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I just built a clone of an LPB-1 pedal, as my first ever guitar pedal project. It works great between my guitar and amp with no other pedals in the chain. When it is placed in a chain with pedals before or after, though, it doesn't work properly. When it shares a power supply with other pedals, it completely blocks any signal from passing through. With its own power supply, though, it works, but also generates a loud 100hz hum. I don't know too much about electronics but I'm confused as to why the pedal would work by itself, but not in series with other effects. What could be causing this to happen?

LPB-1 schematic I am powering the pedal using a standard 9v power supply. I also added a DPDT footswitch, wired as a true bypass switch connected to the input and output jacks.

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  • \$\begingroup\$ Schematic? How exactly are you connecting it 'with other pedals'? \$\endgroup\$ – Bruce Abbott Jul 31 '20 at 3:56
  • \$\begingroup\$ I just edited my question to add the schematic. I've tried placing pedals before or after the LPB-1, connected using standard 1/4" patch cables, but when I turn the pedal on no signal passes through. \$\endgroup\$ – Precipitato Jul 31 '20 at 4:50
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    \$\begingroup\$ The circuit looks quite ordinary and gives no hint of what might be wrong. However it doesn't include the input/output jacks or power supply wiring. Can you provide photos of the unit showing all wiring etc.? What power supply are you using? \$\endgroup\$ – Bruce Abbott Jul 31 '20 at 6:10
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    \$\begingroup\$ A lot more information is needed for people to make a good assessment of what's going wrong. Be really specific. When you "engage" the LPB-1 how are you engaging it? There is no switch in the schematic. Do you just mean plugging it in? When you say "no" signal reaches the amp is it truly NO signal, or is the signal just really small (super-quiet sound, but it's still there)? Does the potentiometer VR1 work normally when the LPB-1 is connected by itself? Does VR1 have any noticeable effect when there is another pedal connected in the chain? \$\endgroup\$ – Mr. Snrub Jul 31 '20 at 6:55
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You haven't explained the power supply setup. If this is powered by its own 9 V battery there should be no problem but if you are using a shared power supply with the other pedals you may have created a short-circuit. Check if the other pedals positive or negative ground. (That might cause a short on the 9 V supply.)

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