A frequency compensation device for providing added compensation to an operational amplifier, such as a bipolar or MOS rail-to-rail output operational amplifier, when the output device of the operational amplifier is in saturation. In one aspect, a thermally conducting filled gel elastomer material or a silicon elastomeric material or elastomeric material, if the material is to be removed, is applied to the die surface to which the heat sink is to be bonded. Accordingly, the image forming apparatus can be manufactured compactly, by mounting four developing devices, e.