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Marshall Divo 2
On this page you can see the build of the Divo read-out display/tool.
Above you see the schematic of the device.The use of two power supply's is because if you put all the meters on 1 supply,in half power mode of the Divo,you get strange readings on the meters that aren't used then.The Dc/Dc converters makes that the meters are independent powered from each other,the power supply has to be a higher voltage as the meters are,because the converters like a little more power.I used Led meters,because I like them more than Lcd,but you can use both for the device.For the connecion with the amp I used a sub-d cable wich I had lying around.
Left : the box was already painted,so I only had to cut out the holes for the meters and connectors.Right : a little art-work to dress up the device.
Left : the meters mounted in the box.Right : the meters pre-wired before assembly.
Left : I made a little rubber shield,to make shure the meters don't make a short on the box.Right : to get things organized,I made a little pcb to mount the parts on.The diodes and resistor of 10 Kohm are for protecting the meter against over-voltage.
Wiring the sub-d connectors,make shure to record the position of the wire.
Left :Calibrating the device with a power supply and a dmm,the multimeter is set on 200 mA,and put in series with the power supply and a resistor of 1 ohm 1 watt.,the voltage/ampere is set to 40.0 mA.Right: here you see the sub-d connector connected to each side of the resistor,and then the meters can be calibrated by turning the little potmeter on the back of them.
Left ; I made a plug on which all meter inputs are connected to each other,this is only for calibration use of the meters.Right : all the parts are mounted in the box,and the box is ready for calibration.
Left: installing the 1 ohm,1 watt,1 % metal film resistor in the Divo's wires,it sits in the wire coming from pin 8 of the tube-socket ( Kathode) and is coloured white.At the interceptor side goes the posive wire from the meter,on the other side of the resistor goes the negative wire of the meter.Right: when ready,isolated with shrink tube.
Left ; the sub-d connector on the backside of the amp,it is fixed on the box of the amp,so the gitter can be removed,and the connector stays in place.Right : testing the device on the amp,tube 1+4 are EL34's biassed with 37 mv,tubes 2+3 are 6550's biassed at 45 mv.
Left; tubes 1+4 selected.Right: tubes 2+3 selected.
Left: all tubes selected.Right: divo switched tubes to standby mode,giving a lower bias voltage.07 July 2012:Also made a 2-meter unit for my 50 watt Jvm.
Above you can see and hear the Divo OV4 in action,also you can see here the working of the footswitch.