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Old 3rd October 2009, 03:34 PM   #1
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Default Tube overdrive for guitar/bass

Hey guys,

I'm looking to build a quick tube overdrive/distortion for instruments (primarily bass guitar). I've looked around on the internet and these forums and haven't been able to to find anything as far as a proper schematic goes. I will use a 12AX7 tube for it. I need a schematic and the specs for a transformer and I'll go from there. What sort of B+ would get what I want? The only control I plan to give it is a gain control, going from very little overdrive, to completely nuts. Any input is greatly appreciated.

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Old 3rd October 2009, 04:50 PM   #2
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Maybe you'll find something here:
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Old 3rd October 2009, 05:04 PM   #3
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I'm afraid there are a few contradictions here ;-) ; finding the really right circuit that works for your tastes might take a while of trying, changing etc.

Don't necessarily say it needs to be tubed either, after having used a (starved tube) pedal for years, I'm now again back to a fairly simple but modified tubescreamer-based circuit. Or maybe you've already 'done the work' & know you'll be liking tube-based the best.
If you want distortion from tubes you need to decide if you want to go the 'cheap'/easier starved-plate route (lower B+) or the 'real' one with higher (normal) tube voltages.

Suggesting at least a second control: level. Some EQ will suit as well imho. A tried & tested (but not necessarily the best solving your needs) is the Real Tube pedal, that circuit should be around the interweb.


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Old 3rd October 2009, 08:00 PM   #4
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Originally Posted by clintrubber View Post

I'm afraid there are a few contradictions here ;-) ; finding the really right If you want distortion from tubes you need to decide if you want to go the 'cheap'/easier starved-plate route (lower B+) or the 'real' one with higher (normal) tube voltages.


We all have different tastes. A trip down to the music store to compare often against $$$.. I prefer a variable B+ only on a P-P stage, and fixed bias neg compensated to draw a reasonable stage current. A double pot and some control circuitry can do this. Power is good with a fairly hardish raucous sound. Can be tricky,the global nfb loop can cause strange sounds, so I drop this around 6-10dB.
There are other methods; hard clipping the grids of finals with diodes as if class B is used; this again with dropped B+. This sounds more solid state..again different amps create different sounds..Ones own choice and other guitar users have other ideas.

All these involve experience of live circuit fudging and the expected sound, not recommended for those new to high voltages in tube amps.
By doing this when playing trumpet, one gets a richer mute sound. I prefer the proper method of a mute corked in the horn of the instrument.

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Old 4th October 2009, 10:03 AM   #5
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For bass guitar think of compressor, instead of distortions.
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