The 51-A S and A 51 are two condenser microphones cardioid directivity was very versatile (overheads, various acoustic instruments, ways, we'll have to envy to all ...).

The 51-S is the same as the 51 plus pad (the practice of sound pressure from source) and a high pass filter (these two characteristics make it more ployvalent that his little brother)

OVERALL OPINION

I had the opportunity to listen several times during the last year for comparisons of microphones for studio and balances and this mic is simply amazing ... Finally, we recognize what we want sound / recording ... So I bought 2 months ago (and this is just the beginning)
That a real microphone in a range of competitive prices.
The curve of frequency response of this microphone is very good.
The only downside (which explains the low price), the production made in china ... but hardly more than a SM58 (I saw was $ 220 with shipping to USA-attention to customs fees, however), it was a real micro "comp" (which will this-not say the same utility).

But happiness ...

Value for money unbeatable ... It deserves a 10 out of 10.