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Amplifier Specs: Input Sensitivity Question

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Chris Grimshaw:

--- Quote from: Douglas Cyr on July 07, 2021, 09:13:29 AM ---Thank you everyone! This is very interesting stuff. So is it safe to say the "volume knob" is actually just scaling the input sensitivity, not adding gain to the signal?

Sensitivity pot all the way to the right = 0 dB attenuation?

What does it mean if my digital amp goes from a -dB value to +dB value on the inputs? (Powersoft T302 - input sensitivity 2.57 Vrms)

--- End quote ---

If you leave all the settings at 0dB and apply no EQ, then 2.57Vrms into that amplifier will produce maximum output. If you set it for +6dB, you'll need 1.385Vrms to reach max. output.

Chris

Peter Morris:

--- Quote from: Douglas Cyr on July 07, 2021, 09:13:29 AM ---Thank you everyone! This is very interesting stuff. So is it safe to say the "volume knob" is actually just scaling the input sensitivity, not adding gain to the signal?

Sensitivity pot all the way to the right = 0 dB attenuation?

What does it mean if my digital amp goes from a -dB value to +dB value on the inputs? (Powersoft T302 - input sensitivity 2.57 Vrms)

--- End quote ---
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This might help - The T302 has a gain of 32 dB or about 40 times ... 2.57 volts x 40 = 102.8 volts  = 1320 watts into 8 ohms (about right - rated 1200W)

You can do it the other way - 2.57 volts = 10.42dBu + 32 dB = 42.42 dBU = 102.3 volts ... about the same as above.

Now you can modify the gain of your T302 with your software (Armonía +) - if you add 6 dB the gain (38 dB) will be 80 times so you will only need 1.285 volts for full power.

Luke Geis:
The gain settings in many amps tend to confuse novice users. The long and short of it is that at some point, amp designers realized that when you got to rated output power with less drive signal ( the level from your mixer ) the users thought it had more power and output. The input attenuator has always been used because you can use it to tune the systems dynamic range for the best signal-to-noise ratio. With a high input sensitivity, any little bit of noise at the input becomes a lot of noise at the output of the amp. If you turn the attenuator down, the noise floor goes down too. The potential output of the amplifier is still the same though, it just requires that much more drive level to achieve full output. With a low sensitivity input, you inherently have a lower noise floor. You will have to send a higher drive level to achieve full output, but it isn't much different than turning down the attenuator as a gross analogy. The problem is that not all mixers and sources have enough output to drive a low input sensitivity amp to full output. Some mixers can only produce +12dbu of output before they clip, so if the amplifier requires +18dbu to achive full rated power, you will clip the mixer before the amp is clipping. Conversely, if you have a mixer capable of producing +24dbu of output, an amp with a high input sensitivity will be clipping LOOOONG before the mixer does. This is why many amps come with adjustable input sensitivity settings. It adjusts the amp to work best for your needs and situations.

Douglas Cyr:
Thanks for all the input everyone, this exactly the information I wanted.

Doug

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