Phono Preamps with "balls" ?

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

@jcarr : There is a real bipolar " problem " against FETs and is that you need perfect matched devices and other problem is to make a precise way for polarization. Designs front end with bipolars is not an easy task and needs more work than with FETS but the rewards makes worth to do it. The unit I'm using is a current fully difirential and totally dual mono design where exist in reality 3 separate circuits: one for MC ( with only two bipolars gain stages. ), one for MM ( this one use MOSFETS not bipolars ) and one line stage.

In design each designer has its own and almost " unique "  skills and as a cartridge designer you know very well that and can understand why the Colibri performs diferent from the Etna or the Ana. All are very good carrtridge designs but are each one " unique "  in its diferent quality level performance. I like all ones but the Colibri makes something than no other cartridge I experienced ( including yours. ) can't do it at the same level and is the precise and clear definition of the very high frequencies. All those 3 designs are different and VDH, you and Ortofon shares the same knowledge levels but different " skills " or the other way around ( I can't find out how to explain those differences. ).

If knowledge and skills levels in designers were evenly then almost all sill sounds the " same " and no one phonopreamp or amps or cartridge or speakers sounds the same.

In cartridges is more complex because the designer must have to do the cartridge voicing and certainly VDH, you and Ortofon uses diifferent system and techniics to do it and with different targets.

Neumann constant: for many years Ortofon used a " golden ears panel " to make several tests to improve its cartridge designs. From many many tests through that " golden ears " panel they concluded that its cartridges must have a peack over 20khz instead totally flat. It was tghrough this high frequency deviation where  that panel agree it was achieved the top quality level performance. Of course that the pannel never knew the frequency response of the different cartridge Ortofon samples they were listening.

Well , the Neumann constant/pole makes that come back the " spark " in the high frequencies that is totally losted with out it and this is what that pannel tell us in a different kind of tests.

I know that you read everything on audio an especially analog and I read too what you posted about the half-speed recording tool.The gentlemans as you that do not like to use the Neumann constant normally never listened and that's why I ask if you did it in your phonopreamp.

@atmasphere : """  I'm not interested in getting it sound like a good stereo. It has to sound like real music. """

me neither. A good SS stereo design always will performs as " real " music, it can't be in other way.

R.