In order to obtain louder effects, you need greater stability (or basis) for your finger and hand actions than forearm weight alone can give. You here need the weight of the entire arm (both of the upper-arm and forearm) to be more or less released. With a medium-sized arm, this will offer ample basis for cantabile^[1] tone in single notes, and for some chord-effects. As you increase the speed at which the fingers move towards the keyboard, you must supply a stable basis of weight to counter act the recoil of the fingers against the keyboard.
Good singing-tone, in the making, feels as if the weight released "produced" the tone. Weight alone, however, does not contain enough components to generate sound. Remember, weight only serves as a basis, and it must correspond to the desired exertion of the finger and hand. When attempting to apply using arm-weight, keep the fulcrums at the 1) hand-knuckle and 2) wrist stable and allow the forearm and upper arm to react to the downward exertion of the hand.

Only one of these three elements of "touch-construction" need be visible during the act of touch that is, visible either as finger, hand or arm movement while the other two remain invisible.

Note: Moreover, you may prompt into being this three-fold combination (of hand and finger for singing tone) in two ways either by thinking of the sensation of the weight-release, or of the exertions implied. Thus (1), you may call up the feeling of the release of the arm-weight, and rely on the finger and hand to do their work by sympathetic reflex-action, owing to the weight being left unsupported.
Or (2), you may call up the sensation of the work being done (by finger-and-hand exertion) and thus allow the required weight lapse to occur, owing to the sympathetic or coordinated sense of the need of a basis.

[1]cantabile: In music, cantabile, an Italian word, means literally "singable" or "songlike". In instrumental music, it is a particular style of playing designed to imitate the human voice.