By Lam Seng Fatt
After testing bi-amping vertically vs horizontally, the next logical thing for me to do was to try bridging amps.
I have seen the ‘bridging’ switch at the back panel of my Bryston 4B SST power amp, but I never had the chance to use it. However, when two Magnet power amps were sent to my house – and they are bridgeable – the opportunity was there for me to test bridging.
Essentially bridging a stereo amp turns it into a mono amp and the power output increases. According to the specs of the Magnet Hyperion Reference One amp, the power output is 250Wrms @ 8Ω from 20Hz – 20khz all channels driven in stereo, 400Wrms @ 4Ω and when bridged, it is a whopping 650Wrms @ 8Ω.
How to bridge an amp?
First of all – and obviously – the stereo power amp must be designed to be bridgeable. Just look at the manual and check the back panel to see if there is a ‘stereo/bridged’ switch.
Then follow the instructions in the manual carefully.
1) Connect the black interconnect to the RIGHT input of the power amp.
2) Connect the positive speaker cable to the right channel (+) of the power amp
3) Connect the negative speaker cable to the left channel (+) of the power amp.
4) Do the same with the other stereo amp.
5) Make sure the switches on both amps are turned to “Bridged”.
I set up the bridged amps as per the instructions on the manual. Then I used the DH Labs Q-10 single biwire first and then the Kimber 12TC speaker cables and ended up using the latter as I preferred its bassier balance.
How did it sound?
First of all, a bridged amp sounds like a very powerful monoblock. The effect is similar to using two normal powerful monoblocks.
The entire soundscape is under tight control, from the bass to the strings. The amps seem to run on limitless power and the dynamics are impressive.
However, bridging loses out to vertical bi-ampinng in terms of holographic imaging – creating the illusion that there is 3D space between the speakers where the musicians and singers are creating music.
Bridging does not create the ‘layering’ of images – the perception of the pianist being seated somewhat behind the guitarist and the singer standing a couple of steps nearer the listener with the drummer further back. There is less depth.
Also with bridging, there are two more consequences – the images become smaller compared with the supersized images when using horizontal bi-amping, and the listener is transported from the front-row to somewhere in the middle of the hall.
After listening to the bridged amps for a while, I switched back to passive vertical bi-amping – I missed that front-row excitement with holographic presentation, especially when playing well-recorded music.
Stick to vertical passive bi-amping. On good recordings, the sound is magical.