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mikek 7th May 2003 08:53 AM

Re: Whom to believe?

Originally posted by mrfeedback
I choose Phred and Hugh.

In my understanding another reason to avoid high slew rate output stages is that this is another means of exciting power supply resonances.
High PSRR or low PSRR, these effects are audible.

Some amplifiers that I have heard such as Metaxas amplifiers with published very high slew rates and bandwidths on first impression sound very 'fast', but after about 5 minutes drive me out of the room as fast as I can go.
In addition these amplifiers (earlier models) are very fragile and go SPLATT at the merest provocation.

In my view slew rates faster than reasonably necessary are not required, and can be seriously deleterious.
Load stability is of the utmost importance in my books, and cannot be substituted.


hi eric..

i did not say high slew rates are necessary.....
i find it disappointing that you should suggest that i did...:(...

Fred has his own agenda in deliberately misrepresenting me....

read through my posts and you'll find i actually agreed with hugh in respect of excessive slew rates being the beef?


Originally posted by AKSA
I have to concur with Eric and Fred.

Load stability is paramount, since failure to ensure it results inevitably in a blown amplifier, with possible destruction of the speakers as well - tweets through HF oscillation, and woofs through overcurrent.



Hugh i am sure you would agree that.....i did not say load stability is unimportant......disappointing.....surprising....

mikek 7th May 2003 09:05 AM

Re: Whom to believe?

Originally posted by Fred Dieckmann
Most of the good amps I have heard have closed loop bandwidths in the 100 kHz to 200 kHz region and conservative phase margins. you know what phase-margin and closed-loop bandwidth are.....? Just a thought...:)

AKSA 7th May 2003 12:34 PM


You are so quickly antagonized; please be tolerant and patient.

I was not in the least concerned about your posts; you have not upset me at all as I was a teacher in a past life and enjoy being challenged, particularly if it shows I am wrong and might learn something.

But your willingness to enjoin abuse with Fred, who is clearly extremely knowledgable and knows all sorts of things I don't, is not flattering to your cause. I notice he is not responding at present; a wise, mature move. What does it matter if someone disagrees with you? Who cares anyway? How world shattering are these opinions we all have? Do they add significantly to the body of knowledge in this technology? Probably not....... And what good does abuse do? Abuse quickly denies you membership of any group, even amongst those who would ordinarily support you, and serves no purpose except to highlight isolation. It seems to me that digital duelling is a bit like road rage; pretty safe, wholely ugly, and utterly unfulfilling.

I really was making no comment about your comments concerning amplifier stability. I am aware you understand it to be a significant quality of audio amplifiers; I was endeavouring to explain to any reader here present why stability was important. I was NOT highlighting any comment you had made. I am conscious that you have strong insights, and wish to keep this discussion cool and academic; to be frank I do not understand the math of shelving filters, don't even know what a bloody shelving filter is (I am not an engineer, sadly, having only qualifications Science and Business Info Tech), but tend to assess all amp circuits on the basis of my experience at design, tinkering, testing, listening, and my intuition at circuit analysis, unaided by PSpice or too much math. Oh, I certainly understand all the routine math of Ohm, Kirchoff, and the reactance formulae, even a little on phase margin and Bode-Nyquist, but I'm no mathematician and would argue strongly that all the math in the world can be deceptive in matters of stability, particularly when there is such a diversity of different speakers out there, all with their own reactance peculiarities.

Now, let's get back to electronics. I was enjoying this!



mrfeedback 7th May 2003 01:04 PM

I Agree With Phred, Hugh And Capslock

Originally posted by capslock
Mikek, are you trying to provoke Fred into loosing his temper? I consider some of your posts here on the border of being rude. Fred may have strong opinions, but he certainly is not clueless or deluded!
Mike, I must say that I consider that some (far too many) of your posts are indeed straight out arrogantly rude, and intentionally offensive, and as such, totally against the spirit of this forum.

This mode of communication may be acceptable on other forums, but not here on DIYaudio.

You are conspicuously new around here, and it is clear that you have not allowed yourself time to settle quietly into this forum, and learn of the experience of the elder members present.
I solemnly suggest that you adopt the spirit of this forum, or else find a different vehicle to display the brashness, immaturity and lack of social etiquette as you have displayed here.

Phred's comments were in response to your distinct lack of reply when asked politely TWICE of your constructional experience - IOW it is to be assumed on available facts that you do not have valid constructional experience.

I have politely asked you TWICE as to the meaning of the gibberish on your profile page and TWICE recieved from you impertinantly rude replies.

Threads have a habit of evolving and just because a subject like load stability is raised does not mean that this is to be taken as a slight on you, your character or your knowledge.
It would be much better on your part to quietly listen, add constructive comment as appropriate and add to the sum of knowledge presented than to protest as you have done here much more than once.

I take it that in future you heed these words, and become a rather more sociable and worthwhile contributor to this little community.
An apology to Phred for your actions would be very much in order also, and required in my opinion.

As part of this process, an honest translation of your profile, and a summary of your study and constructional experience would likely improve your current standing significantly.

Sincerely, Eric.

mrfeedback 8th May 2003 01:59 AM

Fred's full name is Fred Dieckmann - you have been corrected on this previously, and you have very consciously misspelled Fred's surname more than once since.
This is entirely rude and impertinent behaviour on your part, and not acceptable whatsoever.

So what is your problem with answering direct questions ? - lack of any real foundation I am now fully sure.

How long since you left engineering school - last week and still wet behind the ears ?.
We have all met young graduates who are sure that they know all there is to know regarding electronics.
If such engineers were really worth their mettle, then I would not have "25 Years Experience fixing Engineers' mistakes. "

so......mrfeedback, if fred's 'experiance' is vastly superior to my 'ignorance', how come the man is unaware of the fact that secondary breakdown and MOSFET's is oxymoronic..?
This is true only if adequate heatsinking is provided, elsewise mosfets fail just like any other transistor.

to obtain an elementary electronic engineering qualification where i come from, you need to be acquainted with the such elementary stuff........
Did you miss a lesson ?.
Quote: appear not to accept that the contents of my 'profile'......ergo, my CV are none of your business.......untill i decide otherwise?
I actually do not care in the slightest, but in the interests of honesty I thought that you would provide such information so we all have an idea of who we are communicating with.
Your replies furnish this more than adequately.

Eric / - sick of dealing with idiots.

mikek 8th May 2003 03:37 AM


Originally posted by mrfeedback
This is true only if adequate heatsinking is provided, elsewise mosfets fail just like any other transistor.

..the failure mechanism in that case has nothing to do with 'thermal runaway' i fear....:rolleyes:

The prosecution rests:cool:

mikek 8th May 2003 03:45 AM

Re: Whom to believe?

Originally posted by Fred Dieckmann
Arrogance and ignorance are two traits that don't go together very well in my experience.

' your experiance...' you say....HHmmmm...lets tried being both and decided you would settle for one or the other....huh? :)

mikek 8th May 2003 05:03 AM

Re: advice

Originally posted by Fred Dieckmann
Arrogance does not bother me a bit ....... if you have the knowledge to back it. The failure mode I was referring to was excessive peak current into a short. An IRF240 has an on resistance of 0.18 ohms. with a 40 volt supply you have a peak current of about 220 amps. With a 1 ohm source resistor the current is about 34 amps.
...the idea that a MOSFET will pass 220 A short circuit......because it has an on-resistance of .18ohms is laughable.......

....i find it hilarious that you suggest the inclusion of a source resistance in lieu of proper SOA protection...:D

mikek 8th May 2003 05:05 AM

Re: advice

Originally posted by Fred Dieckmann
Arrogance does not bother me a bit ....... if you have the knowledge to back it.

what knowledge are you backing yours up with i wonder....:scratch2:

capslock 12th May 2003 04:37 PM

Sorry to see Mikek sinbinned, I don't think the posts were that bad...

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