Paul Sutherland
From:
Placerville, California
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Posted 26 Feb 2015 4:06 am |
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Is it possible to put a line-out on a vintage Twin Reverb, but only on the vibrato channel? I would want the line-out signal to be post-eq and include the reverb, of course. I specifically do not want to touch the normal channel. Don't ask why. It's complicated.
Anyone have experience with line-outs added to an old Twin? Did it work well, sound good? Or did you regret doing the mod?
PS: I would not be doing the actual work. I would have a competent tech do it.
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It don't mean a thing if it ain't got that swing. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 26 Feb 2015 6:30 am
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Yes indeed. It's quite easily done actually. There's a whole cult of Jerry Garcia guitar fans out there that have been doing this for a long time. Garcia's rig was a Twin Reverb preamp (reverb included) direct out the back to a McIntosh power amp into JBL's.
Typically we remove the Twin's tremolo on/off RCA jack since most people don't use it. Then you have a hole available for a new 1/4" jack. Use a TRS (tip ring sleeve) type. I'll have to dig up a schematic, but there's a place where both the normal and reverb (aka "vibrato") channels meet via a pair of 220k resistors. It's pretty easy to find on the layout or schematic. Then take the input side the one 220k resistor associated with the Reverb channel preamp, and connect it to the TIP of the new output jack. Then where the two 220k resistors meet, we tie that to the RING of the jack.
So what happens is that when you plug in a normal guitar cord to this new preamp-output jack on back, you get the reverb channel's signal, and the sleeve of the guitar-cord-plug touches both the RING and the GND of the jack and that grounds out the signal before the power amp thus muting the Twin's power amp. Then what you have there is a preamp and a silent Twin. The output is pretty hot too.
If you want the Twin still audible along with the preamp signal on back, then you simply don't connect the RING to the 220k resistor node as described.
Brad |
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