I’m not sure if this is the right ar to post this however there seems to it is in a the majority of techy DIY musician here.

You are watching: How to add an effects loop to a tube amp

I simply bought a 1964 Harmony H303a 4W tube Amp. It’s yes, really rad, but verrrry simplistic. Every it has is a volume knob and also three (I have no idea why) inputs. EQ, reverb, tremolo, etc. Deserve to be included as outboard gear, yet most of the I’d prefer to placed after the pre-amp but before the power amp. Has anyone experimented with including an FX loop into amps choose this ? It appears like simple operation. Change two that the three inputs with a send and also return normalled to every other and also connect them right before the strength amp. Is this wrong ? let me know.


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I just looked up that amp and also I'm not really sure if including an fx loop is a very an excellent idea.

First, make certain that amp has actually an isolation transformer. There are conflicting reports about whether that amp has actually an actual strength transformer, and if it doesn't then you should rewire it for safety because otherwise it might be a negative situation every around.

But besides that, that amp is so basic already that i don't see any benefit to having actually an fx loop. It's currently just one input stage and also one output tube.

Usually an fx loop is provided to allow you operation delays and whatnot ~ the gain and distortion of the preamp, come maintain far better clarity.

But v this amp, a lot of the distortion girlfriend will get (unless you use a an increase pedal come slam the former end) is going to come from the power tube distorting, and also at that point it doesn't issue if you use an fx loop or not, due to the fact that your fx signals space going to get distorted too.

Fx loops are most valuable on amps the either have very gainy, distorted preamps, and/or loud and also clean power sections. This amp has neither.

Another problem is the in order to include a working fx loop you will basically require to include at least one more gain stage. The signal coming turn off the 12au6 will certainly be as well high voltage for a pedal, and also the output signal that a pedal will be as well low voltage to get anything beneficial out that the strength tube. Girlfriend will have to attenuate the preamp calculation signal and rise the return signal, so friend will require a pipe or mosfet or other to execute it.

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In short, ns don't see any type of benefit come doing it. FX loops are an excellent but this amp is so straightforward that an fx loop would have all negatives and also no benefits.