"Ground" loops and interference.

[vindaloo]

I've been having a little difficulty arranging a kitchen sound project.

 

2x "Vifantastisch" DIY wall mounted MLTL speakers.

1x TPA3116 amp from deepest China

1x Chromecast Audio or Raspberry Pi

1x ex Thinkpad SMPS - 16V 3.16A

1x LM2596 DC-DC converter or "buck" to drop the 16V to 5V.

 

I have problems! There's rather a lot of noise. I get the odd pop or fart, general background grumbling plus "squrrels" reminiscence of a modem or loading games on a Sinclair Spectrum.

 

If I separate the grounds for the two aspects...

 - Amp on its own

 - Buck plus CCA on its own

 

...there is blissful silence...

 

As soon as the earths are joined, crap city again.

 

Suggestions? Ferrite beads and caps on the DC lines? Or run a ground loop isolator on the audio feed to the amp?

 

J.

[TeflonTom]

Its caused by the power supply units. Basically the ground connection in the audio is derived from a synthetic 'ground' from the transformer, each device does this seperately so you can end up with the grounds having a voltage differential betwen them and hence the noise.

you can get a device called a dti which isolates the grounds and matches the impedance of the source and destination devices, also a di box may do the job..

i see and hear ground loops and thier associated problems daily! Example being a laptop and projector plugged into different phases on a 3 phase mains installation you can get a ground loop induced onto a vga signal cable (analogue) which gives you wavey lines on screen.... or it could be a powered musical instrument plugged into a mixing desk in a remote location gets induced hum ir interference.

[VWD]

In telecoms transmission theory, we were told to earth at the sending end. But is that DC-DC converter a SMPSU type- where you may feed in an earth supply, but the output should be earth free, and are you decoupling to makers recommendation with capacitance/inductance. One recommendation on the 2596 data sheet is to keep the feedback circuit clear of the inductor flux ( see p9 of http://www.ti.com/lit/ds/symlink/lm2596.pdf) and there is an additional filter shown on P9 for problems. As TT says- earth loop problems are legendary and a subject in their own right.

[vindaloo]

Please see piccie below. I only get noise in that config... When the buck and CCA are powered by a separate supply, there's no noise unless I join the grounds (croc clip leads or test leads). Noise is dependent on AMP volume knob and not on source "gain". CCA volume control has no bearing.

 

I am in 2 or 3 minds about what to do....

 

1) Run a 5V USB PSU to the CCA or RasPi and say "F!it!", resulting in two wires leading up to the enclosure.

2) Get a GLI for the audio out from the CCA or RasPi.

3) Try capping and ferrite beading it to death on the DC power and ground lines.

 

TPA3116

LM2596

 

Piccie....

 

J.

[vindaloo]

In telecoms transmission theory, we were told to earth at the sending end. But is that DC-DC converter a SMPSU type- where you may feed in an earth supply, but the output should be earth free, and are you decoupling to makers recommendation with capacitance/inductance. One recommendation on the 2596 data sheet is to keep the feedback circuit clear of the inductor flux ( see p9 of http://www.ti.com/lit/ds/symlink/lm2596.pdf) and there is an additional filter shown on P9 for problems. As TT says- earth loop problems are legendary and a subject in their own right.

 

I had a bit of an oops! moment earlier, when the ground "load" lead broke off during some testing. The interference got much worse and could be reduced by simply pressing the ground wire back onto the solder pad.

 

I have a feeling it's wobbly grounding through the amp on the audio input lead. I'll try a simple GLI to start with.

[vindaloo]

I bought a GLI off Amazon. Best £5.95 I've spent so far on this project. Blissfully quiet now, apart from when music is intended.

 

http://www.amazon.co.uk/dp/B0161F22WQ/ref=pd_lpo_sbs_dp_ss_3?pf_rd_p=569136327&pf_rd_s=lpo-top-stripe&pf_rd_t=201&pf_rd_i=B000NVWB9O&pf_rd_m=A3P5ROKL5A1OLE&pf_rd_r=1A4WG7Y0R9ZF28PNGDNY

 

J.

[vindaloo]

Piccies with descriptions....

 

Building foam versions of the "Vifantastisch"

 

 

Trying out the speakers after construction.

 

After a bit more faffing around I decided I didn't like them. They'd never really provided the sort of tonal balance I like. The were jangly and bass light. so I decided to build another design. The "Woden Baby-labs (labyrinths) Redeye". They mount an Aurasound NS3-193-8A driver.

 

 

After basic contruction.

 

These are much nicer..... They lack being wall-mountable.... With a rear facing port but reach low for a teeny 3"-3.5" driver. Though they won't go as loud as my Tannoy E11s, they get within a hair of dropping as low.... So somewhere around 55-60 hz.

 

Not bad for a 3" cone in a 12"x9"x5" box..... If stand mounted they can be built with the port facing down..... Or up if you up-end the design.

Edited 1 April, 2016 by vindaloo

[lordsummit]

Really interesting. Never heard a single driver unit that really floats my boat, although have heard some very coherent horns. Ultimately though they always seem to lack both bass substance and treble extension. What they get right is amazing. Have you tried single drivers in a transmission line? Much kudos to you for building your own speakers

Sent from my iPhone using Tapatalk

[vindaloo]

Really interesting. Never heard a single driver unit that really floats my boat, although have heard some very coherent horns. Ultimately though they always seem to lack both bass substance and treble extension. What they get right is amazing. Have you tried single drivers in a transmission line? Much kudos to you for building your own speakers

Sent from my iPhone using Tapatalk

 

 

It is a TL.   - Actually, both are TLs. Though maybe building the Vifantastich in FCB makes it not work.

 

For the Redeye: It's a 4x2x1 TL in 12" increments for a 36" path length by my reckoning....  Though I have a simplistic method for calculating corners so I may be a little off.

http://wodendesign.com/downloads/Woden-BabyLabs-081015.pdf

 

J.

[lordsummit]

Yes, can see it when I open my eyes [emoji849][emoji58]. Should sound interesting.

Sent from my iPhone using Tapatalk

[skomaz]

would it not be easier to go for a pair of Q Acoustic 2010i's?

[vindaloo]

would it not be easier to go for a pair of Q Acoustic 2010i's?

 

Where's the fun it that?

 

I've built something and learned a lot whilst doing it.

 

J.

 

J.

[vindaloo]

Latest updates....

 

The Ground Loop isolater I used.

https://www.amazon.co.uk/201-087UK-Jack-Ground-Loop-Isolator/dp/B0161F22WQ

 

Yep, "used"... As I now have an isolating DC DC converter.

https://www.amazon.co.uk/gp/product/B015E4835U/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

That's the only isolating DC DC converter I've seen in "board" form and at a reasonable price. It's rated to 1.5A too, which is nice.

 

Speakers as they are currently...

 

 

Am also playing with the amp plus Chromecast box. Currently it sports the isolating buck and some proper speaker terminals out the back. No piccie yet though.

Edited 15 May, 2016 by vindaloo