Pure tube phono preamp

So, it does not matters an all tube can’t mate those 3 phonolinepreamp targets. Today the best you can do for 10K is to go with SS.

This statement is based on three anecdotal examples. This is a logical fallacy called 'Guilt by Association', wherein because the particular phono stages didn't have accurate RIAA curves and were tube, therefore all preamps with tubes have inaccurate RIAA curves. Like any logical fallacy, this idea is false due to a flaw in the logic.


One valuable bit of test equipment is an inverse RIAA curve which quickly and easily allows one to test and see that the curve in a phono section is accurate. One valuable bit of math are the formulae presented to the AES by Dr. Stanley Lipshitz regarding how to generate RIAA equalization networks. If the latter is used in design, and the former used when testing that design, you can create a phono section with accurate RIAA equalization and it will be seen that whether its tube or solid state is completely irrelevant.

If you are talking about a phono preamp for genuinely low LOMCs, it is not really possible to get the high gain/low noise needed with just tubes.

This statement is false. The trick is to set of the phono preamp design to be fully differential (which is what of ICs do) *and* to use an effective constant current source to really get the tubes to operate differentially.

A differential gain stage has theoretically 6dB less noise than the same thing operating single-ended. Now if you need more than one stage of gain (which you will) then if both are differential, now you have two stages of gain, each with a theoretical 6dB lower noise floor. Even if you are only getting 5dB per stage, this sort of thing adds up- to less noise.


My rule of thumb is the phono section should be quieter than a silent groove on a good LP. That's easily doable. BTW, finding quiet tubes for this is not hard; three tips: First, avoid Russian-made signal tubes. 2nd, avoid NOS tubes, as people have been scouring the countryside looking for low noise NOS signal tubes for decades- most of the really quiet ones were sold off a long time ago. Sure, you *might* be able to find some that are quiet still but seriously finding them will be a real pain or a whole lotta dollars buying 100 tubes to find 5 that are really silent. You're better off just buying new tubes. We buy 12AT7s 100 at a time and we reject about 10% of them. But if we buy Russian tubes of the same type we reject 90% of them. So the third tip is probably buy the tubes from someone that is grading them for LOMC use.