Haveing trouble locating the problem with my TOCT circuit, from the GGG site (http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=128&Itemid=26)
For Q1 I have a pnp 2n3906 instead of the 5087 and for Q2&3 I have a 2n5088 npn instead of the 2n4401's.
I'm getting the following voltages at the Q legs:
Q1 c=2.4 ,b=3.2 ,e=0
Q2 c=8.3 ,b=0 ,e=0
Q3 c=2.35 ,b=0 ,e=0
Checked with multimeter and audio probe, no copper trace pcb breaks, signal stops at the q1. Help pls!
It looks like you've chosen the Neg. Gnd. Version ???
The transistors, if correctly polarized and oriented should work, 4401's tend to be medium gain, 5087's high-ish gain though.
Note the B/E diode orientations and directions for each transistor...being mixed PnP/nPn with a 'flipped over' Q1, The debugee and debuggers all need to be vigilant when observing that the E/B/C and transistor polarity both get 'flipped'.
For instance, if the collector of Q1 is 2.4v, the base of Q2 must be identical because the schematic shows them connected.
All based on the assumption of a Neg. Gnd. build, based on the PNP being in Q1.
yes, sorry - neg ground version - with pre-gain control. The lower leg (e) of q1 is connected on the circuit to the base of q2, trouble is, it's giving me zero volts which I'm sure it should not.
Its a fairchild 2n3906 which should read across with flat side facing me, legs at bottom from left to right: e b c.
yes, sorry - neg ground version - with pre-gain control. The lower leg (e) of q1 is connected on the circuit to the base of q2, trouble is, it's giving me zero volts which I'm sure it should not.
Q1C should measure 220k from ground.
Its a fairchild 2n3906 which should read across with flat side facing me, legs at bottom from left to right: e b c.
Q1 should be a PNP, the emitter goes to the 'upside' on the schematic.
the other transistors are NPN, Q2 is an emitter follower, goes to 'toward' ground [through the 22k emitter resistor. Q3 is an NPN gain stage, the DC bias being the 1k2 collector resistor and the 470ohm emitter resistor.
Signal from Q1 exits the collector and feeds Q2Base.
If signal fails to pass through Q1, test the 'to ground' and 'to Vsupply' resistances from it's E/B/C pins, the DC blocking capacitors always blocked DC..but is another thing you can check for.
Make sure R3 and R4 resistances are placed as shown [all resistors should measure the marked values, attach a DMM lead to ground and make sure all the other grounds 'beep'.
Thanks for the clarity Pete - reqally helpful in understanding for a newbie like me. So the PNP is wrong way round, will double check the resistors and signal paths again now. thanks!