To Filter or Not Filter (Part 4)
Go Discrete
Often the use of discrete circuits is touted as the ultimate expression of the audio design craft. Certainly, going discrete does free us from the shackles of the Op-Amp data-sheet and from the limitations of the manufacturers catalogs, which despite offering 100's of parts usually seem to lack the one with the precise combination of spec's we want. Whatever we want, we design it in.
BUT often discrete designs are not as good as the best modern Op-Amps. With discrete circuitry we can never be as complex modern integrated circuits and this complexity can be used to improve performance.
If we try to imitate integrated circuit Op-Amps in discrete form – we are often ending up with something performing worse, bigger and more expensive than a good and inexpensive Op-Amp chip used right.
Additionally, we can always add discrete parts to extend a good Op-Amp chip that lacks some specific feature we want. Be it an ultra-low noise input stage or a big class A output stage, we can often add these to an otherwise suitable chip and in the process make a hybrid that keeps all the good stuff of the integrated Op-Amp and adds our own desired features with much less complexity and of course cost than a fully discrete design.
At iFi you can find an example of this in the iPhono and its added super low noise MC stage and the added Class A Buffer, that deliver a performance that no single Op-Amp chip could and that would be, if at all possible in purely discrete circuitry, neither small nor particularly affordable.
The iPHONO
(Incidentally, one of the few "objective audio tests" when auditioning a phono stage is to 1) play music as loud as you normally listen at. 2) Then lift the needle. 3) Then listen for the "noise" from the phono section. A good phono stage amplifies only the signal so you should not hear "it" from the normal listening position. A normal phono stage amplifiers the signal AND the noise).
So, realistically, there is just one reason to go fully discrete. To get something that does away completely with the fundamental Op-Amp circuit structure and instead does things radically different, something that allows us to step outside the triangle with its + & - sign and it's fundamental set of unavoidable design compromises.
And this is precisely what we are doing for the Pro line. But, just because it is discrete and not Op-Amp it is not automatically good either.
We do truly think what we are putting in is something rather different in a good way though.
