I have a 2204 DIY that I plan to MOD with an FX loop First I found this and added it to my schematic: But then I found this Merlin schematic Which I like because it is placed between the treble on the tone stack and the MV leaving the MV as the actual MV. Also it is made for high gain which I need as well as clean. In any case there are many Tube Buffered FX Loop designs I have seen online. I have a Digitech GSP1101 which I use for delay and reverb. GSP1101 Loop specs: Loop Input: Impedance: 16K Ohms unbalanced or 20K Ohms balanced Nominal input level: +4 dBu or -10 dBV Maximum input: +23dBu (Level switch at +4 dBu) Loop Output: Impedance: 600 Ohms Nominal output level: -10 dBV (Unity gain from guitar input in BYPASS) Electronic SNR: ≥ 110dB If you had to choose which of the loops I added above which do you think is better for the effect unit I use? Or is there a better choice I am not aware? Maybe some impedance matching suggestions if the Tube FX loop is not already designed appropriately. I know there are solid state loops I could use but I won't because I want to build a tube buffered one. Its more about the building I enjoy than it is the merits of solid state or tube. I am a Gold Star Tube amp'er however. Anyway thanks for input.