Low noise amplifier design fundamentals

[GlidingDutchman]

Some experts will most certainly sneer at this thread but here goed...

I am electronically impaired! Give me any mechinical stuff and I'll figure it out in no-time but electronics... ey!

How does one go about designing a low noise, preamplifier for phono use? Using discreet components... FETs and the like...

Can someone please show me the way as I would very much like to design my very own phonostage and not just build someone else's design...

Dewald

[Gordy]

I guess others can provide specific advice, so I'll stick with the basics:

Buy / read The Art Of Electronics

Search this site for appropriate threads (...many in the Solid State section, including the Vendetta thread, and the thread from X-Pro)

Visit some transistor related sites on the net, such as...
http://www.funwithtransistors.net/
http://www.allaboutcircuits.com/vol_3/chpt_4/5.html
http://paginas.fe.up.pt/~fff/eBook/MDA/MDA.html

Visit some phono amp related sites on the net, such as...
http://users.ece.gatech.edu/~mleach/headamp/
http://andycpublic.50webs.com/phono_preamp.htm
http://www.klaus-boening.de/

Lurk around on http://www.prodigy-pro.com/forum/


Good luck,
G.

[Conrad Hoffman]

Follow Gordy's advice, but IMO almost every practical implementation has already been done. Until you're up to some complicated discrete "opamp" design, chances are that whatever you do will look very much like what somebody else has done, or maybe a combination of a couple designs. In fact, if it didn't, I'd be very suspicious of it.

[GlidingDutchman]

Do you guys think one can design a low noise audio pre-amp with one of these:

http://en.wikipedia.org/wiki/HEMT

http://en.wikipedia.org/wiki/Heteroj...lar_transistor



D

[GlidingDutchman]

Call me crazy but is there any way to construct a pre-pre-pre circuit using one of these ATF-36077?

Weird people has done weird things in the past with great success!

D

[Conrad Hoffman]

No doubt one could build an audio frequency preamp from those very fast RF devices, but why? The amp would be subject to all sorts of stability problems. You'd still need serious RF construction techniques just to get the devices bypassed and rolled off properly. An extra quarter inch (or less) of wire might be the difference between success and failure. There isn't much problem achieving near zero noise levels using very conventional parts- look at the LT1028 which gets its noise level down near the thermal contribution of a 50 ohm resistor. IMO the most important thing is to choose the devices for the impedance level in question. It takes different circuits to optimize noise for a 100 ohm source, vs. a 10kohm source. A reactance generates near zero noise, thus the reason step up transformers work so well for MC phono pickups.