"More" dumb tube stuff

vigilante398

Authorized Vendor
I used to build a tube compressor, and I had a couple people mention they liked to keep the compression level really low and just use the pedal as an always-on tone sweetener, so I made a board for just the tube preamp section without the compression bits, and it sounds pretty damn good. Uses a 12AU7 and a 12AT7, runs around 240V internally.

IMG_20220612_232836.jpg IMG_20220612_232949.jpg
 
I used to build a tube compressor, and I had a couple people mention they liked to keep the compression level really low and just use the pedal as an always-on tone sweetener, so I made a board for just the tube preamp section without the compression bits, and it sounds pretty damn good. Uses a 12AU7 and a 12AT7, runs around 240V internally.

View attachment 27387View attachment 27386
Very cool. How would you describe the difference between the More and the Space Heater?
 
Very cool. How would you describe the difference between the More and the Space Heater?
Space Heater has more grit to it and can get into a mild overdrive, More is completely clean. It will not break up at all unless you're pushing it with something in front. Space Heater uses both 12AX7 stages as gain stages cascaded into each other. There's only one gain stage in More, and it's a pair of 12AU7 stages in parallel. So low gain, but nice fat sound. The 12AT7 is also using the two stages in parallel, but as a cathode follower output buffer.

Yeah, and it looks sparse. Ridiculously sweet.
@vigilante398 , looks like a full-wave rectifier on the power input. I know you've mentioned that before, mind explaining or showing how that works? I know you power the heaters directly from the power supply at 12 or 9 volts.
Yup, I put a bridge rectifier on the power input of all of my pedals for polarity protection. That way not only will the wrong polarity not cause any damage, there is in fact no "wrong" polarity and you can use center positive or center negative, or frankly even AC if you felt so inclined. There is of course a voltage drop, but I use schottky diodes with a low forward voltage so the voltage drop is negligible.

This is the best diagram I could find and I don't feel like drawing my own. You can see that even if you switched the + and - supply, the orientation of the diodes only allows current to flow in the direction I want it to.

Reverse-Polarity-Protection-Using-Bridge-Rectifier.png

I do power the tube heaters directly off the input, and in testing I've found that 7.5V is right around the bare minimum to get the tube to heat up enough to pass signal, and the voltage drop through the diode bridge is only 100mV or so, and 8.9V is plenty to get the tubes heated up.
 
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