Sziklai pair as Vbe Multiplier? - diyAudio
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Old 10th March 2004, 03:24 PM   #1
sam9 is offline sam9  United States
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Default Sziklai pair as Vbe Multiplier?

In his amplifier book near the end of the section on thermal compensation , D.Self describes using a Sziklai pair for the Vbe multiplier. Apart from the possability (probability) that it would oscilate, it has the advantages of very low bias drift and elimination of the trimpot. Self doesn't seem very excited about his own idea.

On Hagerman's website (www.hagtech.com), Hagerman has an article about a "Vbe doubler" with somewhat similar properties although it is not a Sziklai and presumably doesn't have the same oscillation problems.

Has anyone tried to use either of these on a real amp or are they just paper curiosities? Did it work or were there difficulties?

Do either or both of them still require physical contact with output device or heatsink (or driver if CFB)? If yes, do mount both transistors or just one (which)?

If either of these are effective I'm surprised not to have seen anyone attempt to use them.
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Old 10th March 2004, 04:50 PM   #2
jam is offline jam  United States
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The circuit that is on the Hagerman web site has been used by Harmon Kardon and a few others. It still requires that one of the transistors be attached to the heatsink.

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Jam
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Old 10th March 2004, 06:58 PM   #3
sam9 is offline sam9  United States
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Does it matter which one?
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Old 10th March 2004, 07:15 PM   #4
jam is offline jam  United States
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I believe it is the transistor on the right.
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Old 10th March 2004, 09:50 PM   #5
sam9 is offline sam9  United States
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Well, looks like the only way to satisfy my curiosity is to try on or another in my next amp project. It looks like I could layout the standard Vbe multiplier and add a couple of componrnts to the PCB so that I could first use a conventional circuit and when I'm satisfied that's stable and working, change component values and add the second transistor. That way I won't be puzzling whether it is the new circuit or something else that causes any problems.
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Old 14th September 2009, 12:53 PM   #6
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I want detal information of sziklai par
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Old 14th September 2009, 04:18 PM   #7
juma is offline juma  Germany
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Quote:
Originally Posted by deeps2688 View Post
I want detal information of sziklai par
And I want a cherry pie ... now

Mate, use the search button / google is your friend
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Old 14th September 2009, 05:15 PM   #8
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Sam9
---In his amplifier book near the end of the section on thermal compensation , D.Self describes using a Sziklai pair for the Vbe multiplier. Apart from the possability (probability) that it would oscilate, it has the advantages of very low bias drift and elimination of the trimpot. Self doesn't seem very excited about his own idea.---

An important advantage of the Sziklai pair for bias control is the lower dynamic impedance compared to a single transistor.
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Old 14th September 2009, 07:14 PM   #9
Bigun is offline Bigun  Canada
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Originally Posted by sam9 View Post
In his amplifier book near the end of the section on thermal compensation , D.Self describes using a Sziklai pair for the Vbe multiplier.

Has anyone tried to use either of these on a real amp or are they just paper curiosities? Did it work or were there difficulties?
I believe MJL21193 has used this type of multiplier on his Class A 'Nameless' amplifier.

Looking for Feedback on this No Feedback Amp.

Scroll down to the schematic in Post 52. He has built it but hasn't had time to debug it yet.
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Old 14th September 2009, 07:46 PM   #10
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Gareth,
I wonder if it`s stable...
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