Hello residents of Tube-Town!

I have just built an effect loop for my Hammond Organ out of the LND150 kit. My goal was to create the most neutral loop that only balances the level in and out and nothing more. The effect loops I have used earlier have included a tube, and they are OK but I have had some issues with all of them, and they also seem to colour the sound a bit.

I use a tube socket to hijack the signal from the 12BH7 tube in the AO-28 preamp, and grab the signal from the viper of the tone control and 285V+ from the plate. The reason for this tube socket is so I can easily bring the loop to other organs when playing on rental backline.
I built the kit with the recommended voltage divider testing ratio 1:10.

The kit turned out aaalmost perfect, but I am loosing some low end. I tried playing around with send and return volumes, and it's very close but I would love to build a version with no low cut. Unfortunately I don't understand much of the curcuit, does anyone have any tips to how I could modify the kit to get rid of the low frequency loss?

Thank you!

 Hi, the low-end loss is most likely the coupling caps. The kit manual (Rev D, p. 9/10) lists two cap sets: "Tight" with 22 nF for C1–C4, and "Fat" with C1/C3/C4 = 0.47 µF/250 V and C2 = 1 µF/100 V. With 22 nF in front of the 100k send pot alone you get a corner around 70 Hz, more with low-impedance pedals – too high for an organ. Swap to the Fat set and the loop should go down to a few Hz. If it gets too bright afterwards, C7 (500 pF) is optional and can be left out. Your 1:10 divider doesn't affect the bass, keep it.
regards, Robert

Hi,

i implemented the effect loop in a Hammond M103 organ.

Use 0.1uF (100nF) capacitors for the input and output to minimize low end cut.

Important in my implementation were the levels controls, to adjust to the specifics of the organ amplifier