Phono Preamps with "balls" ?

@atmasphere :  "   is a lot harder to build a solid state phono section that does not have RFI  "

maybe you can't or don't know how to do it.

Anyway you have always to " say something " against. Try to be an audiophile, take-off your tube builder hat because is useless in this regards.

R.

Ralph, although I completely agree with you regarding the overriding importance of designing sufficient overload margin and circuit stability into phono stages, while rectification of RF energy (and subsequent intermodulation) is indeed an issue with bipolar transistors due to the base-emitter connection functioning as a diode, JFETs are free of this effect.

A phono stage with JFET front-end devices can therefore be run with input resistors in the megohm range without problem.

The RF rectification issue of bipolar transistors can be reduced if local feedback (emitter resistors) are added, but doing so will worsen the noise, which is the main reason for using a bipolar transistor front end in the first place.

A further problem with a bipolar transistor front-end is the base current, which will go through the cartridge coils (gradually magnetizing the coil former, which is definitely undesirable). And if the input resistor is of high value, the base currents will cause DC offsets, unless the input is capacitor-coupled (a band-aid that wouldn't be necessary with a JFET front-end).

The main difficulties with JFETs are their comparatively low maximum voltage rating, and significant device-to-device variation.

Unlike the situation with bipolar transistor front-ends, both JFET issues are solvable cleanly; the voltage rating with cascoding, and the device variation by measuring and sorting prior to assembly (although this does mean extra work).

kind regards, jonathan

PS. Nor do I accept that there is a need to insert the extra Neumann constant, as listening tests (LP vs. master tape) have not necessarily shown it to be an improvement. And with half-speed LPs, the target frequency will be an octave wrong.

@jcarr

I agree that jfets are the way to go- although I like some of the aspects of the MAT-12s (which are bipolar, but a popular goto for phono front ends), getting them to actually sound right has been a problem so far. The jfets I want to use though aren't made anymore, and even then we had to sort through a pile of them just to find a pair that not only matched (since our circuits are fully differential) but were also quiet.


<snark>

maybe you can't or don't know how to do it.

</snark>

@rauliruegas 

Or maybe I'm just pickier than you. I'm not interested in getting it sound like a good stereo. It has to sound like real music. 

Dear @jcarr : I respect your opinion but bipolars electrically are a better LOMC cartridge. I'm not saying than bipolars are perfect devices ( nothing is. ) but  better match. 

About the Neumann pole exist an advantage and I don't have to explain it to you. The main issue is to have the knowledge level and skills to implement it in the rigth way with out side problems. That Neumann constant must exist in any phono design and has to be the owner who decides if used or not. The cutterheads impedes that the RIAA eq. goes beyond 50khz because burning it self. There is no doubt exist an advantage to listen with than with out it, the issue is how that constant is implemented/designed.

You are not the only one ( @atmasphere here. ) that shares that kind opinion but other designers think the other way around and implemented with good results. Btw, did you try it in your phono stage?
Half-speed?, there are so many " myths " around that kind of recording tool.
@atmasphere , yes you are pickier than me, fine with that.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

Hi @rauliruegas : bipolars are better for LOMCs... how? Please substantiate why.

I specified two key areas in which a JFET front-end is superior to bipolar transistors for use with LOMCs, and also spelled out two areas in which JFETs are weaker (but described the countermeasures).

If you want others to accept your claim that bipolars are better for LOMCs, surely you are capable of describing the issues at a sufficient level of detail for EEs such as Ralph and myself to either concede to your superior wisdom, or refute it.

Regarding the extra Neumann constant, yes I have tried it, and have listened to various other phono stages that incorporated it. While it does change the sound, I don't recall ever feeling that it improved the sound.

Let us keep in mind that not all LPs were cut with Neumann cutting heads; Westrex, Ortofon, Haeco are some well-known alternatives.

By the way, what do you feel of the interaction between the Neumann playback constant and DMM-cut LPs?

kind regards, jonathan