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Topic: Connect Laptop to Amp (Read 11420 times) previous topic - next topic
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Connect Laptop to Amp

Reply #26 –
Quote from: Notat on
If an isolation transformer fixes it, it is most likely* a ground loop. Ground loops don't have to cause a 60 Hz hum. You hear whatever currents are flowing through the ground loop and that's all kinds of crazy stuff in the case of a laptop. Next time it happens, check and see if the laptop plug has a safety ground (3 pin plug) - I'll bet the noisy ones do. It is good design practice to include full-time isolation in systems like this.

The other possibility is that these laptops are putting out an RF component on the audio connection and the RF is being demodulated in your audio system. The transformer works because in addition to isolating it should naturally provide some RF attenuation.

Every laptop seems to have its own "character" when it comes to noise issues, so I wouldn't doubt that the exact cause varies from laptop to laptop - the iso trannies always do the trick, though.

I completely agree that isolation should be the first step in the signal chain in systems such as these, but unfortunately, "good design practice" was not followed on the original design, and the installation is so insanely complex that adding iso transformers on all inputs would be like remodeling your entire kitchen in order to change out the microwave.
"Not sure what the question is, but the answer is probably no."

Connect Laptop to Amp

Reply #27 –
Quote from: greynol on
The coax needs to be of the correct impedance (75 ohms?) to run long distances, or is this not right?


It is supposed to be 75 ohms. And some folks worry about whether the connectors are 75ohm connectors. Some cables use RCA plugs (not 75ohm). BNC connectors would be 75ohms. I suspect this is of little consequence in real world application.

Connect Laptop to Amp

Reply #28 –
Quote from: greynol on
The coax needs to be of the correct impedance (75 ohms?) to run long distances, or is this not right?

Correct, S/PDIF's coax spec is based on composite video transmission, which utilizes 75 ohm coax and connectors.

In fact, you can use good-quality composite video distribution amplifiers to distribute S/PDIF (or AES, for that matter), although there will, of course, be no reclocking of the audio data, so you have to be a little careful as to exactly where in a signal path you utilize them.

Actual digital audio DAs are the preferred solution, of course, but I was on an install a few years ago where AES sync (digital silence) was distributed throughout a fairly large multi-room facility using NTSC DAs. 
It was done for budgetary reasons (they had a bunch of the NTSC DAs leftover from the remodel and upgrade of another facility), but because they had thought the design out carefully and were able to arrange the rooms in such a way that the runs from the main sync generator were kept fairly short (<150' or so), and the NTSC DAs were the first and only DAs in the signal path, it worked just fine.
"Not sure what the question is, but the answer is probably no."
 

Connect Laptop to Amp

Reply #29 –
Quote from: Notat on
Quote from: odyssey on
I still would love to hear jitter. How obvious is it? Do you have any sample of how it sounds? Can you measure it? Can you get rid of it?


Quote from: southisup on
Would there actually be a "loss in audio quality" using the headphone jack rather than a USB DAC to connect to the amp? By this I mean could most people tell the difference in a double blind test?


In both cases, to a first approximation, we're dealing with higher noise floors. You can easily hear your noise floor by playing silence and turning up the gain at your amplifier.

To a second approximation, jitter and interference from internal ground loops etc in digital electronic equipment can result in a non-white noise floor. This sort of noise is more objectionable and easier to hear at lower levels.

I don't believe that jitter increases the noise floor, but that rather it is a type of distortion of the audio signal. If it affected the noise floor then it would be audible over digital silence, which of course it is not.