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davidallancole 26th November 2005 08:14 AM

ccs biased output device
Every amplier schematic I have looked at seems to use a constant current source for the ltp and vas but I have never seen them used for biasing the output devices. Is there a reason for this?

To me it makes sense to use it. From a thermal stand point, if the temperature of the device increases, causing the transistor to draw more current through the base, the ccs would compensate and keep the current the same.

AndrewT 26th November 2005 08:23 AM

try looking a bit further.
There are many VAS topologies that do not use CCS. The Leach clone and Krell clone threads both show this complementary dual LTP with balanced VAS.

Now look at single ended output stages. A few use resistor loading but most use a CCS to improve linearity and efficiency.
Pass is an example but there are very many others.
I think most use a coupling cap to block the DC to the speakers but some use bipolar PSU and then need good DC stability to remove the offset problem.

Good searching

davidallancole 26th November 2005 07:33 PM

Thanks man! You just made me realize what I have already seen. I reviewed some of Pass's amplifiers last night and seen the ccs.

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