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Gary's good tunes 700 build
- Thread starter jbeckva
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Gary it's all packed up ready to go to Lee. I'll be dropping it off in a few... 
Probably silly to ask but even though you bypassed the level controls, are they still on the faceplate for something to attach the knobs to?
I was curious about your own amp described as having a complimentary output section. I've seen the terms fully complimentary and quasi complimentary before, most notably in this forum but have not found an easy to understand explanation. Is it a different array of transistors and if so, what is the benefit over standard configuration?
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Post Number 27:
http://forums.phxaudiotape.com/show...Fully-Comp-PL-400-Using-White-Oak-Components-!!!!!
With fully comp circuit topology, the positive half and negative half of the signal are amplified through the final current gain sections with symmetrical circuit design through the use of NPN drivers in the plus half of the signal and PNP drivers in the minus half of the signal.
The quasi comp used NPN on the plus half, like the full comp version but the minus half had the PNP driver emulated by a combination of a small PNP transistor coupled with 2 NPN pre driver and driver instead of using PNP devices. When the Phase Linear was initially introduced, this is what the designers had available to design with so they went with it.
In the last of the PL400 and PL700 production, PL did convert to fully comp on a small number before end of life of the product.
Some benefits, amp gain is more equal on the positive and negative half of the signal. In the quasi comp version, the gain of the negative side was always higher than the positive half. The global feedback compensated for this difference however and quite effectively nulled it out.
The bias settings are now extremely close for both positive and negative half. Part of this comes from the use of precision 1% resistors in the bias resistor locations, the balance comes from the symmetrical topology.
The current limit protection circuits are also now fully symmetrical leading to a more balanced onset of protection for each of the plus and minus sides.
Of course with this PL400 Backplane board, the configuration of full comp or quasi comp is easily selected by several components, jumpers and of course the choice of output drivers.
In the full comp versions, the MJ21196 (NPN) is used in the pre driver and driver positions on the plus half and the MJ21195 (PNP) is likewise used in the pre driver and driver positions on the minus half.
The use of these outstanding drivers everywhere leads to a more robust output stage as a side benefit.
The quasi comp used NPN on the plus half, like the full comp version but the minus half had the PNP driver emulated by a combination of a small PNP transistor coupled with 2 NPN pre driver and driver instead of using PNP devices. When the Phase Linear was initially introduced, this is what the designers had available to design with so they went with it.
In the last of the PL400 and PL700 production, PL did convert to fully comp on a small number before end of life of the product.
Some benefits, amp gain is more equal on the positive and negative half of the signal. In the quasi comp version, the gain of the negative side was always higher than the positive half. The global feedback compensated for this difference however and quite effectively nulled it out.
The bias settings are now extremely close for both positive and negative half. Part of this comes from the use of precision 1% resistors in the bias resistor locations, the balance comes from the symmetrical topology.
The current limit protection circuits are also now fully symmetrical leading to a more balanced onset of protection for each of the plus and minus sides.
Of course with this PL400 Backplane board, the configuration of full comp or quasi comp is easily selected by several components, jumpers and of course the choice of output drivers.
In the full comp versions, the MJ21196 (NPN) is used in the pre driver and driver positions on the plus half and the MJ21195 (PNP) is likewise used in the pre driver and driver positions on the minus half.
The use of these outstanding drivers everywhere leads to a more robust output stage as a side benefit.
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Interesting and by the sounds of it, any changes at the factory were on the QT. So if my 700B dated from mid 1974, it would have been quasi complimentary? Was it subsequent availability of superior transistors that allowed the shift to fully complimentary in later versions?
My understanding is not great but to me, despite that feedback compensation, unequal gain would seem to invite instability.
Does a WO conversion involve fully complimentary output stages?
My understanding is not great but to me, despite that feedback compensation, unequal gain would seem to invite instability.
Does a WO conversion involve fully complimentary output stages?
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Glad it's doing good for ya Lee! Yeah Gary did the packing.. that was my reaction too, rofl. Got Nick/Doug's in prog for building tonight too.. hehe. Life's indeed good. 
To pack meant monitoring the cardboard recycle bin for several days and about a pint of glue.
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