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Greetings. Wondering if anyone out there has tinkered with effect loop pedal construction or has any suggestions. I have retired my Marshall TSL 100 in exchange for my newly built Trinity 18w Plexi. My issue is that now the rack effects unit I was running in the loop of the Marshall is presenting me with level/impedance mismatch issues in front of the amp. I don't really want to lay out several hundred for a new processor. TC Electronic referred me to the Lehle Parallel, but the cost is quite frankly kinda ridiculous to me. Has anyone else wrestled with this issue and come up with a good homebrew solution? Any help is appreciated!

Quite a while back I was looking for the same thing. I did find a buffered effects loop/blend pedal kit, but I wasn't terribly happy with the results. I don't believe the kit's available anymore. In my experience, if the rack unit is not designed to handle the very low guitar signal by itself, a good low-cost pedal solution is going to be tough to find.

The best solution for me was to set up a passive insert point (switched stereo jack) for each channel & to build loop kits into an external box. Some effects units will work relatively well connected directly to the insert points without any buffer circuitry. A separate insert point will need to be set up for each preamp channel since each channel output is out of phase with the other. The insert points would be between each preamp channel and the phase inverter.

There are quite a few buffered loop kits available for ~$40 & up per each....two required, in this case. If your rack unit is stereo and the stereo signal paths can be fully isolated, you can run both amp channels thru it. Obviously, true stereo effects are out of the question here, but you lose that ability with with an effects loop pedal too. I have an old Lexicon MX200 that works great this way.

A "Klein-ulator" is a fairly flexible/elaborate example of a DIY buffered loop. Schematics are readily available. There are quite a few tube & solid-state kits & schematics out there of varying complexity. Word of warning, though......these buffered loops are intended to be as transparent to the tone as possible, but they DO basically add at least one stage to the preamp circuit, so you may actually change the character of the amp while they're engaged, YMMV. You can still wind up shelling out $150+ by the time you're done.

-End of long non-helpful post-

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We have built serial effect loops into channels with the switched jack, just in front of the phase inverter. As bobo said though, with mixed results.
Here's one that might help you out. Not our design.



Try a google Search for 18 w effect loop.

BTW, you don't need a tube design, a FET design will work fine.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks for the quick replies. In the course of my research I stumbled on to the speaker level to line level concept that would take my signal post amp out and split it between speaker out (load) and a line out to run the effect unit. The Red Box by Hughes and Kettner was one item I found. This of course requires the addition of another power amp, but I think it might be the solution. Does anyone have any experience/advice regarding this approach? Would it be relatively easy/inexpensive to build one of these, or am I better off spending the $130 or more for the commercially made version; or would it be advisable to just run a mic/preamp/effect/power amp configuration and have a chiropractor on call for the extra gear I have to haul? If anyone has a design/schematic I would be most grateful. Thanks in advance!

Stephen, perhaps I just stumbled on to my solution. I was going over the schematic for my amp and noticed there is an optional line out there that looks like it taps off the 8ohm pin of the impedance selector. It does not appear to me that the line out negates the speaker out so I could theoretically run the rack effect off the line out and then through a power amp while running the main amp as my dry signal?????? Do I have that correct? I know just enough about this stuff to make me dangerous......