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Old 3rd November 2014, 12:46 AM   #1
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Default Complementary MOS Preamp

Here's a circuit for a complementary mos gain-of-five preamp using readily available SOT-23 mosfets BSS84 and BSS138. I could have used the BSS159 depletion mode mosfet at the input and saved some parts, but I wanted the challenge of using all enhancement mode parts, which need a little more care for bias.

Why do this? I just snapped up 500 pieces of BSS138 at Electronic Goldmine (cheap!), and wanted to try using them in something worthwhile. I have ready access to the BSS84 as well.

This dodge could also be done with through-hole parts like the Supertex VN0106N3/VP0106N3 and Zetex parts ZVN3306A/ZVP3306A.
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Old 3rd November 2014, 01:15 AM   #2
jcx is online now jcx  United States
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MOS has a reputation for bad 1/f noise, popcorn noise too

some monolithic CMOS op amps look just Ok but not what most would 1st reach for in preamp front end
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Old 3rd November 2014, 01:36 AM   #3
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Mos parts have improved over the decades, so their bad rap may not be entirely justified. I've certainly not had any problems with the ones I've used.

The designer for the Creek RIAA preamps actually used a depletion mode mos part in one of his higher end RIAA designs - it's described somewhere on this site.

Most likely, the noise performance varies quite a bit with the manufacturer. I might be inclined to trust manufacturers like Infineon, NXP, and maybe On Semi over some of the other manufacturers. Dunno about 1/f noise, but popcorn noise can be reduced with a clean fab and good process control.

Anyway, this is a high level line-out type of design. I may try designing and building an MM-type RIAA preamp using the Infineon BSS159 depletion mode mosfet simply out of sheer perversity.... The BSS159s are remarkably consistent from sample to sample. Good process control?
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