2. analog
  3. 1055877785

Phono PreBiamplification



I am amused by the great distain that many audiophiles express regarding tone controls and, especially, equalizers. These same people tout the virtues of their pure analog LP playback systems, completely ignoring the extreme equalization inherent in the RIAA equalization curve which their multikilobuck preamps must implement.

Once upon a time I experimented a bit with what I will call "Phono BiPreamplification", and I think it is an idea which might be worth further development by someone in a position to do so.

The phono signal that comes out of the pickup (what is in the LP groove) has had the low frequencies of the original sound drastically attenuated. (This is necessary so as to enable the stylus to track the groove, and to permit grooves to be more closely spaced on the record). The phono preamp stage boosts the LF range so as to restore proper spectral balance. (It also cuts the High frequencies, but that is another subject).

Later in the playback electronics path there is a crossover network that essentially undoes what the preamp accomplished, so as to direct a signal with LF removed to the midrange and tweeter drivers. How would these drivers sound if their signal had not been subjected to two extreme equalizations? Darned good, if my experiments using a flat response microphone preamp is any indication. Of course an equalized signal would also need to be developed for the woofer (that's where the BiAmp thing comes from) but the tweeter would never see that signal.

Has anyone seen such a preamp? Any ideas on the subject? Is there a manufacturer out there with facilities to build a prototype?
eldartford

Showing 2 responses by eldartford

eldartford OP
4,262 posts
 
Twl...You missed the point. I am not going to do the LF equalization ANYWHERE for the HF signal, so the power amplifier is a non-issue. For the woofer signal, equalization would be done in the usual way in the phono stage.

Obviously the drivers of the speaker need to be suitable for for the X/O frequency that "comes for free" through the RIAA curve. It may be necessary to use some kind of MINIMAL crossover/spectrum equalization (still in the preamp) and perhaps a combination of MID/TWEET high end drivers (with X/O) to get signals that are compatable with existing drivers, but the crossover "grunt work" is accomplished by the RIAA curve. This is the kind of details that need to be worked out by someone who has the time and facilities. The basic idea works...been there, done that.

No reason why an equalizer can't use stepped attenuators instead of sliding pots. I thought that the hangup was about phasing.
eldartford OP
4,262 posts
 
I am disappointed that only one person out of more than a hundred had any comment on this idea. The audio hobby has changed since I was young. Back then our discussions revolved around technical ideas which you could experiment with, like this post, rather than around the subjectively evaluated benefits of various manufactured items, like interconnects, which require only money (no thought) to aquire.

For another example look at my reply to an old post "Does bewiring (sic) decrease wholeness". Has noone got anything to add to my suggestion regarding WHY biwireing might be desirable? I don't know if my idea is right or wrong, but it would be nice to share thoughts on the subject.
More to discover