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Alright, I've beat my head against the wall (figuratively speaking, so far) with this new pedal but so far I've not been able to figure it out. I'm hoping maybe someone here can help me get over this hurdle.
First of all, this is my first pedal, my first time working with ss amplification. I'm an amp guy, built, repaired and tuned lot's of amps, tube amps. I've got a pretty good understanding of tube amp tech and have quite a few amps under my belt. So when the need for a clean boost pedal came up I figured why buy one, I'll build one for the fun of it and the experience. Well, the fun part was in learning bi-polar transistor theory and application, designing it and assembling it, but now it's not so fun.
The design is pretty much based on the old LPB1, which is a pedal I always really liked; but I added a diode clipping circuit to be able to add some dirt if/when needed. The LPB1 schematic is here: http://www.montagar.com/~patj/ehbsters.gif. and my pedal uses pretty much the same boost circuit, using a 2n5088 transistor. For the clipper circuit I just tapped into the boosted circuit after the collector, after the coupling cap prior to the volume pot, and ran two diodes in parallel with opposite polarity, then ran those to a pot wired as a variable resistor then thru a switch to ground. I also added a circuit to allow me to switch the value of the coupling caps, to go from full frequency boost to treble boost.
The problem I'm having is their is no amplification from the transistor. I've ensured I have the collector, base & emitter terminals wired correctly, as per the data sheet and verified with a DMM set to diode check mode. I've made sure the pins on the transistor match the positions indicated on the data sheet, and have them connected as per the schematic. Testing the pedal with a 1k 100mv sine wave I have good signal transfer all the way thru the circuit, from input to the transistor base, but the signal strength drops appreciable across the transistor and is very weak coming out at the collector. I can inject a signal at the collector and it goes right on thru the rest of the pedal just as it should, indicating everything has continuity and the volume pot works as it should. The problem, as near as I've been able to narrow it down, is right at the transistor itself.
DC voltage checks show there is very little current flow across the transistor, I've got 8.75v at the battery, 8.71v at the collector (just .04v dropped across the collector resistor), .92v at the base and .49v at the emitter. My ground connections appear to be good, I'm getting the correct resistance reading to ground in the all the right places.
I have replaced the transistor to verify that I wasn't working with a bad transistor, and I find it hard to believe that I would have two bad transistors, though that's not impossible. I even changed my connections between the emitter and collector to eliminate the chance that I installed them backwards. So far I've got nothing.
I'm new to transistors, so bear with me, but does the fact that I'm getting a signal, weakened though it is, across the transistor, from base to collector, mean that it's trying to conduct, but something is preventing it?
I've followed the circuits out many times, I'm sure it's all connected correctly. What would cause a transistor to not conduct?
First of all, this is my first pedal, my first time working with ss amplification. I'm an amp guy, built, repaired and tuned lot's of amps, tube amps. I've got a pretty good understanding of tube amp tech and have quite a few amps under my belt. So when the need for a clean boost pedal came up I figured why buy one, I'll build one for the fun of it and the experience. Well, the fun part was in learning bi-polar transistor theory and application, designing it and assembling it, but now it's not so fun.
The design is pretty much based on the old LPB1, which is a pedal I always really liked; but I added a diode clipping circuit to be able to add some dirt if/when needed. The LPB1 schematic is here: http://www.montagar.com/~patj/ehbsters.gif. and my pedal uses pretty much the same boost circuit, using a 2n5088 transistor. For the clipper circuit I just tapped into the boosted circuit after the collector, after the coupling cap prior to the volume pot, and ran two diodes in parallel with opposite polarity, then ran those to a pot wired as a variable resistor then thru a switch to ground. I also added a circuit to allow me to switch the value of the coupling caps, to go from full frequency boost to treble boost.
The problem I'm having is their is no amplification from the transistor. I've ensured I have the collector, base & emitter terminals wired correctly, as per the data sheet and verified with a DMM set to diode check mode. I've made sure the pins on the transistor match the positions indicated on the data sheet, and have them connected as per the schematic. Testing the pedal with a 1k 100mv sine wave I have good signal transfer all the way thru the circuit, from input to the transistor base, but the signal strength drops appreciable across the transistor and is very weak coming out at the collector. I can inject a signal at the collector and it goes right on thru the rest of the pedal just as it should, indicating everything has continuity and the volume pot works as it should. The problem, as near as I've been able to narrow it down, is right at the transistor itself.
DC voltage checks show there is very little current flow across the transistor, I've got 8.75v at the battery, 8.71v at the collector (just .04v dropped across the collector resistor), .92v at the base and .49v at the emitter. My ground connections appear to be good, I'm getting the correct resistance reading to ground in the all the right places.
I have replaced the transistor to verify that I wasn't working with a bad transistor, and I find it hard to believe that I would have two bad transistors, though that's not impossible. I even changed my connections between the emitter and collector to eliminate the chance that I installed them backwards. So far I've got nothing.
I'm new to transistors, so bear with me, but does the fact that I'm getting a signal, weakened though it is, across the transistor, from base to collector, mean that it's trying to conduct, but something is preventing it?
I've followed the circuits out many times, I'm sure it's all connected correctly. What would cause a transistor to not conduct?
), so, as Steve said, check that the resistors' values ( colors ) are correct ( I'm not questioning your ability to read the resistors' color code, I'm rather questioning the way some resistors' manufacturers print some colors - It happened to me once that what seemed to be "red" was in fact "orange" - and I'm not colorblind - leading me to a 10x mistaken reading ).
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