Tube Amps / Music Electronics
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|6/22/1999 1:14 PM|
||Re: Dumble...Schematic Source?|
check your email bob!
|6/23/1999 0:17 AM|
I would very much appreciate being able to have this
schematic also, or steer me to where its found, please.
thankyou Ed R.
|6/23/1999 2:02 AM|
Here you go Ed.
It's a zip file over on Steve Ahola's site. Check it out sometime, he's got some nice schematics. The address to his web site is
|6/23/1999 2:49 AM|
I built one for a guy last month out of a boogie clone made by some guy named Decker. One "trick" I did ( is this allowed with a dumble?) is with the volume control. The clean channel breaks up so quick it really needs a master volume, but the preamp really doesn't break up. I stuck a MV on the inv side of the relay and noticed that at low MV settings the amp was clean even with the preamp volume dimed. That feedback loop reduces the gain and also the 2nd stage from clipping. But it seems that the different levels of feedback you get from the loading from the volume pot makes the taper feel strange. So we just took the preamp volume out of the circuit. The treble control wiper goes into the 220k series resistor and into the grid - no 1M to ground. So now it's an amp with a MV but no preamp volume!! Then we stuck in a verb circuit sort of like a fender...
|6/23/1999 3:59 AM|
Do you mean the *overdrive* channel breaks up quickly (hence needing the MV? - sorry I can't quote, I'm on a Lynx based terminal.) I rebuilt the Normal channel of my "designated testbed" (an old Super Six chassis blackfaced with the MV removed) and found the clean channel, with the volume dimed, stayed pretty clean compared to the Vibrato channel (stock BF Fender type). When dimed, the BF Fender side has this lovely harmonic "scream" to it (the attack of the note is fat and "in your face", then the decay distorts and sustains) while the Dumble side is brighter and thinner sounding, but very lush and big. It's a great tone to cop BB king stuff with.
|6/23/1999 1:51 PM|
Hey Dave - are you tying the 2 chs together with a resistive divider like the stock fender design? If so that would drop the level of the signal hitting the inverter by about 40% or so. That's a big part of this design. The dumble has a little less gain in the preamp then the BKF design, but it hits the inv with a much larger signal. So it's a cleaner preamp that can push the pwr amp section harder. That's why we went with the volume control before the inverter. It gave a smoother taper and transition from clean to distortion in the clean channel. We also went with a 5751 for the preamp. A 12AX7 for the O.D., and a 12AT7 for the inverter.
|6/23/1999 5:34 PM|
Nope, the Dumble side goes from the preamp coupling cap to the PI. I got rid of the 220k mix resistor and put a jumper in its place.
Whatever it's doing, I like the sound. I can crank the preamp volume and the amp stays really clean (like the BF side on "7") but with a huge low end. I think I'm going to get rid of the 220k resistor on the BF side and see what happens.
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