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PostPosted: Fri Dec 07, 2018 4:29 pm 
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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 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:
Image

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.
Image

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.
Image

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 :D


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PostPosted: Fri Dec 14, 2018 10:15 am 
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To get effects on ch. 1, jump channels and dial in just a little of ch.2

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PostPosted: Wed Jan 02, 2019 1:06 pm 
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Just one update:

I have discovered there is a hum associated with this unit.
It doesn't sound like 60Hz at all - it's low level, not loud, and doesn't have any of the obnoxious static-y characteristics. It's almost as if someone is playing one low note on an electric keyboard, softly, plugged into your amp.
It took me a while to detect the hum, so it's not glaring and the loop is perfectly useable.
The hum goes away completely when you flip the effects loop bypass switch.

Just a heads up though, this is not a totally noiseless loop.

One thing I haven't tried is with the VRM at higher settings. It may be I am feeding the effects loop less voltage than it ideally wants.
If the hum changes with VRM settings, I'll re-post. I just need to wait for an empty house so I can play loud!


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PostPosted: Thu Jan 03, 2019 3:16 pm 
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What voltage are you running it at?

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PostPosted: Thu Jul 04, 2019 9:25 pm 
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I purchased the same Kit for my 18 watt Plexi a couple of weeks ago but haven’t got around to installing it yet. Are you still experiencing a hum with yours? I’m trying to figure out the best place to install it. I don’t think it’ll quite fit between the speaker jacks and the boost switch; at least not the way the instructions show the placement of the switch. I also need to figure out the best spot to draw B+ from.


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PostPosted: Fri Jul 05, 2019 12:05 am 
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You need to make sure the voltage feeding the Fx unit is not too high. Typically around the PI is good. Metro has a spec for this.

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PostPosted: Fri Jul 05, 2019 1:27 pm 
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Thanks Stephen. I hope to get at it next week. I’ll post a new thread here if I have any questions.


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