Audibility of output coils

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#661
Hi John,


Why I have to put up with insults regarding my age and expeience is beyond me.

Seriously??? I think they're only joking 😀

I have some experience to offer

I'm trying to follow your guides somehow, that's why I'm here ...............................but i only end up scratching my head on how output coil would make a difference. I'm all ears on this issue.


Hartono
 
#662
The most important point is: I DON'T NEED OUTPUT COILS AT THE OUTPUT OF MY AMPLIFIERS ! If you need an output coil, for some reason, then try to keep its value down to a minimum like Halcro and Bob Cordell. Is this such a difficult concept?
Most of you have little or no idea what real hi fi is. That is a shame, but then I have never driven a Ferrari. Maybe, if I did then I could understand why it is so expensive and exotic. It is the same with quality hi fi.
 
#663
john curl said:
Folks, I would like to say something important here.
I try to contribute my experience to this website. As a working audio design engineer for about 40 years , I have some experience to offer.
In my near retirement years, all I hope is to pass on some knowledge to those, who might follow. Why I have to put up with insults regarding my age and expeience is beyond me.
Click to expand...



Oh, lighten up John. It was only a light-hearted tease.

What kind of on-topic knowledge and experience you wish to pass on by boasting about your love life is certainly beyond me, for one.

How about replying to some of Bob's most recent comments on the output impedance of your JC-1?

Cheers,
Glen
 
#664
Bob is wrong. You only have to look at the Halcro DM88 review. Look at the graphs there, that were made exactly the same way by the same person, and compare it to the JC-1 graph that Bob keeps picking and poking at. What do I have to do? Rub your noses in it? Wake up!
 
#665
Hi John,

I'm just asking,please don't get upset.


"Is this such a difficult concept? "


actually yes..................I would be very good if you can help me to understand why the coil degrades the sound, technically.

we can get around of not using coil by making a more stable amp, but we also like to maintain lots of feedback at HF to lower THD. sometimes to do that we would need coil. If you may have a suggestion that this is not the good approach, I would like to now why.


Regards,
Hartono
 
#666
You have to use your ears, and those of skilled listeners over many years, just to get a feel for what added inductance does to the sound. Also, Graham Maynard has TRIED to explain something important to you, but nobody listens! Live your life, and love your coils. It doesn't matter that much to me.
 
#667
john curl said:
Bob is wrong. You only have to look at the Halcro DM88 review. Look at the graphs there, that were made exactly the same way by the same person, and compare it to the JC-1 graph that Bob keeps picking and poking at. What do I have to do? Rub your noses in it? Wake up!
Click to expand...


Thanks John.

Here is the post in question:

http://www.diyaudio.com/forums/showthread.php?postid=1217827#post1217827

It is quite detailed and raises quite a few points. With your burning desire to impart valuable knowledge, could you elaborate a bit on which points are wrong or irrelevant and why?


Cheers,
Glen
 
#668
Where is the DM88 power amp review? This is what you must read first.
All you have to do is look at fig. 1 for the Halcro dm88.
Compare that to Fig. 1 for the Parasound Halo JC-1.
First, you must compare how the Parasound responds to different loads.
Then, you must compare how the dm88 responds to different loads.
Then you may come to understand that Bob is making much about little or nothing, and that simple measurement error is enought to throw off his predictions.
In any case, the Halcro looks much worse in this comparative measurement.
 
#669
Jan,

As promised a few days back the TS model for the speaker I used is shown in the attachment. The model is based on measurements of a Scan Speak 13M8640 unit.

Now I just have to catch up with this thread.

Tony
 

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#672
john curl said:
Estuart, have you NOW realized that there is NO real output coil on the output of the JC-1 amp? That is the point of this thread!
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Uhh........not yet, maybe tomorrow.

john curl said:
By the way, who where you dating 40 years ago? And give me all the details! At least what books you were reading. Do you see how difficult it is to go back so far? [/B]
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40 years ago? What books? Well, I was reading: "Good Manners on Internet Fora" , written by the famous and well respected Mr. Bob Cordell. I can really recommend it, in particular to designers of coil-less amplifiers. Admittedly, I don't remember all the details, but I do remember the most important thing: never be arrogant.

As for amplifiers, I did not ask you all the details, I only asked for two key-parameters. Besides, you do remember that the loop gain was 40dB, but, without specifying at which frequency, this number is pointless, so, I think it is not unreasonable to suppose that you remember the other number too.
Also, you do remember you have applied excessive compensation, so, be prepared that someone ask you how much.

If you ask me, can tell you right now, even without looking in my schematics, how large the compensating caps are in my almost 40 years old amp: left channel 100pF, right channel 100+22pF. So, why can't you?
 
#676
Re: Re: Re: Re: Re: Re: Re: Re: definition of 'rock solid'

G.Kleinschmidt said:
Hi Edmond.

I don't think that there is anything wrong with my approach in this regard. I made an assumption based on my theoretical understanding of the amplifiers operation, and this has been confirmed on the test bench - which I think carries a bit more weight than in simulation.
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Hi Glen,

I'm sorry to say, but you really should read my posts more carefully. In my post#608 I ask:
"How do you KNOW that your method is appropriate for the given application?"
Now, finally you give the answer. Your made an assumption and this is confirmed on the test bench. This implies that you do make use of "foreknowledge". Without this conformation you never could be sure about the reliability of your method. That's my point. Also, I like to point out that your method actually consists of two part: measuring the open loop gain and the bench test from above (no matter you have done this test in the past).

G.Kleinschmidt said:
Because, whith my test equiptment, the method I outlined allows me to quickly and accurately examine the open loop gain and phase response of the amplifier from 0.1Hz to 20MHz.
This gives a lot a valuable information, some of which can be difficult to measure with the loop closed. Also, it is not difficult to implement, especially so since my mainframe dual trace Tektroniks 551 oscilloscope has a Type O operational amplifier plug-in installed, which is eminently suitable for DC servo duties 🙂
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I never said you should measure with a closed loop, see my post#476:
"I disconnect the FB resistor from the output and inject a signal into the FB network in stead of into the input (and of course taking care of DC operating point)."
This is just as easy as your method, but has the advantage of.....enfin, you know already.

G.Kleinschmidt said:
If you're talking about the capacitor from the VAS to the inverting input, the same method works fine, but testing of the inner loop requires a bit of elaboration.

Cheers,
Glen
Click to expand...

No, that is a lag compensating cap (according to Bob, not to Mikeks).
I mean a lead compensation cap (5...10pF), parallel to output FB resistor.

I'm sorry, I have to leave now. Maybe tomorrow.

Cheers, Edmond.
 
#677
Hi PMA,

I'm sort of beginning to see the problem. Heck it might even turn out to be wrong 😀

but this simple experiment might tell a thousand word.

take out your zobel and coil, connect the amp output to the speaker.
connect your scope at the amp output, tap the mid / woofer and see the result.

Hartono
 
#679
john curl said:
Folks, I would like to say something important here.
I try to contribute my experience to this website. As a working audio design engineer for about 40 years , I have some experience to offer.
In my near retirement years, all I hope is to pass on some knowledge to those, who might follow. Why I have to put up with insults regarding my age and experience is beyond me.
Click to expand...


Mr Curl:

I personally feel, and think this feeling is shared by a significant lot, that having you around here is a great asset. Much more so when you show a willingness to keep pushing in the face of sometimes less than polite challenges. You need not be exposed to this yet you willfuly do.

As much as we may congratulate for this, it is not an endorsement for sweeping statements on your part which then do not get fundamented in more detail when asked to do so.

I tried fruitlesly for my part to have you express in a more descriptive way than simply "listen and you will find", what should we focus on to discern defects in that or such design.

Is it asking too much for you to be more specific? Is there an obviuous answer not worth mentioning and I am a dummy?

We are not even asking for circuit design details which rightly belong to company competitive assets.

We are asking simply you to tell which test signals, which kind of music, which type of instruments, rhytms, voices, passages, whatever, have you found in your long experience to be peculiar in the sense of lying bare different weaknesses. Which are the cues you look for from focused attention on details.

We may have our own perceptions and experiences in this respect, but you have offered to share your long experience, a most appreciated gift.

Rodolfo
 
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