hello i have a dunlop wah.
it would only work briefly as the power drained when i disconnected the 9v battery or the 9vdc adapter power supply.
i have connected it to a 5vdc battery power supply and it works fine.
here is the schem. I hope this is enough info for someone to advise me of possible problem,
thanks
it would only work briefly as the power drained when i disconnected the 9v battery or the 9vdc adapter power supply.
i have connected it to a 5vdc battery power supply and it works fine.
here is the schem. I hope this is enough info for someone to advise me of possible problem,
thanks
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Working briefly during power on or power off suggests a classic type of problem which is incorrect biasing.
The first step would be to measure the static DC voltages on all three transistors. So that is nine measurements in total, E,C and B for each. The base voltage may be measured a little innacurately due to the high circuit impedances.
Measure them and report back with the results.
The first step would be to measure the static DC voltages on all three transistors. So that is nine measurements in total, E,C and B for each. The base voltage may be measured a little innacurately due to the high circuit impedances.
Measure them and report back with the results.
thanks for the help, i will check. the voltages were already on the schematic when i downloaded it.
thanks for helping, here are the voltages with just a separate lead plugged in each jack . (no amp or instrument connected)
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Interesting, I don't see any obvious signs of a fault. Perhaps someone else will spot something I missed.
-Gnobuddy
Q0 has a very small collector resistor, so very slight voltage drop across it. The meter isn't showing that slight drop.
The key point is that the emitter voltage Pauld35 measured (4.01 V) shows that Q0 is operating normally - it is an emitter follower, and the emitter is sitting at quite closer to half the battery voltage, exactly as it should. Emitter current is around 400 uA.
So I don't think there is a problem with Q0...
-Gnobuddy
make sure it's not a bad connection that is affected by temperature.
one thing that seems odd/ weird about that schematic that i may be not understanding correctly is where is the supply switching? shouldn't the battery B+ be switched via the input jack to prevent battery drain? no battery clip in the drawing nor is there a dc jack which to the best of my recall is a feature on most Dunlop wahs?
or is this meant to run off a supply?
one thing that seems odd/ weird about that schematic that i may be not understanding correctly is where is the supply switching? shouldn't the battery B+ be switched via the input jack to prevent battery drain? no battery clip in the drawing nor is there a dc jack which to the best of my recall is a feature on most Dunlop wahs?
or is this meant to run off a supply?
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Battery positive is always connected and negative is connected to ground through the input (or output) jack ring connection, when plugging a cable there; it´s the typical pedal supply switching system, so common that nobody bothers to draw it in detail, it is a given.
And that´s not the Factory schematic but an amateur builder´s one.
And that´s not the Factory schematic but an amateur builder´s one.
Perhaps there is a bad (cracked) solder joint or PCB trace, or a broken wire, either in the battery connector, or the soldering to the power jack.
Failure of soldered joints and wires in these areas is relatively frequent, because both these areas experience repeated mechanical stress as batteries are plugged in or unplugged, and the external power plug is inserted and removed.
The fact that the circuit did work on a 5V power supply may turn out to be a red herring - does it always work reliably on the 5V power supply, even if you wiggle the power plug and/or battery connector?
-Gnobuddy
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