Hi everyone!
I am still fairly new to all of this stuff. Needed an amp for my desktop speakers and ended up buying a Pro-Ject MaiA (DAC-Amp-Combo).
When connected without any sources (and also with sources) there is a quiet noise and a faint 7.2kHz (measured with mobile phone) tone.
I have a small desk, so I even notice it from my speakers when the room is quiet.
But it is really apparent when I connect my headphones (32Ohm Focal Listen ) or any IEMs.
They are otherwise dead silent when I connect them to my Focusrite Scarlett 2i2.
Now I think about returning the unit … but I am not sure if this is maybe something that is kinda expected for this kind of device?
It is normally supposed to deliver far more power than just a dedicated headphone amp. Does this change the rules, so that I will run into the same problem for all devices of this class?
Here is an image of the phone measurement. The dark band in the lower spectrogram is the noise floor of the room ( +2 fans) and the brighter parts are me holding the microphone in front of the tweeter.
I would never recommend plugging headphones into a stereo amplifier, they are much more geared towards speakers.
Ah, ok, so that was just a wrong assumption by me then I guess. This thing is really well suited for a desktop setup though.
The noise is there, even without any source connected (all cables pulled). It is actually loudest when the gain is set to zero, gets a little bit quieter when increasing the gain up to approx. 70% and then again louder when going to 100%.
Currently I mostly use the USB connection as input. It too adds some high tones sometimes, depending on what I do with the computer. So maybe I’ll need some sort of USB isolator.
The speakers are passive DIY units that my dad made at some point. 8Ohm I think.
It is plugged into one of those multi socket extension chords, but I pulled all other devices from it for testing. No change.
From the (low resolution) picture you posted, it looks like a combination of grid noise (marked 1) at 50/60 Hz and some switchmode noise from some PSU at 17KHz (marked 2).
You have 2 options:
Get a better PSU
Buy or build a noise filter for the psu like this one
The 50Hz reading is not coming out of the speakers. It is there the entire time (vertical time axis), so it is something else in the room. Maybe the fridge next door or the lamp transformer.
I only held it in front of the tweeter, so the only stuff measured from the speakers is on the right hand side of 1000Hz.
Line number 2 is at 7.2kHz and coming out of the speaker, yes.
Hm, yeah I also thought about replacing the PSU …
But I guess it is most likely that it is responsible for the tone at 7.2kHz. But there is also a lot of evenly distributed noise. (Uncommon for a psu, I think?)
And as I said, it almost doesn’t change when I turn the volume up or down. It is even slightly louder at low gain. So its not like it is amplifying input noise. The noise seems to be added after the amplification?
Is that normal behavior?
