The key points are:
1)
the L-17C's input should be clamped to avoid overdriving, and
2)
additional log stages can be driven from the points labeled Y. These additional log
stages can be connected into the L-17C at the S+ and S- pins (pins 8 and 15).
Keep the capacitance at these pins as low as possible. If you use more than one
log stage, sum the outputs and feed them to S+ and S- through a cascode pair to
minimize capacitance, as shown in Fig. D3.
Fig. D3 (Connection of Additional Log Stages)
The L-17C's normal log stages carry 200 microamps per stage. If you add more than 400
microamps total current, you should connect S+ to S- through a resistor of ~2000 ohms.
As may be seen from Fig. B4, the S+ and S- connections are working into 1000 ohms.
Should you find that the added capacitance of the extra log stages has slowed down the
output more than you would like, you may put a 1.5k to 2k resistor across S+ S-. This
speeds things up, but will also reduce the output slope. Increasing the gain of the L-17C
output to compensate for the diminished slope can also slow down the output somewhat.
Consequently, you may wish to use a buffer amplifier on the output to get the required
slope with the fastest possible rise time. Some of these slowdown effects are
exacerbated by package-associated capacitances, and will be reduced in hybrids.
-D3-
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