Edmond Stuart

Hi Lineup,

As usual, most published Zoebel networks are wrong, including this one from NS.
If the load is 8 Ohm, then the R across the coil should also be 8 Ohm.
Furthermore, a parallel cap across the load is missing.
With 0.7uH and 8 Ohm the correct value is ~11nF.

Cheers,
Edmond.

PS: Zoebel rules!

traderbam

quote:

Originally posted by Edmond Stuart
Hi Lineup,

As usual, most published Zoebel networks are wrong, including this one from NS.
If the load is 8 Ohm, then the R across the coil should also be 8 Ohm.
Furthermore, a parallel cap across the load is missing.
With 0.7uH and 8 Ohm the correct value is ~11nF.

Cheers,
Edmond.

PS: Zoebel rules!

What? :scratch:

Edmond Stuart

quote:

Originally posted by traderbam

What? :scratch:

What what? :scratch:

traderbam

Who is "Zoebel" for a start?

When you have answered that, if your ego permits, perhaps you would justify your prescription for me. ;)

john curl

I think it is Zobel, and you can probably 'Google' it yourself.

phase_accurate

quote:

As usual, most published Zoebel networks are wrong, including this one from NS.
If the load is 8 Ohm, then the R across the coil should also be 8 Ohm.
Furthermore, a parallel cap across the load is missing.
With 0.7uH and 8 Ohm the correct value is ~11nF.

Unfortunately this dimensioning is only right when neither the coil & resistor nor the Zobel are needed at all: When the load is a nice real 8 Ohms !!!

Regards

Charles

Edmond Stuart

For the illiterate, 'oe' stands for 'ő' (o-umlaut). As this character is not always correct displayed on other monitors, I prefer to be on the safe side, and use 'oe', which is the same as 'ő' in German.

BTW, traderbam, you really don't know much, do ya? Even a *.rar file was a mystery for you.

Cheers.

Edmond Stuart

quote:

Originally posted by phase_accurate
Unfortunately this dimensioning is only right when neither the coil & resistor nor the Zobel are needed at all: When the load is a nice real 8 Ohms !!!

Regards

Charles

You're absolutely right, Charles. Happily my speakers are well terminated at HF, as it should be. :smash:

Cheers.

traderbam

You cast an aspersion oen National's circuit, Edmoend. The least yoeu can doe is explain why. Peoeple are trying toe learn soemething here. :)

Christer

quote:

Originally posted by Edmond Stuart
For the illiterate, 'oe' stands for 'Q' (o-umlaut). As this character is not always correct displayed on other monitors, I prefer to be on the safe side, and use 'oe', which is the same as 'Q' in German.

If you want to be on the safe side you should perhaps spell his name correctly. His name was Zobel with a plain ordinary "o", without any omlaut or other ornaments. Since he was born in the USA, we can rule out that he originally spelt his name differently and changed it after immigrating, since he neved immigrated.

Edmond Stuart

quote:

Originally posted by traderbam
You cast an aspersion oen National's circuit, Edmoend. The least yoeu can doe is explain why. Peoeple are trying toe learn soemething here. :)

Regrettable, I've to repeat my myself: you really don't know much, do ya? Even a *.rar file or a Zoebel network is a mystery for you.

BTW, do you really think you're funny with your stupid "oe", or are you just stoned. :tongue:

Edmond Stuart

quote:

Originally posted by Christer
If you want to be on the safe side you should perhaps spell his name correctly. His name was Zobel with a plain ordinary "o", without any omlaut or other ornaments. Since he was born in the USA, we can rule out that he originally spelt his name differently and changed it after immigrating, since he neved immigrated.

Hi Christer,

Hmm...In the past I had a long discussion with Ovidiu (syn08) on this topic and he assured me (with good arguments) that it is Zőbel. Apparently, he is a purist, nothing wrong with that.

Cheers,
Edmond.

BTW, what about installing a spelling checker on your browser. :D

traderbam

quote:

Regrettable, I've to repeat my myself: you really don't know much, do ya? Even a *.rar file or a Zoebel network is a mystery for you.

I certainly have never claimed to be an expert on data compression formats. Should I be?

Perhaps you'll do me and others a favour and explain your improved Zobel for NS's circuit? I'll suspend disbelief, on this occasion, and assume you have something to teach me.

Christer

quote:

Originally posted by Edmond Stuart

Hi Christer,

Hmm...In the past I had a long discussion with Ovidiu (syn08) on this topic and he assured me (with good arguments) that it is ZQbel. Apparently, he is a purist, nothing wrong with that.

His name is obviously of european origin, so if your post showed the right character on my computer, it seems like hungarian origin then, not german (language) origin as I thought. Of course it is possible that his family kept the original spelling of the name even after immigrating, and then Otto Julius Zobel himself used to simplify it. He obviously did spell it with a plain "o" himself, though:
http://en.wikipedia.org/wiki/Otto_Julius_Zobel

Edmond Stuart

quote:

Originally posted by Christer
His name is obviously of european origin, so if your post showed the right character on my computer, it seems like hungarian origin then, not german (language) origin as I thought. Of course it is possible that his family kept the original spelling of the name even after immigrating, and then Otto Julius Zobel himself used to simplify it. He obviously did spell it with a plain "o" himself, though:
http://en.wikipedia.org/wiki/Otto_Julius_Zobel

As I said before, that character (o-umlaut) will not correctly displayed on every PC/monitor.

Anyhow, you have convinced me that, in order to avoid confusion, we should call this chap Zobel, or even better, Dr. Zobel (are you listening too, Ovidiu?)

Eva

The following simulations may help some people understand why the RL network, in addition to the RC, guarantees maximum reliability and stability for any amplifier and with any load.

It's quite easy to find a range of RLC loads capable of bringing *any* amplifier without a LR output network into oscillation and self destruction, but an amplifier with the proper RC and RL output networks is unconditionally stable and can't be disturbed by any load.

I have modelled the load impedance and its phase, as seen from the output stage, for various load capacitances. I have taken the output network of the LM3886 example since it's reasonably well designed. Note how the impedance is nicely resistive and phase is always near 0 above 2Mhz, which is the minimum unity gain bandwidth product of the LM3886 (typical is 8Mhz) according to the datasheet.

This is the purpose of the RC and RL networks, keeping phase and gain controlled and load independent in the critical unity gain crossing region.

Note how very small capacitances like 3.3nF or 10nF reveal that the L and R value choices are a bit on the low side, while bigger capacitance values are the most harmless ones.

Have fun! With this information some people could even end up learning how to design stable amplifiers (after many years making unstable ones) :D

No ears were harmed during the writting of this post :D:D:D

Edmond Stuart

quote:

Originally posted by traderbam
I certainly have never claimed to be an expert on data compression formats. Should I be?

Perhaps you'll do me and others a favour and explain your improved Zobel for NS's circuit? I'll suspend disbelief, on this occasion, and assume you have something to teach me.

Winrar is just as common as winzip. No need to be an expert. Just use it.

As for Zobel, I'm not going to teach you anything as long as you keep trolling here. Besides, it's soooooo basic.

Christer

quote:

Originally posted by Edmond Stuart

As I said before, that character (o-umlaut) will not correctly displayed on every PC/monitor.

On my monitor it looked like the hungarian long version of the vowel written as a german umlaut o. Don't know if that was right or not, but that's why I said hungarian origin.

quote:

Anyhow, you have convinced me that, in order to avoid confusion, we should call this chap Zobel, or even better, Dr. Zobel (are you listening too, Ovidiu?)

I think we should. Had he been an immigrant who used to americanize his name to avoid problems, then I agree it would be appropriate to use the original spelling when referring to him, but since he was born in the USA and used that spelling, I don't think one should do otherwise.

So shall we go on the next confusion then? Should it be called a Zobel filter or a Boucherot cell? It is often pointed out in the literature that these are different names for the same thing. So are they, and if so, which of the two guys should we attribute it to? :)

The wiki article on Zobel filters however seems to suggest that the term Boucherot cell should only be used, if at all, for certain specific implementations of the filter in the context of loudspeakers.

Edmond Stuart

Hi Eva,

Thank you for the sims. Could you do me a favor and repeat the sims, now, without Rsn and Cns, a cap of 11nF across RL and 8 Ohm across the coil, please?

Cheers.

edit: Writing my previous posts, I have, admittedly, overlooked Rsn and Cns, which were a bit drawn out of focus. My apologies for creating confusion (if any).

Bob Cordell

quote:

This is completely wrong. Even designs without negative feedback can get into trouble if not properly isolated from a capacitive load.

Bob

Bob Cordell

quote:

Originally posted by Christer
While I have no opinion whether coils are audible or not, I try to keep a bit of open mind in such issues and I don't mind exercises of hypothetical reasoning. So, if we assume the ouput coil is audible, can we imagine an explanation that might explain it? So let's speculate a bit instead of just dismissing it by adding inductances etc. If for no other reason, so at least just for the fun of it. :)

Tradebarm has already brought up the things that came to my mind too:

1. The coil and the speaker wire have different physical locations, so the explanation might lie there rather than in the inductance per se. As Traderbam said, what about the magnetic field of the coil affecting the small signal circuitry? Since the current dependes on the speaker impedance, the output current may have quite a different spectrum than the output voltage, so if the current induces a voltage in the feedback loop, for instance, perhaps that might distort at least the frequecy response of the amp? What happens if we add the coil just at the output connector instead of on the PCB, for instance? Would John still hear it?

Then, what about the other way around, ie. the coil picking up a field? In a class AB amp, the supply currents are heavily distored. We already know this can affect the circuit by inductive coupling with a bad PCB layout. Well, a coil is much better at picking up magnetic fields than a PCB track is. On the other hand, if this is the case, I suppose it should show up clearly already when testing with a single sine wave.

2. Assume it has something to do with high frequencies, like RFI, slight damped oscillation tendencies of the amp under certain load conditions or maybe back EMF from the speakers can cause fast rising edges with a HF spectrum? Whatever the reason for the HF, maybe we have to think transmission lines here, so we have to consider impedance matching of inner wiring, connectors speaker cable etc. Then perhaps the coil could make thing worse sometimes?

Yes, I know this is mostly very speculative, but if a phenomenon possibly exists, it usually requires quite a bit of speculation and creativity to figure out if it actually exists and why.

These are all very good points. We don't necessarily know that audibility of the coil is a result of a frequency response deviation caused merely by its inductance in the line. As you point out, its audibility could be caused by the magnetic field that it is radiating while passing the large speaker currents (although one would expect an appropriate frequency response test or distortion test to pick something up as a result of such an interaction). Or, as you point out, it could be the coil picking up something, although again we would think that such might be evident in some measurement. It is all indeed perplexing, but the middle road is to assume that large values of inductance can be audible, so keep them as small and well-behaved as possible, but also recognize that a small amount of inductance is prudent for stability into the unknown environment of the real world. I would not be the least surprized if some audible stuff from some high-end amplifiers originates from burst parasitic oscillations occurring as a result of well-intentioned but misguided high-end design practices.

It would certainly be interesting if someone did a coil audibility listening test where the coil was placed in the line at the louspeaker end, where emission and pickup interactions with the electronics of the amplifier would be much less likely.

Cheers,
Bob

syn08

quote:

Originally posted by Edmond Stuart

Anyhow, you have convinced me that, in order to avoid confusion, we should call this chap Zobel, or even better, Dr. Zobel (are you listening too, Ovidiu?)

I was taught german in the 60's when the alphabet was still full of gothic characters (umlaut wovels, scharfes S) and the transition to oe ue etc... was in progress. To me, correct is Zoebel, Goedel, Zuerich but I understand that languages are evolving and simplifying in time. I guess all forms are correct and even google doesn't seem to care about the syntax in the search, returning both. Interesting enough, Analog Devices is using Zoebel in the application note.

Juergen Knoop

quote:

and the transition to oe ue etc... was in progress

never heard of that, oe ue etc is only the second best option, if your typeset does not contain ä,ü,ö...
Anyway, to my knowledge it has always been Zobel and never Zoebel or Zöbel
regards

Edmond Stuart

quote:

Originally posted by Christer

The wiki article on Zobel filters however seems to suggest that the term Boucherot cell should only be used, if at all, for certain specific implementations of the filter in the context of loudspeakers.

Hi Christer,

Indeed, another point of confusion. As for Boucherot cells, wikipedia describes them as RC networks and it's purpose is to keep the load at HF at the same resistive level as the nominal load (many times applied to tube amps, btw)

A Zobel network however, serves two purposes: keeping the load constant (and resistive) and block RFI from outside.

So, the info from wiki is not always as consistent as it should be.

Cheers,
Edmond.

Christer

quote:

Originally posted by syn08

I was taught german in the 60's when the alphabet was still full of gothic characters (umlaut wovels, scharfes S) and the transition to oe ue etc... was in progress. To me, correct is Zoebel, Goedel, Zuerich but I understand that languages are evolving and simplifying in time. I guess all forms are correct and even google doesn't seem to care about the syntax in the search, returning both. Interesting enough, Analog Devices is using Zoebel in the application note.

Yes, but the question is not about transliteration but about what his name actually was. In the cases of Goedel and Zuerich it is perfectly correct as transcriptions into english, since those names are spelled with umlaut in original. But is there any evidence that Zobel should have umlauts in the name? There are only 69 people with that name in Germany
http://www.verwandt.de/karten/absol...C3%25B6bel.html
while there are 11504 with the name Zobel
http://www.verwandt.de/karten/absolut/zobel.html
Googling for hungarian language pages seems not to find anything byt Zobel and Zo'bel (deliberaty slightly wrong to assure readability).

It seems thus most likely that even Otto J Zobels ancestors did spell their name with just an "o" before emigrating the USA.

Maybe there is something about his origins in this link?
http://genforum.genealogy.com/zobel/

Christer

quote:

Originally posted by Edmond Stuart

So, the info from wiki is not always as consistent as it should be.

Absolutely. Wiki is probably more reliable than most internet pages, but not to be trusted. My point was rather that wiki is the only place so far where I have seen both terms mentioned but not as quite the same thing. Everywhere else I have seen it, they have been claimed as alternate names for the same thing.

Anyway, it seem very few people use the term Boucherot cell, so there is probably not much confusion in practice.

traderbam

quote:

Originally posted by Edmond Stuart
As for Zobel, I'm not going to teach you anything as long as you keep trolling here. Besides, it's soooooo basic.

I won't put you on the spot any further. You can't answer the question, there's really no shame in just saying so. :)

syn08

quote:

Originally posted by Juergen Knoop

never heard of that, oe ue etc is only the second best option, if your typeset does not contain ä,ü,ö...

Not necessary in Germany and in particular as the computer age emerged. BTW, is it Juergen or Jürgen?

Edmond Stuart

quote:

Originally posted by traderbam
I won't put you on the spot any further. You can't answer the question, there's really no shame in just saying so. :)

In the past, you have given plenty of evidence why I (and may others) should NOT discussing any topic with you.

For further info, read: E.M. Cherry, "Ironing out distortion", EW+WW, Jan. 1995, pp.19-20, fig. 9a and 9b.

Juergen Knoop

it is Jürgen, I choosed the 'ue' because this is an international board and not all users may have displayed the 'ü' on their screen correctly.
regards

traderbam

Oh Edmond,
Don't lower yourself to character assassination. I criticized the design of your "ultimate amplifier" or what ever it was called - that was over a year ago, wasn't it? Is that what this is about? Get over it, life's too short.

You made a late appearance in this thread and posted your opinion that the NS Zobel circuit that Lineup posted was badly designed (and you said almost all Zobels are badly designed). You then gave a new resistor value and said a capacitor should be put in parallel with the speaker output. I am unfamilar with the scheme you proposed and cannot understand what benefit it would give. So I asked you to explain it for me and Lineup and anyone else who is following this thread.

You don't want to go to the trouble for some reason, that's fine.
I don't have that Cherry article, please send it to me and I'll have a look.

Edmond Stuart

quote:

Originally posted by traderbam
Oh Edmond,
Don't lower yourself to character assassination. I criticized the design of your "ultimate amplifier" or what ever it was called - that was over a year ago, wasn't it? Is that what this is about? Get over it, life's too short.
..............

First, please don't be so pathetic.
Second, read this post again:
http://www.diyaudio.com/forums/show...827#post1553827
Third, not only your comment on the PGP amp was below all standards, also on other topics, like Ovidiu's view on EC and my NFB OPS.

As for Cherry's article, if you don't have a copy, one more reason to keep your mouth shut.

G.Kleinschmidt

quote:

Originally posted by Edmond Stuart
Hi Lineup,

As usual, most published Zoebel networks are wrong, inclu