Paging experts in hi-fi, electronics, computers and possible demonic possession

spkennyuk

Member
Messages
5,932
Chris

Just a suggestion as i am no expert on this subject. But my next step would be to remove the hifiberry boards and try running the sound direct from the PI units headphone out.

Im assuming the hifiberry is a plug in module to give you the phono outs.

If there is no crackle without the hifiberry boards being used as the inputs then you know thats the issue.

My thinking is that whatever is causing the crackle is being picked up by the pins on the hifiberry board. In otherwords its not the PI units at fault or the hifi berry boards its the connection point between the two picking up interference when the second unit is powered on.

If there is no crackle running two units from the phone mini jack outputs on the PI units then try with one hifiberry attached on 1 unit. If you then get crackle swap the hifiberry unit out with the other one. If the crackle stops then it shows the 1st hifiberry is the issue.

Stage 2 if the crackle doesnt stop is try the hifiberry units one at a time in the 2nd PI. Leaving the 1st PI using the mini jack output.

If at that point you get crackle on one hifiberry but not the other then it implies which hifiberry is at fault.

If you get crackle regardless which hifiberry is plugged in but none if the mini jack outputs are used then it suggests that the hifiberries are ok but the connection pins are allowing the interference source to be picked up at the pins.

As i say im no expert im just suggesting the logic i would follow to rule out or rule in the source of the issue.
 

Moz1000

Member
Messages
820
I think you may be creating an earth-loop when you connect-in the second pi. I would try the following:
  1. Dionne t the earth wire in the mains plug of the USB multi-sport.
  2. Disconnect the earth wire in the Rotel amp plug (noting that some amps don't have an earth connection).
  3. Somehow diconnect the shielding, at one end only, in the RCA leads.
  4. Disconnect the shielding in the USB cables, at one end only.
Good luck
Moz
 

lozcb

Member
Messages
12,301
OK I'm stumped at this point.
As some of you know I'm a bit of a music buff and love music around the house.
What I currently have is a couple of Raspberry Pis with HiFiberry DACs attached.
https://www.hifiberry.com/shop/boards/hifiberry-dac-pro/

They are running a custom OS called Volumio
https://volumio.org/

These are all connected to my wired Gb LAN in my server cupboard powered by a multiway USB charger like this:
https://www.amazon.co.uk/gp/product/B00PK1IIJY/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

The drive into a large Rotel power amp via good quality phono cables. The Rotel is basically a 6 channel job, 3 pairs of left and right, which can be bridged or linked but essentially three separate stereo power amps in one **** off box.

Speakers are hardwired. One pair into the bedroom, one pair into the garden.

So they both work wonderfully. Individually.
So either pi connected to either input with either pair of phono cables produces perfect sound in the corresponding location.

BUT if I plug them both in at the same time, there's a terrible hiss / crackle on both pairs of speakers. This is irrespective of if either Pi is playing anything, or even if they have fully booted. The moment you apply power to the second device, the noise starts.

Ah Ha I thought. Power issues. So if I connect one pi to an external PSU everything is fine. So the Anker is not up to the job?

Not so. I have a third pi that I can connect to the Anker and power it up just fine, and no noise on the speakers.

If I have both the pis connected to the Anker and disconnect the phono plugs from one (either one, makes no odds) the noise on both pairs of speakers vanishes.

So
Both Pis on the Anker and connected to the Amp = Crackle
One Pi on the Anker and one Pi on $other PSU. Both connected to the Amp = No crackle
Both Pis on the Anker and only one connected to the Amp = No crackle.

Cables have all been checked (USB and phono, and swapped out)

I'm waiting for another microSD card to arrive tomorrow so I can flash a third Volumio instance and connect that the the third of the stereo pairs of the Rotel to see if that also makes the crackle.

What the **** is going on?

C
Try whistling ,lot less of a headache
 

CatmanV2

Member
Messages
48,549
Thanks, Moz

1+2) None of the devices have an earth connection.
3)That should be doable.
4)That's been done with my second PSU which has only +5v and 0 connections.
Cheers

C
 

CatmanV2

Member
Messages
48,549
Somehow diconnect the shielding, at one end only, in the RCA leads.

OK Interesting.

By carefully removing the phono plugs I managed to do the following:
  1. Disconnect shielding from Garden phono plugs = Bedroom fine. Garden still shows noise
  2. Disconnect shielding from both bedroom phono plugs = lots of nasty hum noise (pretty expected)
  3. Disconnect shielding from one channel of the bedroom phono plugs = Bedroom fine, garden still shows noise.

Will try and configure one with headphones

C
 

CatmanV2

Member
Messages
48,549
Just a suggestion as i am no expert on this subject. But my next step would be to remove the hifiberry boards and try running the sound direct from the PI units headphone out.

The HifiBerry is actually a DAC > phono but close enough
Configured another board to use
  1. Another USB DAC that I had forgotten I had which has a 3.5mm output. = Noise
  2. The onboard 3.5mm jack = Noise.

Utterly mad.

C
 

CatmanV2

Member
Messages
48,549
Are the screens, earthed? At both ends or just one?

Good question. How do we define 'earthed'? There are no connections to the mains ground anywhere on the system
The amp only has a figure 8 2 core plug
The Pi's PSU has the same, and that's clearly disconnected from the 0v line on the Pis anyway.
There's no earth screw on the amp either.

C
 

spkennyuk

Member
Messages
5,932
The HifiBerry is actually a DAC > phono but close enough
Configured another board to use
  1. Another USB DAC that I had forgotten I had which has a 3.5mm output. = Noise
  2. The onboard 3.5mm jack = Noise.
Utterly mad.

C

Im sure the link below will make sense to you. It means nothing to me at all.


May be unrelated but it seems to suggest the audio module itself introduces the crackle.

The other thing i have seen is power cords for the PI units should be short and thick type.

Can you run one of the PI units off a powerbank instead of mains power supply and see if that makes any difference.
 

CatmanV2

Member
Messages
48,549
Cheers. That'd basically be a completely different system and the problem doesn't sound the same.

The only thing I can think of trying is binding the phono cable shields across all the inputs and see.

Or just leave it and use separate PSUs

Just frustrated really ;)

C
 

spkennyuk

Member
Messages
5,932
Cheers. That'd basically be a completely different system and the problem doesn't sound the same.

The only thing I can think of trying is binding the phono cable shields across all the inputs and see.

Or just leave it and use separate PSUs

Just frustrated really ;)

C

Just wrap it all in tin foil and then put it in the microwave on full power for a few minutes. It wont crackle any longer and you may need a new microwave :)
 

allandwf

Member
Messages
10,958
I can only draw comparisons with my signal, instrumentation cabling. It is normal for me to ground/earth the screens at one end, normally source, and the other end left floating. It does sound like a screen, earthing issue.
 

CatmanV2

Member
Messages
48,549
I can only draw comparisons with my signal, instrumentation cabling. It is normal for me to ground/earth the screens at one end, normally source, and the other end left floating. It does sound like a screen, earthing issue.

Makes sense, if only I had a ground to connect it to!

C
 

CatmanV2

Member
Messages
48,549
Well that makes a **** of an improvement.

If I connect a GLI (ground loop isolator) onto the Garden inputs, no noise in the bedroom (ooooerrr) and a teeeny tiny bit in the garden. Totally inaudible unless you are kneeling down next to the speakers.

If I connect another CLI to the inputs of the Bedroom, all **** breaks loose with the amp going into protection mode and a disturbing smell of hot

But, I think, only on the Bedroom outputs. Feels more like a cabling issue.

I need to connect the third Pi, but looks like I have a solution

C
 
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