In most implementations of the circuit. The QSC's only have two stages of current gain (even the RMX5050!) and you need all the drive you can get out of the op amp. The 5532 was made for driving 600 ohm loads at full signal swing, the TLxxx's cannot. Therefore, they distort when asked to. If the outputs are darlingtons you effectively have a triple and the TL072 will drive it just fine. Crown uses a similar op amp on the low side of the grounded bridge (which is essentially a QSC amp with a triple EF output).
"In most implementations of the circuit. The QSC's only have two stages of current gain (even the RMX5050!) and you need all the drive you can get out of the op amp. The 5532 was made for driving 600 ohm loads at full signal swing, the TLxxx's cannot. Therefore, they distort when asked to. If the outputs are darlingtons you effectively have a triple and the TL072 will drive it just fine. Crown uses a similar op amp on the low side of the grounded bridge (which is essentially a QSC amp with a triple EF output). "
You can use a TL072 on the low side in a Crown because the input will not drive it into phase reversal.
"can you explain to me how the qsc clip indicator works? its basically just a bridge rectifier feeding an led. "
The output of the opamp is very low until the amplifier clips, then the feedback drives the output as high as it can go (making the bridge conduct).
You can use a TL072 on the low side in a Crown because the input will not drive it into phase reversal.
"can you explain to me how the qsc clip indicator works? its basically just a bridge rectifier feeding an led. "
The output of the opamp is very low until the amplifier clips, then the feedback drives the output as high as it can go (making the bridge conduct).
Here QSC's basic describtion:
http://www.qscaudio.com/support/library/papers/amptalk.pdf
and a thread abbout this:
http://www.diyaudio.com/forums/solid-state/169988-qsc-topology-but-without-opamp.html
and to post #103 about
http://www.diyaudio.com/forums/soli...t-complementary-ab-bipolar-amplifiers-11.html
not only QSC uses this output stage topology - go to post #17 about
http://www.diyaudio.com/forums/soli...on-type-k4000-k-4000-mkii-2x1000w-4ohm-2.html
more brands are ATC and Altec:
http://www.atcloudspeakers.com.au/index.php/amplifiers/atc-spa2-150-power-amplifier
http://www.vintagealtecinfo.com/Altec 9446A Power Amplifier6.html
I think, there are some more brands which uses this output stage topology.
I call them "OUT=GND". Other terms, that I read therefore, are "Floating Ground", Grounded Output", "Grounded Source", "Virtual GND" and "Floating supply". All these terms don't really describe, what is meant.
I want to find more informations and associated papers about this topology by google.
Is there a colloquial term in English therefore?
For me the greatest advantage is, that any silicone rubber insulating heat sink washers (mostly reinforced with fibreglass) for mounting of the power semiconductors are no longer necessary. This means a strongly reduced thermal transition resistance to the associated heatsinks.
On the other hand, this topology is difficult to control and tends to be ringing (oscillating), even without an OP-AMP in the negative feedback loop. Lead-lag compensation steps for perfect square wave behaviour are difficult to find, because the rules therefore seems to be different than usual. I would like to know the basic procedure. Who knows basic articles about this?
The associated patent must be this:
Two stage push-pull MOSFET power amplifier
Also the attached PDF is of interest - here it is possible to realize a sliding transition of the GND output connection.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.