Friday, October 22, 2010
Pass B1 driver stage
After construction of the ESP P37a I was fired up to build another vero-brd. wonder. This is the Pass B1 preamp/driver cct. brd. which went into the black anodized Hammond case. Two jFETs do all the work in this preamp. One jFET is just a constant current source (CCS) for the other. So really only one jFET sees the signal. Simple and effective. The problem is because this is a source follow there is no gain. In fact only 85% of what goes in comes out. But it comes out very well.
Two 10,000uf caps provide power filter and storage. A 50K Alps pot controls input level and large 1uf PIO Russian military caps de-couples the preamp. a 10uf poly provides output. 2SK170 (BL) jFETs are used.
Placement of components on vero-brd. is critical unless you want span the brd. with links. For me there is a lot of thought which goes into component placement to ensure links are at a minimum.