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Diy ultra low noise suggestions
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Old 17th November 2018, 12:36 PM   #1
Serracin is offline Serracin
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Default Diy ultra low noise suggestions

Need a circuit for an ultra low noise, headphones amplifier, with a few millivolts in, possibly, microvolts. Ultimate quality, not necessary!
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Old 17th November 2018, 08:36 PM   #2
PRR is offline PRR  United States
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Put a preamp in front of any suitable headphone amp.
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Old 17th November 2018, 09:01 PM   #3
lineup is offline lineup  Sweden
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A headphone needs 1 or a couple of Volts.
The gain you need is like 1000.

Yes, first amplify using a good preamp.
Then feed into a headphone amplifier.

The preamp can be only one opamp of good quality.
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Old 17th November 2018, 09:54 PM   #4
MarcelvdG is offline MarcelvdG  Netherlands
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What source impedance and what application are you thinking about? You can only noise-optimize an amplifier when you roughly know the source impedance.
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Old 17th November 2018, 09:55 PM   #5
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Despite the praises of the NE5532 , it’s stil not good enough for background noise!
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Old 17th November 2018, 10:00 PM   #6
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Out of the various op and small power amps , similar to NE5532, TDA 2822 etc , want the best as of background noise, something like a practical, not theoretical at or less than 1 uvolts noise level. It’s needed for a performance HF radio reciever. They often use the noisy LM386, want something better.
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Old 18th November 2018, 07:00 AM   #7
MarcelvdG is offline MarcelvdG  Netherlands
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Again, what's the impedance driving the amplifier?

If it's very low, you can make a gain stage with an LT1028 or AD797 followed by a headphone amplifier, when it's not so low, a modern JFET op-amp is more suitable. In both cases you have to keep the resistance of the feedback network low because of its thermal noise.

In both cases a discrete gain stage with a BF862 or similar high transconductance JFET should work well, or with a bunch of them in parallel if needed. If the impedance is low, you could also make a discrete amplifier with a good bipolar transistor (like the 2SC2547, if you can still get them somewhere).
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Old 18th November 2018, 07:26 AM   #8
MarcelvdG is offline MarcelvdG  Netherlands
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If the impedance is low, this thread could be of interest:

ultra-low noise transistors.

By the way, are you sure it is the amplifier setting the noise floor, not the atmospheric noise or the radio front-end?
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Old 18th November 2018, 08:05 AM   #9
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HF radio reception is by nature, noisy. I am designing a low noise receiver , and want to keep the internal noise as low as possible. Most designs make use of the LM386, but, it’s inherited noisy.

Not yet sure about the z input to the af amplifier yet, but could be from 50 ohms to 10k !
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Old 18th November 2018, 08:05 AM   #10
cowanaudio is offline cowanaudio  Australia
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Quote:
Originally Posted by MarcelvdG View Post

By the way, are you sure it is the amplifier setting the noise floor, not the atmospheric noise or the radio front-end?
That's exactly where the dominant source of noise is. Reducing noise down stream will have little effect.
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