Quote:

Me too!

I think the key is "after connecting interconnects" the hum starts. That is what happens with me. My amp has a single earth. A grounded shield on the input cables did not help me.

I think this means you have a ground-loop, or mains contamination of the source signal. Having done some reading diagnosing these is trickier than it sounds.

Build a ground-lifter (a plug/socket with the earth disconnected) to  use simply to diagnose the problem by breaking loops. A ground-lifter may not be 100% safe as a final solution. And try powering various components in the hifi chain unearthed to mains (as long as one component is earthed there will be a ground connection for all components through the shield of the RCAs.)

This did not work for me.

My next step is to get an electrician to check out the Ze of our household earthing and the earth-bonding (expensive equipment and know-how required). My understanding is that it is not good simply to connect your own earthiing rod, but that Incomer Earth as it is called should be formally tested and fixed if it is inadequate. Have any building contractors been working near your house recently?

Does your hum change with the volume setting? Mine does.

My sympathies - this can be a frustrating problem!

Nope, the shields are only connected at one end, not both.  

Steve

To exclude a ground loop, lift the ground on your cd player (use a socket/plug with the earth disconnected) and attach it to your amp with RCA cable. Leave your amp earthed. Disconnect everything else from your hifi chain.

Switch both on. If the hum is still there and unchanged then it is NOT a ground loop because you have broken the signal return path through earth which might have been causing the loop.

I have tried this but for me the hum is still there. I believe this means either there is earth contamination from some other electrical device, or earth is inadequate. I have tried a few possible culprits for contamination without success (central heating boiler etc).

It seems there is no simple test for adequacy of your earth - this is a job for an electrician. I'm going to speak to the electricians at work to see what they suggest.

None of mine either, sll: the hum doesn't show up in my T-Amps, my Push-pull valve amp, nor my solid state amp. However apparently SET topology is extremely sensitive to mains / earth borne interference. I think this is partly to do with the air-gapped output transformers, push-pull valve amps do not require these, and so are much less susceptible to hum.

One of the reasons that SETs tend to be more expensive than other amp types is the design, and component costs required to suppress this interference (and also to ensure good frequency extension).

(Info culled from lots of web searching - I am no expert!)

There are many ways to handle grounding schemes when trying to put this kit into a chassis and remote mounting the input jacks, pot, or both.

Below is the recommended method that will work in wood or metal chassis.

It's important to understand that shielded cables must be used and that the shield must only be grounded at one end, and it must be the correct end as shown in the diagram.

I have been "tweaking" my Zkit1 for a while now, gradually coaxing more and more power out of it.  Somewhere along the way, the hum got so loud that I couldn't ignore it anymore.  Today I looked into it, and found a fix that virtually eliminated the hum I was experiencing on the bench.  Unfortunately there is still audible hum when the amp is in system, but it is substantially lower than what it use to be.


Two 14 gauge solid wires (out of a chunk of Romax) connected to the RCA input connector shields on one end and ground on the other - where the ground connects to the negative terminals of the two (3 in my case) large power supply capacitors (which is where I ground the volume controls).  The solid wire worked quite a bit better than any stranded wire I tried, and the ground point by the power supply capacitors worked much better than going straight to the earth ground connection.

I don't think this was a ground loop problem.  The hum was dependent on the volume control setting (more volume, more hum) and went away when the RCA input cable was unplugged.  On the bench, when I had my signal generator connected as the source, the hum was present when the signal generator was connected to the Zkit1 even when the signal generator was turned off and unplugged.  After installing the two solid wires there was no hum when the signal generator was connected.

Dan

Thanks dank
I've solved my problem your help.
See two brown wire from RCA jacks to taper

Thanks Alan
It doesn't touch it

SLL

Glad to hear your hum problem is fixed.  Did you ever try solid wire rather than stranded?  In my case it worked much better.  I would be interested to know if solid worked different from stranded in your case.  When I first investigated the problem, I was using light guage clip on jumper wires (that look similar in size to the brown wire you are using) and found that the more jumpers I clipped on - in parallel - the more the hum was reduced.  A good size solid wire did the same job as about 6 of my jumper wires, and a single good size stranded wire did no better than a single small gage jumper wire.

DanK

OK - tried fully bypassing that trace. Mounted the RCAs right beside the pot, and connected them directly. Kept one of the original grounds grounded - as per schematic.

Well it certainly changed things. Now constant hum - the same at all volumes. Loud buzz if input is disconnected. Music is there.

So, plugged in soldering iron, and undid all the changes. Now back to before - hum varying with volume, acceptable level.

Will give this bypass wire thing a go I suppose. Nothing to lose.

(and soldering-iron burn on fingertip - that'll teach me to rush things)

Cheers Dank. I suspect I could get away with 1pm on the dial if my speakers weren't so flippin' sensitive! It's 11am for me ...

OK, got some solid core here - let's try ...

Did it. And yes it helps a lot - thanks guys. Still not sure why ...

Hello Alan,

I am trying to figure out where you used the solid wire and it eliminated the minor hum when mvoing the volume above 11 o'clock?  I have the same problem.

I have to say that I really love the sound I am getting... wow.... I have recently added a ZenHead as the preamp and now I can get the volume I want .... Oh my... sooooo nice...

Thanks,
Dean

Continued work on what's left of my hum problem reveled that the hum caused by the amp when it is in the system was indeed a "ground loop".  I was able to measure 6 mv difference between the chassis of my PC (source) and the shield of the input RCA connectors at the Zkit1.  The new 3rd solid wire in the picture reduced this to 0 mv, the lowest volt scale on my meter.  While still not totally silent, you now have to strain to hear hum from the listening chair in between songs, and this is with the Zkit1 volume set at max.  Most of the hum now is actually coming from the subwoofer amp.

The new 3rd solid wire ties the power transformer neutrals (red/yel and grn/yel) to the two other solid wires previously installed.  It did not seem to make a difference to either move the earth ground wire to the new wire (eliminating an inch or two of trace) or to jump straight to the earth connection on the AC receptacle with solid wire, so I left the earth connection unchanged.



Happy Thanksgiving

DanK

I have just order a couple of these.

http://www.dcispec.com/index.html


I hope this sovles my plate amp hum but we will haft to wait and see.


HT-EXT

Hi Evo -  re your questions

1. Would be fine - some folk have published ZKit1 pictures and have done just that. I like the scary voltages in a box.

2. Up to you - but PCB connectors mean that the force associated with connecting/disconnecting RCAs / speaker cables will be directly to the PCB. Personally I prefer to have connection forces applied to the case - some connectors are a tight fit!

Another advantage of mounting the speaker connections on the case is that this allows you to shorten the signal path: the output transformer leads can be directly attached to the speaker connections instead of having to rejoin the PCB.

For a wooden case, you only need GND to mains earth.

Let us know how you go!