SSM2167 Gate question

I'm designing a product using a couple of these preamps. I have them in a custom dev board now and for the most part things are fine. However, I've discovered that need all of the features of this device EXCEPT the noise gate. I understand the concept of having one there, and at first I thought it would be a good thing. My problem is that some of the signal levels coming in from the WL93 subminiature condenser mic are so small that i guess it's close to the noise floor of the preamp. This application requires me to pick up ambient noise in the room, not just high sound pressure levels like I would get if it were being used to mic someone speaking directly into it. I tried 5K and even 10K resistors on the gate pin but they killed the ambient levels I need to get.

I like the expansion/compression performance of the device and when i take the gate resistor completely off pin 7 it lets everything in the background through nicely. I'm concerned because the datasheet advises against using anything over a 5K resistor because "The noise floor of the SSM2167 prevents the noise gate from being lowered further without causing problems". I am also getting some pumping noise presumably from the level detector capacitor at times as well. Is there any way to effectively and reliably turn off the noise gate/level detector of this device?  I have not started playing with different values of level detector caps yet.. I have some on order.

Thanks

Chris

Top Replies

    •  Analog Employees 
    Jul 4, 2012 +1

    Have you looked at the SSM2166? This preamp is similar to the SSM2167, but is a bit more flexible. Specifically, its noise gate threshold can be set to a lower point, between 300 uV rms and 20 mV rms …

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    •  Analog Employees 
    on Jul 4, 2012 12:38 AM over 8 years ago

    Have you looked at the SSM2166? This preamp is similar to the SSM2167, but is a bit more flexible. Specifically, its noise gate threshold can be set to a lower point, between 300 uV rms and 20 mV rms (-70 to -34 dBV). This is compared to a range of 1 mV rms to 10 mV rms (-55 to -40 dBV) for the SSM2167. The SSM2166 also has an adjustable rotation point, while this is fixed on the SSM2167.

    If you still want to use the SSM2166 (it sounds like you have already designed hardware, after all), then might you be able to use a microphone with higher sensitivity? It looks like the WL93 has a -38 dBV sensitivity. If you use a different mic with higher sensitivity than that one, then you'd be shifting the dynamic range of the mic output up in voltage. If the shift is high enough, then you might be able to pull the ambient noise up above the level of the noise gate threshold.

    Do you know what the SPL of the ambient signals you're trying to capture is? How far below the noise gate threshold is the ambient noise?

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    •  Analog Employees 
    on Jul 4, 2012 12:38 AM over 8 years ago

    Have you looked at the SSM2166? This preamp is similar to the SSM2167, but is a bit more flexible. Specifically, its noise gate threshold can be set to a lower point, between 300 uV rms and 20 mV rms (-70 to -34 dBV). This is compared to a range of 1 mV rms to 10 mV rms (-55 to -40 dBV) for the SSM2167. The SSM2166 also has an adjustable rotation point, while this is fixed on the SSM2167.

    If you still want to use the SSM2166 (it sounds like you have already designed hardware, after all), then might you be able to use a microphone with higher sensitivity? It looks like the WL93 has a -38 dBV sensitivity. If you use a different mic with higher sensitivity than that one, then you'd be shifting the dynamic range of the mic output up in voltage. If the shift is high enough, then you might be able to pull the ambient noise up above the level of the noise gate threshold.

    Do you know what the SPL of the ambient signals you're trying to capture is? How far below the noise gate threshold is the ambient noise?

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