TubeWorks Pure Tube TW303 SMOOTH

[soulsonic]

Hi all, I recently had one of these rarely-seen TubeWorks TW303 pedals in for repair. I tried looking around for a schematic and found nothing, so I have traced it out to share with the rest of the community.
Here is the article I wrote about it on my DIY page:
http://solgrind.wordpress.com/2008/03/13/tubeworks-pure-tube-tw303-smooth/

It is interesting to note that it uses the same PCB as the RT-901 Real Tube and RT-903 Blue Tube pedals, so we now have the basic topology for the 5-knob Tube Drivers of this era. I have never seen the schematics for these anywhere (except for sale!), so hopefully, fellow DIYers might be able to find some good tricks in this circuit for reference or experimental use.
The FET switching bypass circuit has become a no-no in the DIY and boutique world, but it really doesn't sound bad in this pedal at all!
Overall, I'd say it has a really nice overdrive tone. Though it may be totally cliché to use the word "warm" to describe a tube circuit, that really is the most appropriate term in this case - very warm!

[mojotron]

Thanks - I really love their RT2100 series amps - I still use a few on a daily basis after sell all of my other ones. The circuit looks like the preamp of those amps - interesting.

I also have liked the 911/TubeDriver from TubeWorks. 

[Mick Bailey]

Interesting to compare the tube section to the Shaka Tube - anyone know if the shared cathode resistor/cap makes any difference, as opposed to the separate items in the Shaka?

[soulsonic]

Interesting to compare the tube section to the Shaka Tube - anyone know if the shared cathode resistor/cap makes any difference, as opposed to the separate items in the Shaka?

It will definitely make a difference. Using separate resistors for each cathode allows you to individually tailor the biasing of each stage independently. In the case of this circuit, they chose not to, but in some cases you may want/need to, depending on what you want to happen in the circuit. Some Tube Drivers have a trim pot for adjusting the overall bias of the tube stage to optimize the sound for the given requirements.

[Mick Bailey]

I was thinking more of a direct comparison with the shaka - identical values for both sections (shaka) v shared values (tubeworks). Also interesting is that the cathode bypass cap connects to ground, rather than -12v B. Can you tell me what the reasoning behind this would be, as opposed to connecting the cap right across the resistor?

[DavidRavenMoon]

Cool.  I have a Blue Tube I bought new.  I've been wanting to add an output buffer to it... now I have something to look at as far as a circuit.

[DougH]

Looks like the BK Butler tube driver is the basic template for all this stuff. I've seen other TW schems too and it appears they are all variations on pretty much the same theme, with slight tweaks to the tone stack and etc.