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In Reply to: RE: Shunt Reguated 45 upgrade kit interest posted by Nme on June 07, 2007 at 13:47:24
I don't know yet if or when we will offer a special 45 kit. That was the original intent when we started to look at the design many months ago, and this shunt reg conversion is being done to test the market potential for more 45 projects.
PJ has explained why the gain of this circuit is what it is. There aren't any good choices for a higher gain tube that can properly drive the 45 grid and also work as a shunt regulator for the whole amp. So to make a change to a higher gain driver we're talking about separate tubes, which means a chassis redesign. If we're going to go to that trouble there may be other changes to consider as well. For example I'd like to do a direct coupled version with an actively loaded 45. For that we would need a new power supply and a fair amount of time spent prototyping.
FWIW I haven't found passive controls to be optimal always. I've had a couple of instances where owners of very high end, high resolution systems have asked me to install a Foreplay III based gain stage at their passive control in order to correct sonic deficiencies they were experiencing.
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