[FallenAngel]

I changed the headphone jack wiring to make it non-switching on the ground.

Right now this is what I have in terms of grounds:

Inputs/AlienDAC all combined to a single wire going to the POT.

Pot has 2 ground wires (one twisted with Right channel, other twisted with Left channel) going to CKK-III.

Single ground wire going from CKK-III Output Ground to Headphone jack.

Headphone jack has 2 ground wires (one twisted with Right channel switched, other twisted with Left channel switched) going to either GainClone.

GainClones have a ground wire going to the star ground.

The AlienDAC also has a ground wire going to the star ground (this removes the computer related noise from getting into the equation).



There is only one power supply (the one for the GainClones) and it creates a ground. This ground is connected to each of the GainClones which in turn gets connected to the star ground.

The CKK-III center ground does not go to the star ground currently. The Output Ground (which is basically the CKK-III Ground) is connected to each of the GainClones.

Won't wiring the GainClone PSU ground to a point with the GainClone grounds as well as the CKK-III ground make 4 ground loops since the grounds are already all connected? Won't this create multiple paths to the same locations via this star or am I missing something elementary?

Thanks

 

[amb]

A picture is worth a thousand words... here is what I suggest:

 

[amb]

After thinking it through a bit, I would modify the above diagram by changing the headphone jack ground return to the CK2III OG pad, and move the connection from there to the global star point to go from the CK2III's local star point instead.

 

[FallenAngel]

Amb - I rewired everything into a central star as per the diagram (and update with headphone jack going to OG on CKK-III and CKK-III local ground going to central star.

The result is unfortunately disappointing since there is even more hum than before

Before it was hard to hear unless I put my head beside the speaker, now I hear it clearly from 2 feet away. I think it might be due to the fact that I now have unshielded signal wires which are not twisted with grounds going from the CKK-III to the GainClones (about 8 inches long) and from the GainClones to the output jacks (another 8 inches).

Damn, now I'm really stuck on what to do with this thing and getting shielded cable is going to take some time.

 

[amb]

Hmm, CK2III's output impedance is low, so an unshielded signal wire from there to your gainclones shouldn't be too sensitive to interference. Ditto the gainclone's outputs to the speaker terminals. The most sensitive wiring is at the inputs, and particularly after the volume pot.

I think it might be worthwhile to troubleshoot in stages to determine where the hum is coming from. Does the hum vary with volume control setting? Do you hear hum through headphones? Also, leaving all ground wiring intact, disconnect the signal connections at your gainclone's inputs and temporarily short the inputs to ground. Do you still have hum through the speakers?

No question about it, when you have a complex setup like this, hum/noise is always an issue that might rear its ugly head.

 

[FallenAngel]

I'll have to go through all those steps tomorrow, but for now I did do some debugging and this is what I found.

Hum does not change with volume, it really sounds like the transformer.

There is no noise from any headphone (there was some before). I tried the most sensitive headphones I have - Grado SR225 and the X3 IEMs, still no noise. The noise seems to only come from the speakers. I haven't tried shorting input to ground, but when I plug in headphones (gainclone input is just left disconnected, there is no noise from the speakers).

 

[MisterX]

What is the little circuit in the upper left hand corner?
What happens if you move the alien DAC all of the way to right side of the case (looks like there is enough wire to manage that).
Finally, what happens when you touch any of the input jacks (does the hum get louder or quieter)?

 

[amb]

If there is no hum through the headphones, then your hum problem is coming from the gainclone section (the last stage in the chain).

 

[FallenAngel]

MisterX
The little circuit is a line filter - like this, but simplified. It's a Varistor followed by an X-type cap across the lines, 2 Y-types to ground and then a 220K 2W resistor across the lines.

I tried moving the DAC around, including taking it out of the box, it doesn't really help. The hum is there no matter what source I use.

When touching the input jacks, the hum doesn't get better or worse as far as I can tell.

abm
I would presume you're right, it's what will fix it that we'll have to figure out. I'll be playing with it more today, maybe trying some shielded cable that I have around, maybe it will fix it.

Thanks guys. I'll report back when I have something more and would appreciate any other ideas until then.

 

[FallenAngel]

Very strange thing I found when shorting the input of the gainclone to ground. It seems that when I short it at the headphone jack (leaving a signal wire to run bare along the case), there is tons of noise. When I short the input at the actual GainClone PCB, it doesn't sound like there is any noise.

I also just replaced the wires from the headphone jack to the gainclone with shielded ones, with the shield connected on the gainclone PCB side to a ground. I don't think this did much to remove the noise though.

I just tried to remove the headphone jack and muting relay out of the circuit by connecting the gainclone signal straight to the output of the CKK-III and still there is noise, although I think there is slightly less than before. I also bypassed the output wire from the gainclone PCB to the speaker outputs by touching the speaker wire straight to the (although I didn't expect this to be a big difference anyway) - still noise.

Now I'm really confused as to where it could be coming from.

The few key things that I think are important are:

1) Moving the wires between the POT and CKK-III board changes how much noise there is.

2) Shorting GainClone input to ground at the GainClone PCB produces NO NOISE while shorting it at the headphone jack does.

3) Taking muting relay and headphone jack out of equation produces slightly less noise.

Maybe it's time to find out how to shield that transformer. Any suggestions?

 

[FallenAngel]

Hey guys,

I finally got some Mu-Metal shielding (a great price at $10 for a sheet from The Electronic Goldmine) and they have some crazy prices on 1K trimpots at $2 for 10!

So I applied the Mu-Metal and the buzzing went to about 50%. Since there was still some buzzing out of one speaker, I decided to try again moving the transformer and after twisting it around a few times, I got a nice position where there was absolutely no buzzing noise!

Thanks to everybody that helped, much appreciated, this is definitely one of the most enjoyable projects I've ever built, and the non-audiophile significant other is happy to have some nice speakers to watch movies with

Thanks again everyone!