I was going to reply to Edmond for claiming that I am wrong with regard to differential sensing between the signal input and voltage at the output node of a NFB amplifier, with the input filter between that signal input and the first base;
but, you know what guys,
I give up !!!
Not because I feel defeated by any theoretical proof against my writing, for there has been abject failure in this regard, but because of all the totally un-necessary and pedantic argument !
And this from those who lecture/write, where there is a very great burden relating to what they feed young minds of the 'future'.
I have been making an effort for what I thought was the benefit of others, but the posturing of some here, who frankly ought to know better (if they do actually know their theory as well as they claim to when they refute my words), are deliberately creating such a smokescreen that worthwhile discussion becomes clouded.
It is not me who feels as if the loser; for when this happens I feel sorry for others who read this thread.
There are many better things for me to do in life than allow my time to be so unproductively wasted in this way.
Good luck with your investigations Tony !
When you have findings the experts will shout - not valid - and they will then suggest a 'valid' test signal that is nothing like what real music looks like !!!
but, you know what guys,
I give up !!!
Not because I feel defeated by any theoretical proof against my writing, for there has been abject failure in this regard, but because of all the totally un-necessary and pedantic argument !
And this from those who lecture/write, where there is a very great burden relating to what they feed young minds of the 'future'.
I have been making an effort for what I thought was the benefit of others, but the posturing of some here, who frankly ought to know better (if they do actually know their theory as well as they claim to when they refute my words), are deliberately creating such a smokescreen that worthwhile discussion becomes clouded.
It is not me who feels as if the loser; for when this happens I feel sorry for others who read this thread.
There are many better things for me to do in life than allow my time to be so unproductively wasted in this way.
Good luck with your investigations Tony !
When you have findings the experts will shout - not valid - and they will then suggest a 'valid' test signal that is nothing like what real music looks like !!!
Define sensing network
Aagh! (out of breath) Have finally caught up again.
Before going right back to interesting post by Conrad -
Please folks, I cannot see that one can define "sensing" that rigidly. Yes, it is perhaps more accurate to just mention NFB network, but then that is also more vague. In the sense (is that a pun?) that nfb arriving at the input will look around at whatever networks are immediately there to judge what it is supposed to do, its action will be dependant on, i.e. in a sense sense (work that out for yourselves
) what is going on there and be influenced by it. I think this is a case for grasping what was intended and not for grammar - goodness knows that is a limited enough vehicle for transporting one through this subject unless a whole lot of "grasping" is exercised.
It has been conceded, but it can be quite illuminating on Spice to fiddle with an amplifier's input works and its effect on nfb, especially with semiconductors. Best is to have matters as constant as possible there.
Regards
Aagh! (out of breath) Have finally caught up again.
Before going right back to interesting post by Conrad -
Please folks, I cannot see that one can define "sensing" that rigidly. Yes, it is perhaps more accurate to just mention NFB network, but then that is also more vague. In the sense (is that a pun?) that nfb arriving at the input will look around at whatever networks are immediately there to judge what it is supposed to do, its action will be dependant on, i.e. in a sense sense (work that out for yourselves
) what is going on there and be influenced by it. I think this is a case for grasping what was intended and not for grammar - goodness knows that is a limited enough vehicle for transporting one through this subject unless a whole lot of "grasping" is exercised.It has been conceded, but it can be quite illuminating on Spice to fiddle with an amplifier's input works and its effect on nfb, especially with semiconductors. Best is to have matters as constant as possible there.
Regards
Hi Conrad
I thought I'd solved the direction sensitivity by making the output coil (mostly) non-directional with a toroidal.
But now I'm not so sure even this is any use ...
Picture is of first trial made some time ago. Details for anyone interested (if there are any left) re 39 turns 20 swg (0.9mm) half-inch /13 mm core (drill) and then folded into toroid around same half-inch drill at centre. Inductance 3.3uH.
cheers
John
I thought I'd solved the direction sensitivity by making the output coil (mostly) non-directional with a toroidal.
But now I'm not so sure even this is any use ...
Picture is of first trial made some time ago. Details for anyone interested (if there are any left) re 39 turns 20 swg (0.9mm) half-inch /13 mm core (drill) and then folded into toroid around same half-inch drill at centre. Inductance 3.3uH.
cheers
John
Attachments
john curl said:
Hi John,
I'm not the slightest bit attached to o/p chokes. If it turns out I prefer the sound of amps without them I will go with it.....but right now I am just asking: do you think that 0.5uH in parallel with a 1 ohm resistor will have the bad audio signature compared with higher value resistors that are normally used - did you try this combination ?
cheers
mike
Conrad,
Your #417 (not sure which part of it to quote).
Yes, that is interesting. What is the response (square wave etc.) like on open circuit? What did you terminate this (those) with?
Point being that there must be something capacitive there for the inductor to start "performing", and that can vary as you would know. My amplifier had a peak round about 13 MHz, both on Spice and in practice (which by the way also showed that the p.c. etc. did not have that much of an influence, to my own surprise).
So many posts here, but I wonder if someone did put this output capacitance thing (which is the reason for the presence of the inductor) in perspective somewhere with regard to practical values. John said that an electrostatic loudspeaker presents 1 ohm or such in series with quite a few uF (sorry I cannot find that now); apart for that, for myself I am hard put to visualise a load capacitance (mostly cable) of more than some 50nF in domestic applications. Again, I am not the type to compete for honours in outperforming everyone else (found to my surprise that society never rushed up to erect a monument for me). If that is OK then that is what I safeguard for. Design is a compromise and this is not as high up on the priority list as other matters.
But perhaps you would comment on my first paragraphs?
Regards.
Your #417 (not sure which part of it to quote).
Yes, that is interesting. What is the response (square wave etc.) like on open circuit? What did you terminate this (those) with?
Point being that there must be something capacitive there for the inductor to start "performing", and that can vary as you would know. My amplifier had a peak round about 13 MHz, both on Spice and in practice (which by the way also showed that the p.c. etc. did not have that much of an influence, to my own surprise).
So many posts here, but I wonder if someone did put this output capacitance thing (which is the reason for the presence of the inductor) in perspective somewhere with regard to practical values. John said that an electrostatic loudspeaker presents 1 ohm or such in series with quite a few uF (sorry I cannot find that now); apart for that, for myself I am hard put to visualise a load capacitance (mostly cable) of more than some 50nF in domestic applications. Again, I am not the type to compete for honours in outperforming everyone else (found to my surprise that society never rushed up to erect a monument for me). If that is OK then that is what I safeguard for. Design is a compromise and this is not as high up on the priority list as other matters.
But perhaps you would comment on my first paragraphs?
Regards.
john curl said:
Hi John,
Can you tell us more about this AB test that convinced you that output coils are audible?
How big was the coil involved?
How did you A-B an identical amplifier with and without a coil? Or was it an A-B between two different amplifiers, one using a coil and one not using a coil?
Do you base your opinion that coils degrade the sound on this one A-B test, or have you done lots of checks of amplifiers with and without coils?
How do you know that the amplifier using the coil in this test was not a bad implementation of a coil?
What kind of speakers were you driving in this test?
Did you follow up with any tests on the amplifier in question to see if there was a measurable frequency response difference or distortion difference with and without the coil that could account for the perceived degradation in audio quality?
Thanks,
Bob
peufeu said:
Look into Principle Component Analysis (PCA). Makes current two dimensional measurements look like Stone Age tools. I can't say I've mastered it, not even close, but I can see it's potential.
Listening still beats all, if you can do it with an open mind. Last week, out of curiosity, I dug out a couple of coils removed from an amp years ago; 25 turns of approximately 18ga wire wrapped around a 1.8 ohm 10 watt WW resistor. Probably out of a Dynaco 400, and set it up to A/B test. Placed it outside the amp so I could easily insert/remove it from the + speaker path.
20-30 cycles later listening to a few recordings, most interesting: Neil Young Live at Massey hall.
With the coil in series there was a noticeable/slight drop in level, a loss of hall bloom (for lack of a better description); kind of like a diminishing of the reverberant quality on the vocals and guitar.
And a slight sandy quality added to the vocals, which are very impressive on the Neil recording.
Just a few observations from the dark side.
Mike.
Man, I can't even keep track of this thread anymore. Johan- nothing unusual as a load, I was just doing bench tests of an old amp design, and trying different output coils. Just an 8 ohms resistive load. After reading here, I wondered what I had and wanted to see what different values did, as I have measurement equipment I didn't have when I built the thing. I do remember building it the first time using a coil/resistor almost identical to the carbon comp I described here, and having nothing but trouble. It never dawned on me that the coil could be the problem. Because the coil and resistor are wired together, they can be treated as a black box. You attach the pair to the vector impedance meter and a very straightforward answer comes back for any given frequency. What's in the box to give that result is of little importance to the amp, only it's impedance and phase angle. Other than pickup issues, which I haven't seen, and amplitude linearity, which shouldn't be an issue with a non-magnetic core, there isn't much more to tell. It's just very interesting to me that the "preferred solution" using a lump type carbon comp resistor, good to many hundreds of MHz, with a nice large diameter heavy gage coil around it, gave me trouble. The, IMO, "less desirable" spiral pattern resistor, with magnetic metal end caps, was the part that caused the amplifier to behave properly. I had so much trouble to begin with because of preconceived audiophile notions about metal end caps and slightly inductive resistors. I'm vastly more interested in component measurements now, rather than succumbing to stupid cosmetic issues and pseudoscience.
John- I thought of winding a coil and bending it into a toroid, but never tried it. IMO, it's a much more preferable configuration. I believe you can get non-magnetic ceramic toroids from Amidon or a similar company. Did you know that the large General Radio inductance standards are huge toroids wound on non-magnetic cores, packed in powdered cork for mechanical isolation and stability?
John C- I can't speak for others, and have asked you nothing, but have to say that I do enjoy looking for the reasons behind sonic differences. I'm willing to investigate some pretty far fetched (to me anyway) ideas, but I'm sure people feel disappointment and probably disloyalty when I find some rational explanation for what's going on. The problem as I see it, is two-fold. Most claimed sonic differences disappear when the many pitfalls of comparison are addressed. People with great knowledge and experience seem just as vulnerable to those pitfalls as anybody else. I do it myself, almost as if there were a Jekyll and Hyde nature to audiophiles. Cold and rational one minute, then all excited about some capacitor change when things sound really good. The second problem is that when differences really do exist, people tend to blame/attribute them to the wrong things. They change A and hear something, then assume it was A that's the fundamental cause, when A really triggered B and C and whatever else. Since the pitfalls are mostly well known, yes, I place the burden of disclosure on those who hear differences that conventional engineering suggests are unhearable. Without disclosure, there isn't much to discuss, which is why we're all here.
John- I thought of winding a coil and bending it into a toroid, but never tried it. IMO, it's a much more preferable configuration. I believe you can get non-magnetic ceramic toroids from Amidon or a similar company. Did you know that the large General Radio inductance standards are huge toroids wound on non-magnetic cores, packed in powdered cork for mechanical isolation and stability?
John C- I can't speak for others, and have asked you nothing, but have to say that I do enjoy looking for the reasons behind sonic differences. I'm willing to investigate some pretty far fetched (to me anyway) ideas, but I'm sure people feel disappointment and probably disloyalty when I find some rational explanation for what's going on. The problem as I see it, is two-fold. Most claimed sonic differences disappear when the many pitfalls of comparison are addressed. People with great knowledge and experience seem just as vulnerable to those pitfalls as anybody else. I do it myself, almost as if there were a Jekyll and Hyde nature to audiophiles. Cold and rational one minute, then all excited about some capacitor change when things sound really good. The second problem is that when differences really do exist, people tend to blame/attribute them to the wrong things. They change A and hear something, then assume it was A that's the fundamental cause, when A really triggered B and C and whatever else. Since the pitfalls are mostly well known, yes, I place the burden of disclosure on those who hear differences that conventional engineering suggests are unhearable. Without disclosure, there isn't much to discuss, which is why we're all here.
estuart said:
There's an interesting observation I'll throw in here. Back in post 148 it was mentioned that touching an input signal lead supplied a local high power radio transmitters signal into the (all of) amp.
What does this say about the input filter, or for that matter the ground reference for the feedback? What does it say about the performance of the output stage? All is not what it seems (what the simulation tells you).
Another observation from the darkside. I'll get bored and go away soon, I just needed a diversion tonight.
Mike.
janneman said:
Hi Jan,
The last pic was the error voltage (coil output - time delayed input) added to the source sine wave before rectification. I did this to get some idea of the harmonic content caused by the coil. If I removed the coil and did the same thing I would get no harmonics as the driving amplifier was a "perfect" VCVS. You're right about the harmonic content of the rectified signal of course. There are harmonics all over the place which means I couldn't see the effect of the coil by simply looking at the coil output only.
I'm travelling at the moment so won't be able to post the coil equiv cct until Friday probably but will do so then.
Cheers,
Tony
Hartono said:
Hi Hartono,
I did check on a couple of music sequences before I ran the sim. I was lucky enough to have a demo CD to hand with one track consisting of only a drum kit. The initial transient of many of the drum hits, although short, looked very much like a half sine put through a filter which is what I used as the source wavefrom - albeit it repeated so I could get an FFT plot of the result.
Cheers,
Tony
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