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Hi All,
I'm working on a preamp that is designed to either work with an existing amp that has an FX send/return or to be dropped in favor of the amp's own preamp with a panel switch. I've included the schematic and the footswitch wiring diagram. Everything on the preamp itself works (although it will need some tweaking to sound right) but I'm having problems with the footswitch. This is patterned on a Dumble preamp. The first triode is clean and is the default sound when neither of the stomp switches are activated. The footswitch diagram shows three leads coming in; O (overdrive, H HRM overdrive and Both) Those are the negative leads from three relay coils.
When the #1 switch is on, the overdrive relay is activated and the LED goes on. That works fine. When the #2 switch is on, all three relays are activated. The LED tied to the Both switch activates. The overdrive is activated through a resistor but not an LED to keep track of things on the pedal. That also works fine. The hitch is when both switch are on. The Both relay won't activate -- I think for lack of juice -- although both LEDs light-up. I'm a little surprised because when both switches are on, the HRM relay is open so there are only two of the three relays on. If I short the relay with a screwdriver against the chassis it does turn on and will stay in the normally-open position until the field is collapsed by using the switch or disconnecting the power.
The supply itself is pretty stout. I'm using 5v relays in a regulated system as shown on the diagram. Right now I have a 1 ohm resistor across the voltage regulator giving me about 6.1 volts but that is just an experiment. There is another switch on the pedal for a preamp boost that is not in this circuit but does pull power. I also have a panel indicator light on the same circuit that pulls power. That I could easily tie to the heaters if necessary. When I check the voltage on unused relays it is steady at 6.1 volts which makes me think my problem is in the resistors and LEDs in the path when grounding the coils.
I'm not married to any of this. It might be someone will take a look and recommend an easy fix. It could be that a more extensive re-work is a better idea. Either way, any comments or suggestions you could offer would be appreciated. Thanks, Skip
I'm working on a preamp that is designed to either work with an existing amp that has an FX send/return or to be dropped in favor of the amp's own preamp with a panel switch. I've included the schematic and the footswitch wiring diagram. Everything on the preamp itself works (although it will need some tweaking to sound right) but I'm having problems with the footswitch. This is patterned on a Dumble preamp. The first triode is clean and is the default sound when neither of the stomp switches are activated. The footswitch diagram shows three leads coming in; O (overdrive, H HRM overdrive and Both) Those are the negative leads from three relay coils.
When the #1 switch is on, the overdrive relay is activated and the LED goes on. That works fine. When the #2 switch is on, all three relays are activated. The LED tied to the Both switch activates. The overdrive is activated through a resistor but not an LED to keep track of things on the pedal. That also works fine. The hitch is when both switch are on. The Both relay won't activate -- I think for lack of juice -- although both LEDs light-up. I'm a little surprised because when both switches are on, the HRM relay is open so there are only two of the three relays on. If I short the relay with a screwdriver against the chassis it does turn on and will stay in the normally-open position until the field is collapsed by using the switch or disconnecting the power.
The supply itself is pretty stout. I'm using 5v relays in a regulated system as shown on the diagram. Right now I have a 1 ohm resistor across the voltage regulator giving me about 6.1 volts but that is just an experiment. There is another switch on the pedal for a preamp boost that is not in this circuit but does pull power. I also have a panel indicator light on the same circuit that pulls power. That I could easily tie to the heaters if necessary. When I check the voltage on unused relays it is steady at 6.1 volts which makes me think my problem is in the resistors and LEDs in the path when grounding the coils.
I'm not married to any of this. It might be someone will take a look and recommend an easy fix. It could be that a more extensive re-work is a better idea. Either way, any comments or suggestions you could offer would be appreciated. Thanks, Skip
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