Quasi-complementary Output Stage question.

[Tequilataz]

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?

[chrisbx1975x]

it will still just be quasi.

aside from that, bridged is generally only a good idea if you need very high output and are not concered with quality, distortion or other types of potential.

[juma]

Originally Posted by chrisbx1975x

it will still just be quasi.

aside from that, bridged is generally only a good idea if you need very high output and are not concered with quality, distortion or other types of potential.

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.

[nigelwright7557]

Originally Posted by Tequilataz

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?

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.

[sakis]

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

[AndrewT]

Hi,
forget about bridging until you know how and why amplifiers work.
When you can design an amplifier on the back of a fag packet, you are ready to start investigating the pros and cons of bridging.

[chrisbx1975x]

obviously the current capability is higher. the fundamentals of the separate circuits remain the same, two quasi complimentary circuits bridged. quasi has inferior characteristics to full, you are only bridging them.

make the circuit and find out.

[Tequilataz]

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?

[PeteMcK]

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

[CBS240]

obviously the current capability is higher. the fundamentals of the separate circuits remain the same, two quasi complimentary circuits bridged.

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.