FX loops coming to Metro.

[SDM]

Hi.
I have a question here. Has anyone added a footswitch to their Zero Loss FX Loop so that the bypass function could be chosen via the footswitch instead of the manual switch on the backpanel? For example if you wanna switch on/off the loop in the middle of a song?

Are there any pros and cons? And if someone has done it, how?
Thanks!!!

I would be interested in this. Are there simple layouts we could use to make this?
I'd be up for designing one with a buffer so it doesn't *pop* in.

That would call for replacing the dpdt with a cliff or a Switchcraft
so you could plug your ¼" in (coming from the footswitch.)
Do I understand this correctly ?
The newly built footswitch would plug in the newly installed female jack and ground when engaged
thus replacing the dpdt's function in & out of the circuit. Is that right ?

A relay could replace the manual bypass switch, nothing need be extraordinary about it, relay simply just replaces the physical switch. May want to wire the switching up a bit differently if popping is an issue, but that's an easy matter to tend to.

An early prototype ZL loop actually had this capability (as well as optionally running V1 on DC heat, see pic below), but board size, needing to connect to heater supply and such (extra complication basically) led us to rule it out. We figured it would just be easier/simplest (if someone wanted to effectively switch loop/all effects in/out on the fly) to just use a bypass box added within the loop to accomplish global effect switching.

[Johnny Bloody]

Hi Steve,

I'm not a technician but I'm considering to purchase a zero loss fx lopp to install by myself in my original Marshall JMP 2203 of 1976. I carried the amp to the Official Marshall Repair and Support Service in Spain and they put in the amp an original Marshall FX loop. When I tried it at home I was surprising because the sound was an incredible piece of crap...

I have been reading instruccions to install your loop but the first thing I have seen is that the schematics and the components in my amp are diferent or they are in diferent positions. Could I send you a photo of the amp (inside) and tell me how can I do the installation, please?

Thank you!

[Johnny Bloody]

Here is a inside photo of my JMP 2203. I hope you could help me...

Thanks!

[SDM]

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).

[Johnny Bloody]

Wow!! Amazing explanation. Thank you so much, Steve! I´m going to try it!!

But first, one last question: Do you think it is possible to desold one of the jacks on the zero loss fx circuit to set it in the hole (the hole that there is in the amp yet because of the other fx loop installation) and to plug it in the circuit via a small wires. In this way i haven´t to do more holes on the case. (Maybe it´s a ridiculous question).

Thank you so much for everything.

[SDM]

Not a ridiculous question at all, a few have indeed taken one or both (typically the latter) jacks off the ZL board, run short wires between board and jacks placed into into existing Marshall FX holes to replace the stock loop in their amps. Will need to figure a way to secure the ZL board in there (add a standoff or two or such depending on how you go), but can be done. The ZL bypass switch switch can be mounted in an existing switch hole too, or even omitted if desired as well.

Jacks are soldered on the ZL PCB well, will want to use a good desoldering braid/solder sucker/bulb to carefully free them, have some experience working with PCBs so as not to damage anything in the process. May be possible, if you've not ordered a ZL loop yet , to ask Metro to just leave the jacks off the board when you do order. Would make things much easier of course, could opt to use/order jacks with lugs then (instead of reusing the PCB mount versions) too. Not sure if they'll do that though, makes testing procedure more difficult, and likely they assemble them in batches these days, but doesn't hurt to ask.

[Johnny Bloody]

Great! I´ve just purchased my ZL FX loop!

Thanks again Steve.

[nico21]

Steeve,

Will it work if i just build a stupid box with IN and OUT jacks, and just a pot inside, to use it in your loop as volume control? if yes will a 1meg pot ok? or maybe 250k?

Thanks for your help!

[SDM]

Yeah the old pot in a box will work in the loop. ZL Loop is buffered and very low output impedance, so either pot value would be fine. Lower resistance = lower potential noise imparted from the resistance theoretically, but really not too much a concern in an application like this.

That said, don't need a loop to just add just a (basically master) volume here of course, no loop use 1meg pot or opt for PPIMV. Either could be remotely bypassed with a relay or such too. Could even set up a switchable dual volume controls, though would need to add a footswitch jack, relay power supply, volume control/s and such on/in the amp somewhere (and won't have the other advantages of a loop of course). For some could be more a pain than just installing the loop, but possibly another option for you worth a mention.

If you want/need to keep the box/volume control some distance away from the amp though, remotely mounted/accessible, perhaps easily bypassable too, then a buffered loop is indeed a good idea to avoid losses the cables alone would otherwise impart.

Hope that helps.

[nico21]

Thanks steve, cool you answerd

need the loop for my delay, adding a box with one or two volume pots will be a bonus to footswitch beetwen different volumes

Nicolas

[SDM]

No problem, hope both you and Johnney both enjoy your ZL loops!

[Johnny Bloody]

Hello Johnny,

(...)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. (...)

Hi Again Steve,

I have received my loop yet! I´m installing it now and I´m stuck in step 15. I´d like to know if I have to remove completely one of 10k resistors and replace it with the 5,6K. Maybe I haven´t understand correctly but Is it possible to add the 5.6 k resistor in parallel to one of 10K ones or I have to remove completely the 10K. and put in its place the 5.6k one?

Accordong to Marshall circuit and the resistor colors the two resistors are 1w. resistors and not 2w. Do I have to change it in this way?

I hope you can help me again...

Thanks!

[SDM]

First off, step 15 is considered optional, so you don't have to do anything with that 10K if you do not want to. If you leave it as is though, PI and preamp voltages will be a bit lower than before/stock. This may tonally be a good or bad thing to you, may not even notice the difference, but is a personal taste kind of thing. Main idea of the ZL loop is to avoid tonal change, hence step 15 exists to get PI and preamp voltages back to where they were before the loop went in.

So can try without doing anything in regards to step 15 (doesn't hurt anything at all if concerned about that) see if you like or don't notice the bit lower PI and preamp voltages. If you do want PI and preamp voltages back to stock, then you'll need to tweak the TOTAL value of that resistor to get it to 5.6K (approx). So step in step 15 when it is said to use a 5.6K resistor, the intent was to completely remove the existing 10K, swap in a 5.6K 2watt resistor in its place. Easy to do on the turret board amps/kits, but not as easy on a PCB amp like yours as you'd need to lift the PCB to (carefully) remove/swap in the 5.6K resistor.

So, an alternate option here is to add a resistor in parallel to the existing 10K to get approx 5.6K total value for the parallel resistors. If you have a 12K 2 watt resistor in your bag of bits, this will get you to 5.5K total resistance when soldered parallel to the existing 10K, well close enough. Optionally could use a 15K (total resistance would then be 6K, still close enough). Go higher values in parallel, will raise your PI and preamp voltages towards stock, but not as much so the higher the parallel resistor is. Go lower like using a 10K, you'd get 5K total resistance and PI and preamp voltages will be higher than they were stock, can't generally recommend that -though it greatly depends on your starting B+.

So, in short, yeah the instructions meant to totally swap out the 10K for a 5.6K in step 15. If you want to try without doing anything for step 15 for starters, can give that a go, no harm no foul. If you notice a tonal change that you do not like, just want to get stock PI and preamp voltages regardless, and do not wish to lift the board to swap that 10K out for a 5.6K, then can solder a 12K or 15K 2 watt resistor parallel to the existing 10K (hopefully will have at least one of these values in the bag of bits that comes with the loop). Solder in carefully to avoid having the stock resistor move or compromise its stock board connections as you do so. Can of course just opt to lift the PCB and swap the 10K out for a 5.6K 2 watt resistor too, ultimately up to you.

[Johnny Bloody]

All right Steve! I´ve tried to not to change anything about step 15. I´ve tested everything and I´ve just plugged my guitar. All I can say is... Wow!!!!!!! Amazing Sound!!! After months of searching finally I have all my Fxs on my favourite amp with all his amazing tone!! I don´t recognize any change in tone about voltaje changes as you described.

Once again thanks so much for everything and congratulations for this incredible FX Loop.

With Kind Regards,

Johnny

[Jofipe]

Is the Zero Loss loop completely bypassed when it's not in use? I'm considering it for my '78 JMP... i LOVE the tone of it, and don't wanna change that for recording... but I need a loop for gigging it.