No Sound unless laptop is charging [resolved]

[hpleung]

I just completed a Crack build. It appears to be working fine when a Laptop is connected to a DAC, then in turn connects to the Crack.

However, the moment I disconnect the laptop charger - the sound stops. All other connection stays the same.  For testing, I tried with a different portable source (with guaranteed sound output) and there is no sound from the Crack.

Any idea?

[Paul Birkeland]

Charger vs. no charger having an impact would tend to have me looking at power saving options in your OS that may be disabling things to preserve battery power.  The Crack doesn't know whether your laptop is being charged or not, so there isn't really anything to debug on that end if it otherwise works fine.

[hpleung]

I tend to agree with you - it is super odd. I wish i can post a video - I can show a demo. But here are what i am observing. Any idea on what could be going on is appreciated.

1. I use "Cambridge Audio Streamer" as source. There is sound from the crack and it works. But there is a hum; so i decided to try a different source.
2. I use a mac Laptop headphone output and convert that to Line Source for the Crack. When Laptop is charging, there is sound from the crack. If Laptop is not charging, the sound stops.

Note: I checked that it is not battery saver issue. I also checked that there is still sound coming from the laptop even though i disconnected the charger.

Looks to me like there is something wrong; like i did a bad connection. Any pointers would be appreciated.

[Paul Birkeland]

It certainly doesn't hurt to reflow all your connections.  Tell me more about the hum you're hearing.  If you listen to a 60Hz and then a 120Hz tone, does it sound like either?

[hpleung]

The hum sounds more like the 60hz...but less "low frequency". I used youtube 60hz and 120hz video as reference.

I also tried a different source - Benchmark DAC1. And it still have the hum.

Any pointers on how to get rid of the hum?

[Deluk]

Does the Crack work if you don't have the DAC in circuit? Laptop to crack or a phone to Crack?

[Deke609]

Charger vs. no charger having an impact would tend to have me looking at power saving options in your OS that may be disabling things to preserve battery power.  The Crack doesn't know whether your laptop is being charged or not, so there isn't really anything to debug on that end if it otherwise works fine.

+1

This is what I would focus on. A few years ago my son got a keyboard app on his Chromebook that was supposed to light up the keys on his keyboard to indicate which keys were to be played when. For the life of me I couldn't get it to work ... until I plugged in the power supply adapter to the Chromebook. It turned out that the laptop was set up to cut off the USB outputs when operating on battery power. Never bothered to see if I could change that setting b/c it was simple enough to keep the Chromebook plugged in.

cheers, Derek

[hpleung]

Actually, I'd like to follow Paul's lead and focus on the Hum and less of the laptop issue. How can i debug the hum? Any pointers well appreciated.

[Paul Birkeland]

Is the hum there with nothing plugged into the Crack and the volume turned all the way down?

[hpleung]

Ok looks like i just needed to tighten the ground screw. No more hum. All sounds great right now. Thanks.

[Paul Birkeland]

If one screw is loose, I would tighten all of them.

[hpleung]

Hi,

So my cracks works and sounds outstanding when i use my cambridge audio RCA output or my benchmark DAC RCA output - it works fine and no hum. However, if i use a DAC output (e.g. Chord), no sound is heard. I also tried another DAC - (SMSL) and still no sound is heard. I also tried a personal player (Sony) and no sound is heard. I have tested that both of these devices works outside of the Crack.

So, perhaps the output of the RCA for those devices is too low for the crack to pick it up? Or any idea what is going on here?

Thanks.

[Doc B.]

my benchmark DAC RCA output - it works fine and no hum. However, if i use a DAC output (e.g. Chord), no sound is heard.

This is not very clear. By "a DAC output (e.g. Chord)", is this also an analog RCA output?

[hpleung]

Yes...the chord DAC takes USB as input and output analog signal via RCA.

[Paul Birkeland]

The Crack will amplify whatever appears at its inputs.  If you are feeding the Crack from a jack that is intended to power headphones and is USB powered, the output may deactivate if it doesn't sense a low impedance mode present.  You may need to get a pair of 100 ohm resistors and add them to the RCA plugs on your cables if this is what you're running into.