Talk:Bridged and paralleled amplifiers

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Created the paralleled amplifier article, merged the paralleled & bridged amplifier articles into this one. Rohitbd 09:44, 18 September 2005 (UTC)

[edit] The 4x power myth

"For example, if an amplifier can deliver a maximum of 100 W each into two 8 O loads in stereo mode, the same amplifier when bridged will deliver 400 W into a single 8 O load."

This is wrong, despite being often said. An amplifier can not double its current and power ratings simply by being connected to a different load. Each amplifier still has the same p, i and v ratings it had before. If you feed a single load with 2 amplifiers each of power rating P, connected in whatever fashion, it is not possible for the amps to suddenly have an output rating of 2P each.

A bridged output enables twice the voltage swing on the load. Thus a given power rail (or rails) can deliver upto 4x the power _using a different amplifier of different design & ratings_. This is why bridged amps are popular in car audio, they avoid the need to convert the low 14v supply to a higher voltage. Tabby 17:36, 3 December 2007 (UTC)

Well, look at it conversely...if an amp is designed to be operable into a 4 ohms load, then two such amps can be easily bridged into a single 8 ohms load. If one amp can drive 10W into 4 ohms then while bridging into 8 ohms, the total power delivered is 20W (same as two amps pusing 10W into 4 ohms each). Now consider a single amp driving 8 ohms (but capable of driving 4 ohms too): The power delivered is 5W (half of that into 4 ohms). So two 5W amps when bridged into 8 ohms should now drive 4x the power, i.e., 20W (as above). Rohitbd (talk) 13:37, 2 January 2008 (UTC)

I think you're assuming that current rating has some direct relationship with power rating. Amps are limited by their supply voltage and by the rate at which they can dissipate heat without being destroyed. An amp could be capable of sourcing a bazillion amps without being destroyed, but if the supply voltage is limited to a 9 V battery, the amp will have a very low power rating. Connecting two of them in bridged configuration into the same load will allow 4x the power, no? — Omegatron 02:42, 3 January 2008 (UTC)

[edit] DC offset & blocking capacitors

"One requirement of this configuration is that the output DC offset voltage of the amplifiers must always be equal (in magnitude and sign), preferably as close to zero as possible at no signal. Unequal offset will cause some direct current to flow through the load and the amplifiers, wasting power in all three. Practically, a small offset may be acceptable depending on final requirements or specifications."

No, this is a requirement for direct coupled capacitorless outputs, and applies equally to bridged and single ended drive. It has nothing to do with bridged outputs per se.

Bridged amps usually do use capacitorless output because the bridge topology makes this an inviting opportunity to save cost, but not all bridged amps do so, or can, and other amp types also often use capacitorless outputs.

Bridged amps can, and in a minority of cases do, run perfectly happily with unmatched and not very stable output offsets plus an output capacitor to block any dc offset.

"Amplifiers that use a single supply with an internal DC offset (at half the supply voltage for maximum undistorted voltage swing) must not drive that direct current into the load, so they typically use output coupling capacitors so that the speaker sees zero volts DC. In the case of a bridged amplifier, however, this is not necessary, since if both amplifiers have the same offset, the net voltage across the load is zero."

This isnt really true, though there is some truth within it. The fact that each output of a bridged amp quiesces at nominally the same V does not make it suitable for capacitorless working. For _any_ amplifier, small and stable V_offset is required for a capacitorless output, and such a condition is not automatic simply because a pair of amps are bridged. There have been numerous cases of hobbyists not appreciating this, and bridged capacitorless amps destroying themselves and/or speakers as a result. Tabby 17:36, 3 December 2007 (UTC)