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Noisy Purifi amplifiers

amarsicola

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Because the gain is doubled, and hence any noise (internal from the amp, or coming from the source) is also doubled.
Starting from the math or @sarumbear in one of the first posts:

"Sound levels in a quite studio is around 20dBSPL. Loud club (disco) level is around 100dBSPL at 1m. It translates to 110dBSPL at 10cm. Assuming that is the maximum volume your system is set to you should start hearing noise from an amplifier that has a noise figure of 90dB or less. Purifi spec is 116dB SINAD, 26dB better"

So i tend to disagree, even if noise is double you add just around 6dB in the equation and the Purifi should be 20dB better than noise floor.
You shouldn't be hearing absolutely anything even with the higher gain configuration of the Audiophonics if properly designed.
 

antcollinet

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Starting from the math or @sarumbear in one of the first posts:

"Sound levels in a quite studio is around 20dBSPL. Loud club (disco) level is around 100dBSPL at 1m. It translates to 110dBSPL at 10cm. Assuming that is the maximum volume your system is set to you should start hearing noise from an amplifier that has a noise figure of 90dB or less. Purifi spec is 116dB SINAD, 26dB better"

So i tend to disagree, even if noise is double you add just around 6dB in the equation and the Purifi should be 20dB better than noise floor.
You shouldn't be hearing absolutely anything even with the higher gain configuration of the Audiophonics if properly designed.
Vco stated that the noise was not there with a shorted input. Which means the noise source is not inside the amp, but external (or pickup in a high impedance input - all amps have noise measured with input shorted)
 

amarsicola

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...after opening the amp that feeling turned out to be right. It was set to "Configuration 2" for approx. 2.25V RMS. So I removed the gain jumper to get to the 4.2V RMS configuration. And gone was all the noise ...
Vco said the noise was gone by changing configuration of gain jumpers, or am i missing something?
 
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vco1

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Vco says… ;)

I did a couple of things. More or less at the same time. So it’s hard to know which of those were responsible for removing the noise.

1, I shortened the rca inputs. They were not in use. Don’t think that had much effect. If any.
2. I changed the config of the gain jumper. That most likely removed the noise. At least a fair bit.
3. I noticed the noise level is also dependent on the input being in use. That is, if the input device (a Topping DX7Pro) is off, there seems to be more noise (like noticeable more) than when it’s switched on.

Bottom line is that the amps are quiet with all of the above ‘measures’. And I’m not that curious to do further investigations. I prefer to listen to music and enjoy my new setup.
 
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