Hi Everybody, My question is this. If 2 identical amplifiers that have a Quasi complementary output stage are run in bridged mode, Will the gain of the positive and negative halves of the cycle now be identical and will all characteristics remain the same throughout the entire operating range?
Actually, properly done, bridging will improve "quality, distortion or other types of potential"
Main concern is current drive capability since in bridged amp, every half of the bridge handles only half of the load impedance.
Original amp's topology (being quasi or not) has nothing to do with it.
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A difference will be the amps now have to output twice as much current.
This is fine so long as the amps are capable of this.
Otherwise they might need a power supply upgrade. more output transistors and bigger heatsinks.
in theory this might work .... but there is a couple of parameters more
----one, that amplifiers channels should perform the same ( this doesnt apply only soundwise there is other characterisitics like idle stability , safety procedures ,input limmiting if existing )
----two , i presume that in a bridge mode the safety measures have to be far more sophisticated to be able to handle that ammount of current in the amplifier .
finally i would like to say that in a PA amlifier the schematic /topology of amplifier is only 25% of the story ....the rest 75 is the protection methods
happy regards sakis
----one, that amplifiers channels should perform the same ( this doesnt apply only soundwise there is other characterisitics like idle stability , safety procedures ,input limmiting if existing )
----two , i presume that in a bridge mode the safety measures have to be far more sophisticated to be able to handle that ammount of current in the amplifier .
finally i would like to say that in a PA amlifier the schematic /topology of amplifier is only 25% of the story ....the rest 75 is the protection methods
happy regards sakis
Thanks for the replies ,however I don't think I phrased my question correctly. I'll explain further. The author of the solid state design book I have states that the big disadvatage of the quasi-complementary design is that the gain of both halves are "almost identical" . Am I correct in assumming that the difference is in that the upper darlington (positive) section ,the current delivered to the load is the base current plus the collector current, while in the lower compound -complementary (Negative) part , the output current delivered is only the collector current?
FWIW, the EA Playmaster Twin 40 deals with the asymmetry by adding a diode & cap between the collector of the output transistor and the emitter of the PNP driver
here's an example with the 'Baxandall' diode:
http://ebaudio.com/sub_amp_project/60-100W-PA.pdf
here's an example with the 'Baxandall' diode:
http://ebaudio.com/sub_amp_project/60-100W-PA.pdf
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In proper bridging, you should have double the load Z in order to maintain safe output current. You should not be able to get any more output power than the two amps would normally produce separately, just that it is all into a single load. IOW, the current is the same. If you bridge the min load for one channel across both, then you are overloading the amps.
IMHO, bridging can be better, but the amp should be designed for it. IOW, connecting together two single end amps (+ output to gnd) driven by opposite phases of signal
is not the same as a balanced amp.(+output to -output) Typically, for a balanced amp each phase of the VAS is biased by the other and share the same common mode bias source.
Bridging cancels low order even harmonics, particularly the 2nd.
And replaces them with smaller, but higher order, harmonics.
Trade that often measures better, but measurement isn't everything.
As for a bridge always making a circuit more complicated, Class D
would be one notable exception. Bridge tied load is maybe one of
the easiest ways to Class D. or AD.
And replaces them with smaller, but higher order, harmonics.
Trade that often measures better, but measurement isn't everything.
As for a bridge always making a circuit more complicated, Class D
would be one notable exception. Bridge tied load is maybe one of
the easiest ways to Class D. or AD.
what is it that you dont agree or understand ????
a 2x50w amplifier will produce 100w in only 8 ohms load ..... driving this to 4ohms load will present a 2 ohm load for every sub amplifier and that is something that the original amp wasnt designed for ....
this was the theory approach
in practice though and now days sophisticated protection methods like inpout compressors or limmiters . advanced VI limmiters simple or palsive can do tricks like that but generally at full power things are marginal .....
by the book or the same reasons you will notice that an average 120w @8R amplifier presented in the forum will have a minimum of 4 transistors in the out and no protection at all ( VI limmiters )
classic japanese amplifier will produce almost the same power with only two transitors taken as a fact that transistors are going to be seriously stresed at full power contition versus long time of operation and in any case the amp if "abused " at this level will eventually overheat or totally fail .
now you may choose the way you like to go
kind regards sakis
This was the original question, and it has more to do with a quasi output topology than with bridgeing:
Assuming that the gains of the halves of a quasi push-pull amp are not equal (and this isa ctually an assumptiona s there are several ways to construct a quasicomplementary amp, not all of which produce gain asymetry), two bridged amps of wuch construction will still have gain symetry as at any given time one top and one bottom half are driving the load. However, without a whole lot of parameters and qualifications, this means next to nothing in terms of 'amp quality'.Just like there are numerous ways to construct a quasicomplementary amp, there are also numerous ways to make it bridged, or perhaps, more properly said, balanced output - and all of them have pros and cons, which of course, add up in the finished amplifier.
Assuming that the gains of the halves of a quasi push-pull amp are not equal (and this isa ctually an assumptiona s there are several ways to construct a quasicomplementary amp, not all of which produce gain asymetry), two bridged amps of wuch construction will still have gain symetry as at any given time one top and one bottom half are driving the load. However, without a whole lot of parameters and qualifications, this means next to nothing in terms of 'amp quality'.Just like there are numerous ways to construct a quasicomplementary amp, there are also numerous ways to make it bridged, or perhaps, more properly said, balanced output - and all of them have pros and cons, which of course, add up in the finished amplifier.
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