In an amongst the guitar building I decided to break out the soldering iron to build an overdrive pedal – as light relief. I had stumbled across the “Valvecaster” schematic and layout at Beavis Audio.
This is a very simple circuit that uses a 12AU7 valve, running at a low voltage. Because it is running at such low voltage it is very easy to overdrive.
The schematic specifies an operating voltage of 9v but I decided to bump it up to 12v to give a fraction more headroom. I chose one from the tangle of old wall-warts I have tucked away in a drawer. It could use a battery but I suspect that the current draw for heating the valve would suck a PP9 dry in a matter of minutes.
If you search for “valvecaster” at Youtube, you’ll find plenty of examples of the pedal in action. One of the common comments is that this is a naturally “dark” sounding pedal. This was not exactly what I was after and so I was going to experiment with different types of tone stacks. As laid out in the schematic it includes a simple treble cut tone control. Even turned up full this would only make the pedal darker, allowing treble frequencies to escape to earth. I decided, initially, to build it with no EQ, and then add it later. One of the results of this was that it is not a dark pedal at all. It is wonderfully balanced and punchy just as it is, and it’ll not be getting any additional EQ added. To remove the tone control I just eliminated the 10nF capacitor (C2) and the A100k potentiometer (VR2).
I reused an old enclosure I had laying around, which I shot with a coat of black nitro-cellulose and a very light top coat of gold (both left over from my Shaftesbury restoration). The gold coat is thin enough to allow just a hint of the black to show through.
The chemistry geeks amongst you may, by now, have worked out where the inspiration for the name and colour came from.
I have yet to print up and apply the decals for the pedal but there’s the standard 1/4″ input and output jacks round the back. The top has the valve, a true-bypass footswitch and the power toggle switch. On the front, left to right, are the gain, a dummy pot (filling up a surplus hole in the old enclosure) and the output volume.
When I was buying the parts for this I also got hold of a 12AT7 valve. This works well too. It is more subtle and has less gain, but in some ways is all the better for it; smoother, warmer and just a bit less wild.
You can listen to a quick demo of Goldie with the 12AU7, that I recorded for my friend Alfie Lanos, who was really helpful in helping me plan this one out.
It was recorded on my mobile phone so the sound quality is not the best, but gives you an idea of what the pedal does.
Dave Mac's Window on the World 
Just got the Goldie reference 🙂
Another cool project. I’ve never built anything with a valve. I really ought to try some more electronics some time. I know there are plenty of circuits on-line these days.
The valve looks a bit exposed. I assume you won’t be hitting the switch with your foot.
I can use my foot, but very carefully. This is definitely not a road-worthy pedal.
hello, can i sue no true bypass in this pedal. thanks
Yes, mine is wired up with a true-bypass 3PDT footswitch,
If you need any help working out the circuit diagram for implementing true bypass, just let me know and I’ll try and find my original hand-drawn circuit diagram.
Hi I’ve never built a pedal before, I have a bit or soldering knowledge, is this a decent choice for a first build? And do you have/use any step by step instructions. I really want to built one of these I think they are awesome!
Thanks. For a first build it might be a step too far, because there are no step-by-step instructions and you have to figure it out yourself to a certain extent. I’d personally suggest something like “The Persuader” from modkitsdiy for a first project of this type. Not only do you get decent instructions but they’re also there to support if things don’t work. You can find details of The Persuader at http://www.modkitsdiy.com/pedal/persuader. Hope this helps.
I’m really intrigued with this project. I’ve been wanting to build a Valvecaster for a while, but I have no need for a tone control.
I have a couple questions about the build:
1. You write that, to get rid of the tone control, you eliminated Pot VR2 and Cap C2. Did you actually mean “Cap C4” instead? According to the schematic, C4 is the 10nF cap coming off the tone pot.
2. With the tone circuit removed, does Cap C3 then get wired straight from pin 6 on the valve to tab 3 on the volume pot?
I don’t mean to be critical, I just want to clarify before I start building.
Also, I had read elsewhere that the Valvecaster is no good with humbuckers, but yours sounds great. Did you use a different value for cap C1?
Finally, I’d love to see the diagram for the True Bypass version. You can email me directly at uncleleon@uncleleon.com
You did a really impressive job on this. I hope mine turns out half as nice.
1. Yes you’re right. That should read cap C4
2. Yes.
No criticism taken at all! 🙂
No, I used the 47nF for C1. It sounded great with humbuckers (the clip above is actually a guitar with P90s). I think that removing the tone control really does brighten things up because you’ve removed one of the routes for treble to bleed to ground.
For the true bypass aspect of the schematic I grafted together the circuit at http://www.beavisaudio.com/techpages/PedalHacker/index.htm (just replace the send/return with the input/output to the Valvecaster).
Hope this helps.
Thanks for the response. I can’t wait to start building this version.
I’m looking forward to seeing how it goes. Mine is currently dismantled waiting for a rebuild/enhancement. I’m going to rebuild it with two valve sockets, so that I can switch between the 12AT7 and 12AU7. Have also been toying with the idea of adding the tone control back in but making it switchable (adding a SPST switch between C4 and the output jack sleeve).
This really looks great! I have one question: can I use 12ax7 in this scheme? I bought them for my amp but didn’t need. This could be used as preamp?
I don’t know for sure. I’ve only tried it with the 12AU7 and 12AT7. Of the two I prefer the 12AT7. If you google for “12ax7 valvecaster” you’ll find a youtube video of someone who has used a 12AX7. Sounds very low gain to me. There’s also a link to a pdf file that explains that it is not well suited. Depends on the sound you’re after though.
Can you provide voltage ratings for the Caps and wattages for the resistors used in the build? Thanks! Looking forward to building this one soon! Cheers
I used whatever I had lying around which, from memory, were 25v and 0.5w respectively.
Hey there, the link with the bypass is broken. I’m a newbie but, I’m followed the diagram and wired it right. Where I think I’ve gone wrong is putting in a light and on/off switch any help would be great. I have the light meeting with the positive side of the 9vol at 5th pin then -> the light -> on switch -> the output and then a have the negative starting at the input-> the light -> output.
I’d definitely suggest that first you try and get it working without a light. I’m finding it hard to visualise what you describe but it sounds like you’re putting the light in parallel with the valve, which means that the current has a path that allows it to “avoid” the valve altogether. I suspect you may need to wire the light into an independent part of the circuit. There’s a good article about bypass schematics (incl LEDs) at http://www.geofex.com/article_folders/bypass/bypass.htm
Hope that helps.
Hi dvd, I tried to build the MODKITS DIY tube pedal and that is a hard build. they have so much crammed inside a tiny box with strips and points that unless your really an expert and soldering and assembling fine electronics you can easily muck it up. as I did and upon first switch on I got a puff od grey smoke a noise that went “PFFFFFFHHHHHHHTTTT” then nothing.. this looks alot easier and something I’d lke to try. seeing as I have a box now and a tube socket and a suicidal eagerness to either electrocute myself for the dozenth time or get ultimate tube overdrive tone…haha
where would i find the parts list for the caps and resistors? the second diagram looks easy enought o build and have some space between wires.
gavin
Hi Gavin. The best thing to do would be to head over to http://www.beavisaudio.com/projects/ValveCaster/ and they have a full parts list. They also have a PCB-less layout. I originally built this but found it a bit “tight” so shifted the components to a simple veroboard layout.
There is also a HUGE discussion of this pedal over at http://www.diystompboxes.com/smfforum/index.php?topic=63479.0 which covers lots of mods, alternative tubes etc.
cool, like i said i have a housing and tube socket and some strips to solder stuff too. ill just use the parts i can salvage from that build but get new resistors etc. Ill have a long llok thru that thread tonight.
Hope your well dave
I’m really well Gavin thanks. Enjoying your tour tales on facebook. How were Dinosaur Jr? Loved that pic of the line of Marshalls.
Hi, this looks really interesting, I’m planning to build valve over drive for a bass. So do you think this will work with a bass? I mean if it doesn’t cut low frequencies so bass would still be a bass 😉 I’m no expert in this but if I’m right maybe change of some capacities and resistances would be sufficient.
Hi. I’ve not tried it but after a quick google found this demo of one being used with a bass. https://soundcloud.com/jimmy-rocket/wild-goose-demo-on-bass
Sounds good to me. Good luck and let me know how you get on.
Hi, so finnaly a was able to put it together and i realized that it doesn’t work and I don’t know why. There’s to much noise in signal, basically it’s more noise and little signal in background, interesting think is, when I close Tone on bass, noise disappears (same with different one). Another think is that signal is too weak, I tried with old Bassman and noise was according to the volume but signal wans’t.I can’t identify this problem. I’m using 12AX7 instead of AU (I had few of themat home 😉 ), I’m not sure if I used good types of capacitors, values are Ok, but it’s ceramic caps, and I made PCB according to this http://www.aronnelson.com/gallery/main.php/v/Renegadrian/Valvecaster+v0_5.jpg.html . So please, do you have any idea what’s the problem? thank you
Assuming you’ve checked everything else then I think it might be the 12AX7 that is causing the problem. The gain factor for the AX is much higher than the AU or AT. http://www.thetubestore.com/Gain-Factor
I found this piece which specifically mentions that the 12AX7 doesn’t work well with the valvecaster design. http://www.aronnelson.com/DIYFiles/up/12AU7-6111_Valve_Caster_Summary_Rev002.pdf
Hope this helps.
Ok, thanks, I’ll try AU and see if it helps, it would be really great if problem is just a tube. I hope so 😉
Fingers crossed! All the best.
Hi, Great build!
I’ve recently built this, having no electronics knowledge. Made this in the pcb-less format, and it sounds great! stuck with a 12au7. The only issue i have had is trying to cram it into a tiny enclosure.
Built it with no bypass or LED, but this is the next step. Any advise on fitting those?
Also, if i were to fit a 9v socket as opposed to battery fitment, would i need to do anything special?
Regards,
D
Thanks Darren. For adding the bypass and LED, most pedals use a very similar wiring approach. There’s a good picture of it at http://www.beavisaudio.com/techpages/StompboxWiring/
And yes, fitting a 9v socket is as simple as replacing the battery clip, or if you want the option of using both, it is covered by the above picture/schematic.
Hope that helps.
like your articles…quality stuff. thanks for sharing.
Thanks for the feedback. Much appreciated.
Hey, I am going to build this pedal but a really want it to be a distortion pedal. Should I switch out any components? Some gain/tone settings? Different tube? Thanks in advance.
If you really want a distortion then I don’t think this is the right project. The difference between overdrive and distortion is subjective but this circuit is much more of a “creamy” sound than a hard-edged distortion. If you do keep going then the 12AU7 would probably be a better tube than the 12AT7 (I haven’t tried anything else). There’s not much I’d change in terms of components but I found it to be much brighter by taking out the tone control circuit completely. With any project like this I’d suggest that you build it exactly as laid out on breadboard, get it working, and then experiment with settings and components.
Hi Sir. The website of Beavis studio is no longer active.
Then, please, coul you give me the values of the resistors and capacitors on the second schematic.
Thank you very much.
Gege from Belgium
Hi. You can find all the component values at https://cdn.instructables.com/FRO/3O11/IRSB1BUG/FRO3O11IRSB1BUG.MEDIUM.gif
Hi Sir,
I’ll try to build Valvecaster but I’m a bit confused because I found a difference in the diagrams above. According to the first one, pin 1 of b50k pot must be connected all together with pin 2(middle) to the ground and pin 3 should go to the valve pin 3, BUT on the second diagram (pcb-less) is different- pin 1 is not connected, pin 2 goes to the valve pin 3 and pin 3 is connected to ground. It’s the same with the tone control pot. Maybe I am wrong. Can you help me please?
Reblogged this on Scheidegger Studios.
Hi, that looks to be a cool pedal as it’s finally built up. I have already ordered the components and i can barely wait until they arrive. Anyway, here a question please: Is it possible to remove the tone control and replace it with some stationary resistor or cap to keep the tone constantly clean. Having the pedal so simple as possible with less knobs would be great. Thanks in advance, greetings…
That is a really interesting idea. It would be possible to replace with plain resistors. What I’d suggest would be to build it on breadboard the same as the schematic, tweak the settings until you’ve got the sound you want, then measure the resistance of the pots between left and centre pins and right and centre pins. That will tell you what value of resistors to use.
The alternative, which I’d recommend, would be to build it with trim potentiometers. They’ll live inside the enclosure and keep things simple, but still give you the option to open it up and adjust settings.
Thank you for your quick response and for your recommendation for a trimpot as well. The trimpot option would also be a smart option indeed.
My actual purpose is here having an optional tone control where i can switch between a clean boost (for bass guitar) and an overdrive control by using a 2 way toggle switch.
Please my another question here: as i take a look at the datasheet informations of 12AU7, the input voltage is given to be 300V and that makes me wonder about whether that 9V input voltage of this circuit will be efficient enough to heat up the tube in all. Is there a second part of the circuit with a higher value of input voltage which i am probably missing?
thanks again,
I’ll answer these in reverse order. You’re right about this tube generally needing 300v and with 9v there is barely enough to heat the tube but that is what allows it to be overdriven so easily. The lack of plate voltage removes every bit of headroom the tube has.
That said, I used a 14-15v laptop power supply from my parts box so you are not restricted to 9v.
This under-powered and easily overdriven nature though means that this is totally unsuitable for any sort of clean boost for anything, let alone a bass, so you might want to rethink that aspect.
could you please share some schematic of 3dpt switch knob to the circuit?
I don’t have one. You could try Googling.