Retro - A fully symetrical phono stage with RIAA filter

[Joshua_G]

Conversion to the black religion – analog vinyl records … the converted ones never turn back to digital … (which is what happened to me).

[Russ White]

I look at it this way, I am an eclectic audiophile.

I doubt I will give up any one thing for another. Instead I will try my best to enjoy them all.

[eyoung]

Ditto

[Joshua_G]

Being now a pious and extremists religious in the black religion, eclecticism is behind me, like in many cases of the newly converts …

[rickmcinnis]

Since this is all the rage.

Would be easier to implement with op amps.

One does have a hard time returning to digital from analog but what do you do for the records that are only available on CD?

I am not one to speak, since getting a turntable set up after two years of abstinence I have yet to re-connect the digital stuff. I am sure I will eventually. But then that is what I said six weeks ago. It is getting close to six months now ...

Allen Wright's missing time constant could certainly make a better sounding phono amp.

[Russ White]

Originally Posted by Allen Wright

Russ,
Bravo on your fully symmetrical phono pre. Why 99% of people treat this balanced symmetrical signal source as unbalanced is beyond me.

We do it with tubes and zero NFB, but yours is a good as I've seen with ICs.

But you could add a tweak to the RIAA curve that more accurately mirrors what goes down on the disc:

http://www.vacuumstate.com/fileupload/SP_15_Article.pdf

See #4, "Add the missing time constant".

Regards, Allen (vacuum State)

Thanks Allen.

I will certainly take a look.

Cheers!
Russ

[Russ White]

Ok So at least in simulation adding something like 15uH and 4.7R in series with C1 gets me darn close to replacing the missing time constant. Perhaps I will just leave spots for those, and they can be jumped if people don't want it.

Any thoughts? Better approach?

[Russ White]

Here is the response curve with the L and R in series with C1

[BrianL]

Misc. comments:

"DNR" -- I questioned because that is not a standard technical abbreviation as far as I know. Much like the strange use on this forum of the term "trafo" to mean transformer. Who invented this?

EQ: Hagerman and Wright advocate the so-called "Neumann pole" - debunked multiple times, most recently in Stereophile a few months ago. Lipshitz' paper is the definitive work on the topic -- and you need to get DC to 10kHz correct before you even start to worry about the Neumann pole pros/cons. I can send a copy of Lipshitz if you need it. Walt Jung's Audio Amateur article was on an inverse network. (It's amazing how so many youngsters are ignorant of such basic information. A few minutes with Google should point you to enough references to start researching. A few years ago an applications engineer from TI published some info about RIAA EQ where he stated that it was impossible to design such a circuit mathematically and the only way to get it right was by fiddling with component values in SPICE -- obviously did zero research on the topic)

"balanced differential" is perhaps a misnomer for a phono cartridge. With the exception of strange devices like the Decca, the L and R coils on either MM, MC or MI are floating in 'electrical space' if not specifically tied to chassis ground (one channel usually to the cartridge/cable/chassis ground but in your application this would be lifted). If not connected to ground they are not 'balanced' as they are not symmetrically referenced to circuit ground and are not 'differential' until connected to a differential input stage.

I need to ponder the latest schematic with the two FDAs. There seem to be more 'moving parts' with odd connections that I need to ponder. So, Russ, are these FDAs OPA1632 or THS4131 ? :-)

Keep up the good work, Russ. I enjoy both analog and digital, but must admit there's a level of tweaking and DIY that can be done with Vinyl that can't be done as readily in digital. I.E., a DIYer can actually build a phono playback setup from scratch (save for cartridge and the actual drive motor); you can't do that with a CD player.

[Russ White]

Hi Brian,

Thanks for the input.

Either FDA should work fine.

As for the "differentialness" of the cartridge signal. Both ends of the cartridge output are tied to VOCM, so they do have the same voltage reference. Now it is true, both are not referenced to GND, but that does not matter at all. In practice it works beautifully.

Cheers!
Russ