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Old 10th February 2011, 08:53 PM   #1
Stee is offline Stee  Italy
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Default MY BEST OTL PREAMPLIFIER

this project is Working and you need absolutley
because it's able to rebuild the acoustic scene
just as you like
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Old 10th February 2011, 10:56 PM   #2
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Err.....

I see an SRPP line-stage.....

BTW, cant make head nor tail of your website!
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Old 11th February 2011, 09:50 PM   #3
Stee is offline Stee  Italy
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Default the OTL's Output Stage

is a minimalist mosfet power amplifier
with Halfer variation
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Old 11th February 2011, 10:58 PM   #4
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Hmm.....

Whats 'Halfer-Variation'.....?? Google refers to some kind of genetic research...

Guess all chip amps and nearly all discrete silicon amps these days are OTL....

Prefer 'Proper' Tube OTL myself....

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Old 12th February 2011, 10:18 AM   #5
Stee is offline Stee  Italy
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Default Single ended push-pull, (SEPP)

ok the correct name is this in Title
important have same gain in each rail

Hafler It features Jim Strickland’s
trans•nova circuitry and his brilliant discovery,
Dynamically Invariant AMplification Optimized

---> suorces are on GND
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Last edited by Stee; 12th February 2011 at 10:23 AM.
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Old 12th February 2011, 12:27 PM   #6
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Err....

But, The Gain Isnt equal, Is It!

Thats why Julias Futterman had the bottom end of phase-splitter sitting on the O/P to accomodate for the difference in Drive Needed between the Top tube, and the Bottom tube, as their gains are different, but the tubes were not both acting as 'Cathode-followers' so 'Technics' (I think....) inverted the drive as well, so that both tubes act as followers and lower the O/P impedance.....!

--This was always the issue with the SRPP/SEPP type out-put stage...

To achieve symetrical wave form output, you would need unequal resistors in the concertina phase-splitter, to accomodate for the difference in drive requirements--Or do the 'Futterman' thing....

Top tube is acting like cathode-follower (little less than unity gain) while bottom tube acts as common-cathode (That has gain more than 1) in the SRPP

In your Transistorised schematic, You have Complementary Transistors (MOSFETS) a P channel and N channel....

Sadly a Positron Valve/Tube does NOT exist, so any Tube circuit is 'Quasi Complementary' and not a true complementary o/p stage....

In your First Schematic, You have Unequal Phase-Splitter resistors, compensating for the difference in gain between top and bottom....

Last edited by Alastair E; 12th February 2011 at 12:48 PM. Reason: clarification
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Old 12th February 2011, 12:55 PM   #7
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Yes, a silly design. It will only balance at one particular load impedance. At other impedances the two output valves could assist or work against each other. A genuine SRPP might be better, although that is load dependent too.
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Old 12th February 2011, 01:06 PM   #8
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Quote:
Originally Posted by DF96 View Post
Yes, a silly design. It will only balance at one particular load impedance. At other impedances the two output valves could assist or work against each other. A genuine SRPP might be better, although that is load dependent too.

Nah, I wouldnt go quite that far!

With a few tweaks, it can easily be turned into an 'Inverted Futterman' and give prob. extremely good results as a low O/P imp pre-amp or headphone-amp...

As it is however, I think the very load-dependant O/P will make for pretty high 2nd and 3rd harmonic--which could be exactly what the O/P wants--if he wants a guitar pre-amp or effects device....

I have NO idea where all the strange references like 'Halfer-Variation' come from though....
Just because a scheme has a wicked name, dont mean its gonna work well!
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Old 13th February 2011, 05:08 AM   #9
Stee is offline Stee  Italy
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probably cathode-follower have little less than unity gain
but WORKS very good - for sure

Think the Hafler's Output Stage need a Feedback loop?
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Old 13th February 2011, 11:40 AM   #10
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Quote:
Originally Posted by Stee View Post
probably cathode-follower have little less than unity gain
but WORKS very good - for sure

Think the Hafler's Output Stage need a Feedback loop?


Oh dear, You Really ARE missing the point, I'm afraid.....

You claim that in your Tube scheme that the gain must be equal on both top/bottom rails, and it clearly Isnt!

Cannot apply 'Hafler' to it

'Hafler thing' will apply ONLY to a Fully COMPLEMENTARY (P channel, + N channel) O/P stage, and whether it requires feedback in this discussion is irrelevent, as we are NOT talking Hafler stage with your TUBE pre-amp....

Tube scheme is NOT Fully Complementary, Gains are Different top/bottom UNLIKE Hafler thing you are trying to make, where the gains are the same approximately....

Who cares, If you Like its sound, then you have achieved what you're after

Personally, IMHO I would Not consider your Tube pre-amp a 'HiFi' device, but more like, an Effects device, for 'stage' use.....

Last edited by Alastair E; 13th February 2011 at 11:48 AM. Reason: correction
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