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Thread: How to set amplifier input sensitivity.

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    Default How to set amplifier input sensitivity.

    I have a quad 520, it looks like this

    Quad 520f.JPG

    You see it has two nobs on it to adjust the input sensitivity.

    How do I find the optimal setting? Trial and error?

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    Senior Member bigshot's Avatar
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    It probably doesn't matter where you set it as long as it isn't all the way up or all the way down. Line level should be fine without adjusting in most cases.
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    In fact, I had it all the way up and wondered why the sound sounded amplified, as if the acoustic instruments were amplified. Anyway, better now.

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    It was clipping? Yikes!
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    Your advice has made a huge difference, I was on the point of dumping the amp, or the speakers! I’m really pleased now. Thanks for your input.
    Last edited by Mandryka; Jun-06-2019 at 12:46.

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    I've always wondered why designers would put a knob on something that is capable of totally messing it up. They could have made the range narrower so it didn't clip. I guess they were more interested in it being a "feature" than having it be user friendly and functional. Weird.

    I had a noise reduction unit once that I never turned the knob up over 25% because it massacred the sound if I turned it any higher. I can't imagine what you would use it that high for. They could have made the knob not go so high, but I guess "more is better".
    Last edited by bigshot; Jun-06-2019 at 17:31.
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    Senior Member millionrainbows's Avatar
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    Are people running input sources directly in to the power amp, without a preamp? I can see how the feature could help if there is no preamp.
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    Yes, if he has only one source and a way to adjust gain, he really doesn't need a preamp. I wouldn't be able to get by with something as bare bones as this myself, but I guess I can see an application.

    It sounds like he was adjusting the gain at the source though. Otherwise he wouldn't have been able to turn it all the way up to clipping. If that's the case, I would leave it at the middle detent and just adjust the volume on the source.
    Last edited by bigshot; Jun-14-2019 at 16:38.
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    What is "current dumping" all about, in reference to Mandryka's amp?
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    I think it's a design that is inexpensive to manufacture and produces good sound quality. We don't see it much here in the US. There are other ways to skin the cat that are more popular.
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    I do indeed run my source, a DAC, directly into the power amp and control volume digitally. That way there’s no colouration caused by a preamp.

    I couldn’t begin to explain how current dumping works, what it’s about is minimising distortion in class B.

    I had a scary incident yesterday with a quad amp, not the 520 but a 303.

    I touched it and the metal case was really hot! It was playing fine.

    Well, to cut a long story short, the problem wasn’t with the amp at all. It was with the DAC, which had failed and was emitting ultrasound, causing the output of the amp to short circuit.

    The reason I said scary was that, when I was testing things to try to find out what the problem was I was shocked by how quickly the amp’s heatsinks got hot, it was like someone has lit a Bunsen burner in there!

    Apparently it could have done a lot of damage, to both amp and tweeters. Fortunately no damage done - which is saying something about the build quality of the Quad amp.
    Last edited by Mandryka; Jun-14-2019 at 21:09.

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    Quote Originally Posted by Mandryka View Post
    I do indeed run my source, a DAC, directly into the power amp and control volume digitally. That way there’s no colouration caused by a preamp.
    That would be true if your DAC was outputting a digital signal, and your power amp had a digital input.
    But that's not the case; your power amp needs an analog signal, which it gets after the DAC has converted it from digital. So the OUTPUT of your DAC is still analog. Its analog stage could add distortion, be too strong, or too weak. The "digital volume" into the DAC has no real bearing on what level signal is going in to the power amp.
    "The way out is through the door. Why is it that no one will use this method?"
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    "In Spring! In the creation of art it must be as it is in Spring!" -Arnold Schoenberg

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    "I don't mind dying, as long as I can still breathe." ---Me

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    Quote Originally Posted by Mandryka View Post
    I do indeed run my source, a DAC, directly into the power amp and control volume digitally. That way there’s no colouration caused by a preamp.
    That would be true if your DAC was outputting a digital signal, and your power amp had a digital input.
    But that's not the case; your power amp needs an analog signal, which it gets after the DAC has converted it from digital. So the OUTPUT of your DAC is still analog. Its analog stage could add distortion, be too strong, or too weak. The "digital volume" into the DAC has no real bearing on what level signal is going in to the power amp.

    The DAC probably has a "ceiling" of so-and-so volts, which is called "line level." Of course, the input signal will also vary this. How strong of a "line level" sounds best for your amp?

    Why not bypass all volume control? I suspect your DAC has one because it is designed for headphone listening.
    Last edited by millionrainbows; Jun-17-2019 at 05:09.
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    "In Spring! In the creation of art it must be as it is in Spring!" -Arnold Schoenberg

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    "I don't mind dying, as long as I can still breathe." ---Me

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    Preamps don't generally color the sound. There has to be something wrong with it to do that. What he's doing works. Why buy black electronic boxes you don't need? I'd just use a digital volume control on the source and set the amp at the zero setting. That works fine.
    Last edited by bigshot; Jun-17-2019 at 08:33.
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    Quote Originally Posted by millionrainbows View Post
    That would be true if your DAC was outputting a digital signal, and your power amp had a digital input.
    But that's not the case; your power amp needs an analog signal, which it gets after the DAC has converted it from digital. So the OUTPUT of your DAC is still analog. Its analog stage could add distortion, be too strong, or too weak. The "digital volume" into the DAC has no real bearing on what level signal is going in to the power amp.

    The DAC probably has a "ceiling" of so-and-so volts, which is called "line level." Of course, the input signal will also vary this. How strong of a "line level" sounds best for your amp?
    Correct, and the sound quality of a DAC is greatly determined by the quality of the output stage.

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