Knight of Tone pedal - 9 / 18v?

[rpark71]

Hi all,

I've started a PCB Mania Knight of Tone pedal build and the build instructions (to me at least) seem a bit fuzzy on the voltage doubler part of the circuit. I can only find one image of another build of v3 - surely other people have done it, as modelled on  Analogman King of Tone. The photo I've found has a toggle switch on the top back side, above the DC jack and is labelled 9/18v switch. In the build instructions, it says the TC1044 IC is 'in charge of voltage doubler section', but its not obvious if this is an extra modification (if you know how) or part of standard build - the BOM lists that IC3 as part of the standard version, so am assuming I populate the whole pcb. I'm happy to have as 9v, if that's standard, but just a bit confused as doesn't show anything on the drilling template either for a switch. PCB Mania facebook support wasn't much help, so thought I'd try here as friendly person helped me get two pedals up and running! Have included pic of pcb, schematic and wiring diagram. Any help welcome!

Thanks, Rich

[WormBoy]

What I get from the building instructions is that 18V with voltage doubler is the standard version as mr. PCB Mania intended. The switch on the photo you've found is obviously from an enthousiast who added a 'non-standard' switch. The PCB does not seem to anticipate such a switch, so that'll be a bit of a hack.

[rpark71]

Hi - ok thanks. Does that mean you'd power it with 18v or 9v and then that part of the circuit doubles it internally? The build docs does specify power as 20mA (9v). But just reading again I think it answers my query, it says:

Another mod included here is the internal Charge pump, that takes the 9v input and doubles it to 18v, giving this way much more headroom and clarity. This can be easily bypassed as it's explained on the graphic bellow. (Schematic I think they mean)

Thanks again!

[mjg]

The usual is to power it with 9v, and the charge pump will double that to 18v internally. 

IC3 on the board you show is the charge pump, so that is definitely intended by the person who designed that board. 

If you don't want to worry about changing between an internal 9v and 18v, just ignore that switch that you see in the image.  The 18v is probably going to sound better to most people I'd think. 

Oh, and don't try to power the thing with an external 18v.  That would most likely make things very unhappy and melted. 

[WormBoy]

Hi - ok thanks. Does that mean you'd power it with 18v or 9v and then that part of the circuit doubles it internally?

As mjg said: if you use IC3, don't power it with 18v ... smoke will come out and bad fumes. There's no overvoltage protection on board, and max allowable voltage on charge pumps will be less than 18v (and you would have to worry even more about voltage ratings of caps).

It would not be too hard to bypass the charge pump part of the circuit, and run the circuit on a wall wart that puts out 9-18v. It is not explained in the build doc, as far as I can see, but the schematic helps.

The pedal will sound different at 9 and 18v. Not sure what is 'better'. On my to do list, I still have to try running a tubescreamer at LESS than 9v, just to get more 'stress' from the opamp and less contribution from the diodes. On YT, you're bound to find comparisons with 9-18v, so you can see what you like best.

[rpark71]

Great, thanks for the clear answers mjg and WormBoy, about it being powered at 9v and the 18v is internal on the circuit. It's that photo with the switch that got me confused most I think and that as a newbie was not understanding in the instructions! Cheers, I don't want a smoking and melted pedal! 

[rpark71]

...actually, to quote Columbo, just one more thing...

On the finished photo again, it shows the labels on the two DPDT switches are reversed, Overdrive/Boost/Distortion for left switch (side A on the pcb) and Distortion/Boost/Overdrive (side B on pcb) - is this standard/correct, with both switches flicked left (as in photo) you'd get overdrive one side and distortion on the other. Or this another modification they've done? Just thinking of my own labelling being correct and understanding the pcb better. The diodes below switches do mirror each other on the pcb, so I think makes sense?

[WormBoy]

...actually, to quote Columbo, just one more thing...

I see that you are from a certain vintage 

On the finished photo again, it shows the labels on the two DPDT switches are reversed, Overdrive/Boost/Distortion for left switch (side A on the pcb) and Distortion/Boost/Overdrive (side B on pcb) - is this standard/correct, with both switches flicked left (as in photo) you'd get overdrive one side and distortion on the other. Or this another modification they've done? Just thinking of my own labelling being correct and understanding the pcb better. The diodes below switches do mirror each other on the pcb, so I think makes sense?

When in doubt, I always use a multimeter set for continuity. That will tell me which pads of the switches are connected to what (together with a look at the schematic). Then you have to realise that the switch poles are opposite to the position of the toggle (so switch to the right means that the left-most poles are connected). There is unfortunately nothing in the build doc to help you here, and no 'standard' way to do it. The build/labelling on the photo might be correct or it might not. Measure and you know  .

[rpark71]

Vintage Columbo...tv gold!

Great, thanks - that's a good practical plan I understand!

Cheers, Rich