Tube boost + overdrive running off a 9 volt battery

[Renegadrian]

Nice job! 

[Yeahno]

Okay...I've figured out what my next build will be: A Twin ValveMaster (TwinMaster? DualMaster?).

Here's the original circuit:


Would like some help straightening out my plan on it though...

If my thinking is correct, I should be able to simple double up the Vero layout, passing the output of the C3 1uF cap to pin to a 47nF cap on pin 2 of the second tube and into the second copy of the circuit.

The Gain control doubles up in the same location. The Tone control moves to the output of C3 in the second circuit (C7, I suppose) and the Volume pot moves as well.

Questions:

1. Are the assumptions above correct? If not, what changes will I need to make.

2. I'm assuming that keeping the Gain controls is the right thing to do, as opposed to keeping the Volume control on the first tube, right?

3. In the fantasy dreamworld in which I live, I want to add a second footswitch to it, but I'm not clear how to wire it. Looked at the TwinCaster schematics, but they're single footswitch too. Each footswitch would kick in the gain from each tube, the idea being that with the first tube in, I get the creamy, light breakup, with the second, I get a more overdriven sound. Can anyone point me to a schematic that does this?

4. Any point introducing a little bias pot for each tube? If so, where would I do that and roughly what value would I use? I've read that the 12AU7 is self-biasing, so maybe this is moot.

An interesting thing I've noticed: I bought some new 12AU7 for this and swapped them into the ValveMaster and noticed how much quieter they are than the older tube. I guess tubes get louder over time, or maybe there's a burn-in period where the tube becomes more efficient?

Thanks!

[zambo]

yes is the answer to your questions. With a good power supply you can do a lot of different things with this design and its pretty safe. That being said, make sure you have a good cap on the input and output of whatever circuit you come up with. Also, when you double up the tubes you get a bit more output and its to much for some amps. I dont know it will hurt them but I think its safe to assume that overdriving the input of an amp can mess things up if its too much. for switching just make it a true bypass system because its easy. the first switch is on or bypass. When its on, feed the signal to another valvy that is on or bypass. the out put retuns to the first switch. You end up with on/off and a more/less set of switches. I have a schematic here somewhere but dont know where. here is kind of a crappy idea of what im talking about  http://i1108.photobucket.com/albums/h408/7Ambo707/schematic001.jpg

[zambo]

I made mine with 3 tubes. If you want distortion 3 tubes is about the minimum in my opinion. If you just want slight overdrive and more than slight overdrive, two is good. Your caps will probably need to be smaller to compensate for the added bass and teble fizziness can be controlled with the tone knobs. 500pf and .001uf caps across the plate resistors work well too for controlling fizz. .002 is nice on the input caps. Hope that helps 

[Yeahno]

yes is the answer to your questions. With a good power supply you can do a lot of different things with this design and its pretty safe. That being said, make sure you have a good cap on the input and output of whatever circuit you come up with. Also, when you double up the tubes you get a bit more output and its to much for some amps. I dont know it will hurt them but I think its safe to assume that overdriving the input of an amp can mess things up if its too much.

Gotcha. I don't think I'm in danger of this, but I'll keep an eye open for it.

for switching just make it a true bypass system because its easy. the first switch is on or bypass. When its on, feed the signal to another valvy that is on or bypass. the out put retuns to the first switch. You end up with on/off and a more/less set of switches. I have a schematic here somewhere but dont know where. here is kind of a crappy idea of what im talking about  http://i1108.photobucket.com/albums/h408/7Ambo707/schematic001.jpg

HAH! I was looking at your sketch earlier. I think it's absolutely what I'm looking for. Any chance you could draw it more clearly? I can't reliably see which traces go where and I don't understand the nomenclature of where the pin outs go on VC1 to VC3.

[Yeahno]

I made mine with 3 tubes. If you want distortion 3 tubes is about the minimum in my opinion. If you just want slight overdrive and more than slight overdrive, two is good. Your caps will probably need to be smaller to compensate for the added bass and teble fizziness can be controlled with the tone knobs. 500pf and .001uf caps across the plate resistors work well too for controlling fizz. .002 is nice on the input caps. Hope that helps 

Have a look at this. It's not verified, but I think it's accurate. The parts values follow the original ValveMaster, not my mod to it.



Parts List

[Renegadrian]

it looks correct at a first glance - thanks for citing me in the layout! 

[juansolo]

This is very similar to something we did ages ago. I think it's lurking deep in the resesses of this thread but it bears posting again.

Though we run the plates using a charge pump to get a bit more headroom (worth doing).

This is the one we used when we ran them from a 12v supply with pump:



Then we have the ones that run from a 9v supply:



Here's the charge pump we use at the moment which is nice and compact and nigh on 60v for the plates. It's Renegadrians vero with a regulator strapped to it to run the heaters at 6v. The other one has a buffer on as we had some issues once running one valve pedal into another. We just tend to stick a buffer on the output of whichever one we do now.



Pretty sure this is the schematic the vero is based on:



Another one we did, which has a very different flavour and is every bit as good was the ultra simple BBT. Same power and buffer things apply:



We miniturised this also with submini:



Then squished it onto a vero, tube is mounted on the back of the board for packaging:



Finally the last one we did was the BTT, this one's a little more involved:



These are all verified, pics of them over on my site: http://juansolo.demon.co.uk/stompage/toob.html

[Renegadrian]

juan thx for all the images! guess they can be pretty helpful to someone! 

[Yeahno]

My brain hurts.

I've been trying to work out zambo's switching, putting into terms that I can understand, but I'm stumped.



As you can see, I have no clue what to do about the top left of S2. I'm not even sure that the pins are correct as labelled.

Help?

Also, I think that I made a mistake in the TwinMaster. I've got a jumper from the output of Stage 1 to the input of Stage 2, which effectively means that Stage 1 and 2 will always be running, no? So I think I have to remove the jumper and land the output of Stage 1 on S2, which then kicks in and routes it either to the output (Stage 1 only) or to Stage 2, then to output.

Help. Help, help, help.

[zambo]

Hey , sorry i wasnt on yesterday!! I guess I missed this! Ok just aproach it logicly.you have to decide what order you want the boosting to go in. I like to have a vlave caster on and then boost it with another one before it. You want a switch that goes On/Bypass, and another switch for More/Less dirt right? Ok so S1 has the input from your guitar and goes out to S2 which is wired up for valvecater/or bypass. S2 goes out to the other valve caster input ( less dirt) then  the return pin of S1 and then the signal goes to output. Does that make sense? So S1 sends your signal straight through ( true bypass) or to S2. S2 sends the signal to a vlavecaster ( the dirty boost ) which then cascades into the other valvecaster ( slight boost) or straight through to a single valve caster which has its output to the return of S1 and then to output. Its a loop with another loop inside. I will draw it out again 

[zambo]

heres a better pic. Ignore the led's for now they are the easy part anyway http://i1108.photobucket.com/albums/h408/7Ambo707/twincasterswitching002.jpg 

[Yeahno]

It's starting to look like I'm serious about this TwinMaster thing. Got all the fittings in. No board or wiring yet, but it's an incentive to sort the switch wiring and board out.



I think the pots, left to right, will be Vol, Tone, Gain, More (Gain 2).

Left switch is In/Bypass. Right switch is More (second gainstage), complete with obligatory, over-the-top white LED, all in a 1590BB box.

zambo: I think I get this drawing.

S2, when out, passes In from S1, across the jumper and into the input from gainstage 2. Gainstage 2's output then lands back on S1 and out to Volume(?)

S2, when in, diverts In to gainstage 1. The output of gainstage 1 is then passed to the input of gainstage 2, which then lands back on S1 and out to Volume(?).

Cool. I think I get this. You're not adding a second gainstage after the first stage, you're adding a gainstage before it, causing it to presumably overdrive the one that's engaged.

Thanks for the help!

[Yeahno]

zambo,

Here's the complete switching, as I understand it.



Am I getting it?

[zambo]

Looks good to me. Yep you are switching in a stage to overdrive the stage that was on. If you reverse the order it just gets super loud and acts like a volume boost. also nice but not what most people are looking for. If this doesnt give you enough distortion then you can add a solid state boost ( like a fet boost or whatever you like) in front of the boost stage and it should drive it enough to make anyone happy. I did it on a pedal recently and it was pretty mean. I used an SHO type of design only with the irf510 mosfet ( cause you can get it at radioshack) but i am sure there are better ones for this purpose. 

[Yeahno]

Looks good to me. Yep you are switching in a stage to overdrive the stage that was on. If you reverse the order it just gets super loud and acts like a volume boost. also nice but not what most people are looking for. If this doesnt give you enough distortion then you can add a solid state boost ( like a fet boost or whatever you like) in front of the boost stage and it should drive it enough to make anyone happy. I did it on a pedal recently and it was pretty mean. I used an SHO type of design only with the irf510 mosfet ( cause you can get it at radioshack) but i am sure there are better ones for this purpose. 

Yeah, you're right, that's exactly what I'd accidentally done. Overdriving the stage that's already on is what I'm after.

There's a GGG Ross compressor clone before it that is capable of making the signal hotter and puts the existing ValveMaster into OD sooner, so I'll start there and see what happens. Or maybe, I should be putting the tube first and letting it compress naturally, then feeding that to the Ross.

[zambo]

i would go guitar>compressor>tubes>amp, but thats just me. Overdriving the compressor with tubes would be kind of defeat the point. Its an opinion 

[kupfer_m]

Here's my take on the Valvecaster:

Slightly modified schematic with 7pin tubes. 6C4(=1/2 12AU7) and 6AB4(=1/2 12AT7) can be used.
The valves run on 20V, the heaters in series on 12V.

[Yeahno]

Nice job. That's a great looking build. I've got all kinds of questions.

1. How did you do the plate? Etched?

2. How did you mod the schematic?

3. What's the switch do? Input cap switching?

4. How did you form the protection rail behind the tubes?

5. I've tried switching the 12AT7 for 12AU7 and in every single schematic, I get significantly lower output. I'm running everything at 12V. Is 20V the magic?

6. What's the paint?

[kupfer_m]

Hi

1. How did you do the plate? Etched?

Yes, etched with ferric chloride.

2. How did you mod the schematic?

Here's my schematic :

3. What's the switch do? Input cap switching?

Yes (see schematic)

4. How did you form the protection rail behind the tubes?

It's from an old RF-test set.

5. I've tried switching the 12AT7 for 12AU7 and in every single schematic, I get significantly lower output. I'm running everything at 12V. Is 20V the magic?

I found 20V a lot nicer than 12V but I can't remember having lower output with the 12AT7 type. Will do some tests tonight.

6. What's the paint?

It is a prepainted box I bought some years ago (at tubetown.de I think) and I finally used it!

Regards,
Jim