I recently bought Casio Celviano AP-700 for my son. Being an audiophile, I was not happy with the audio quality of AP-700 built-in speakers. Since I already have some unused components, I decided to use a pair of KEF LS50 bookshelf speakers, Odyssey Audio Khartago SE stereo power amplifier, and Sunfire HRS-12 active subwoofer.
The line output from AP-700 goes into HRS-12 line level input. The HRS-12 has a built-in 70 Hz high-pass passive crossover which I use for connection to Khartago amp. Once connected and powered up, I discovered that the Casio AC adapter is very noisy. I can hear AC hum from the speakers which disappeared when the AC adapter is switched off. The placement of the adapter is also so critical that when any audio interconnect or speaker cables are near the adapter, the AC hum becomes louder.
The original AP-700 AC adapter is AD-E24500LW which supplies 24V up to 5A. The same AC adapter is used for AP-650 and the Celviano Grand Hybrids. The AP-700 rated power consumption is 28W. The GP-500 rated power consumption is 38W. All these models consume less than 2A of 24V DC. The adapter output voltage is stable at 24.23. To be on the safe side, I sourced 24V DC 3A linear regulated power supply. The DC power connector is Lumberg 163606 (rated 24V 2A) which I ordered from RS Online. The measured voltage from the linear PS is about the same at 24.26. I don’t think 0.03V difference will damage the AP-700.
Wow, what a big difference it makes to the sound. Not just the AC hum is gone, but I am hearing better subtlety and nuance. I am sharing this information so that if you plan to use external speakers with your Casio digital piano, please consider replacing the switching adapter to linear power supply.