benny_profane
Well-known member
Beyond those indicated to be 35v, what voltage rating do the other caps in the simulcast need to be?
On mine, for the larger caps I just used heat shrink as insurance on the exposed leads and didn't insert them all the way down then kinda bent em over. Sorta like this...
View attachment 1476
Simulcast
Finished up another one. The Simulcast. Definitely going on my board. It sounds fantastic into a clean amp and even better when the amp is pushing harder. I will probably build the next one with an A25k pot for volume as it can get crazy loud a quarter way up the dial in high gain mode. Thanks...forum.pedalpcb.com
Ah okay. So you shifted C3, C10, and C8 (in the edit to the reply above)? I looked at your build report after I posted the first reply and noticed that your caps in the top row didn't match with the silk screen. I figured that that is what you had done. Thanks for the picture and explanation! It's odd there aren't 6.3mm 120u 35V caps. Mouser has some listed as 'New!', but they are non-stocked.
Sorry, typo, I meant C6. You could sub 100uF for the 120uF caps and not hear the difference. Here's the deal with capacitor voltage ratings: you want some margin. You don't want to run 25V caps at 25V. I prefer at least 20% margin. Vcc will run at about 26V if the input is 9V. Fresh batteries and most power supplies deliver more like 9.2V. That will make Vcc closer to 27V. A 35V cap will have 30% margin.
Cheers. That makes sense. I didn’t really consider that since there’s power filtering before the charge pump.C3 & C10 are power supply bypass caps. Any AC noise that tries to get on the power bus gets shunted to ground thru those caps. What's so special about the 120uF value? Nothing. Anything in the ballpark will work.
The TC1044, LT1054 and ICL7660 charge pumps are capable of voltage inversion (making -9V from +9V) and voltage multiplication. They all do pretty much the same thing and are more-or-less pin-compatible. In the case of voltage multiplication, the charge pump switches pin 2 between pin 8 (9V in) and pin 3 (ground). C12 & C14 ride on pin 2. When pin 2 is connected to ground, C12 and C14 are charged by D1 & D3, respectively. When pin 2 is connected to +9V, the charges on C12 & C14 are dumped thru D2 & D4 into C13 and C15. For the moment, we'll ignore the diode drops for simplicity. Since C12 is charged to 9V when pin 2 is low, when pin 2 goes high, the + side of C12 is now at 18V and C12 dumps its charge into C13. C14 gets its charge from C13, so it gets charged to 18V when pin 2 is low and when pin 2 goes high, the + side of C14 goes to 27V and dumps it's charge into C15. It's similar to a bucket brigade. Here's how you calculate the output voltage from a multiplier like this:
1) Count the number of capacitors connected to pin 2 and add 1. In this case, that number is 3.
2) Multiply that number by the input voltage, usually 9.0V to 9.2V. 3 * 9.2V = 27.6V
3) Subtract out the diode drops. Schottkys like 1N5817 drop about 0.2V each and there are 4 of them, so in this case we subtract 0.8V. 27.6V - 0.8V = 26.8V. That's the approximate output voltage of the multiplier.
In some pedals the diodes are 1N400x, which have a drop of about 0.65V each.
You can multiply the voltage as high as you like by adding more diodes and capacitors. The only limitations are the voltage ratings of the capacitors and the amount of power you need to deliver.
And that concludes tonight's lesson on charge pump voltage multipliers.
The TC1044, LT1054 and ICL7660 charge pumps are capable of voltage inversion (making -9V from +9V) and voltage multiplication. They all do pretty much the same thing and are more-or-less pin-compatible. In the case of voltage multiplication, the charge pump switches pin 2 between pin 8 (9V in) and pin 3 (ground). C12 & C14 ride on pin 2. When pin 2 is connected to ground, C12 and C14 are charged by D1 & D3, respectively. When pin 2 is connected to +9V, the charges on C12 & C14 are dumped thru D2 & D4 into C13 and C15. For the moment, we'll ignore the diode drops for simplicity. Since C12 is charged to 9V when pin 2 is low, when pin 2 goes high, the + side of C12 is now at 18V and C12 dumps its charge into C13. C14 gets its charge from C13, so it gets charged to 18V when pin 2 is low and when pin 2 goes high, the + side of C14 goes to 27V and dumps it's charge into C15. It's similar to a bucket brigade. Here's how you calculate the output voltage from a multiplier like this:
1) Count the number of capacitors connected to pin 2 and add 1. In this case, that number is 3.
2) Multiply that number by the input voltage, usually 9.0V to 9.2V. 3 * 9.2V = 27.6V
3) Subtract out the diode drops. Schottkys like 1N5817 drop about 0.2V each and there are 4 of them, so in this case we subtract 0.8V. 27.6V - 0.8V = 26.8V. That's the approximate output voltage of the multiplier.
In some pedals the diodes are 1N400x, which have a drop of about 0.65V each.
You can multiply the voltage as high as you like by adding more diodes and capacitors. The only limitations are the voltage ratings of the capacitors and the amount of power you need to deliver.
And that concludes tonight's lesson on charge pump voltage multipliers.
Sorry, typo, I meant C6. You could sub 100uF for the 120uF caps and not hear the difference.