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After doing some maintenance on this Sunn Beta Bass Amplifier for one of CenterStaging’s Guitar Dept former managers, he wanted to know if I could build him a Foot Pedal box for it. I had the Service Manual for the product line, and while the image quality of the schematics was ‘fuzzy’ as to values and text, I had the essential material to cobble one together. Apparently the street price on an original is quite staggering.
When I had the chassis open before, during maintenance, I noticed what looked like an AMP panel mount connector for the Foot Pedal. I got the model number on the part off the inside flange of the connector, and found the appropriate TE Connectivity/AMP catalog containing that series, finally getting the correlating plug, strain relief and the insert contacts to make up a mating connector. But, as I expected, the cost of that connector was over $28 less tax/shpg. So, scraped that idea. When I had the AMP panel mount removed, I measured the chassis hole size, and it was right in range for changing over to a Switchcraft B3M connector (male XLR), which I had a full box of, Gold Pin variety.
So, I looked at the Hammond 1590 series die-cast aluminum boxes, selected a 1590DDFL BK Black box that measured roughly 8.5” x 4.7” x 1.45”. The drawing was wrong, in showing the removable panel was that containing the flange mtg holes. What arrived had the flange panel welded to the box.
I was planning on placing a Switchcraft D3F connector on it’s side on the end of the box, centered. Now there’s a flange in the way to contend with for tooling. The box wall thickness was just under 0.10”. And, with the need of a 15/16” hole to be cut/punched in a 1.3” high panel, that ruled out using a Greenlee chassis punch.
I have a Whittney XX Chassis Punch and full set of punches, though as material thickness increases, being able to punch thru thicker panels fades rapidly. I also have a really nice set of Machinist Hole Saws, which thread onto a variety of mandrils. I didn’t have a 15/16” saw, but did have a 7/8” dia saw. Mandril shank was 1/4”, so I’d have to punch a ¼” hole on the end of the box. I use calipers, adjustable machinist squares, scribe & automatic center punch in my layout work for this sort of thing, so it got me quickly to the center point to tool up the Whittney Punch. Wall thickness was close to the limit of being able to drive the punch thru the material, and took all the strength I had to punch thru. Then, mounted the box to the bench top, so I could drive the 7/8” hole saw thru the box using my hand drill. Then, opened the hole up to fit the connector using a ½” to 1” tapered reamer. With that connector fitting properly, I center-punched the two mtg holes for the #4-40 screws. Drilled and tapped those two holes, and mounted the connector.
I had ordered a pair of SPST push button switches, three panel mount LED assemblies that fit thru a 5/16” hole, and a 12-position Turret board to mount the components to work with the switches and LED’s. Board had swagged in #4-40 standoffs, so I just had to locate the two mtg holes thru the bottom plate to mate with that. More caliper work to land the mtg holes, then drilled & countersunk those mtg holes, and had the circuit board mounted close to one side of the box. Placed the two switches evenly centered along the panel, with their associated indicator LED’s spaced about their horizontal placement. Punched the two ¼” holes for the ½” hole saw to drill thru, and then loaded a 0.312” Whittney Punch set into the XX tool and punched the three LED panel mount holes. Mounted the switches and LED’s to see what it looked like. Looked reasonable for a foot to work the switches.
Drew up a quick diagram to place the components needed for the circuit. The only stumbling block I came upon was the max current rating of the GRN LED, being 25mA. The circuit indicated 33mA would be flowing when that GRN LED was lit. I wasn’t able to add any current limiting resistor on that LED, as it affected the circuit logic. But, adding additional GRN LED’s across the panel LED solved that. I looked at the effective brightness of all three panel LED’s, and decided to use two additional GRN LED’s across the panel mount LED, keeping the LED current to around 11mA.
So, wired up the board, first laying in the buss wire, with Teflon sleeving around various posts to complete the GND, ‘P’ and ‘S’ control lines. Then, installed the components, installed the circuit board into the box, and wired up the XLR connector. Added a solder lug to ground the box. Then wired up the two switches and three LED’s. Added spot ties to the two groups of wires (BOTH circuit, Ch Select circuit).
Plugged in a mic cable between the box and amp connector, plugged in a guitar cable to the Both Inputs jack, and powered it up. Everything worked as expected. Parts cost was about $85, and only charged $50 labor to build it, though it took way more hours than that to go thru the details, track down the parts, fabricate the box, wire it up, etc. I probably racked up 10 hrs or more from start to finish. I should have just changed to the XLR mic cable approach right off, having wasted a bunch of time finding a source for that $28+ mating connector Sunn selected!
When I had the chassis open before, during maintenance, I noticed what looked like an AMP panel mount connector for the Foot Pedal. I got the model number on the part off the inside flange of the connector, and found the appropriate TE Connectivity/AMP catalog containing that series, finally getting the correlating plug, strain relief and the insert contacts to make up a mating connector. But, as I expected, the cost of that connector was over $28 less tax/shpg. So, scraped that idea. When I had the AMP panel mount removed, I measured the chassis hole size, and it was right in range for changing over to a Switchcraft B3M connector (male XLR), which I had a full box of, Gold Pin variety.
So, I looked at the Hammond 1590 series die-cast aluminum boxes, selected a 1590DDFL BK Black box that measured roughly 8.5” x 4.7” x 1.45”. The drawing was wrong, in showing the removable panel was that containing the flange mtg holes. What arrived had the flange panel welded to the box.
I was planning on placing a Switchcraft D3F connector on it’s side on the end of the box, centered. Now there’s a flange in the way to contend with for tooling. The box wall thickness was just under 0.10”. And, with the need of a 15/16” hole to be cut/punched in a 1.3” high panel, that ruled out using a Greenlee chassis punch.
I have a Whittney XX Chassis Punch and full set of punches, though as material thickness increases, being able to punch thru thicker panels fades rapidly. I also have a really nice set of Machinist Hole Saws, which thread onto a variety of mandrils. I didn’t have a 15/16” saw, but did have a 7/8” dia saw. Mandril shank was 1/4”, so I’d have to punch a ¼” hole on the end of the box. I use calipers, adjustable machinist squares, scribe & automatic center punch in my layout work for this sort of thing, so it got me quickly to the center point to tool up the Whittney Punch. Wall thickness was close to the limit of being able to drive the punch thru the material, and took all the strength I had to punch thru. Then, mounted the box to the bench top, so I could drive the 7/8” hole saw thru the box using my hand drill. Then, opened the hole up to fit the connector using a ½” to 1” tapered reamer. With that connector fitting properly, I center-punched the two mtg holes for the #4-40 screws. Drilled and tapped those two holes, and mounted the connector.
I had ordered a pair of SPST push button switches, three panel mount LED assemblies that fit thru a 5/16” hole, and a 12-position Turret board to mount the components to work with the switches and LED’s. Board had swagged in #4-40 standoffs, so I just had to locate the two mtg holes thru the bottom plate to mate with that. More caliper work to land the mtg holes, then drilled & countersunk those mtg holes, and had the circuit board mounted close to one side of the box. Placed the two switches evenly centered along the panel, with their associated indicator LED’s spaced about their horizontal placement. Punched the two ¼” holes for the ½” hole saw to drill thru, and then loaded a 0.312” Whittney Punch set into the XX tool and punched the three LED panel mount holes. Mounted the switches and LED’s to see what it looked like. Looked reasonable for a foot to work the switches.
Drew up a quick diagram to place the components needed for the circuit. The only stumbling block I came upon was the max current rating of the GRN LED, being 25mA. The circuit indicated 33mA would be flowing when that GRN LED was lit. I wasn’t able to add any current limiting resistor on that LED, as it affected the circuit logic. But, adding additional GRN LED’s across the panel LED solved that. I looked at the effective brightness of all three panel LED’s, and decided to use two additional GRN LED’s across the panel mount LED, keeping the LED current to around 11mA.
So, wired up the board, first laying in the buss wire, with Teflon sleeving around various posts to complete the GND, ‘P’ and ‘S’ control lines. Then, installed the components, installed the circuit board into the box, and wired up the XLR connector. Added a solder lug to ground the box. Then wired up the two switches and three LED’s. Added spot ties to the two groups of wires (BOTH circuit, Ch Select circuit).
Plugged in a mic cable between the box and amp connector, plugged in a guitar cable to the Both Inputs jack, and powered it up. Everything worked as expected. Parts cost was about $85, and only charged $50 labor to build it, though it took way more hours than that to go thru the details, track down the parts, fabricate the box, wire it up, etc. I probably racked up 10 hrs or more from start to finish. I should have just changed to the XLR mic cable approach right off, having wasted a bunch of time finding a source for that $28+ mating connector Sunn selected!
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