s2
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Reply with quote | #1 |
The boost2 is an all-tube treble boost pedal in the family of the famous Dallas Rangemaster. The circuit is very similar, except it uses a 12AX7 instead of a transistor.
Here is a small gallery showing the pedal which resulted from this project: http://s2amps.phanfare.com/album/55883#imageID=2646042
It is useful for adding a tube gain stage in front of an amplifier to drive the amp's preamp and power tubes harder for more saturation and overdrive. It is also capable of overdriving itself if you set the bias control high.
Use this pedal to brighten up a dark amp or clear up a muddy humbucker. You can also tweak the schematic to make it full-range or nearly full-range by simply removing one cap and replacing another if you just want to build a versatile boost pedal.
Controls are Saturation, Bias, and Boost. Saturation is a pre gain control. Bias sets the bias of the 2nd cascaded triode, and Boost sets the output level.
The circuit is not true bypass. It is what I call Clinton (almost true) bypass. The footswitch switches the input directly to the output when not engaged, but you still have the effect of the 1M grid leak resistor pulling on the circuit. The effect is minimal, so I choose not to worry about it. You can experiment with simply removing that resistor, increasing its value, switching it out, or other schemes for true bypass, but be aware that pops and clicks in the switch are likely to result from charging and discharging of the coupling caps.
For power, I used a 12VAC 500mA wall wart (Mouser 412-212054) coupled with a small Hammond 12VAC - 230VAC 500 mA (Mouser 546-186B12) transformer to supply the high voltage.
I used the incoming 12VAC to supply the tube filaments (wired in series to pins 4 and 5) and also hooked it up to the 12VAC side of the Hammond PT to give me 230VAC on the secondary with just enough current to supply the tube's plates at about 230VDC after rectification with a full-wave bridge capsule. Finally, I used the incoming 12VAC with a 820R 1/4W current limiting resistor to feed the LED. I did not find that using a DC filament and LED supply is a worthwhile effort if lead dress is good.
There should be enough information in the attached drawings to build one of these. I hope to find the time to write detailed instructions and post them in PDF format, but for now...
Attached Images:
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nomad100
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s2
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Reply with quote | #3 |
Kind of. Preamp tubes sound different depending upon how they are biased. The bias control lets you go from very cold (~10.5K) to very warm (470R) and find your own sweet spot. If you set it warm and set the saturation high, you can also use this pedal as an overdrive.
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s2
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Reply with quote | #4 |
Also, if you want to make it a full-range boost effect, omit the input capacitor (the .0047uF), and change both coupling caps to .047uF.
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s2
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Reply with quote | #5 |
I have a limited number of leftover boards available for sale for $25 plus $6.25 shipping. These boards are stuffed with parts and the backsides are wired and soldered already.
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kydu0
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kydu0
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Reply with quote | #7 |
Hello..Sorry to sound like such a NOOB..but what is the grey circle on the left of the board labeled 1A 400 V? |
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s2
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Reply with quote | #8 |
Quote: Originally Posted by kydu0Hello..Sorry to sound like such a NOOB..but what is the grey circle on the left of the board labeled 1A 400 V?
That is a full wave bridge rectifier capsule.
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s2
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Reply with quote | #9 |
Quote: Originally Posted by kydu0Hello..Sorry to sound like such a NOOB..but what is the grey circle on the left of the board labeled 1A 400 V?
As a matter of fact, I do. Just PayPal to sales@s2amps.com to reserve yours!
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