Leach MC Headamp

[tmblack]

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

[tschrama]

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

[tmblack]

Thanks. How did you measure the noise?
He recommended the 2N4401/2N4403 which I believe are still available.

Tom

EE

[jcx]

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

[analog_sa]

but its hard to argue with the convinence and performance of the ad797 or lt1028

Even harder to argue with a cheap amorphous Lundahl

[tmblack]

Even harder to argue with a cheap amorphous Lundahl

Which model and how much?

Tom

EE

[tschrama]

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.

[rayfutrell]

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

[analog_sa]

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.

[tmblack]

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