PROCEDURE: MANLEY VOXBOX® modifications to increase gain from 50 to 60dB max. 7/1/2007

PURPOSE: This mod updates older Voxboxes to current version (MVBX###) for more gain: 40, 45, 50, 55, 60dB

SERIAL NUMBERS:  Units this procedure pertains to are MVB000 - MVB737

ABILITY REQUIRED: It is presumed you can solder, work on gear, read resistor color code values, and read schematics.

PARTS REQUIRED:

a)     1 x 56K 2 watt Metal Oxide resistor

b)     1 x 220K 2 watt Metal Oxide resistor

c)     1 x 28K 1/4 watt or 1/2 watt Metal Film resistor

d)     1 x 75K 1/4 watt or 1/2 watt Metal Film resistor

e)     1 x 140K 1/4 watt or 1/2 watt Metal Film resistor

f)     1 x 324K 1/4 watt or 1/2 watt Metal Film resistor

g)     1 x 5.11K 1/4 watt or 1/2 watt Metal Film resistor

h)     1 x 12AX7 VACUUM TUBE tested for lowest noise

i)     1 x 14" Mogami shielded wire terminated with two inner (+) cores soldered together on both ends, shield drain wire addressable on one end, cut off and insulated off on the other end.

j)     1" piece of shrink tubing

k)      some nice 2% silver solder

l)     1 x replacement engraved micpre insert panel showing 40-45-50-60 dB gain markings

m)      Instructions and drawings for procedure

TOOLS REQUIRED:

a)      #1 OR #2 PHILLIPS SCREWDRIVER to remove top and bottom covers

b)   ELECTRONICS SMALL WIRE CUTTERS

c)   ELECTRONICS SMALL PLIERS FOR LEAD FORMING

d)   ELECTRONICS DESOLDERING TOOL

e)   SOLDERING IRON W/ 1/8" or 1/16" CHISEL TIP (700*) AND SOLDER

f)   HEAT SOURCE FOR SHRINK TUBING

g)  7/64" HEX KEY (ALLEN KEY)

h)  1/16" HEX KEY (ALLEN KEY)

i)  15MM WRENCH, NUT DRIVER, OR ADJUSTABLE SPANNER

INSTRUCTIONS FOR UPDATING MANLEY VOXBOX TO 60DB GAIN

Note: "Right" and "left" and "front" and "back" directions are valid if we presume you are looking at the unit from the top, facing the front panel. (Front panel towards you).

1.  Replace the 22K resistor going to pin 1 (anode) of the 6072 tube with the 56K 2 watt Metal Oxide resistor (a).

2.  Replace the 100K resistor going to pin 6 (other anode) of the 6072 with the 220K 2 watt Metal Oxide resistor (b).

3.  Directly behind the gain select switch are the 5 gain select resistors. Leave the 10K in place. Just to the left of the 10K is a 17K, change the 17K to 28K, change the 28K to 75K; change the 47K to 140K; and change the 75K to 324K. Thus your five resistors that set the gain will read left to right: 324K, 140K, 75K, 28K, and 10K.

4.  Locate the OPA2604 IC (opamp) behind and to the left of the gain select switch. Change the 100K resistor that is connected between pin 6 and 7 to 5.11K(g).

5.  Locate the small 0.1uf 63v ceramic capacitor connected to pin 5 of the OPA2604 IC through a 10K resistor. It's a little bypass cap and will be either blue or tan in color. Desolder and lift out the right leg of the capacitor which goes to the opto (point “A” on the schematic).

6.  Slide the piece of shrink tubing over the 14" Mogami wire (i) so that you can insulate the connection you are about to make. Solder the signal wire (+) of the shielded cable supplied with this kit to the lifted lead of the 0.1uf capacitor. You will use the end of the Mogami cable that has only the (+) joined hot leads coming out of it. Slide the shrink tubing back over your joint and shrink it so it won't short out to anything.

7.  Find the two 30K 1/2 watt resistors located on the upper level I/O PC board between the “Preamp out” and the “Insert in” Jacks. Route the Mogami cable around the left side of the unit to go to these two 30K resistors. Attach the other signal end (+) of the shielded cable to the back leg of the 30K resistor on the left.

8.   Attach the shield wire (-) of the cable to the back leg of the 30K resistor on the right. Or attach the shield wire to pin 1 of either of the adjacent XLR connectors. You are grounding the shield of the wire by doing this.

9.   Replace the 6072 tube with a 12AX7.

10. Using your fingers, unscrew the switch end cap of the Phantom Power switch and put it aside.

11. Use your 15mm wrench (i) to remove the nut that holds the 1/4" Direct Input jack to the front panel.

12. Use your 1/16" Hex Key (h) to loosen both grub screws on each knob and remove both knobs on the micpre section.

13. Use your  7/64" hex key (g) to remove the 3pcs stainless steel 4-40 screws that secure the black engraved insert to the mother faceplate. Gently pry out the old insert and install the new one, then put back the knobs and phantom switch end cap as easily as you removed them.

14. Re-calibrate the compressor section referring to steps 3 through 5 of the calibration procedure in the owner’s manual.

For further info or to order this kit, please contact our service department.
If you would like to send your unit in and have Paul do this for you, please contact him at the address below:

Location of this page online: 

http://www.manleylabs.com/techpage/voxboxgain.html