I have a CA901 electric piano that I am hoping to use with effect/loop pedals. It has pretty amazing speakers and put some effort into having the sound from the piano vibrate the frame a little. A nice goal would be to be able to use these speakers with an effect pedal.

So I grabbed a Twin Looper pedal and tried plugging in a L R Stereo 1/4" cable from the output on the keyboard to the looper. I then I took the L R output and converted it to a double sided stereo 1/8" cable and into the input of the piano.

That input stereo jack is listed on the specs as being so that other instruments can go through the piano.

The screeching sound this made was horrendous. Should definitely be used in a horror film. Clearly I created a feedback loop. But what's odd about it is I could get the looper to play through the speakers so long as the line in gain and overall volume was low. One little decibel over the limit and the screeching comes loud.

What I dont get is how is this a feedback loop? The looper doesn't actually pass through the audio (which is confusing to me personally but convenient here) so there is nothing technically to form that loop right? Is something faulty with the pedal maybe?

Given the specs of the piano do you think there is any way to get this working?

If not can anyone recommend a cheap bedroom amp that is small and I could put on-top of the keyboard as a compromise please? Most of the ones for keyboards seem bulky. I am always going to be at arms length from the piano so it doesnt need to really amplify much.