Question About Bridging Amplifiers and Low-Impedance Loads

[Ross6860]

I have a pair of JBL UREI 6260 power amps that can be run bridged. Bridged, they are rated at 300 wpc into 16 ohms, and 600 wpc into 8 ohms.

http://www.jblpro.com/pub/obsolete/6200ser.pdf

http://www.jblproservice.com/pdf/Vintage JBL-UREI Electronics/JBL-6230_ 6260manual.pdf

As stereo amps they are rated at 150 wpc and 300 wpc into 8 ohms and 4 ohms, respectively.

So what happens if they are bridged and run as quasi mono-blocs with low-impedance loads? Something like an AR3a, Infinity RSII, Infinity 9 Kappa, KEF 104/2, etc.

 

[tygr]

You can't both 'bridge' them for more power per channel and still handle low impedance loads. Just doesn't work.

 

[Blue Shadow]

You can't both 'bridge' them for more power per channel and still handle low impedance loads. Just doesn't work.

Well unless the stereo amp is designed to run a 1 Ohm load, in which case it would want to see a 2-Ohm load when bridged. Each channel of a bridged amp sees half the total load and most amps can't do a speaker less than 8Ω when bridged. Check specs to see what the amp will do, if they specify that.

 

[Ross6860]

Thanks for the info.

I guess that's why they don't rate them below 8 ohms, bridged.

 

[bimasta]

For 3–4 years I drove Quad 63 electrostatics with bridged amps rated at 225W into 8ohms: Audionics CC2. The Quads are supposed to be difficult, often dropping to 2ohms and lower, no-go territory for bridged amps. But they sounded magnificent, my favorites with the Quads. During that time I used other amps, tube and SS — Accuphase P300, VAC 80/80, Pioneer Spec 2, Altec 1570B, Krell (forget model, 100W, not Class A), Quad's own 405 designed for the 63 — but always went back to the CC2's.

I don't know why or how they worked together so well when they aren't supposed to, nor draw any conclusions from this one example.

 

[elshout]

You could get by on low volume usage. Overheating will be the ultimate issue if driven hard.