tirsdag 18. juli 2017

BA662 pinout

While drawing up various uses of the Roland IR3109 VCF-chip, I needed to make an Eagle part for the OTA used in the resonance circuit. My initial circuit was the one from the Jupiter 4 service manual, and it uses a BA662, IC17:



The service manual only shows a part using four pins while the BA662 has 9:
This shows that the BA662 is actually an OTA and a buffer combined into one package. The buffer is apparently not used in the JP-4, so how is it disabled?

The Juno-6 and Juno-60 service manuals answers the question:
Pin four, the buffer control, is connected to -V and the buffer input is connected to +V. The buffer output, as expected, is not connected to anything.

Incidently, the IR3109 itself is just four OTAs, four buffers and an exponential converter connected to the control of each OTA.

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