AURAL SUPERCHARGER UPDATE
Because of the bulk of email I received in response to my article in Listener about using an electronic crossover I have added these comments to answer your questions:
RECEIVERS: Many of you want to know how to use your integrated receivers with an electronic crossover. YOU CAN IF YOU CAN DISCONNECT YOUR PREAMP SECTION FROM YOUR AMPLIFIER SECTION. Not all receivers offers you this capability.
You would take the output of your preamp and connect it to your electronic crossover. Then ONE set of outputs of your electronic crossover goes back into the INPUTS of your integrated amp's amplifier section. You have to decide what part of your speaker system you will use this amplifier section for. Because it is solid state it would be best to use it on woofers. This means you will need at least one more amplifier for your "midrange and or tweeter".
TUBE AMPS: PUSH/PULL VERSUS SINGLE ENDED? This question depends on the relative efficiency of your speakers...IN A SENSE. If you want to use a tube amp on your woofers and your woofers are below 90 db efficient use a pentode push/pull. Push/pull amplifiers control woofers better. Because the midrange/tweeter section of your speaker doesn't need as much power, you may be able to use a single-ended amplifier.
The combination of an EL84 pentode push/pull and EL34 or 6550 push/pull amp on the woofers should work great with most speaker systems.
If you have very high efficiency speakers SETs are the way to go. They are more refined, don't have the "slam" of push/pull, but have a unique mystery.
BLENDING SOLID STATE AND TUBE AMPS: Because you probably own a solid state amp, there is nothing wrong with starting here, because all you have to do is buy an electronic crossover and one more amp. A low powered used tube amp could work here. While this is not optimal, it is a big step in the right direction.
THREE AND FOUR WAY SPEAKERS: As a youth I went gonzo and had a four way system with separate tube amplifiers on each section, but there is not reason to go crazy. Consider this simple approach and it is one often used by speaker manufacturers in the 1960s. Use a separate amplifier on your woofer by disconnecting all of the passive crossover parts for this driver. If you have a three way system then leave the passive crossover intact between the midrange and tweeter. This is an important point: remove the crossover parts that filter out all of the low frequency signals going to the midrange. Set your crossover for the midrange crossover point (for example 800 Hz). You now only have the passive crossover parts in place that matches the midrange to the tweeter and use one amplifier that is responsible for this frequency range.
Of course you can use three separate amplifiers, and remove all of the passive crossover parts.
SUBWOOFER INTEGRATION: One of the greatest advantages for an audio system is removing the lowest frequency burden from the amplifier that is amplifying your midrange. Removing the low frequency range from your woofer is also a great benefit. BUT AS I POINT OUT IN MY NEW SERIES OF ARTICLES ON SUBWOOFERS INTEGRATING THEM INTO YOUR ROOM IS NOT EASY.
SPEAKER MANUFACTURERS THAT COMPLAIN, THROW TEMPER TANTRUMS, OR DON'T COOPERATE: How technically complex is a passive crossover design? Your fish tank is more complex. How top secret is the design? No more top secret than the centerfold of Playboy Magazine. So why do speaker manufacturers get so unstable over a concept that they know will dramatically improve the sound quality of their product? Do I have to write a book about the dismal condition of the average speaker designer's ego?
At worst you are talking about spending an hour or two of work. I have done these conversions in less than fifteen minutes. You will need a screwdriver, a wire cutter, a soldering iron, and you may need a drill and some extra speaker terminals. There is absolutely no danger of shocks, and you can always reconnect everything the old way.
Ask your speaker manufacturer for a diagram of the crossover and if you need help ask your "nerd" friend to help you. Don't be embarrassed to ask for technical/mechanical help from a buddy. This is really dumb-ass mechanical work.
DANGER: THE PARADOX OF CLARITY: Major adjustment ahead. You might think something is wrong with your system. You will have to properly balance the gain of your different amplifiers. This tuning process is a big advantage. That is the good news. You will also hear what seems like twice as much information. Not everyone is ready for this level of clarity.
WHAT SHOULD I BUY AND WHERE: Once you get on this path there is no going back to the "normal condom aural matrix", which is why I, again, suggest start slow and cheap. Buy used equipment if you want. This is a new skill like learning to ride a motorcycle.
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