Adding reverb to the Normal channel on a DRRI?

[Denny]

Does anyone know how to do this mod?

Denny

[danieldroukas]

There are a couple methods I know of, one presented by Kevin O'Connor and the other by Gerald Weber. I've only ever used O'Connor's and it's worked fine for me in my Twin Reverb and should work the same for your Deluxe.

O'Connor's Method: If you view the schematic, you can run a jumper cable from the anode of V1b (normal channel, the gain stage after the tone stack) to the anode of V2b (vibrato channel, gain stage after its tone stack). You then remove the normal channel's path to the mixing resistor (for you, this would be done by cutting the connection between C5 and R12). O'Connor calls this method "Equal Weighting of Fender Preamp Channels" and is detailed in Fig. 50-40 of TUT1.

Weber's Method: Actually, it seems that I've lost this reference. I know he detailed it in an issue of Vintage Guitar only a few issues back. Could someone fill us in on this one?

EDIT: grammatical error.

[danieldroukas]

Found Weber's Method...

Weber's Method (From July 2006 issue of Vintage Guitar, pg. 112):

"There are a couple methods to do it; my favorite method also adds vibrato to the normal channel. To do it, you will need : a 500pF capacitor (200-volt or better); a 1-meg resistor (1/2 watt); a 3.3-meg resistor (1/2 watt); hookup wire; a soldering pencil and solder.

"Remove the chassis from the cabinet and locate the reverb-driver tube (in most Fenders, it's the third preamp tube from the end); it'll be a 12AT7, and the reverb-driver transformer will be connected to it. If you look at the socket, you'll notice that pins 1 and 6 are tied together, pins 2 and 7 are tied together, and pins 3 and 8 are tied together. You'll want to seperate pins 2 and 7 (these are the grids). After the two are seperated, you'll notice one of these pins will have wire going to the board. On the pin that does not have anything going to it, connect one end of the 1-meg resistor, one end of the 500pF cap, and one end of the hookup wire. Solder all three to the pin. Now take the other end of the 1-meg resistor and solder it to ground. At this point, the 500-pF cap will have one end soldered, and the other end sticking in the air.

"The first preamp tube's pin 6 goes to a coupling cap (usually 0.047uF) on the board. Notice a wire comes out of the board near the other end of the cap. This wire goes from there to one of the 220K resistors that feed the phase inverter input. (If you don't know where the phase inverter input is, it's the other end of the capacitor that connects to pin 2 of the preamp tube next to the output tubes.) You're going to disconnect that wire from the 220K resistor and move it to the loose end of the 500-pF cap. You may need to shorten this wire to keep everything neat. Don't solder this yet, as you'll later need to add another wire to this connection.

"Next, take the 3.3-meg resistor and put it across the 10-pF cap. These will be connected to each other in parallel. Locate pin 7 of the fourth preamp tube, which will already have a wire attached to it -- leave it there, but add one end of the resistor/cap subassembly leaving zero lead length so the other end of the resisor/cap subassembly stands up in the air. Solder this connection.

"Finally, connect a piece of hookup wire to the loose end of the resistor/cap subassembly. The other end of this wire goes to the same 500-pF cap that was installed earlier near the reverb driver tube. The airborne end of the 500-pF cap is the correct end to connect and solder the wire to. So basically, you'll end up with two wires soldered to the 500-pF cap.

"This will give you a little bit more gain in the normal channel, about the same amount as the reverb channel. If you want to lose some gain, you can solder a wire from ground to the loose end of the 220K resistor that you removed a wire from earlier. This will clean it up. If there is excessive nosie, you may need to replace all the new hookup wire with shielded wire. When using shielded wire, make sure and ground the shielding, but only at one end. The other end of the wire should be clean (and maybe shrink-tubed) to insulate the shielding."


Whew.... typed this without looking at the screen much. Grammatical errors may have found their way in. If something seems counterintuitive let me know and I'll make sure I typed it correctly.