What is the optimum -3db bandwidth for amplifiers with feedback ?

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Gigapod

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Joined 2006
gigapod.free.fr
wwood said:
Hi Jacco,

What do you mean by "highly unnatural harmonic distr. spectrum"?

Bill
Click to expand...

AFAIK tube amps have mostly low order even harmonics, BJT amps with NFB have approx. equal amounts of even and odd harmonics with amplitude decreasing with order, and FET amps with NFB, due to their very high bandwidth, have a flatter harmonics spectrum, i.e. with a higher percentage of high-order harmonics than BJT and tubes.
 
W

wwood

Member
Joined 2001
Hi Adam,

Sorry for not responding to your post (#36). I went off to look up the paper and then forgot to get back to you. Also, I did not find the paper (not lost, just well buried in my unique filing system). The paper is the series of articles that Baxandall did in wireless world that included a great section on NFB. I got a copy of the articles from Jacco Vermeulen.

A site that has similar information and an extension of the Baxandall work is http://www.angelfire.com/ab3/mjramp/harmonics.html.

Hope that this helps.


Hi Mikelm,

Yes, you live down the road from me. I am in the twin cities. We will have to meet some time.


Bill
 
lineup

lineup

Member
Joined 2005
thanks
wwood

I will also take a look at that paper and this site:
http://www.angelfire.com/ab3/mjramp/harmonics.html

(I post the link again, as you have added one fullstop: ( . )
this makes link not working = not found


Regards
lineup

PS. edit
-----------------------------
this is a very good page, at same website ( Renardson Audio Designs )
with lots of good information:
DESIGNING AUDIO POWER AMPLIFIERS

:) lineup
 
mikelm

mikelm

Member
Joined 2003
darkfenriz said:


Well, it is hard to say.
At first I run the prototype heavily over-compesated, so having probably around 300kHz BW and <20V/us SR.
After changing compensation to 'optimal' cap value and probably improving BW to some 1.2Mhz and SR to around 90V/us and having much more feedback at 10-40kHz range, the difference was hardly noticable, maybe some trebles slightly improved along with resolution of percussion timbre (cymbals, rides, crashes), but this wasn't revolutionary improvement, maybe placebo effect as this wasn't AB comparison.
What's interesting the stability was actually better with optimum compensation compared to over-lagging.

regards
Adam
Click to expand...

Hi Adam,

We seem to be more or less on the same page

I seem to notice the same difference - those extra fine details add in a nice texture which, for me, makes the reproduction close to an acoustic live performance. This is particularly important with full orchestra playing loud with a fine layer of strings on the top, as it were.

If you have this extra feed back then, I guess u will also have a similar improvement in PSRR in the same frequency region. So how much of this small audible difference can be accredited to lower harmonic distortion and how much to lower noise is hard to say - I guess it depends also on how quiet the power supply is in the first place.

Depending on how the compensation is applied I also notice this better stability with optimum compensation - at least in spice. I find for this fast kind of amp with optimum compensation, a miller cap seems to be the best method. With slower amps I would not use this method.

thanks for your input

mike
 
K

KISS

Member
Joined 2007
I got caught in the dot link problem too. Checked my automatically parsed link, then used the edit function after it posted and moved the dot after the trailing vbb code for a URL. e.g. "[]the link.[]" to "[]the link[]." which will work. I think vbulletin has a bug.
 
lineup

lineup

Member
Joined 2005
KISS said:
I got caught in the dot link problem too. Checked my automatically parsed link, then used the edit function after it posted and moved the dot after the trailing vbb code for a URL. e.g. "[]the link.[]" to "[]the link[]." which will work. I think vbulletin has a bug.
Click to expand...

like 30 minutes after post we can edit
this is good!
I thought it was less time than this.
Some boards have only 10 or 5 minutes editing time.

-----------------------

Yes, if you use the URL tag around links
it tells the software where link ends, and eventual 'outside characters' begin.

I have never experienced that board will add a fullstop after anything - links or not.

When we do not use URL tags, or does not use Button 'http://' in Edit menu
anything beginning with www. or http:// is automatically transformed into links.
Even characters follwing right after, without at least 1 space, are included in this link.


putting one character, except space, BEFORE the link, will result in it becomes no link.
as links is those beginning with http:// or www. and nothing else.

Examples
ww.google.com - will not be link
[/u]www.google.com - will not be a link - same if you put bold tags without spaces around the link, or any other character
www.google.comx will be a link, but not very good
www.google.com x - will work
www.google.com/index.html - a better one - as there is such a page

The length of an automatically created link, is UNTIL comes one SPACE character
 
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