It is necessary at the start of any amplifier design to estimate the number of stages required. The required overall gain can be deduced from the input available and the output required. With low level transistor amplifiers it is usually best to consider the stages as current amplifiers, and to evaluate the current gain requirements. In some applications it may be convenient to include a stage mainly for some manipulation other than signal amplification, such as impedance transformation or frequency response control. Also with many amplifiers some negative feedback will be included and in this case the gain requirements of the amplifier without feedback must be greater, depending upon the amount of feedback.