Tube boost + overdrive running off a 9 volt battery

[Aren]

Tried a clean mod today - replace R2 with a 100k resistor and R3 with a 47K. It clean out nice, but not entirely. It works pretty nice on an acoustic guitar miced with an electret condenser microphone (battery powered), but the circuit itself is too noisy to get an actual usable result (hiss/buzz - maybe RF - that is very apparent when the signal is amplified enough to get a usable signal from the microphone, especially if I run an LA-light compressor after it). Any thoughts? Filter caps, maybe?

[Salvatore]

Just a thought - can anyone think of a 12V tube preamp (space charge tubes, maybe?) that will be clean enough to be used as a microphone preamp?

A low voltage mic pre would be godsend, but to get the amplification/sig to noise ratio right, I suppose you can´t get around space charge tubes.
Don´t know if it´s a good idea, but I found this overdrive schematic running from 9 volts AC (upped to 48 volts, so it might double as phantom power as well).
It uses a (very cheep, around 2 bucks) low voltage pcf802 tube, it might be transformed in a mic pre by putting 2 in series and tinker with it ?

http://www.tubepower.de/german/main_de.html
http://www.tubepower.de/pictures/projects/RTD-1-Live-schematic.jpg

[Chawk]

http://www.eurotubes.com/euro-e.htm
Some info on tubes from some SUPER awesome guys.
they only sell JJ tubes but matt is right, the EC802 is a 12au7 or ECC82 variant. But it should definitely work.

Any pics matt? maybe one of use with a working valvey can spot the issue? also, what are you using for power?

No pics yet... I finally got this thing up and running over the weekend (thanks to Adriano's vero layout). The tube I ended up using was a ECC82. I was attempting to make this for a combo pedal coupled with a Dist + but the two didn't seem to like working with each other to my ears. Combining the two lost a bit of what makes the Valvecaster so nice with the warm smooth overdrive. I seem to think that a good combo might be more along the fuzz side I'm gonna keep experimenting to see what sounds the best. Thanks for everyone's help in getting this running! I'll let you know what I come up with.

Matt

[Renegadrian]

No pics yet... I finally got this thing up and running over the weekend (thanks to Adriano's vero layout).
Matt

Happy it worked out right, I told ya!!! 

[juancra]

Hi!

I'm about to start building this awesome proyect, and want to ask a few questions to assure myself that i'm not going to waste any 12ax7 or other precious tubes in it . I readed the entire post about a hundred times and couldn't figure out what is the best voltage / tube config. I understad that when effect is used at 9v the 12au7 is the best choice, but what is the best when powering at 12v? Do I need to change any component value to drive it at that particular voltage?

I was also thinking about the possibility to add a "clipping module" to the stock configuration. Let's say I put on the pcb various tipes of clipping  diodes (leds, GE, Si and the like) and select them through a rotary switch. It would be possible? I though that I could add another small cheap tube configured as a clipping diode to make it a even more massive proyect. Could this be possible?

Thanks for anyone who could help me, I always have too much ideas but less knowledge to carry them on.
Sebastian

[Renegadrian]

Sebastian, I built 2 of them - they are intended to work at 9V or 12V, I prefer the second. Some hiss remains from DC and a voltage regulator is a good solution to make it deadly silent. As for the valves, 12AU7 is the main choice while 12AT7s work good too. 12AX7s just sound boomy...Not a good choice at all.
Whichever voltage you'll use, you don't have to make any change in the components, just the voltage regulator (7812 for 12V or 7809 for 9V)
You may want to change some components that change a bit its sound, but again it's your choice, may you need a cleaner box or a good overdriven sound. Tone control - I got rid of it, found it not so useful...Again, you decide...
As for the clipping module, haven't tried it yet, so you can be the pioneer and report your experiments here!!! 

[andrew_k]

juancra: I've also built a couple and much prefer 12v. I was getting a lot of hum using old RCA 12AU7s at 9v, but even with a brand new JJ valve it sounds better at 12. I'm not using a voltage regulator as I get no noise from my power supply.

re clipping diodes, I have tried symmetrical and asymmetrical configurations using various Si diodes, Ge diodes, red/green/yellow LEDs and mosfets. None of them resulted in a more musical/pleasing sound than the standard valvecaster. I also tried adding a JFET gain stage before the clipping diodes and/or a mosfet boost after and found that while it managed to bring the clipped signal up to the same volume as the non clipped signal, it was mushy and a little noisy (especially on the breadboard!). Another thing I tried was an EHX Muff Fuzz between the tube and the tone stack.

All of these experiments were interesting, some more usable than others, but all made "just another distortion" that to my ears was no better (and usually worse) than other distortion circuits that don't use a valve. All of the various experiments lost the mellow/warm drive that makes the valvecaster a fun circuit and either made it a mushy distortion or thin and crappy if smaller caps where used to reduce bass.

I don't want to discourage you from experimenting, just trying to pass on what I've already tried

[brett]

Hi

either made it a mushy distortion

you might find that it helps to lower the value of the grid-to-ground resistor.  220k to 470k are good values.  1M is probably too high.  Higher values "store" super-low frequency charge on the grid.
cheers

[juancra]

Andrew and Adrian!

Thanks a lot for your quick response! I thought about adding the diode clipping to make this proyect more " interesting"  to me 'cause it's the first serious proyect for my pedalboard and I wanted to have more "flavors" of it more than just a tone boost . With this new info I'm not sure if I will carry on with that mod, I think I'll just add a booster (don't know exactly which) before or after the effect and that will be all. About the hum issues Adrian found, I'll make a pcb that has the placements for the filtering portion. If it hums with my wall wart, i'll add what's necessary. Talking about tubes, I'm about to purchase a new Sovtek 12AU7, Is that a good tube brand?. How can I assure the tube is new?

[andrew_k]

you might find that it helps to lower the value of the grid-to-ground resistor.  220k to 470k are good values.  1M is probably too high. 

Thanks for the tip Brett I probably should have mentioned that I had already replaced that resistor with a 470k

juancra: There are sooo many bargain 12AU7s on eBay. No need to get new ones, the old ones are probably better. Just make sure they state in the auction that they've been tested and stick with a seller who sells a lot of tubes if you're uncertain.

[Renegadrian]

I totally second what Andrew wrote... I tried my Valvies with a SHO and with an AMZ Mosfet Booster, both before and after, and with my on board Stratoblaster. What they add to the sound is not that great for me, going from "uhm, okay" to "Hell, no!!!" 

Seb, about the hiss I wrote...I have non regulated wall warts, and that simple mod gave me a deadly silent circuit...just the 3 pin regulator and a electrolytic on the power jack...that's it!!! 

And as for the tubes, I went shopping on Evilbay  this past week, I got 8 Sylvania for $32 shipped to Rome IT, it's like 2.50 Euros each...nuff said...

Also, I'd suggest you to try some different brands, each one I tried has its own character...

[juancra]

After all this talking you guys convinced me to go for the easy money and just build the valvy "as is". I will only add the filter section.

Regarding tubes, Here in south america we don't have Ebay, we have MercadoLibre, who has a "non-agression pact" with Ebay, but it is also a jungle.. Every time im about to buy something I think i'm going to get a plastic empty box :S .. , but I think i will go for a Toshiba 12AU7 for 10$ and pray for everything to go OK

Once again, I must say you guys at Diystompboxes rules!

[Fender56]

I was wondering if it is necessary to let the preamp tube to warm-up before applying the plate voltage (even if it is around 12V) in order to extend their life? Or is it more a concern for power amp tubes, or tubes that run at "regular B+ voltages" (200V and +).

[frequencycentral]

Saw this t-shirt on eBay - made me laugh! And no, its not my auction - I'm in the UK

http://cgi.ebay.co.uk/Rare-12AU7-Twin-Triode-Tube-T-Shirt-True-Geeks-Only_W0QQitemZ150234662850QQihZ005QQcategoryZ48710QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

[ItZaLLgOOd]

I lost track after the first 8 pages but has anybody tried a tone stack instead of just a tone control?  If so what were the results?

[kurtlives]

I imagine it wouldnt be all that great....probbly less gain/output.

[Renegadrian]

In my little Valvy experiments, I removed the tone control...I just feel that the GREAT tone that comes out of the tube is well worth left unprocessed tonally speaking...

[frequencycentral]

I was thinking of trying one of these:

http://www.tube-town.net/diy/tt-sam/tt-sam-sch01.JPG

[frequencycentral]

..................specifically the tonestacks with the valvecaster (not the amp)!

[andrew_k]

I lost track after the first 8 pages but has anybody tried a tone stack instead of just a tone control?  If so what were the results?

I tried a big muff tone stack. Not impressed. For me, this circuit needs midrange punch, and gets even more from removing the tone control entirely.