One of the most common emails I get from around the world is about bi-amp using an electronic crossover, so here is an update
THE PARADOX OF ADVANCED CLARITY AND TRANSIENT RESPONSE COUPLED WITH LOWER IM DISTORTION: The minute you remove your passive crossover you receive the above advantages which may now may reveal other problems in your loudspeaker. Passive crossover can smooth over lots of problems, so at first you will be upset...that is the eternal paradox of greater clarity...but dont give up.
SET AND PP AMPLIFIERS HAVE COMPLETELY DIFFERENT AURAL MATRIX: The wave front of these two different type of amplifiers is very different, especially if the PP has lots of feedback which it typically does. Push/Pull circuits tend to be very wide and narrow, while SET tend to be narrower and deeper. PP tends to have more of its dynamics lower down and SET have most of its dynamic energy in the midrange. If you want to blend these two different types of amplifiers be aware of this when choosing amplifiers.
THE HARMONICS/TONE OF DIRECTLY HEATED TRIODES AND PENTODES ARE VERY DIFFERENT: If you are using a 300B on the midrange and tweeters and a pentode on the woofer you will hear the tonal discontinuity. If you must use a pentode amplifier with a 300B I suggest that the EL 34 is probably your best match harmonically.
FINDING THE CORRECT CROSSOVER SLOPES TAKE TIME: Experiment with 6, 12, 18 and 24 db slopes and mix and match to get optimal results. There are no rules here...just your ears. Always use a simple voice recording for getting the midrange right.
YOU CAN BLEND A PUSH/PULL WITH A SET: I have been very thrilled by the combination of a push/pull 300B and 300B SET, and combination of a 300B push/pull and a 2A3 SET, and (strange as this may seem) a 300B SET on woofers and a 300B push/pull on the tweeter...but these are all directly heated triodes, and have similar tone and dynamics.
THE DIRECTLY HEATED TRIODE MARTINI: The combination of the 300B SET on the woofers and 2A3s SET on tweeter can be very sublime, and remember once you remove your passive crossover you amplifiers have gained an equivalent of 30% more power.
A TRICK REVEALED: Try experimenting with different brands of your input tubes...nothing is better at quickly adjusting the tone of a tube amplifier...the best way to make them sound harder or softer.
IT IS WORTH THE TROUBLE: Once you take your rubbers off, it is much easier to run faster, and there is no going back.
THE OLD HIGH SCHOOL GIRLFRIEND SHOCK: After you have been working with your new bi-amp system for a while go back and reconnect your passive crossover. Do you remember when you bumped into your high school sweetheart that you hadnt seen in twenty years, and you wondered....That is what I was madly in love with. And remember everything else, meaning distortion, in your audio chain will be more apparent.
e-mail Dr. Harvey "Gizmo" Rosenberg: firstname.lastname@example.org
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