April 5, 2020 at 1:47 pm #12225Big OParticipant
Starting to work on my next project, a MKI bender that has a charge pump. I want to use a GuitarPCB 3PDT board for the footswitch as I have several of these lying around. The charge pump in the circuit board has the LED running off of it, but I would like to use the GuitarPCB 3PDT board for mounting the LED. If I use the 3PDT board are there going to be polarity issues? If not, should I jumper the CLR (R10) and the LED positions on the board if I want to use the 3PDT board for the LED? See the charge pump section on the schematic below.
And an additional unrelated question. The circuit calls for a 25uF cap, but all I can find is a 22uF. Would it be okay to use the 22uF in parallel with a 3.3uF cap for 25.3uF total, or are tolerances such that I would need exactly 25uF for the circuit to function properly? If I need the exact value I would use the 22uF in parallel with three 1uF caps for 25uF total as I have these on hand, however, it would just require a larger off board capacitor array.April 5, 2020 at 3:39 pm #12228BillyModerator
Your LED in the schematic is powered from +9v before it’s inverted
You could just run a power and ground from the DC jack to your 3PDT board and use as normal
The values given were common back in the day but not so much now so just use your nearest modern value 22uf etc there’s no need to paralell values it’ll work fine
There’s 20% tolerance so you could get a 22uf that’s nearer 25uf but as I say no need to do that
I’ve built many positive ground circuits and it still confuses me, but it’s only the actual circuit that requires negative power, ground would still be 0v just positive! everything else will work from normal power the LED as you know is just an indicator so as long as it gets power to its anode and ground to its cathode it’ll work when switched being separate from the main circuit
I think it was Tonmann that said the best way to think of it is negative power it still requires 9v power and a 0v ground reference that’s how I avoid confusing myselfApril 6, 2020 at 1:13 pm #12254Big OParticipant
Thanks so much for the help. I will soon begin the build once my Trigeminal Neuralgia abates. Probably not as bad as getting Covid 19, but severe facial pain does not help with concentrating on soldering a PCB.
Then it’s on to a 4 track fuzz, which I wouldn’t have had to build except for tossing out my old Hitachi D-850 three head cassette deck about 15 years ago when I got my first guitar pedal. And I thought that what I was doing by plugging my guitar into the deck and the deck out to the amp was unique and something nobody had ever done before. It seems like everything I thought I had come up with guitar wise was not a novel idea. But then again the internet was not available in the 70’s and 80’s.
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