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Need help understanding what went wrong - biamping with 2 different amps.

Posted by carcass93 (A) on January 12, 2015 at 12:49:38

First of all, all's well that ends well - nothing is permanently damaged. Here's what happened:

I'm playing with a tube amp now, and up to a moderately high volume, it sounds wonderful - beats my resident, and very good, SS amp in 3D soundstage, and especially naturalness of human voice. The problem is that "moderately high" is not how I normally listen :-). At my preferred levels, on tracks with prominent bass, things fall apart - the distortion is readily audible.

No problem, I thought, because the tube amp was aquired with the intention of trying it in passive bi-amping configuration, in part inspired by review linked below, where reviewer bi-amped the speakers that are direct predecessors of mine. Of course, I'll need some means - high-quality volume pot, for instance - of matching the output voltage at speaker terminals at the crossover frequency (225 Hz). Not having those means right now, and the volume subjectively very close between the two amps at the same position of VC on the preamp, I decided to give it a try anyway. After all, there's protection circuitry in tube amp, and the SS one is chock-full of fuses - what could possibly go wrong?

Long story short - it worked, and sounded very good, with slight overabundance of lower frequencies (so, SS amp must be a bit louder). I listened several times during the day, leaving everything powered. Then, in the evening, decided to take the tube amp out of picture, switch speaker cables to SS amp, and compare to its sound standalone. Unlike the power-on sequence, where I turned tube amp ON first, waited for it to actually start (soft start - couple of minutes), and then turned ON SS amp, I turned OFF the tube amp first, then SS. After switching speaker cables to SS amp, and turning it on, there was no signal through the speakers - and investigation showed that it blew the 10A rail fuse. There was nothing audible (pop or anything) through the speakers when tube amp was turned off.

Now - obviously, the first recommendation is "don't do that anymore". Second is to reverse power-off sequence. However, I would like to understand what happened, and whether the idea of biamping in such fashion is viable at all.

Thoughts?

• Passive biamping example   (Open in New Window)

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