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Query re setup of  SSM2166

Question asked by andrewdwork on Feb 12, 2018
Latest reply on Feb 23, 2018 by JinoL

Hi, I have several datasheets for this device. Revision F removes all setup info. Revision E appears to have the first two steps of set up reversed. I have a revision B from the Web that makes more sense. Essentially the rotation point set up and VCA gain setups are reversed in revision E. The gain has  to be set before the rotation point can be adjusted correctly.

The input to the VCA and buffer is about 200mV withthe pream gain set to unity. Pins  5 & 6 are linked. I am using the VCA gain set to about 2 and this gives an accurate rotation point at 540mV (which I need for the unit I am running). The limiting action is very effective from about 200mV RMS input with a compression ratio of about 2:1 to over 1V RMS input.

The down side is that the value of R gain is hyper-critical, I have 1.43K 1% fitted, and the gain does vary a little from device to device from my observations of 10 units. By attenuating the input and operating with gain, R gain becomes less critical but, the rotation point setting is then not so effective at limiting the output. With Rgain = 1.43K, the limiting is really very effective as described above.

Is this because above the rotation point the gain is still present, and so the limiting action is less than at unity gain?

The gain vs gain adjust resistor graph suggests that the values were obtained with pin2 at gnd. Pin2 to gnd through 330Ohms is supposed to mute the device. Should this read pin 12 (power down?)

Any clarification would be useful.