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Old 16th December 2005, 03:59 PM   #11
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Any chance that this subject is about "noise" only birds can hear?
Once again, bashing the Professor is still not a good idea.
But then, please carry on. It's yur amp.

Regards
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Old 16th December 2005, 04:42 PM   #12
lineup is offline lineup  Sweden
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Quote:
Originally posted by acenovelty
Any chance that this subject is about "noise" only birds can hear?
Once again, bashing the Professor is still not a good idea.
But then, please carry on. It's yur amp.

Regards
No, bashing a professor in electronics about an amplifier detail in one of his designs
is something you normally should try to avoid

In this case I think he did smash 2 flies in one smash.
The zener diodes serves 2 purposes in a good way:
- provide a constant current to input stage
- setting operation voltage for cascoding transistors in input stage

There are more sofisticated and maybe better ways to do these both things,
but no other such simple way, as Leach is using.
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Old 16th December 2005, 07:56 PM   #13
pooge is offline pooge  United States
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Quote:
Originally posted by BobEllis
[B]Earlier versions did not have the zeners. IIRC, they were added at Ver 4.4 along with some other value tweaks along the way to the current version. The amp will run fine without them, and seems to fit Guru's preference for resistive biasing of cascodes.
I recall that he used the zeners in Ver. 4.2, dropped them in the 4.3, and then brought them back again. Never was able to find out what led to these changes.
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Old 17th December 2005, 10:34 AM   #14
AndrewT is offline AndrewT  Scotland
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Hi,

Leach Low TIM 1976 and on have Zener referenced tail current resistor with capacitor bypass.
Version II combined the cascode with the tail resistor from the common Zener reference.
Version 4 introduced the dual series Zeners on each half.
Version 4.5 still follows this.

Can you post V4.2 & V4.3 schematics showing the changes you refer to?
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Old 17th December 2005, 10:41 AM   #15
AndrewT is offline AndrewT  Scotland
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Hi Jacco & others,
the zener reference can be eliminated and replaced with a pure resistor string or LED string BUT the reference voltage does not have to remain at +-40V.
You could reduce down to a 2, 3 or 4 LED string or equivalent resistor string ( about 4V to 7V).
The CB capacitance of the input transistors would rise slightly at this lower voltage.
Q. Is CB capacitance an issue?
Q. Is more benefit gained by reducing the CE voltage across the input transistors?
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Old 17th December 2005, 11:20 PM   #16
AJT is offline AJT  Philippines
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Quote:
You could reduce down to a 2, 3 or 4 LED string or equivalent resistor string ( about 4V to 7V).
is this voltage enough for the cascoded transistor, i remember, the 40volts also serves as base ref voltage for the cascode, so now the long tail pair operates at a much higher collector voltage?
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Old 17th December 2005, 11:52 PM   #17
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Howdy Tony,
Seems there's just lots of folks that have the idea they are smarter than Dr. Leach about this amp topology. Can't recall any of them having achieved professorship.

Regards
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Old 18th December 2005, 04:17 AM   #18
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You're precious Ace,

Some of us couldn't wait to get out of acadaemia and into the real world designing amplifiers for a living, rather than dabbling on a state wage.

Not to demean Mr Leach but if I went for medical treatment I would rather a 'hands on' experienced clinician than an acadaemic.

I hung my career on my ability to design amplifiers. Still do.


Cheers,
Greg
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Old 18th December 2005, 04:24 AM   #19
AJT is offline AJT  Philippines
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Quote:
Originally posted by acenovelty
Howdy Tony,
Seems there's just lots of folks that have the idea they are smarter than Dr. Leach about this amp topology. Can't recall any of them having achieved professorship.

Regards




i am pretty confident prof. leach knows what he is doing....i have built a lot of his super leach amps.
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Old 18th December 2005, 04:34 AM   #20
AJT is offline AJT  Philippines
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Quote:
Not to demean Mr Leach but if I went for medical treatment I would rather a 'hands on' experienced clinician than an acadaemic.
afaik, these leach amps were used by prof. leach in teaching his classes and from the late 70's there could have been hundreds of students of his who have built these amps, and a countless hundreds around the world, all under his guidance and supervision! myself have exchanged emails with him, very accomodating and unselfish guy. not driven by how many amps he can sell, just a plain desire to share.!

if this is not "hands on" i do not know what is!

how many of his students that learned from him could have gone on designing their own amps.

there are many who can build great sounding amps from others' designs, but ask them how the thing works and they do not know a thing!

theory and practice always go together! otherwise there will be blind leading blinds, and lames trying to boogie with fellow lames!



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