When the heatsink is anodised, the transistor is electrical isolated from the heatsink, so the problems listed above are not relevant.
Years ago, I built an amp that uses 5-Pairs CFP output stage without washers. MJL4281/4302 outputs, just grease. Heatsinks were mounted in wooden case, and NPN devices got their own heatsink, so did the PNP with their own heatsink, and the only voltage difference between the two heatsinks, was the VDrop on the 0.15ohm output collector (emitter) resistors.
No Shock hazard, no hot transistors. Survived a few short circuits, including a blown voice coil, NO output protection, just a 6.3A fuse in the power supply.
It can be done, and very simple!
No Shock hazard, no hot transistors. Survived a few short circuits, including a blown voice coil, NO output protection, just a 6.3A fuse in the power supply.
It can be done, and very simple!
but I see alot of the amps still use mica isolators even after anodizing. Isnt anodizing fragile enough?
apart from just this heatsink aspect QSC designs are mostly with BJT based IC in the input stage which itself with degrade the quality.
I would thinks so Given the drilling and tapping of Mounting holes necessary for the devices themselves.
Going for a big enough Heatsink to deal with the Mica 'losses' would seem the clever path.
Unless Firmly fixated on production costs 😉
Hi Guys
As mentioned, QSC uses a grounded-collector output circuit that allows direct bolting of the output transistors to the heat sink. There are far more CONS to this circuit than there are PROS for it or for the mechanical arrangement.
The only two PROs are:
Electrically, only the output devices and drivers see the full supply voltage.
Mechanically, thermal resistance is reduced by the elimination of the mica between the BJT and heatsink. This expands to include the benefit of error reduction in the use of thermal grease - a universally abused substance.
The CONs are mall electrical. The supply is built as the usual split-rail but is pulled around by the output stage. The CT of the supply is the speaker output. This means that the PT has the full audio signal impressed upon it and across the insulation to the mains. With such a large AC signal impressed across the capacitance thereof the leakage currents through the PT are quite high.
Since the feedback take-off point is not directly controlled, the THD of this type of circuit is never what one would call hifi. Frankly, it is quite miserable.
Have fun
As mentioned, QSC uses a grounded-collector output circuit that allows direct bolting of the output transistors to the heat sink. There are far more CONS to this circuit than there are PROS for it or for the mechanical arrangement.
The only two PROs are:
Electrically, only the output devices and drivers see the full supply voltage.
Mechanically, thermal resistance is reduced by the elimination of the mica between the BJT and heatsink. This expands to include the benefit of error reduction in the use of thermal grease - a universally abused substance.
The CONs are mall electrical. The supply is built as the usual split-rail but is pulled around by the output stage. The CT of the supply is the speaker output. This means that the PT has the full audio signal impressed upon it and across the insulation to the mains. With such a large AC signal impressed across the capacitance thereof the leakage currents through the PT are quite high.
Since the feedback take-off point is not directly controlled, the THD of this type of circuit is never what one would call hifi. Frankly, it is quite miserable.
Have fun
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