GGG Boutique Boost

[outoftune]

http://www.generalguitargadgets.com/pdf/ggg_joam_sc_b.pdf

I'm not exactly sure if anything is wrong with my build but just to be sure it's at its full potential I have a couple questions. Is the 1n4005 necessary, or would any in that series do? Also if anyone knows approximately what the transistor voltages should be that would be very helpful as well. Thanks.

[Mark Hammer]

Really anything would do....including nothing.  The diode is just there for protection against those instances where, just as you're about to attach the battery or supply power, the phone/doorbell/car-alarm rings or your better half asks you a question and you look up.  If the power supplied is opposite to the polarity it's supposed to be, anything over the forward voltage of the diode will be conveniently directed towards ground.

But why is a 1N4005 shown?  You may well ask.  That's basically for those instances where the power supply may be on the "hefty" side.  You wouldn't want a lesser diode waving its hand, muttering "Right this way to ground, gents!" to a 3A supply, only to have the diode fry and immediately send the power to the circuit itself.

I suppose, you could probably replace the 1N4005 with a couple of 1N914 types (same orientation as each other and as the 1N4005) in parallel, to make that path a little more robust and hold up to the application of wrong-polarity power supplies.

[outoftune]

Thanks Mark, I didn't think it looked like it was doing much of anything... now that that's answered, anybody know what the transistor voltages should be?

[petemoore]

  Mu amp.
  1 gain stage.
the top Jfet sets bias [around 4.5v] for the bottom Jfet's Drain.
  so...Jfet that does the amplifying is the bottom one.
  I'll speculate, but posting of voltages from X circuit makes it easier to spot something wierd, bias will vary one Mu to Mu 2...Jfet variation is mostly resposible for this, part tolerances also.
  So the bottom jfet to amplify the source must be higher than the gate by X amount, depending on the Jfet, and both should be like...low voltage I guess ~<2v maybe more.
  The voltage divider sets the source voltage of the top Jfet at around 1/2v, test the voltage divider voltage/gate voltage for 1/2v.
  The much better reads than the above are at GEO. Posting voltage is the best way to debug it, also read the debugging page.