Post
by SDM » Mon Jun 17, 2013 9:29 pm
Hello Johnny,
These PCBs closely mimic the turret board amps, so parts are generally located in the same place, the "flow" of the board is the same -if that makes sense.
To make things clearer and possibly make for a more simple ZL loop install in this case:
First step is to remove the Marshall loop (and ADDED power supply bits for it) completely. Basically, remove everything they added -except you can reuse that gray coated shielded wire if you wish, will simplify things a bit, so can just detach/desolder it from the Marshall loop board, leave soldered as is to Master and treble pots, don't touch that end. This also means you would not need to worry about removing the wire in step 6, it's already gone.
Now see the (poorly) edited pic below. You do not need to position the loop board where it is shown here on the back panel, I just put it in that spot to cover the Marshall loop. Do note the holes for the Marshall loop are closer spaced that the ZL loop, so more drilling (or hole skewing) would be required.
From there, in the ZL instructions step 1, the "measure here" point is now the leg of the 10K resistor on the main PCB there circled in yellow. Amp is to be stock now (aside from the shielded wire if you left in), running normally, be sure master is set to 0 for now (won't have sound without shielded wire hooked up on other end for now), follow directions to get a DC voltage from that yellow circled resistor leg. Using this voltage, use the chart in step 1 to determine the decoupling (dropping) resistor value you need to use. This resistor is drawn in as the blue circled "?" resistor below, and one leg of it will attach to that yellow circled resistor leg you measured, the other end will feed the loop board power as per instructions.
Follow rest of directions as normal until you hit steps 10 and 11. If you decide to keep the existing shielded wire (as is drawn below), you simply need to attach the red inner conductor wire to the left middle lug of the switch, that's all you need to do for these steps. Alternately you can remove the existing shielded wire and follow steps 10 and 11 as per instructions, up to you.
Same as previous paragraph goes for step 12 if you use the existing shielded wire, but now just hook up the blue inner conductor wire to the right middle lug of the switch.
If you do/did keep the existing shielded wire, you can also skip step 13.
Follow the instructions again until you hit step 15. Here, the green circled resistor below is what this step applies to. Can choose to change (or parallel a resistor to change) the value as per the ZL loop instructions. That should do it.
Hopefully this covers what you needed to know, and all that said: If any of the above is confusing or you are unsure of your ability to work safely in a high voltage environment, please take it to a GOOD tech to convert the loop for you. That, or see if maybe there is an experienced forum member nearby that could possibly help you out. Be safe is the main point, and I hope you do enjoy the ZL loop if you do choose to install one (or have one installed for you).
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