A quick tube (valve) fuzz box

[DrNomis_44]

@ Lawry: I just had a listen to the demo clip you uploaded to Soundcloud and I think it sounds great, might have a go at building one since I've got a spare 9-pin valve socket with a shield in amongst my bits and pieces, I also have a diecast aluminium box I could use too.


If you're after some 47uF caps that are rated for 450V you can get them from Jaycar Electronics, I know that you're only getting about 70V, the 450V DC rating of the caps should ensure that they can handle the voltage with ample to spare.

Have you tried using a 12AT7 or a 12AX7 valve in your pedal design?, the 12AT7 and 12AX7 have different gain factors compared to the 12AU7, but they have the same pin connections and therefore should work fine.

[WeirdBits]

Finally got a chance to do some tinkering... and now I too can spend some time in Purgatory!

It's definitely a single coil pedal in my mind. With humbuckers it seems a bit too much or too little to me, whereas single coils seem to work nicely. YMMV.

Here's a quick run down on my build. It's Lawry's version 2 of the circuit (thanks Lawry) but with the addition of 12v/9v switching via a 4 pole slide switch and some extra bits (so that I can use a 9v supply if I don't have a 12v supply set up).

Initial layout showing where track breaks need to be:


Track breaks in place:


Working out where I can squeeze the 9v extras in on the board (6v regulator and caps):



Extra track breaks for the new bits (the three on the right) to isolate them from the existing circuit:


cont...

[WeirdBits]

Links in place, wiggly left one is the common for the 9v parts:


The enclosure I was going to use wasn't as deep as I thought, so I decided to reuse the box from my first ever pedal built several decades ago. The existing holes weren't quite in the places I needed, but I could make it work:


Marking out the new layout:




cont...

[WeirdBits]

Implements of destruction... needed for the big tube hole:


Holes drilled, filed and hopefully all in the right place:




Quick mockup to make sure everything is mostly right:


cont...

[WeirdBits]

More mockups:



Components added:




cont...

[WeirdBits]

Test fitting board in enclosure (this is where the existing holes made things awkward):


A little bracket to hold the board in place:


I'm using a tri-colour LED so I can have one colour for bypass and then a colour each for 12v and 9v active:


Loom prep:


Wiring:


cont...

[WeirdBits]

Installing the wiring into the enclosure... normal sensible people do this outside the box. Things are getting tight:


Everything is connected, time to add the heatsink to the regulator (double-sided heat tape, then bolted to box):


All internals in place, don't ask me how long it took to get the nut on the heatsink bolt:

The 4-pole slide switch selects between 12v and 9v supply. For 12v the tube heaters are in series via pins 4 & 5 as per Lawry's build and fed directly from the 12v. With the 9v the heaters are swapped to parallel across pins 4 & 5 with a ground added to pin 9 and fed via the output from the 6v regulator circuit added to the board.

Noise maker installed:


Caged up and ready to rumble... hopefully:


cont...

[WeirdBits]

Amazingly, it worked first time!

Red on bypass (9v or 12v):


Violet active on 9v:


Yellowy Green active on 12v:


Basically, the RGB LED always has the red on and then either the blue (9v) or green (12v) is added when active giving violet and yellow-green respectively.

Done and done. I was going to paint the enclosure when I first planned this, but now I'm thinking I'll leave it... at least for now.


I still need to experiment with the sounds and how it changes with the voltage. It has a little less 'oomph' on 9v but the overall sound isn't that different. I've only tried it on a little solid-state amp so far, but it gave that a bit of tube-ishness which was nice. I used a 12AU7 tube like Lawry's, but may try a few alternatives when/if I get time. Thanks again for the circuit and inspiration Lawry!

[DrNomis_44]

Amazingly, it worked first time!

Red on bypass (9v or 12v):


Violet active on 9v:


Yellowy Green active on 12v:


Basically, the RGB LED always has the red on and then either the blue (9v) or green (12v) is added when active giving violet and yellow-green respectively.

Done and done. I was going to paint the enclosure when I first planned this, but now I'm thinking I'll leave it... at least for now.


I still need to experiment with the sounds and how it changes with the voltage. It has a little less 'oomph' on 9v but the overall sound isn't that different. I've only tried it on a little solid-state amp so far, but it gave that a bit of tube-ishness which was nice. I used a 12AU7 tube like Lawry's, but may try a few alternatives when/if I get time. Thanks again for the circuit and inspiration Lawry!

That looks wicked, I like the effect you get with the holes drilled in the metal valve shield, gives it a retro-vibe, I'm going to have to have a go at making one of these next year, I still have some spare valves which I can use in my build.

Also, the tri-coloured led is a nice cool touch.

[DrNomis_44]

And, young Scott, you have mad a deal with the devil. Or at least his Dirty Angel. So be prepared for Purgatory.

Today's phase:
Got me a box and mounted everything inside. (Weird Note: For some reason it picks up more noise inside the box so I'll have to work on that).
However, it's getting closer.

Next step is to come up with some artwork to make the box look perty.

One thing you could try doing to get rid of the noise is to connect the metal of the case to circuit ground, the case will then act as a Faraday Shield for all the internal electronics, also, make sure that any shielded audio wire you use for the input wiring has it's shield braiding connected to ground at one end of the wire, this will prevent earth-loops in the input wiring from inducing hum-noise into the input, the control grid of a 12AU7, 12AT7, 12AX7 operates at a very high impedance, meaning that it takes very little current to drive it, as a consequence it tends to be very sensitive to noise pickup.


I'm going to try bread-boarding the Purgatory V2 circuit over the Christmas holidays and see if I can come up with some cool mods to the circuit, I can think of at least a couple that I'm interested in trying out, one mod is to add a 3-Band passive EQ tone control after the second triode gain-stage, you could either use the Fender 3-Band EQ component values, or, the Marshall 3-Band EQ component values, I'm considering using a Mosfet, such as the 2N7000, as a Common Source amplifier stage to act as a buffer for the second triode gain stage so that the 3-Band EQ doesn't present too much of a load to the second triode gain stage, the result should be a tone that is a bit brighter, the other mod is to add an extra gain stage at the front end of the circuit, again made up of a 2N7000 Mosfet, this should increase the amount of gain attainable from the circuit, I will have to check to see if the mods will work as intended though.