Zero Loss Effects Loop install with Voltage Attenuator

Discussion in 'Amp Tech Center' started by alathIN, Dec 7, 2018.

  1. alathIN

    alathIN Tele-Holic

    Oct 25, 2017
    My next rookie amp builder project is a standalone reverb, and it looked to be easier to build one that would go in an effects loop rather than in front of the amp.
    So shortly after completing my first amp build - Trinity TC-15 - I ordered a Metropolous Zero Loss Effects Loop.

    The zero loss circuit is powered by B+. Since I built my amp with Trinity's optional VRM - an attenuator that works by decreasing B+ - it would often be getting power supply well below the recommended voltage range.

    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 a spiky power source, so smart people suggested I should use an additional 47uF filtering cap on the zero loss power supply line. 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 printed a decal at Kinko's.

    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 you 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 over on the Trinity forum 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

    The real fun will come when I get my standalone reverb-trem unit on line.... but that project is at a very embryonic stage.
    Paul-T likes this.
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