| Electronics > Beginners |
| Just how bad is it? Audio mixer with headphone amp. |
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| paulca:
I do have the 1Khz square scope calibration signal... It might at least be square. |
| paulca:
Also it's slightly odd that the amps do not seem to be amplifying the noise much, they seem to just be modulating their output with it. Maybe that makes sense as the noise is not on the inputs, but the power rail. |
| BrianHG:
--- Quote from: paulca on February 27, 2018, 08:54:06 pm ---The PC output is a Texas Instruments PCM2707 USB DAC, but I was trying to use a YouTube video :-[ I might install audacity again at some point. --- End quote --- Arrrggg, 48khz 16bit as a reference. Even bottom of the line motherboard/laptop audio chipsets usually are better quality as long as you have a good grounding on you cable. These bottom end USB Dacs are only good if you need another sound card source. There do exist high quality USB dacs, but, the PCM2707 isn't one of them. Here is 2 samples, 24khz square which will come out as sine and 12khz square sampled at 48khz. |
| paulca:
Scoped them from the audio out and they both show as sine waves. Slight wobbly, but I was holding the probe to the jack plug. :) Come to think... you can't really do a 20Khz square wave with a 48Khz digital source, not very well anyway, it's going to filter down to a sine anyway isn't it? Hang on a moment. I doubted my little chinese friend. I hooked it up and got these: and... pushing it a bit. The output is not attenuatable though and it's a bit much to be putting into the pre-amp. I can try tomorrow evening, can't tonight, I also need to use the little generator up to a jack plug. |
| paulca:
--- Quote from: BrianHG on February 27, 2018, 09:09:40 pm ---Even bottom of the line motherboard/laptop audio chipsets usually are better quality as long as you have a good grounding on you cable. These bottom end USB Dacs are only good if you need another sound card source. There do exist high quality USB dacs, but, the PCM2707 isn't one of them. --- End quote --- That PCM2707 sounds a thousand times better than my Intel HDA on my motherboard. Maybe not in it's sound reproduction, but in the fact that the PC onboard sound is completely saturated in video card noise. Was sending me nuts until I happened to hook up that DAC which is a £3 board from Alice on ebay. No more noise. My my audio project, which this thread's amp is the heart of I hope to use a PCM2902 or similar. I'm open to suggestions. |
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