Bigman80
Grandmaster
The HiFi Bear/Audioaddicts/Bigbottle Owner
Posts: 16,398
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Post by Bigman80 on Dec 15, 2020 10:25:36 GMT
Feel free to provide an answer and i'll collate the best ones and make this topic a sticky.
Answers should be in laymans terms!
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Post by misterc on Dec 15, 2020 10:28:04 GMT
Later this week Oli I will demonstrate the 50/75 Ohm reflection issue I display on the scope for you but I will use the Lecroy 12 bit badboy and take some screen shots so the guys can understand what is happening to their signals due the reflections in the cabling.
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Bigman80
Grandmaster
The HiFi Bear/Audioaddicts/Bigbottle Owner
Posts: 16,398
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Post by Bigman80 on Dec 15, 2020 10:47:15 GMT
Later this week Oli I will demonstrate the 50/75 Ohm reflection issue I demonstrate on the scope for you but I will use the Lecroy 12 bit badboy and take some screen shots so the guiys can understand what is happening to their signals due the reflections in the cabling. Thank you Tony, i was hoping you would say that. But keep it very simple as i have intentions to keep this very beginner friendly. Imagine explaining it to a 10 year old  |
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Post by electronumpty on Dec 15, 2020 10:52:47 GMT
Good topic , I read about it all the time and still am none the wiser.
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Bigman80
Grandmaster
The HiFi Bear/Audioaddicts/Bigbottle Owner
Posts: 16,398
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Post by Bigman80 on Dec 15, 2020 10:57:18 GMT
Good topic , I read about it all the time and still am none the wiser. I am hoping we can create a sort of beginners guide to the topics that are most likely talked about or are misunderstood. The Digital video i stiky'd earlier this week was the starting point that got my brain going and as we have some super minds on this forum, i thought we need to make use of them! lol |
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Post by firebottle on Dec 15, 2020 12:04:13 GMT
I am assuming you are talking about digital interconnections.
Firstly Impedance isn't the same as Resistance. The Impedance of a circuit is the effective resistance of an electric circuit or component to alternating current, arising from the combined effects of ohmic resistance and reactance.
Simple explanation:
In radio frequency installations it is usually best to achieve the closest impedance match so that the maximum power transfer is achieved.
With digital signals 'power' transfer isn't important however a mismatched circuit will still suffer from reflections of the signal back down the transmission line. Reflected signals upset the quality of the signal.
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Bigman80
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The HiFi Bear/Audioaddicts/Bigbottle Owner
Posts: 16,398
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Post by Bigman80 on Dec 15, 2020 12:08:31 GMT
I am assuming you are talking about digital interconnections. Firstly Impedance isn't the same as Resistance. The Impedance of a circuit is the effective resistance of an electric circuit or component to alternating current, arising from the combined effects of ohmic resistance and reactance. Simple explanation: In radio frequency installations it is usually best to achieve the closest impedance match so that the maximum power transfer is achieved. With digital signals 'power' transfer isn't important however a mismatched circuit will still suffer from reflections of the signal back down the transmission line. Reflected signals upset the quality of the signal. no, more along the lines of when matching a preamp to a power amp, but the 50/75ohm cable thing is a useful addition. Ie, the meaning of driving a high impedance etc. |
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Post by firebottle on Dec 15, 2020 12:47:07 GMT
Impedance 'matching' as such doesn't apply to low level audio signals for one important reason. We are not trying to achieve the best power match, i.e. the maximum voltage and current such as a transmitter into an antenna.
An audio interconnection (not speaker output) is usually only specified as a voltage. The current level is to all intents and purposes immaterial.
To keep the voltage high the 'load' impedance/resistance is kept high, 10k ohms or more, and the source impedance/resistance is kept low, usually less than a few 100 ohms.
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Bigman80
Grandmaster
The HiFi Bear/Audioaddicts/Bigbottle Owner
Posts: 16,398
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Post by Bigman80 on Dec 15, 2020 13:22:21 GMT
Impedance 'matching' as such doesn't apply to low level audio signals for one important reason. We are not trying to achieve the best power match, i.e. the maximum voltage and current such as a transmitter into an antenna. An audio interconnection (not speaker output) is usually only specified as a voltage. The current level is to all intents and purposes immaterial. To keep the voltage high the 'load' impedance/resistance is kept high, 10k ohms or more, and the source impedance/resistance is kept low, usually less than a few 100 ohms. So then why is there the idea of "mismated components" |
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Post by macca on Dec 15, 2020 13:45:01 GMT
input impedance of the power amp should be at least ten times, ideally twenty times or more the output impedance of the pre-amp.
If not you can get roll off of higher frequencies and a general 'lack of drive.'
usually it's not a problem but with a passive pre connected to a power amp of lower than usual input impedance you can get this issue in 'the real world.'
Capacitance matching can also be an issue but I confess I don't really understand that.
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Post by rexton on Dec 15, 2020 16:46:52 GMT
What a great idea Oli, awaiting Tony's answers, should be good stuff.
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