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Old 29th April 2012, 02:28 AM   #91
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R2 is neither a CCS nor a bootstrap,
therefore current in Q1 is variable.
VBE of Q1 not held constant.
Does it matter? I dunno...

You have eliminated Q1 VBE resistor,
that was responsible for bleeding a
constant reserve current that serves
to assure output transistors stay on.

A misbehaving load could turn off a
fast recovering Schottky, but would
be unable to shut off either of the
slow recovering output transistors.

-----

OK I see it now.
The top Q2 (why do you have 2 Q2's?)
conducts R1 to U1 as a reserve current.
The bottom Q2 conducts R2 as a reserve.

Last edited by kenpeter; 29th April 2012 at 02:34 AM.
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Old 29th April 2012, 04:39 AM   #92
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Quote:
Originally Posted by kenpeter View Post
R2 is neither a CCS nor a bootstrap,
therefore current in Q1 is variable.
VBE of Q1 not held constant.
Does it matter? I dunno...
I probably should go with a bootstrap or JFET instead of R1. The simulated harmonics became nicer with just a plain R1 - from memory, H2 increased.

Quote:
You have eliminated Q1 VBE resistor,
that was responsible for bleeding a
constant reserve current that serves
to assure output transistors stay on.
I merged that resistor with another that was intended to bias the driving opamp into Class-A. It works, but maybe the value needs experimenting with.


Quote:
The top Q2 (why do you have 2 Q2's?)
Sorry, the lower one should be Q3.

I goofed while relabeling the Qs before exporting the schematic (they tend to start with numbers like Q11, Q13, etc. because I sometimes cut them down from some larger circuit like a discrete opamp, and I relabel them left-to-right, top-to-bottom for convenience. LTSpice catches these duplicates, but only if a simulation run is attempted.)

BTW, check out my LF03 discrete opamp schematic at your convenience - I just built the first prototype a couple of days ago, and it does sound good with the present Class-A push-pull output stage.

However, it could potentially give similar performance at lower quiescent current with your non-switching Class-AB stage.

LF03 discrete opamp

I'll post the prototype parts list shortly.
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Old 10th May 2013, 07:46 PM   #93
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Quote:
Originally Posted by steph_tsf View Post
At fisrt glance, the Ben Duncan books looks quite general. Digging into the individual chapters, the big and positive surprise is to realize how precise and accurate Ben Duncan is. The appendixes are unvaluable, plenty of references, plenty of historical info. Many many thanks for pointing this great source of info !

Page 133, about the non-switching amplifiers, it reads :
"This involved a kind of positive feedback, and carrying the risk of blowing-up the output stage ! It also relies on the switching of small diodes, which ameliorated and displaced, rather than overcoming the switching problem".
I guess Ben Duncan didn't wanted to write explicitely that the Technics SynchroBias, marketed as "New Class A", was displacing the problem instead of solving it. The Technics "New Class A" is thus a little bit apart. It should be clear and remembered that JVC "Super-A", Pioneer "Non Switching" and Sansui "Tanaka Non-Switching" are not relying on diodes to be switched.

It is amazing to see the LT1166 biasing integrated circuit, being ignored. Were there commercial power amplifiers using a LT1166 biasing integrated circuit ?

Like Margan, what's worrying me is the behaviour of the output stage when driving a complex load like a loudspeaker. Some optimizations like the ones discussed here may prove unable to cope with capacitive, inductive, or varying impedance loads, especially on non-periodic, non-static, non-symetric input signals like music is. In this context, is there a LTspice standard test gig I can use, for better knowing the behaviour of the output stage ?

Cheers,
Steph
Today I contact LT Technology in this matter because I want to know any Commercial Audio amplifier devices with LT1166 inside.
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Old 10th May 2013, 08:18 PM   #94
mlloyd1 is offline mlloyd1  United States
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good luck with that.
it is unusual for device suppliers to say what products are using their specific devices.

mlloyd1

Quote:
Originally Posted by tiefbassuebertr View Post
Today I contact LT Technology in this matter because I want to know any Commercial Audio amplifier devices with LT1166 inside.
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Old 11th May 2013, 01:28 PM   #95
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Quote:
Originally Posted by tiefbassuebertr View Post
Today I contact LT Technology in this matter because I want to know any Commercial Audio amplifier devices with LT1166 inside.
I don't know of any commercial amplifier manufacturer using the LT1166, but I could definitely be wrong. I have always thought it a great part when properly used. Part of the problem is that it is intended for use with MOSFET output stages, and will not work (straightforwardly) with all MOSFETs, due to its need for bias voltage that is a function of gate threshold voltage. Moreover, the designs shown in the datasheet generally are not the best. I show some ways to use the LT1166 in my book.

Cheers,
Bob
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