Adobe .PDF of the same schematic: http://72.52.250.47/images/D104.pdf
Paul, W9AC ----- Original Message ----- From: "Paul Christensen" <w...@arrl.net> To: <elecraft@mailman.qth.net> Sent: Thursday, July 22, 2010 5:29 PM Subject: K3 - D104 Buffer Schematic > Last night, I built up the following D104 buffer circuit as discussed by > Joe, W4TV. > > Joe's idea works very well. The difference between this circuit and other > D104 buffer circuits as seen on the Internet is that it is powered > directly from the K3's mic lead when the bias menu is activated. One > benefit is that the circuit can be ported to a PC sound card. Another > benefit for most builders: Only one part is required -- either a J201 or > MPF-102 nFET transistor. When using the PC input configuration shown, I > also had good results with a Samsung NC10 netbook. > > I tried the MPF-102 and J201, and each works well, although the J201 FET > can be operated with an Ids current down to 0.5 mA. R89 in the K3 limits > the Ids current. The minimum Ids spec for the MPF-102 is 2.0 mA but seems > to perform the same, albeit with slightly less gain as expected. The > D104 cartridge level is relatively high anyway and I found that in either > configuration, the K3's mic menu could be set for the "low gain" setting. > Also note the inclusion of the optional Rg and Rs resistors. My > breadboarded pre-amp is stable without those components and the gate > biases just fine. I'm also not too concerned about static here in > Florida. At 15-cents ea., the FET is easy and cheap enough to change. > > Finally, if RFI becomes an issue, it may be helpful to experiment with a > bifilar-wound, common-mode choke at the shielded cable entry, close to the > FET. I would try that before attempting differential-mode abatement > techniques (e.g, bypass caps to ground). Similarly, the mic cable at the > K3 connector end can be wound through a #31 core, if necessary. > > Paul, W9AC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
