Stratoblaster rules...?

Started by petemoore, November 15, 2009, 09:37:39 PM

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petemoore

  This measures in every possible way [tested for shorts, resistances, continuities, audio probed..all cool except..the transistors can't seem to bias, J201's.
 The SBB schematic: http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=64&Itemid=99999999
 battery is at 8.20:
 22k to V+ From drain
 Drain biased at 3.05v.
 Source is 2.40v, gate is 2.41v
 They're not connected.
 Source to ground measures ok, 11k or so. [Ground>10uf 10v cap>50k pot>source also gets this].
 Gate to ground with the transistor In is 11k7, with the transistor Out it jumps up to 370k, this is through exactly ''2x470ks + the 100ohm'' in series.
  Maybe both transistors are funny the same way...
This is the kinda thing that beats ya up !
 Pretty hard to figure out why the dern gate, at the bottom, with nothing else near or touching [I tested for and found N/C except the places supposed to connect].
 There's literally nothing there under the gate...except the 2x470k's [to make a ~1meg gate bias resistor.
 J201, Gate/Source/Drain [with legs down, looking at the print.
 
Convention creates following, following creates convention.

brett

Hi Pete
The gate should be at 0 V, so I'd guess that one of the 2x470k resistors is dead or not making contact.  It doesn't take much to move the voltage on a disconnected gate (even static from a nearby hand can shift an unconnected JFET gate by volts.  That makes me think - what about a JFET-controlled Theremin!!). 
With Vgs of 0 V, the JFET is fully "on".
cheers
Brett Robinson
Let a hundred flowers bloom, let a hundred schools of thought contend. (Mao Zedong)

petemoore

Hi Pete
The gate should be at 0 V, so I'd guess that one of the 2x470k resistors is dead or not making contact.  It doesn't take much to move the voltage on a disconnected gate (even static from a nearby hand can shift an unconnected JFET gate by volts.  That makes me think - what about a JFET-controlled Theremin!!).  
With Vgs of 0 V, the JFET is fully "on".
cheers

 That all makes sense, I can't figure out how 470k's seriesed measures what I say 370k? and only 11.7K with the transistor in there...yukk,,there's not anything around the bottom of the socket to confuse matters, simple 1 thing goes to the gate [the 100ohmer] where intput and the 1Meg should be is where I used a couple 470k's to get the gate bias resistor.
 I tried everything, DC check on output, R checks everywhere, N/C checks all over the board, voltage checks...but it don't matter because the LPB took over, I'll work on other boost later.
 This Small Stone volume drop is hard to get past, that's what I need one huge boost to recover from, the LPB almost does it.
Convention creates following, following creates convention.

petemoore

#3
J201, Gate/Source/Drain [with legs down, looking at the print.
 Wrong.
 Drain>Source>Gate  
 lJ201l
   l l l    [Legs down]
  DSG
  This works out good, that DIST+ sure needed this one up front !
  I remember that was it before, now it is again ! Great sound and from clean to thick distortion sound available +/0 unity volume, with 1 stomphit.[I like that hard-pre-boost into clipper sound]. Three knobs, the SB's gain knob is now the gain knob, treble cut and volume.
  Gain of DIST+ circuit fixed to ground [full on] sounds good, soon I'll have a switch there for gain control.   
Convention creates following, following creates convention.