Talk:Bridged and paralleled amplifiers

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

message: H-Bridge refers to a fairly specific circuit.  As such, it is not the correct term in general.  Transformer coupled amplifiers, resistively loaded, and certian other amplifiers may not fit this discription very well.  I don't think I've ever seen "h-bridge" used outside of a switchmode context.  Mag-amp based designs likely don't fall well into this category.  —Preceding unsigned comment added by 71.32.46.111 (talk) 09:32, 28 September 2008 (UTC)
thread_title: H-Bridge

message: "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)
replies: text: 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)
replies: text: The myth section is misleading. Bridging amplifiers to get well over 2x power is quite normal in situations where a limited supply rail means that otherwise unfeasibly low loudspeaker impedances would be required.  Stub Mandrel (talk) 16:12, 26 January 2018 (UTC)
replies: text: Stub, only if the power supplies are underwhelming for the rest of the amp and your building circuit(s) they're on can handle it does doubling the number of supplies suddenly have much advantage. The way most pro bridgeable stereo amps are rated is for their bridge mode up to their 1% THD point and then measured for their respective lower THD in stereo mode at arbitrary divisions of that rating per impedence for each channel and the fact their limiters are then set by design based on that means you usually get two-thirds more available voltage bridging than the simple summation of the individual stereo channels at that given impedence, but at the expense of increased distortion, stress on the components, heat, and risk of shut down.  This seeming increase in available gain is partly an artifact of rating, measurement, and hardware limiting and not really real, and a little part of it is a real power increase, albeit poor-quality gain increase by running the unit with floating ground and in a forced lower impedence state.  If the amp is also not completely up to spec, all that distortion, stress, heat, and risk of shut down gets even worse and the lifespan will be much lower for the amp when bridged.  Two-thirds more voltage is only an increase in 4.4dB and less than double the perceived volume even at 20hz and is WAY less than double the volume at higher frequencies where you need about four times the gain (+12dB) to actually double the volume.  So it usually makes no sense to run a pair (or multiples of a pair) of identical subs from a single bridgeable stereo amp in bridge mode for such a moddest increase of available low-quality headroom instead of just running the amp in cleaner, safer stereo mode that will also keep the sound in stereo if you do, what little stereo imaging there is in the sub frequencies.  -DJ Reticuli 2605:A000:1301:8B09:9CBB:419B:92A6:76AC (talk) 22:24, 8 March 2019 (UTC)
thread_title: The 4x power myth

message: "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)
thread_title: DC offset & blocking capacitors

message: I have moved the following from the main article. The context is indicated by comment annotations E1 and E2 in the main article.
=== E1 ===
(edit) Because the above is so authoritively written, I am loathe to overwrite the "facts"in this section. Perhaps the originator will choose to investigate and clarify. It should read TWICE the power. see other edits below when the formula above is used correctly (end of edit)
(edit2) No, it is 4 times. when you double voltage, current doubles too, so four times output. This really should be in the talk page...
=== E2 ===
(Edit) The statements above fail to mention that when two amplifiers are connected in bridge mode the output impedance of the pair is DOUBLED. Thus, if "2R" is substituted for "R" in the formula given, (together with the implied "2Vsquared) it will be seen that the output power is also DOUBLED and not quadrupled as stated. 
The first one appears correct to me; the second one I cannot comment on (My experience in analogue circuit design - and particularly amplifier design - is lacking) OwenS | T | C | 13:28, 3 September 2010 (UTC)
thread_title:  Moved from main page (Ref: Expert needed) 

message: (Edit) The statements above fail to mention that when two amplifiers are connected in bridge mode the output impedance of the pair is DOUBLED. Thus, if "2R" is substituted for "R" in the formula given, (together with the implied "2Vsquared) it will be seen that the output power is also DOUBLED and not quadrupled as stated. 
The first one appears correct to me; the second one I cannot comment on (My experience in analogue circuit design - and particularly amplifier design - is lacking) OwenS | T | C | 13:28, 3 September 2010 (UTC)
thread_title:  E2 

message: Also the Bridge-tied load BTL article should be merged here, or at least the duplication eliminated somehow. 86.121.137.150 (talk) 21:16, 9 December 2014 (UTC)
replies: text: Agreed and  Klbrain (talk) 13:10, 6 August 2017 (UTC)
thread_title:  Merger of ''Bridge-tied load'' and ''Bridged and paralleled amplifiers''