Design Procedure
Prior to starting any new project, a clear idea of what is being designed is needed; in other words, list the objectives and necessary performance goals of the design first. So, for example, when designing a preamplifier, start with the source and proceed to the load; that is, begin with the cartridge and move from the first stage through the last. For this design example, the overarching objective is a phono preamplifier for use with medium output moving magnet cartridges.

1.  How much gain is needed for this type of cartridge?
For most moving magnet cartridges, a final gain of 40 dB should prove adequate. Forty dB of gain translates into a ratio of 100:1 for the output voltage divided by the input voltage. This value is seemingly well within tube circuit reach, since a 12AX7 has an amplification factor of 100. Unfortunately, more gain is needed, since the RIAA equalization imposed on the record decreases gain at the low frequencies by a factor of ten (-20 dB) relative to the mid-band frequencies. Thus the gain of the preamplifier prior to equalization must be at least a ratio of 1000:1 (60 dB) to achieve the 40 dB figure after equalization.     
                   
2. Passive or active RIAA equalization?

The advantage to active lies in consistency, reduced noise and distortion; its disadvantage lies in possible instabilities or overload conditions, and unequal feedback ratios across the audio spectrum. On the other hand, passive equalization is always stable and cannot be over-loaded; its disadvantage lies in the insertion loss and the frequency dependent load impedance it represents to the preceding stage. For this design example, a passive equalization network is used; if active had been chosen, more gain would be needed to buffer the feedback (feedback uses the extra gain to reduce the     distortion and noise). If the passive stage is placed the end of the amplifier, a better signal to noise ratio will result; if placed before the amplifiers, a better overload characteristic. Consequently, the passive equalization stage is usually placed within two gain stages because it yields a preamp with both a good overload threshold and a fairly quiet output. One further advantage of this placement lies in the buffering of the equalization network from the following stages in the preamplifier and tape monitor loops.

3. How to partition the total gain between gain stages?
Because of the fairly limited amount of gain any simple tube circuit can yield, a split approaching 50-50 is probably the most achievable. For this design example we assumed a moving magnet cartridge, which requires a final gain of 60 dB excluding the loss from the RIAA equalization. Thus, each gain stage should deliver a gain of  about 30 dB or 31.6 : 1.