Another %^&*roft walton question

[Ice-9]

I'm asking this question as i've been unable to find an answer to it, I've finished building my psu that has all the requirements i need, the voltage multiplier section is based on a 4049 chip running the c/w ladder which is 4 stages giving me about 60v from a 15v supply. The thing is i want to add a few more stages to get around 90v.

I know this is not a problem but space is, so  i was wondering if anyone knows if it's possible to use tant bead caps instead of electro's in the c/w ladder. The multiplier ladder i'm using has the caps in series so the voltage rating isn't a problem.

[R.G.]

Tantalum beads are electro caps, just made from tantalum metal instead of aluminum. Tantalum pentoxide has an even higher capacitance multiplication factor than aluminum oxide, so tantalum is smaller for the same capacitance*voltage product than aluminum.

As long as they are never reverse biased, they should work wherever aluminum works and you can afford them.

[Ice-9]

Thanks R.G. That is the answer i was hoping for. I happen to have a bag full of tants so i will use them. 

[earthtonesaudio]

I'm currently looking into using a %^&*roft-Walton multiplier also, similar to yours but at lower voltages.  If your oscillator is putting out 15V p-p, which I assume it is since you're using a 4049, you only need 3 stages to get ~90V.  4 stages will give you over 100V.
(based on this nice little page I found recently): http://www.cosmicrays.org/muon-%^&*roft-walton-calculation.php

But I'm curious about using polarized caps in there.  Seems like when you first apply power, the caps are all discharged and the input is more positive, but once it's working the output is the more positive voltage. 

[Ripthorn]

This is a cool idea.  Two questions: do you use buffered or unbuffered 4049's and what kind of current can this supply provide?

[earthtonesaudio]

This is a cool idea.  Two questions: do you use buffered or unbuffered 4049's and what kind of current can this supply provide?

I think the chip variety shouldn't matter as it's really the oscillator frequency + capacity that determines the current capabilites... but I think the buffered variety would probably charge it up faster.

[Ripthorn]

Too bad I tossed out my one buffered chip thinking it was useless for stompbox stuff.  Oh well.

[gez]

Haven't seen the schematic you're using, but presumably it uses diodes and caps to double/triple/whatever the 'AC' (pulsed square?) voltage.  Make sure you check the voltage ratings of the tantalum caps.  It's difficult to find ones with high ratings (in the UK, at any rate).

Edit: sorry, didn't see that you said ratings weren't a problem (checked the wiki entry and understand now). 

[Ice-9]

Thanks for the link to the calculator Earthtonesaudio, i have 4 stages in mine at the moment and from 15v i get at each stage 15v, 30v,  45v,  60v or  just under at each stage. (to be sure of how many stages i have the circuit has 8 diodes and 8 caps) the frequency that the 4049 works at must make a huge difference in the output of the stages (the calc give me 1500v over 3 stages if i change the freq???)
Anyway the newcastle sunderland derby match is about to kick off so i will finish this post later.

[Ice-9]

Well its snowing here in northern england so i've took a day off work, (don't like the idea of falling off my motorcycle) anyway ,what better than to put my time into this project. This is to be a valve drive pedal powered from an ac adapter and when i start on the actual signal part of the circuit i will start a new thread about it, but for now i have made a pcb and soldered the the circuit together.

@Earthtonesaudio, I am using the hef4049bp as it was the only one i could find in my parts bin, i have not checked the datasheet but i assume its a buffered one but  i am prob wrong.

It comprises of ac input (no battery)
rectifier
+12/ -12v regulated for powerering the circuits that will need split rail psu using 78 /7912 regs at max 100ma (T092)
+12 regulated 1.5a for powerering the heaters in the 12ax7 (T022 package)
+15v regulated for the  c/w ladder to power the plates. 7815 T092 (atm i'm getting 60v here) later on i might redo it to get 90+ volts.

I have also included both in/out jacks, footswitch , led and pulldown resistors.

You might ask why put the jacks etc on the same pcb near the noisy psu, well the answer is that i want to see if the audio side is going to pick up any noise from it, it doesn't after first tests,
and also it is an easy way to set up the rest of the circuit on bread board and connect to this in/out pcb.


work so far

I wish this effect to have a 3 band tone with gain and level pots. I will be using a 12ax7 valve and also there WILL be op amps in there which may or may not have diode clipping as well.