The Pass Pub: The High-End Off Topic Thread

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lineup

lineup

Member
Joined 2005
There must be at least 10 more born 1951.
Only I knoqw, that when I have had my birthday, 22 May,
it wont take long until there is a new topic started
probably in June
to congratulate him: Pass

what have I to do before I earn such things as a topic to congrat me?

We are all equals in forum.
At least in my eyes.
But some fanclubs make their own Gods.
Like as if one child born is not of same value as another.

I am not complaining or campanjning. I only want to point to the severe unfainess done to all, except to a few lucky guys.
Treated with sliversticks.
--

Anybody in for a Pro-Korean JH Babowana fanclub?
So we can start celebrate this deserving great guy's geborensrtag .. every year.

Sorry people, I wasnt enough off topic to get banned this time.
But when you are drunken, it is not easy to type in my broken english.
Neither will a drunken modertator in this PUB
know the faintest idea what is OFF or ON
... according to Forum StoneHard Rulings.


Cheers Zen Mod!
And thanks for being the one you are.
I do not even remember where you live. man --
--- but my drunken mind whispers former Jugoslav .. maybe Serbia, Kroatia .. ??
Who cares, if we are all born equal
and not being that one more equal than others :D :D :D
 
Gyuri

Gyuri

Member
Joined 2003
White Lily.

Maybe, that I was laughed at again, no problem, but this "song" is one of my favourites.
This suits my balanced F4 amplifier very well.

Laurie Anderson White Lily lyrics:

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=26253154

What Fassbinder film is it?
The one-armed man walks into a flower shop and says:
What flower expresses days go by
and they just keep going by endlessly
pulling you into the future.
Days go by
endlessly
Endlessly pulling you into the future.
and the florist says:
White Lily

http://6aw5rw.bay.livefilestore.com...GP5bw_kM-B4yBwyOPGv2o0TsJoh7pf/White Lily.JPG

http://www.fassbinderfoundation.de/en/filme_detail.php?id=40
 
Babowana

Babowana

Formerly "jh6you". R.I.P.
Joined 2006
aheadamp.com
Papa,

Sorry, I couldn't make the drawing better than this . . .

:)
 

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luvdunhill

luvdunhill

Member
Joined 2006
I have a quick question for the masters of off-topic. My question is about the second graph on this Datasheet

I have 30V bench supply and a resistor to source 150mA of current. Since Vds = Vgs when testing (according to the Zenv3 documentation) and this value ranges from 3.20V to 3.55V depending on the sample. Ambient temperature is 60C for all samples and the devices are not heatsinked, but enclosed in a box with a probe to verify when 60C is reached to take the Vgs reading. I don't know if anyone has done things this way, but it seems to be very repeatable. Anyways, back to my quesiton... the second graph is at 25C and it looks like if we take the 3.50V for Vds = Vgs there should be 233mA of current. Would this value drop this much because of the case temperature? I just wanted to see if I was in the right ball park.

The compliments are about 1V less Vds on average (same voltage and current) and I can almost convince myself of this looking at the Datasheet At Vds = Vgs = 2V for example, the Nch says ~180mA @ 25C and the Pch says 100mA @ 25C. I'm not sure how to do some calculations to see if this difference would result in approximately 1V lower Vds I see for the Nch, is this possible?
 
luvdunhill

luvdunhill

Member
Joined 2006
Nelson Pass said:
Graph #4 looks to show about a 30% or so drop in Vgs over that
temperature range, so it appears reasonable.

:cool:
Click to expand...

excellent! This makes since.

One more question. When paralleling MOSFETs, how do you determine the best value of the ballast resistor? I have four of each polarity of these paralleled with 2 ohm ballast resistors (sorta like F4 output stage), with the MOSFETs chosen at random. Now I've matched them to Vds 0.01V or so. Is this a case where one needs to be able to measure distortion? Could I just lower the values until the voltage drop across the resistors isn't equal? Is there somewhere I could read some more on this perhaps?
 
luvdunhill

luvdunhill

Member
Joined 2006
ok, so let me try again :)

Starting with the F5, the resistors in the output stage are 0.47R and the voltage drop is 0.6V. 3W resistors are speced and this is roughly 4 times the power at quiescent current.

Now, with the F4, the resistors are 0.47R and voltage drop is 0.25V and 3W resistors are used.

So, in the case of F4, why not cut the 0.47R value in half, assuming well-matched devices, and you could parallel two 0.47R resistors together to get the lower value? At what point does it make sense to stop lowering this value, at the point where the voltage drop across this resistor varies by a certain amount, due to matching becoming increasingly important as this value decreases?

Is 4x the power at quiescent current used in the F5 a good rule of thumb to size output resistors?
 
Nelson Pass

Nelson Pass

The one and only
Joined 2001
Paid Member
Usually it's a matter of what class the OS will operate in, what
damping factor you want, and how much thermal stability you need.

As a simple rule, you want the lowest values that are consistent with
good current sharing (matching) and thermal stability. 0.47 ohms
is a convenient figure, but it can easily range from 0.1 to 1.0 per device.

:cool:
 
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