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Old 8th July 2011, 07:24 PM   #91
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Quote:
Originally Posted by homemodder View Post
Os Is the second pic the performance of the Luxman clone amp ??, that looks pretty good.
Yup , that's the luxman. green LED's and all. I have the prototype running my sub now. I will show the full stereo version in "solid state picture" soon.

Quote:
No nead for some exotic circuit.
2 led ccs's , exotic ?? The diamond triple is both more oscillation proof and thermally stabilizes better. Just 2 semi's , 2 led's and a resistor. Pre-driver/driver Vbe totally cancels out.

Dadod , you realize - we are in Halcro territory now ! (sub PPM)

OS
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Last edited by ostripper; 8th July 2011 at 07:37 PM.
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Old 8th July 2011, 07:34 PM   #92
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Originally Posted by jcx View Post
but "harmonic killer" really has no accepted meaning - apparently referring to cascode above?
So stiff , that was Dadod's original term. I just referenced that to the luxman as that seemed to describe the effect of the cascode. If we can not have fun on the forum without too much confusion , what is the point ?

As a reference , the subjective banter on most of this forum really has no meaning either - except to those generating it (or profiting off of it. )

OS
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Old 9th July 2011, 08:15 AM   #93
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Quote:
Originally Posted by Bigun View Post
Is this without gnf ?
No.
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Old 9th July 2011, 08:19 AM   #94
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Quote:
Originally Posted by ostripper View Post
Yup , that's the luxman. green LED's and all. I have the prototype running my sub now. I will show the full stereo version in "solid state picture" soon.

2 led ccs's , exotic ?? The diamond triple is both more oscillation proof and thermally stabilizes better. Just 2 semi's , 2 led's and a resistor. Pre-driver/driver Vbe totally cancels out.

Dadod , you realize - we are in Halcro territory now ! (sub PPM)

OS
I was not referring to your circuit,
dado
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Old 9th July 2011, 03:35 PM   #95
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Hey , Dadod ... Carlos (DX) is now doing the CCS + bootstrap on his new precision 3. His just uses a BJT CCS , but it is fully functional.

OS
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Old 10th July 2011, 04:37 PM   #96
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Here are some more photos.
R88 was increased in value(from 33R to 68R) as the drivers were a bit to hot for my taste. Now driver current was set to 20mA. I did not hear any difference in the sound quality.
I will not change anything any more and this is simple stable excellent sounding amp.
dado
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Old 29th July 2011, 02:40 PM   #97
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Quote:
Originally Posted by dadod View Post
I noticed strange behavior durin simulation with 20Hz close to clipping.
The reson was in capacitance multipliers. I changed R26, R29 from 1kohm to 100ohm and R27, R28 from 33kohm to 10kohm and all was OK after that.
It looks that the capacitors connected to multiplying trensistors were loaded to slowly trough 1kohm. That manifested itself only at very low frequencies.
First diagram is with old multipliers.
dado
I was wrong regarding the reason for this behavior. It is not capacitance multiplier but to small value of the protecting resistor(R19) in preVAS emitter follower(Q7) collector. With incresed value from 220ohm to 1kohm all was OK even with original capacitance multiplier.
Be aver of this resistor as 220 ohm is not enough to protect Q7 to be burnt in the case of clipping.
1 - to small resistor
2 - increased to 1K
dado
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Old 29th July 2011, 03:44 PM   #98
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Default Many opinions.....

Quote:
Originally Posted by dadod View Post
I was wrong regarding the reason for this behavior. It is not capacitance multiplier but to small value of the protecting resistor(R19) in preVAS emitter follower(Q7) collector. With incresed value from 220ohm to 1kohm all was OK even with original capacitance multiplier.
Be aver of this resistor as 220 ohm is not enough to protect Q7 to be burnt in the case of clipping.
1 - to small resistor
2 - increased to 1K
dado
Yours = increase VAS ef resistor to 1k
mine = tested with 2sa992 +2sa1381 / 220R , warm 992 at clipping + no CRO errata.
Cordell = add a third transistor to shunt the ef at clip.
DX= use a larger EF device.

I like the higher value resistance method. I might change DIYA amp to at least 470R even as 220R works at 45V supplies.
Other methods are either overkill - "sonickill" or just plain silly.
OS
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Old 29th July 2011, 04:19 PM   #99
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In the simulation you will not see this, but at low frequencies, 20Hz per example.
I did not test with R/C power filtering, maybe you can try with DIYA.
dado
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Old 13th September 2011, 09:46 AM   #100
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Quote:
Originally Posted by jcx View Post
I can't see the rational for cutting loop gain at audio frequencies - the very complete follow up analysis of Otala's ideas show his prescription of flat audio frequency loop gain is not in fact "the cure" for TIM/SID/FM IMD
the analysis and hardware measurements showed that high/"sloping" loop feedback can be used freely with other circuit modifications that do minimize these "time/phase" distortions
Walt Jung and Marshall Leach both published amp designs incorporating the flat audio frequency loop gain characteristic - and then later published that they had changed positions and determined that high feedback did not worsen Otala's proposed distortions

the sole "reason" to try flat audio frequency loop gain is the anecdotal comments by people who freely state that DBT is too "insensitive" to reveal differences in listening tests of amps designed according to their "principles"

I don't know of any reason to worry over loop gain peaking - although it is "inefficient" in the Bode Integral feedback limit analysis for a broad working band
but it is certainly minimized by allowing the gain to be large with multiple slopes in the audio frequency range

I would consider guarding/shielding the mirror out/VAS buffer end node just to maximize loop gain
After readig "The F-word or, why there is no such thing as to much feedback" by Bruno Putzeys http://www.linearaudio.net/userfiles...olume_1_BP.pdf I decided to lower VAS gain, in case if there is enough gain at 20kHz, in my next project too.
Here what Bruno says and that explain some of reasons why I like the sound more that way:

"A second step in the experiment consisted of placing a resistor across compensation capacitor C
that reduced DC gain to the same value as that at 20kHz (fig 12, trace 4). The test amplifier was of
the folded-cascode persuasion which allowed this. At this stage, loop gain has indeed been reduced
across the full audio range. I surmise that, since the amplifier’s distortion was never negligible, making
it constant across the audio band makes it fly under the psychoacoustic radar more easily.
My own subjective experience would support this. To my ears, amplifiers with the normal 20dB/decade
behaviour but whose distortion is not negligible at the end of the audio range have glassy midhighs,
a “superglue stereo image” as KK once put it and the illusion of spectacularly, unnaturally
tight and impossibly controlled bass. Some love this, and seceded into a subculture of ultra-beefy
amplifiers. I don’t and when forced to make a choice I’ll take higher but consistent distortion across
the band."
dado
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