GK-1 just finished....burning in ! - SOLVED HUM

Felipe · « **on:** 26 Feb 2006, 10:21 pm »

Hello ppl,

So i finished it. I was surprised for getting it right at the 1st time, i guess it pays to be meticulous and patient

In the end of the day (its now 22h15) it began to sing, coupled to the 100N finished last month. I guess i have to wait some days to give it a proper evaluation but....i can say now that i am already happy with it

IT DOES HAVE a little problem ... a little HUM. Not hearable unless i put my ears next to the speaker but....its there. I gues i should shield the INPUTS and OUTPUTS cat5 wire. Before i put the GK1 into the chain the AKSAs were dead quiet...

Its a low frequency HUM. Is it from the trans ?

Hugh, thanks for this wonderfull product. I am waiting for the final cosmetics accessories and ill post some pics.

Best regards.

rabbitz · « **Reply #1 on:** 27 Feb 2006, 02:14 am »

Another is born and Hugh's instructions make it so easy to get it firing first time.

I think all the GK-1's have a little hum and is the nature of the beast with tubes. Can only hear the hum in mine with the ear up to the speaker.

Enjoy

AKSA · « **Reply #2 on:** 27 Feb 2006, 03:32 am »

Felipe,

Hum is more likely to be earthing.

Use a star earth based around the volume control.

Connect this star earth to all the inputs, outputs and metalwork, including one wire to chassis, and even one to the body of the volume control.

Coax is a good idea, I now admit, on the lines to and from the analog pcb, but don't overearth. That is, only have ONE braid connection from each point (input/output pcb notably) to the star earth. Two connections will cause an earth loop.

Very faint hum audible only within six inches of the speaker is acceptable, but it should not be audible at all from the listening position. Completely eliminating hum is extremely difficult on any preamp.

Congratulations, Felipe!! I'm very glad you like it; this is designed to 100% pull at your heartstrings - engagement is the principle goal.

Cheers,

Hugh

Felipe · « **Reply #3 on:** 27 Feb 2006, 11:44 am »

Ok, thank you for the suggestions, let me just update my findings :

- I seem to have 2 types of hum :

1. The first is a very low frequency that appears after 4 to 5 seconds after i turn on the preamp . And then again it takes 5 seconds to disappear when i switch off the preamp ( leaving the AKSA always on of course ).
Never heard this type, dont know how i am getting rid of it. Ill try Hugh's recommendations.

2. The second is perceptible right after switch on of the amp. Now THIS one i recognize. Its the same old hum that was present before shielding the RCA wire inputs on the AKSA. So i think i know how to remove this one...its probably coming from the unshielded input/output inside the GK1.

I'll address both at a time. 1 question :

- I have a 100% wodden box. Inside i have the trans completly surrounded by copper plates, at the front near the switch.
The PCB is in the middle next to the copper plate, but i guess its ok because it acts as a shiled right ? At least that was the intuit.
The volume control is at the back near the inputs/outputs. SHOULD IT BE INSIDE THE COPPER PLATES ??

Are the wires TO and FROM the volume control hum sensitive ? MUST i shield those too ??

Thank you....
Best regards..

AKSA · « **Reply #4 on:** 27 Feb 2006, 08:37 pm »

Felipe,

It's a good idea to shield all the signal wires.

Another trick, from Rom (thanks Rom!), is to insulate the transformer body from the chassis by mounting it on some insulating material such as hard plastic, and don't connect the ES shield to IEC mains ground. He also suggests not connecting the GK1 earth to chassis (though I've had some success with this approach).

Cheers,

Hugh

Felipe · « **Reply #5 on:** 27 Feb 2006, 09:11 pm »

Ok now i am confused....

Not connect the ES shield from the transformer to Mains Earth ?? What do i connect it to then ? Nothing ? Just leave that terminal unplugged ?

Not connect GK-1 earth to chassis ? Was it ever to connect ? I did'nt !!
I have the following :

ES from the transformers to MAINS EARTH
Copper plates surrounding transformers to MAINS EARTH
Transformers bolted directly to copper plates so making contact

I have nothing connecting the preamp ground of the GK1 to mains earth...i thought that was prohibitive....

AKSA · « **Reply #6 on:** 27 Feb 2006, 09:43 pm »

Felipe,

That's it; don't connect ES to mains or chassis. NOTHING is right!!

Copper plates to mains earth is fine.

But see if you can insulate the transformers from chassis. I've not tried this, but Romeo, who is an exceptional technician who works on satellites, assures me it reduces hum, so give it a try.

Cheers,

Hugh

Felipe · « **Reply #7 on:** 27 Feb 2006, 10:26 pm »

Thank you Hugh, will try this tomorrow.

So MAINS EARTH connects to copper plates and thats it. Nothing else uses mains earth ?

If that doesnt help, i'll try to shiel all CAT5 wire i have to PCB ( input , output , volume control pot ). Thats a lot of shielding....

AKSA · « **Reply #8 on:** 27 Feb 2006, 11:07 pm »

Yes, that's it Felipe.

Nothing else to mains earth; just the chassis and the copper shielding around the trafo (which may not be necessary, in fact).

Try the easy options first; it may not be necessary to use all shielded signal cable.

Cheers,

Hugh

Felipe · « **Reply #9 on:** 28 Feb 2006, 11:14 am »

OK, tried that done that. No effect what so ever.

Unplugging the MAINS EARTH was easy, as the AKSA doesnt use it also, i just removed it from the wall. No effect.

Tried to re-attacht the earth and isolate the transformers with a plastic base. Disconnected the ES terminal. No effect. Same HUM.

Removed the top copper plate....no effect...it seems to me the copper plates around the trans are not doing anything....

Tried 1 more thing...with the lid open pushed the PCB to the back away from the trans. This gave a distance of about 5cm from the start of the pcb to the vertical copper plate surrounding the trans. No effect .

Next step would be shielding all input/output wire but....i think that wont solve it either. This is just NOT the usual HUM i had with the AKSA. It doesnt respond to touching and moving components. Its just THERE !!

Its a low frequency hum. It seems rather low...but the problem is i can HEAR it from the listening position, in quite passages or when the CD is not running....its definetly there. Does the GK1 have this inherit HUM ?
I am really picky when it comes to noise....i love silence.

PSP · « **Reply #10 on:** 28 Feb 2006, 06:00 pm »

Felipe,
My GK-1R is quiet until your ear is about 10 - 20cm from the drivers, then I hear 60 and/or 120Hz hum. I did have trouble initially, though. As Hugh points out, hum is extremely system dependent, and also build dependent. When we each make our own choices about layout, grounding schemes, etc. we each then have our own unique hum problem to solve. Jens had quite a battle too, and some of his old posts here may be helpful to you.

Be assured that the GK-1 is a quiet design. When I finally solved my hum problem, the GK-1 was very, very quiet (there was no hum, but I could barely hear a little hiss with my ear very close to the tweeter) . Now, there is a bit more hum, probably because I've put in a new CDP and added a HT processor... I probably have a small ground loop problem somewhere, but it's not worth pursuit.

Good luck,
Peter

AKSA · « **Reply #11 on:** 3 Mar 2006, 11:31 am »

Felipe,

How are you getting on with your hum issues?

Remember - one star earth, using the volume control ground as the central point.

Everything to and from this point.

Cheers,

Hugh

Felipe · « **Reply #12 on:** 4 Mar 2006, 02:58 pm »

All this earthing techniques made me confused about 1 thing :

- What do i connect to STAR EARTH around the volume pot ?
Just The shielding braids... or do i connect the RCA grounds also ???

I have 2 RCA inputs and 2 RCA outputs...both channels are separate , dont make any contact. I dont have a common GK1 ground, i have 2, one for each channel. Should i connect the 2 ?

The RCA ground from the input does not make contact with RCA ground output. Should it ? I dont think so....but this earthing schemes are making me crazy....

THERE IS A "LINK" WORD ON THE PCB CONNECTING THESE 2 GND...BUT I DID NOT CONNECT THEM BECAUSE THERE WAS NO INDICATION TO DO SO ON THE INSTRUCTIONS. I only fitted the wire link below the valves ! The GND from the input and the one besides R17 (not present) are not connected. They have a 10ohm measured resistance between the 2 .
I figured, if they were to be connected, Hugh would tell so.

I will not shield the RCA GND output. This connects direcly to star earth ! No point in shieding, right? AS FOR THE RCA GND input...well it depends on where is conected to....are or are NOT the GND input/output connected?

Thanks...

Felipe · « **Reply #13 on:** 4 Mar 2006, 05:36 pm »

I've just realized 1 more thing :

IF i connect the GND from the GK1 to the star earth around the Volume Pot wich is connected to chassis and MAINS EARTH..... WONT IT ESTABLISH A CONNECTION ON THE AKSA :

MAINS EARTH --> AKSA STAR EARTH (P.supply) --> Input RCA GND ????

In the AKSA manual it is written in BOLD never to connect star earth to input ground...... but i would be doing so in the GK-1 side !!! ????

Now i am totally blured............

AKSA · « **Reply #14 on:** 4 Mar 2006, 09:59 pm »

Felipe,

You have a GK1-EL. This couldn't be much simpler. Here's my suggestion for one channel, the other is identical.

1. RCA INPUT to analog board. Braid this (that is, use coax), and connect each braid end to the RCA and the signal ground point on the analog pcb. MAKE SURE THE RCA GROUND IS NOT CONNECTED TO CHASSIS.

2. SS output to top of volume control. Use coax. No braid connection on the analog board, braid connection to volume control ground end, which becomes Star Earth.

3. Volume control wiper to tube section. Use coax. No braid connection on the analog board, braid connection to volume control ground end, which is of course Star Earth.

4. Tube output to RCA output. Use coax. Braid connection on the analog board (ground, the thick spine between SS and tube sections) and connect also at the RCA. AGAIN, MAKE SURE THE RCA GROUND IS NOT CONNECTED TO CHASSIS.

5. Two single wires from Star Earth to earth to their respective earths on the analog board.

6. Two wires from volume control ground (= star earth) to chassis might be a good idea; you have to try it. It may not reduce hum; keep an open mind on this approach.

7. Last but not least, connect CHASSIS and the two transformer Electro static shields to IEC power earth.

That should do it......

Further refinements involve lifting the transformer off the chassis, insulating it electrically from chassis. No wire changes, though.

Hope this dispels the confusion!!

Cheers,

Hugh

Felipe · « **Reply #15 on:** 4 Mar 2006, 11:20 pm »

Is'nt the output GND the same GND that connects to the STAR EARTH ?
I dont see any other GND PIN.....

Because if the Output GND connects to Volume Pot GND, that connects to STAR EARTH wich connects to CHASSIS......

aurelius · « **Reply #16 on:** 4 Mar 2006, 11:32 pm »

Felipe,

Is your chassis all-metal?

I had a significant hum issue that was resolved when I grounded the body of the volume pot... my enclosure was aluminium lined wood, but the pot touched wood only.

Just a thought.

Felipe · « **Reply #17 on:** 5 Mar 2006, 12:24 am »

My chassis is wood only.
It has a copper enclosure inside to accomodate the transformers, and that is what i am grounding. The pot touches wood only like yours...

Did you connect the body of the pot to MAINS EARTH or to GK1 earth ?

AKSA · « **Reply #18 on:** 5 Mar 2006, 01:42 am »

Hi Felipe,

Quote

Is'nt the output GND the same GND that connects to the STAR EARTH ?
I dont see any other GND PIN.....

Yes, true, but Mark is correct too, try grounding the body of the pot to star earth.

You do not have to connect star earth to chassis; that's not required, although it's a simple matter to listen if so doing actually reduces hum. Usually it does not.

Cheers,

Hugh

aurelius · « **Reply #19 on:** 5 Mar 2006, 02:03 am »

I've actually aligator-clipped the star earth of my AKSA 55N+ box to the pot shaft, but will eventually solder one end of a wire to a washer or large soldering tag and the other end back to a GK-1 earth point (the washer will be used as part of the pot-chassis fixing gear.

BTW, the "hum" that this fixed was a rumble that could easily be heard from the listening position and was increadibly annoying. One night my loosely fitted wooden knob fell off the pot shaft. When I touched the shaft to turn the volume down, I noticed a significant decrease in hum... problem found!