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DIY Tube Preamp question

#101
Add a master volume pot at the output maybe? Not sure exactly what your circuit looks like so I'm not sure what the value should be (not so low as to load the preamp output down too much but not so high as to make driving a lower impedance load problematic either). There may be a better place to put it (maybe before the last stage) depending...


Bass4lyf said:
Hey guys, its been a while since my last post. The preamp has been built and everything is working nicely. When my internet is faster I will post picks up of the build process.

Anyway, the gain from the output is way too high. I wired a bypass switch into the preamp and have been comparing. Ive noticed that when the preamp is plugged into my bass amp, I have no problems, works well. But when I plug the preamp into my recording interface, even though the interface is not clipping, it distorts alot so I have to use a second pedal to turn it down. What can I do to bring down the gain?
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#102
I do have a master control. I guess thats all I will need. I did actually make a mistake though, when plugged into my recording interface, I did compare the amount of gain from just my bass to the amount of gain of my bass through the preamp. Obviously the preamp is gonna be heaps louder because that is what its meant to do :eek: haha my bad.

Now Ive been thinking of ways to get a valve distortion overdrive out of the preamp. Ive noticed that when I turn off the bias voltage, (to go in standby mode I guess) the voltage slowly drops as it drains from the filter caps or whatever it does. Ive noticed that when I keep playing (guitar or bass plugged in), when the voltage drops to a certain voltage I get a nice distortion (not an insane amount). So I guess the tubes are getting 'starved'. The distortion only lasts for like 20 seconds because the voltage continues to drop down til it gets to 0v.

Heres my question, can I add a normal pot to the preamp that is connected to the bias voltage? That way when the pot is on full, I get all the bias voltage for a strong clean warm sound and then when I want a dirty overdrive or a soft distortion, I can back off that pot to lower the bias voltage and get the sound that I want? Will that work? Will it be practical? I guess its a bias trimpot, but on the outside so it can be adjusted at any time. I really like the sound it produces when the voltage drops and want to use it.
 

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