[fred]

I am nearly ready to call my GK-1R complete, but in testing it I have encounted a HUM problem.  Hugh kindly stepped me through an isolation process and we determined the GK-1 is not actually causing the hum.  When I connected the GK-1 to my AKSA, hum was audible in both channels.  However, when the interconnects are removed from the GK-1 (but still plugged into the AKSA, unconnected at the other end), the hum continues (this exhonerated the GK-1).  

It is curious because the same interconnects have been used to connect the AKSA to my old preamp (actually, a Yamaha A/V receiver).  No hum occurs in that arrangement, for some reason.  SO on the one hand, it appears the cables are the culprit, since hum occurs simply by connecting them to the AKSA (while the other end dangles).  However, the hum miraculously disappears as soon as the other end is connected to my A/V receiver.  Is there a way to teach my GK-1 this same magic?

I even bought new cables (clearly marked as "double shielded") and hum still occurs when they are plugged into the AKSA (still disappearing when connected to the magical A/V receiver).

I am stumped as to what to try next.  Does anyone have any suggestions?

[AKSA]

Hi Fred,

Sorry you are experiencing difficulties;  most tube circuits are buggers for hum until you sort out the wire routing.

1.  Try using shielded coax from wiper of volume control to mute connection on the relay pcb.

2.  Try running a wire from GK-1 ground to Star Earth on the AKSA.

Both should scotch it;  #1 addresses hum induction into a high impedance point, and #2 addresses a potential earth loop.

Hope this helps,

Cheers,

Hugh

[fred]

1. Try using shielded coax from wiper of volume control to mute connection on the relay pcb.

I see two wires connecting above the mute relay, one for left channel, one for right.  Are these the wires you mean (with coax, one will be inner, the other outer)?

Meanwhile, I'll open up the AKSA and attach a wire to the star earth (I presume the same Cat5e wire will suffice).

[AKSA]

Hi Fred,

Nah, one coax for left channel, with shield earthed, and likewise for the right channel.

Yes, CAT5E will be fine for interlinking the earths......

Cheers,

Hugh

[fred]

I did the things you suggested, but the hum continues.  Here's a rundown:
1) installed the coax - not clear if this had much effect, but previously, the mute button caused the hum to attenuate.  Now the hum is constant with or without mute selected.
2) connected GK-1 ground to AKSA star-earth: reduced the hum a few dB, but still very audible,

As mentioned previously, the AKSA produces hum as soon as input cables are connected to it.  Then, the hum is reduced (not eliminated) when it is plugged into a powered-off GK-1.  When the GK-1 is switched on, the hum slowly increases (I suppose this is while the tubes heat up).

And, as I said, the AKSA is ultra quiet when the same cables are plugged into my A/V receiver (acting as preamp).

(edited): And here's something new: I finally connected the sub output from the GK-1 to my powered subwoofer.  When I did this, hum became considerably worse from the main speakers, and a new low frequency hum came from the subwoofer.

Very frustrating.    

[Tinker]

As mentioned previously, the AKSA produces hum as soon as input cables are connected to it. Then, the hum is reduced (not eliminated) when it is plugged into a powered-off GK-1. When the GK-1 is switched on, the hum slowly increases (I suppose this is while the tubes heat up).

Out of interest, when you have the GK-1 connected to the AKSA (with the GK-1 on), what do you have on the input of the GK-1 and what source is selected?

[fred]

Out of interest, when you have the GK-1 connected to the AKSA (with the GK-1 on), what do you have on the input of the GK-1 and what source is selected?

I have a CD player, through a Perpetual Technologies DAC, connected to it.  The other GK-1 inputs are shorted RCA adapters, and the hum is also present when these inputs are selected.

[AKSA]

Fred,

There has to be something wrong, since my GK-1 and those of others do not hum at all, in fact has won plaudits for their silence.

Have you run an earth wire (CAT5E is sufficient) from the relay pcb (at the 'Sig Gnd' point near R11) to the earth point near R17/17' on the analog pcb?

It definitely sounds like an earth loop.

Cheers,

Hugh

[fred]

Have you run an earth wire (CAT5E is sufficient) from the relay pcb (at the 'Sig Gnd' point near R11) to the earth point near R17/17' on the analog pcb?

No - I do run a ground wire, twisted with signal wire, but it's attached to the 'GND' post (on the analog board) just above the "signal' post- next to R1 (rather than the one by R17).  Does it make a difference?  Is this the problem?

[AKSA]

Fred,

Might well be the problem.  Have you connected:

1.  Right side of C8 lead to left (negative) side of C18 (solder under pcb).
2.  Same for C8' and C18'.
3.  Removed LINK just below C8 (just don't fit it)
4.  Now run the wire from the relay pcb back to the GND connection just to the left of R17.

This is in the instructions, in fact, but checking won't do any harm.

Cheers,

Hugh

[fred]

1. Right side of C8 lead to left (negative) side of C18 (solder under pcb).

YES

2. Same for C8' and C18'.  

YES

3. Removed LINK just below C8 (just don't fit it)

Correct - never fitted

4. Now run the wire from the relay pcb back to the GND connection just to the left of R17.

Done

The main speakers still hum - I notice no difference.

(edited): I noticed that when the GK-1 earth is NOT connected to the AKSA star-earth, the subwoofer has very little hum.  When I connect these earths (prior to connecting the sub) the hum is reduced. Then when I connect the sub, the hum is worse than ever.   If I use the sub, I'm better off not connecting GK-1 and AKSA earths.  If I do NOT use the sub, I'm better off connecting the earths.

Should I consider purchasing a "ground isolator?" such as:
http://www.jensen-transformers.com/ci2rr.html

[AKSA]

Fred,

Try connecting the ground return on the digital supply, termination 1 on CONN2B (and the right hand power connection on the 4th row of pins on each relay;  they are all conjoined to pin 1) to the signal earth at LINK1 (which is a 10R resistor) in the center of the relay pcb just above CONN2B.  Just run a wire offcut from a resistor, should do it nicely.

I cannot dismiss the notion that digital earth noise might be intruding, though it's unlikely.

If you disconnect all sources from the preamp, Fred, and use shorting RCAs on all inputs, with the amp/speaker connected, does hum go away?

Cheers,

Hugh

[fred]

                           

The hum is banished!

This problem was a bear to diagnose, and Hugh and I had been struggling with this almost constantly for 2 weeks.  In the end, the problem turned out to be simple.

The root of my problem: a wooden enclosure.  A metal enclosure has unavoidable contact with various things like the volume potentiometer, and the shielding.  A wooden enclosure does not - hence, grounding problems.  

Should you stay away from wooden enclosures?  Certainly not! Wood is so easy to work with.  Simply run wires around to the relevant parts, and you're fine.

Now my GK-1 is dead quiet (when it should be, that is!)  The sound seems beutiful and refined to me - and it isn't even broken in.

  Thanks, Hugh, for your untiring technical help and especially for the encouragement when I was most frustrated and distraught.

                           

[AKSA]

Fred,

This is wonderful!!     Thank you so much for sharing this on the forum - it helps others building their GK-1s and allays fears potential builders might have that hum might be a problem.

Fred raises an interesting point, not mentioned here before.  A timber enclosure looks great, makes it a piece of furniture, but the absence of shielding metal enclosing the componentry creates potential hum problems.  You can then spend weeks trying to isolate this damnable hum.  

Fred solved his problem by enclosing all the important pcbs, transformers and the pot in thin mu metal shields, and then connecting the shields together with a wire to chassis earth.  I twigged to this idea late in the piece     and offer my apologies to Fred, who worked like a trooper to get it together, never losing patience or throwing it on the ground and stomping on it......  

Fred even rang me from Houston to share the good news;  I was most flattered!    

Gudonya, Fred, youse dun bonza, mate!

Cheers,

Hugh

[Larry]

The hum is banished!

This problem was a bear to diagnose, and Hugh and I had been struggling with this almost constantly for 2 weeks.  In the end, the problem turned out to be simple.

The root of my problem: a wooden enclosure.  A metal enclosure has unavoidable contact with various things like  ...

Happy to see your problem is solved. But it seems the cause is not really identified.

If it's a grounding problem, the metal enclosure will not help. Grounding problem should be solved by proper grounding  

A metal enclosure is for shielding external interferences, not internal, not grounding loop. If your room or your system setup has no serious interferences, you can get away from hum with a wooden enclosure, as some builders do.

You might have accidentally solved the real grounding problem while changing your enclosure as the wiring plan or/and layout had been changed somehow from one enclosure to the other.

If your room and system setup (floating metal enclosures that emit interferences) have strong interferences, a grounded metal enclosure can help shield them from intruding your component.

PS. AC cabling makes obvious effects on hum in some cases.  The wiring plans of AC cables before and after the components in the chain can cause hum as well, due to external loops. In particular, I found the sources, like CD/DVD players, have much to do to cause hum of this type, as these days, most of their enclosures using 2 core power cables are not grounded and their own internal grounding plans do not take into considerations of how the input and output are connected to other components' circuitry. ( by lazy engineers or hardworking engineers under deadline or cost pressures). (In this case, the metal enclosure may work as a inteference relay as well to polute the environment electromagnetically.) If an external ground loop is the problem, swapping the AC connector's polarity can reduce or kill the hum (swap it at the 8-shaped socket of the CD players or any source components.) Swapping the hot and cold wires connecting to the transformers in your own component can help too, in some cases.