A lot of folks like the Metropolous Zero Loss Effects Loop. My unverified understanding is the advantage of active loops like this is that they make up for any loss of signal strength or tone caused by the extra cables and connections and whatever is going on in the effects pedals themselves. In particular, the keep you from losing treble. Also, they provide
Geometry Dash a signal that guitar-level pedals can cope with, unlike a normal effects loop which is at pre-amp'd level and may not get along with some pedals. I'm working on a stand-alone reverb that will go in an effects loop, and I think it will avoid some problems if I can have a circuit to match the signals as needed.
Metropolous is mosly about Marshall-type amps and the instructions are definitely geared that way. If your amp isn't in the Marshall family you will have some adapting to do. I didn't get a lot of help on the Metropolous forum, for what its worth - thankfully I got good suggestions from Stephen "the Holy Ghost" and from folks on the EL34 forum.
One of the tricks I ran into was that zero loss loop has a circuit board that is powered off of your B+. You have to take a voltage reading whereever you're tapping the current and use a coupling resistor to get the right voltage (there is a chart for this in the instructions).
My concern was that since I have a VRM, my B+ voltages are always changing.
The only place I could tap "upstream" of the VRM was before the standby switch, off the first filtering cap (on a TC15 that is the first half of a can capacitor).
That meant likely a very noisy signal, so the advice I got was to use an additional 47uF filtering cap to smooth out the voltage I am feeding to the zero loss loop. There was a conveniently located empty spot in the chassis, so I put in an extra terminal strip (it's a big cap and I didn't want it just hanging in the air). Instead of a wire lead, I just used the coupling resistor to bridge from the can cap source to the terminal strip. Here's what that wound up looking like:
I couldn't find a spot to put the zero loss board that I was 100% happy with, but I wound up putting it just over V3 (I guess it's just under when you're done and the amp is right side up again!). And it wound up that putting the board upside down fit better. This made it slightly tricky to get the wires the right length but not too bad. It does get a little crowded where you run the new leads to the effects loop take off and return points suggested by Trinity.
Here's what it looks like from the back. I knew I would never remember which jack was which, so I had a decal printed.
I did have a "what the heck is going on" moment until I realized I had forgotten to put a needed jumper wire across two terminals of the bypass switch.
For some reason Metropolous sends you two-conductor shielded wire, and twist the conductors together to use them as one. This made the wire a bit bulky and hard to work with. I'm not sure why they did it this way but I figured there might be a reason for it and used the wire they sent.
If you install the effects loop where suggested by Trinity, it only works on Channel 2. I'm pretty sure that's correct and not just an error on my part, because I remember this same issue mentioned in an add-on reverb thread and it does make sense looking at the schematic.
So far quite pleased with this installation.
I haven't tried an A-B comparison test yet. I will say that my entry level Zoom multieffects unit has never sounded so good. But then again, until a couple weeks ago I never had an amp this good either
Labeling your jacks is a thoughtful touch, ensuring that you can easily identify which jack is which. Mentioning that you did this to avoid confusion is good for context.
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