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Old 9th January 2009, 06:23 PM   #651
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Quote:
By steve D. - Hi ostripper. I'm not sure how much power you need (or want) but I have built amps with 1200W at 8 ohm using my Krill design. Would that be enough?
For me.. 300w for the hungry sub and 120w+ for the fullranges will do, but for the young un's, they crave POWER ,so triples or
mosfets (maybe both) to get to that magic 3-400 watts will
be neccessary.

My problem with the triple is "getting there" .I changed
devices, emitter resistor values, base stoppers..etc.
I need to create a better (more APT) T- comp (6 Vbe's now),
as the "Beast" will no longer be a frugalamp.

My problem with the mosfets is that I can't (don't know how ) to set up the .SUBCKT models in LT.
maybe that can be resolved..

Quote:
By homemodder - Os why dont you use the cfp ef, works well
I thought CPF OPS's were just as "squirrly" (prone
to oscillate) as triples , doug self says so because of the local
feedback loop. Mr self also does not want to discuss triples
,so it seems. any answers to these problems would be
helpful.
OS
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Old 9th January 2009, 06:25 PM   #652
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Quote:
By andy C .Looks like Q14 emitter and collector are swapped.
OOOPS, that is a big one!!!!
OS

Edit.. What I did was sim the triple, got oscillation , ditched the
predrivers, then went back to the original to post schema
but screwed up PNP (the OOOps)...
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Old 9th January 2009, 06:41 PM   #653
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Andy beat me to it, othervise works no problem.

Andy I played a bit around with the input stage and and now must try real time for listening. Using the cascode and dropping the cfp in this case brings no improvement or reduction in THD but it seems it has to be the one or the other. Transient wise the cascode allows slightly extended bandwith.
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Old 9th January 2009, 06:44 PM   #654
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here is the problem.. i wonder if it is just normal for triples..
It only happens with clipping or induced crossover distortion
(I had sustained oscillations before... ) and only at
HF (10khz and beyond)..

plot posted below..
OS
Attached Images
File Type: gif fa3hposc.gif (7.3 KB, 410 views)
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Old 9th January 2009, 06:45 PM   #655
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Os i mean a ef where the driver is a cfp. What is the double ksa2690 you have there, a darlington ??
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Old 9th January 2009, 06:56 PM   #656
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Quote:
By homemodder - What is the double ksa2690 you have there, a darlington ??

I think that is just the device description set by the .model.
Homemodder or andy, do either of you know how to do
the .subcrk model... I still want to play with the MOSFETS
(downloaded the whole IRF model library).
OS
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Old 9th January 2009, 07:13 PM   #657
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I see no reason (in the schematic) for the amp to do what is shown in the sim. Also, if that is a clipped waveform, how does the oscillation extend well above the power supply rail? I suspect you may have a sim problem that will not show up in a real unit.
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Old 9th January 2009, 07:56 PM   #658
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Os if you look on the lt scad3 file, near the end their is instruction on how to do this page 190 thereabouts, ive deleted my copy, but its near the end.

Is this coming from outputstage alone, have you tried the input stage with a ideal output. I am looking at it at 20khz but cant get rid of it.
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Old 9th January 2009, 10:41 PM   #659
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Quote:
Originally posted by ostripper
. . . as the "Beast" will no longer be a frugalamp. . .
Frugabeast!!

Hmm, thinking. . . 600w to 8R with capacity for 1.2kw to 4R?
Does that play the speakers twice as loud as a 60w amplifier?
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Old 10th January 2009, 12:00 AM   #660
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Quote:
By steve dunlap - how does the oscillation extend well above the power supply rail
I did that Sim on the FA3 HP and ran it with 90V rails.

Quote:
From homemodder - Is this coming from outputstage alone, have you tried the input stage with a ideal output.
I tried it on the real (sub) , no warm zobel... on the sim at
20khz with both clipping and induced Xover distortion.. NO
problem. Only with the triple... but it DOES greatly reduce
with larger emitter "suckout cap" across the main drivers.
the VAS seems to be the problem , by changing loopgain and
lowering Ic (3-4mA) solves this.


Quote:
Hmm, thinking. . . 600w to 8R with capacity for 1.2kw to 4R?
That is wishful thinking. One would need 14 OP devices to
acheive that (SOA). I would even recommend Class D at that
point. UCD 700 amp is only 4X6 inches with NO heat..

Quote:
By dwb - Does that play the speakers twice as loud as a 60w amplifier
you would only get 10-11 DB over the normal frugalamp..
for all those devices.. In simulation I clipped at 170V p-p
(roughly 1500W) but that is way over rated..
I would like to go the "quasi" route and just use 6-8 NPN
IRF 250's to get my 300W.. it might even stay "frugal" with
that arrangement..
OS

OS
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