Bi-amping
Copyright 2017 © Troels Gravesen

 
Quite a few have asked for some graphic illustration of the physical set-up of bi-amping, so here's my contribution.

Normally your amplifier consists of a pre-amplifier (line-stage)  and a power-amplifier, an integrated amplifier. If you listen to vinyl you may also have a phono-amplifier (RIAA stage), thus three stages of amplification. Most common is an integrated amplifier combining the line-stage and power amp. Sometimes even the phono-stage may be included in the integrated amplifier, which was common after 1970 until CD dominated vinyl playback. But we're seeing more amps these days with a RIAA stage included.

The rationale behind bi-amping is to have your favourite low(er)-wattage pet amp running the midrange and tweeter and a rugged power horse running the bass driver(s). The benefits can be huge. That is, if we're talking larger 3-4-way systems with a point of crossover between bass and midrange of no more than 200 Hz - to my experience. If you have two identical power amplifiers it obviously doesn't matter and you can use it in any system, being 2-way, 3-way, or more.

If you have an integrated amplifier - and no line-out facility - you're in trouble, as you need a line-signal to feed the amplifier running your bass speakers. Unless you have the electronic skills to pull out the line signal from the vault of your amplifier. Not always that easy...

To do bi-amping you need to know the gain (amplification) of your power amps. This gain is specified in dB. Normally a line-stage will have some 10-20 dB gain and your power amplifier some 20-26 dB gain. How this gain is divided between pre-amp and power-amp is up to the constructer of the amplifiers. Some power-amps, like Nelson Pass, usually have low-gain, like 15-20 dB, which requires a line-stage with significant amplification, some 20+ dB. As a rule of thumb, we should have some 40 dB gain in total. Less can do for high-efficiency speakers, more for low-efficiency.

My line-stage has 14 dB gain and my GlowMaster has 26 dB gain, thus 40 dB in total. This requires my current Hypex power amp to run also 26 dB gain, and it does.
If you don't know the gain of your power amplifier and if it is not specified in your product description, ask your supplier. This you must know.

Let's assume you have a pre-amplifier and you most likely have only a single pair of line-out phono sockets - and you need two. Very simple: You buy a pair of splitters. Search eBay and you find them in abundance - and at no price:
http://www.ebay.co.uk/itm/231588212825
http://www.ebay.co.uk/itm/Gold-Plated-RCA-Phono-Splitter

         

Above you have splitters for standard phono cables and for standard XLR balanced cables. Plug it into your pre-amp and you have two out-puts.


           
Above an XLR to phono plug if you need this. They can be had the other way around too, from phono to XLR.

 

 



Click drawings to view large




Conventional bi-amping









Bi-amping with a DSP dual digital amp.