difference between bridged and parallel?

[jarthel]

the lm4780 can be bridged or paralleled.

can someone explain the difference?

thank you
ps. I searched but nothing came up

[jackinnj]

the bridged chipamp will have somewhat lower distortion, but PdMax is much higher, thus the max allowable rail voltage for a given output impedance is lower.

the paralleled chipamp is great for low impedance loads, distortion is a trifle higher.

you can mix and match to your heart's desire, i think that the bridged version sounds great with speakers with a nominal 8 ohm load.

[AndrewT]

Hi,
look up the chipamp datsheets. Most of them show the circuits for both parallel operation and for bridging.

The parallel chipamp allows loads of half impedance to be driven safely.

The bridged chipamp allows double the impedance to be driven at up to double the power.

Take an example that can drive 60W into 8r0 from +-35Vdc supply rails.

A parallel pair will put out almost 120W into 4r0 from +-35Vdc.

A bridged pair will put out about 120W into 16r from +-35Vdc. Not a particularly popular speaker option today.

Take your parallel pair and bridge them into a quad. This would boost the maximum power to about 240W into 8r0.

Note, that throughout I refer to a non reactive load of 4r0, 8r0 or 16r.
Speakers are reactive. The worst case loading appears to be about 75% of the nominal load, i.e. 8ohm gives about 6r0 and some phase angle which asks for more current and combines high voltage with current output. But, unfortunately the actual worst case for starting and stopping of a transient approaches about half the expected reactance. The chipamp is asked to deliver short term transients into loads near 35% to 40% of the nominal speaker impedance. The protection circuits inside the chipamps do not like high currents, nor high temperatures nor high voltages, particularly when all these can occur at the same time. I recommend that you interpret National's advice on maximum power into the selected load to apply to the worst case loading of 35% to 40% of the nominal speaker load. On that basis most single chipamps should never be asked to deliver maximum power into loads of less than 8ohm (reactive). If one were to adopt the lower supply voltages that National give data on, then by ensuring that the maximum output current never hits the VI limiting, then lower impedances can be driven.

[Yomanze]

What about a 6ohm load? I've got a pair of original Mission 780SEs that like a bit of current.

Cheers

[AndrewT]

Originally posted by Yomanze
What about a 6ohm load? I've got a pair of original Mission 780SEs that like a bit of current.

Cheers

Hi,
If you accept my logic then a 6ohm capable chip amp should be designed to deliver it's maximum voltage and maximum current into 2r4.
This is for short term loading only and not for heatsink sizing, since the worst loading can ONLY occur on starting and stopping of sudden change transients.
Design the heatsink and power supply side for 4r8.

[peranders]

Originally posted by jarthel
the lm4780 can be bridged or paralleled.

can someone explain the difference?

thank you
ps. I searched but nothing came up

A LM4780 is 2 x LM3886 in one package.

More info here:
http://www.national.com/an/AN/AN-1192.pdf