Possible Clues:

• Pipe organ stop
• 'Help up Father, with a boy and stop on the organ (8)'
• Organ stop representing the characteristic organ sound
• By the sound of it, paid up over a boy of his
• Entire range of voice or musical instrument
• Whole range or compass of tones
• I'd stop on the organ over a man and his boy
• Organ stop; sad piano (anag.)
• Stop playing piano with sad arrangement
• Othello's enemy