Halfer Phono stage mod

[rayfutrell]

"Would need a little guidance of which fet replaces which BJT."
You can't just replace a BJT with a JFET, Keep in mind that a BJT is a normally off device and you have to bias them on to work properly and a JFET is a normally on device and you have to bias them off a little for them to work properly. Completely different biasing. You are talking about a complete redesign.

 

[al2002]

Here;s a first cut on a 2x2 inch PCB. The SMT analog of the 2N4400, 2N4403 are the MMBT versions BUT these are obsolete even though Rochester Elec has tens of thousands. There are some needed adjustments to use the ZXTN2018F, ZXTP2027F which are about as low noise as you can go with an SMT bipolar:

It would be worthwhile to replace the 4401/4403 with ZTX 851/951.

 

[cygnus x1]

It was more about keeping the board layout than anything. Looks like I will be doing something like the BA-3 "preamp" circuit, so yes a complete redesign. So as for a pre-preamp, the Pacific circuit is no good?

 

[jackinnj]

It would be worthwhile to replace the 4401/4403 with ZTX 851/951.

ZXTP2027F = ZTX951. They need to have much higher Ic to attain the lowest noise levels.

 

[al2002]

True, but the Hafler 110 power supply can handle the extra current.

 

[jackinnj]

Full credit to Douglas Self's Moving Coil Pre-Preamplifier -- two channels will fit into the DH-112 box if you can do SMT. It's discussed in his book.