QSC audio - floating supply amplifiers

[steph_tsf]

hello, from where comes the floating supply amplifier topology ? Why are there so few commercial designs based on floating supplies ? Of course we have QSC, but apart from them ? I've seen the ALTEC-LANSING 9446A, kind of QSC copycat, but that's all.

[sakis]

behringer does clone them also ... in a very reliable way also i could say for a chinese made amp

the original goal was a PA amlifier that will be impossible to blow ...or lets say idiot proof ...amazing amps for subs but other than that their sound is average .... very usefull and more effective than typical class AB amps but still the sound quality is kinda lower than others

[megajocke]

The Crown grounded bridge amplifiers also have floating power supplies.

[llwhtt]

Peavey too!

Craig

[Sebastiaan]

Dear,

The old Crown Macrotech's with grounded Bridge where so awesome on the bass. All schematics are available on the crown website. Very interesting topology.

A dutch audiophile company called "van Medevoort" Used the same principe in the 90's on his monobloc amplifiers, with again awesome tight bass. He just used one big capacitor for the floating supply.

With kind regards,
Bas

[davada]

Originally Posted by steph_tsf

hello, from where comes the floating supply amplifier topology ? Why are there so few commercial designs based on floating supplies ? Of course we have QSC, but apart from them ? I've seen the ALTEC-LANSING 9446A, kind of QSC copycat, but that's all.

By 'floating supply amplifier topology' I think you are referring to the QSC's MX series and other models where the load was connected between the center tap of the mains transformer and to ,what would normally be looked at as, the output of the amplifier.

Lets take the MX1500 for example. This design topology is very efficient but is less stable than a generic amplifier approach. The topology has to be heavily compensated for stability resulting in a lower slew rate relative to the amount of power these amps output.

The MX1500 is capable of an output of 1500W in bridge mode and has a slew rate of 20v/us. This is not very fast for this level of power and I think this amp would run into problems in the upper mid to high frequencies at high power levels.

I have heard many complaints about the sound quality of these amps when they are used for mid and high frequency applications. My response to that, IMO, was why would you use an amp for full range when it was intended for low frequency application. I'm not sure QSC would agree with this.

David.

[steph_tsf]

Originally Posted by davada

The MX1500 is capable of an output of 1500W in bridge mode and has a slew rate of 20v/us. This is not very fast for this level of power and I think this amp would run into problems in the upper mid to high frequencies at high power levels.

Yes indeed when you look to a QSC MX schematic, it is incredibly simple and you get the impression that there is some magic enabling you to use a NE5532 opamp powered by +15V and -15V as input stage and driver, just before the big power transistors. There is no VAS (voltage amplifier stage) is such arrangement. This is quite confusing. Where are the components defining the slew rate ? What's the magic, actually ? And I still don't understand the topology if used in bridged mode like Crown Marcro-Tech 600 does. Any help much appreciated.

[llwhtt]

I don't think you can compare the QSC circuit with the Crown Macro-tech 600, they are completely different. The Crown has basically two amplifiers per channel. One is for the audio and the other controls what side (+ or -) of the power supply gets grounded. There is NO center tap on the power xfmr and only one filter capacitor per channel. The only reference to ground for the power supply is the above mentioned "slave" amplifier. For a positive going signal the negative side of the power supply goes towards ground and vice versa. You can go to the Crown site and download the schematic to see what I'm trying to explain. The right side of the power section (high side) is for the audio and the left side is the power supply (low side).

Craig

[teemuk]

Seeburg also used the floating supply circuit in their jukebox amplifiers. Unlike Quilter Sound, they even managed to patent it.

[bear]

Take a look at Jim Strickland's patented amplifier the TNT 200 marketed by Acoustat. Pre-dates QSC by a decade or more, if I am correct. Same connection where the load is in the PS ground...

An interesting concept.