Pure tube phono preamp

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.  Hence the need to use opamps, FETs, SUTs, etc., to do so.  Even the ARC Reference Phono 10 uses FETs in addition to tubes.

Of all the options available to get the high gain/low noise needed for LOMCs, many prefer using an SUT because it is a passive device (no active circuitry or power needed).  If the SUT is properly designed and mates well with your cart, they can not only be no/low noise, but also provide more dynamics, liveliness, and texture.  YMMV. 

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.

Dear @tyan42 : This is what I posted in other forum on the same thread subject:

""" For me the functions of a phonolinepreamp first than all is that can achieve an accurated inverse RIAA eq with zero frequency deviation at each phono stage channels ( both channels should have evenly frequency about. ), other main target is to have active high gain to handle any output level cartridge ( LOMC or MM). As a fact phono stages exist because these two main targets/functions.

We need that high gain but we need it along very low noise. These 3 targets are the heart of any phonolinepreamp and the true challenges to any manufacturer because it’s really a hard task to achieve those targets at the same time ( even for SS electronics. ).

I like many phonolinepreamp in the market some of them already mentioned here: FM Acoustics, Gryphon, Spectral, CH, D’angostino, etc, etc.
Yes only SS because tubes in this specific function can’t do it and I owned from humble ( Jolida. ) to top design tubes electronics by around 10 years so I’m not speaking of my preferences but audio devices that its technology can in true be nearest to those targets..

This is only an opinion and I think is valid as any of your opinions.

I don’t like very much to talk about tubes in phono stages but I will put an example through Aesthetix IO ( I listened the first time at A.Porter house and latter on 3 more times in other systems. ) where they say the unit has active high gain with low noise and yes it has 80db of gain that’s a tribute for an all tube design but unfortunatelly failed on noise level that was measured a poor A-weigthed 57db and where the RIAA eq. deviation has ( by manufacturer spec. ) a high 0.5db swing deviation.
That frequency response goes even worst because it depends of the control volumen that at different volume position different frequency response.

RIAA eq. frequency deviation levels is critical because in theory must be to mimic in inverse way the recording RIAA eq. to we can have a flat frequency response.
Not an easy task even for SS designs because that eq. is not a " delicated/tiny " one but goes from around -20db to +20db, this is a huge equalization with several problems not only about frequency response but phase and other issues.

Look, graphic equalizers in the audio market as Accuphase, Soundcraftsmen, Crown, Klark-Teknic, etc, etc. ( I owned all and other ones been parametrics. ) in the best case its control levels by octave or 1/3 octaves can give you a range between: -15db to +15db and the RIAA demands -,+ 20dbs ! ! """



Here an all, 35K+ dollars, tube design by Lamm and you can see that is not really accurated on the RIAA inverse eq.:

https://lammindustries.com/pages/phono-stage-lp1/

but the Aesthetix I/O is over 16K dollars and can't do it.

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.
Today SS electronics are really good designs and way different to the 20-30 years ago designs, even for less than 10K you can meet everything any one can desires about with any cartridge.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

Luxman EQ500...dead quiet!

I am glad Atma-sphere spoke up about his MP1 and MP3. I am a happy owner of an MP1 for about 25 years.

up the thread, someone asked about the mating of a SUT to a current drive phono stage. That can’t be done. It’s almost an oxymoron. SUTs step up voltage at the expense of current. At the input of a current driven phono stage, current is needed and voltage is not relevant.