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Old 30th November 2005, 03:46 AM   #1
tmblack is offline tmblack  United Kingdom
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Default Leach MC Headamp

Anyone try to build one of 3 versions of this?
I like to know if anyone is still using it or are there better circuits?

Tom

EE
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Old 30th November 2005, 07:36 AM   #2
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I build something very similar, much based on those designs , but noise is still too high. Using BC550c/BC560c I get around 2nV/rtHz. I think you are better of building a jfet pre-pre-amp.


grz,
Thijs
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Old 30th November 2005, 02:22 PM   #3
tmblack is offline tmblack  United Kingdom
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Thanks. How did you measure the noise?
He recommended the 2N4401/2N4403 which I believe are still available.

Tom

EE
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Old 30th November 2005, 02:39 PM   #4
jcx is offline jcx  United States
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bjt should be fine for mc pre, look at national semi an-222 for good intro to the theory - analog devices still makes a few PMI ultra low noise transistors

but its hard to argue with the convinence and performance of the ad797 or lt1028
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Old 30th November 2005, 05:25 PM   #5
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Quote:
but its hard to argue with the convinence and performance of the ad797 or lt1028
Even harder to argue with a cheap amorphous Lundahl
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Old 1st December 2005, 02:52 PM   #6
tmblack is offline tmblack  United Kingdom
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Even harder to argue with a cheap amorphous Lundahl
Which model and how much?

Tom

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Old 1st December 2005, 05:07 PM   #7
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I measure the noise with my sound card and a ultra-low-noise pre amp based on 4 parallel 2SK369 jfets. It has a noise floor of less than 0.35nV/rtHz.
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Old 1st December 2005, 06:18 PM   #8
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There is a variation of the Leach head amp at http://www.st-and.demon.co.uk/Audio/700/700page5.html . For a head amp you need transistors with very low base spreading resistance. This usually means power transistors or special (high priced) transistors designed for low base resistance.

Regards,
Ray
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Old 1st December 2005, 08:18 PM   #9
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Quote:
Originally posted by tmblack

Which model and how much?

Tom

EE
i have a 9206. don't remember the price but it was lunch money ($100?). Yes, there are better transformers but not under $300-$400.
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Old 2nd December 2005, 01:59 PM   #10
tmblack is offline tmblack  United Kingdom
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Quote:
I measure the noise with my sound card and a ultra-low-noise pre amp based on 4 parallel 2SK369 jfets. It has a noise floor of less than 0.35nV/rtHz
Fantastic result!
Can you tell us what software is used to make the measurement or maybe there is a link to find that out?

Tom

EE
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