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Old 15th July 2006, 07:41 AM   #1
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Default QSC power amp

Hi! http://www.qscaudio.com/support/tech...rt/schems1.htm what do you think of QSC , very goods amps whit the main power 0 = OUTPUTS yes, hot speakers , all power transistors whit alls pnp and npn collectors grounded . you short the outputs no problem just change fuses . they can run a full power 24 hours a day and the sound its SUPERB
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Old 16th July 2006, 11:57 AM   #2
djk is offline djk
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Glad you like yours.

Ways to improve your QSC:

Add power supply bypass caps, 22F per rail makes the bass sound much tighter.

Add 0.1F film bypass to all electrolytics in the signal path, bass sounds better, highs sound cleaner.

Remove current loading resistors on the output of the 5532 opamps, makes the amplifier sound much more dynamic. Be sure and use an external speaker fuse for protection against load faults.

There is still room for improvement, but these are the easy ones that make a big difference, and cost very little.
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Old 16th July 2006, 05:58 PM   #3
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i'm not allowed to do any modifications to my customers , repair this monsters means for olds equipements caps and for the new switching power supply amps complete main boards , for intermediates 50 Hz power supply models sometime few transistors and/or voltage amps modules . and often some little problem whit 15 Volts zeners diodes and resistors . but y use an USA 900 for test of TASCAM equipments and if you think your modifications will improve the superb sound of my amp y will tray to do it . tanks .
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Old 16th July 2006, 08:06 PM   #4
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the main question : nobody built amps like this . all powers transistors collecteur grounded . no mica no compound . npn/pnp all toghether . you short outputs /no problem 24hday full power it's OK.linear amps plenty of bass and treble and medium as well .c'ant be . i now . need to try . yet still it mouve . eppur si muove .
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Old 17th July 2006, 02:38 AM   #5
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Is anyone aware of a source for a schematic. It sounds like an interesting design. Mike.
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Old 17th July 2006, 03:01 AM   #6
Enzo is offline Enzo  United States
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Aroound here we call that "flying rails" and many amps are made that way. Even small Peavey solid state amps are often wired that way. Or at least grounded emitter.

If you would ground the emitter in a conventional PP output stage, why not reverse things and ground the collectors and run the rails to the emitters? Then the output xstrs can be grounded removing the need for insulators etc.

The first post included a link to the QSC schematic collection.

The EX, MX, and USA series are not all that old and are typical. the Powerlite and PLX series are switchers.

In their flying rail circuit, the speaker is between the main filter cap common and ground. The "output" of the power stage is also grounded.

To the uninitiated, this arrangement looks counterintuitive at first, but once you look at it a bit, the amp topology is not all that strange, and it is just a change of frame of reference.
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Old 17th July 2006, 03:05 AM   #7
imix500 is offline imix500  United States
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Aren't the crown MA/MT series the same way? -The heatsinks are hot?
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Old 17th July 2006, 04:42 AM   #8
thejohn is offline thejohn  South Africa
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Quite a few PA amps are designed this way. Apart from my QSC I know the there are a couple of Peavey's and I forget what else. QSC schematics are mostly available for free download from QSC website...
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Old 17th July 2006, 04:43 AM   #9
thejohn is offline thejohn  South Africa
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...which is linked to in the first post!
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Old 17th July 2006, 07:50 PM   #10
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Quote:
Originally posted by Enzo

The first post included a link to the QSC schematic collection.


I missed the link , Thanks.
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