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

hifryer · « **Reply #40 on:** 9 Mar 2006, 10:57 am »

copper / mu-metal seems like a complex and expensive approach where some thing simple would do!

use thicker mild steel or easier - put the traffos inside a heavy mild steel section.

Rom · « **Reply #41 on:** 9 Mar 2006, 11:02 am »

Hi Felipe,

Try to totally isolate the transformer by having them out of your box lined with copper plate.

I know this is a bit of an odd as this is really out of the norm.

The first thing you need to know was where the hum is coming from, if all the recommended guideline did not work, which from my experience I have tried a lot , grounding, shielding, making all the signal ground common in one point , coaxials, none on them work with my hum problem which lead to search where its coming from, earth loop to start which lead to a simple solution, which really work well with me. Total isolation.

I know how you feel as I did the same on mine, after the hum issue , I would say that my TLP sings much better than ever.

I hope that help.

cheers
rom

AKSA · « **Reply #42 on:** 9 Mar 2006, 08:51 pm »

Felipe,

50cm from the speaker sounds a bit far to me. It should not be audible beyond about 10cms. What is the sensitivity of the speaker?

This is getting out of hand. Can you send me some detail pictures of your installation, including the foil side of the analog pcb and the RCA inputs and outputs? I'd suggest at least 5 Megapixels, good lighting and good focus if you can do it......

Cheers,

Hugh

stvnharr · « **Reply #43 on:** 9 Mar 2006, 10:38 pm »

I've been following this since the beginning as I was looking to transfer my GK-1 from the ugly 3U Jaycar case to a new smaller and nicer looking case of aluminum and wood. I did this this week. When I started to lay things out I found the transformers to be a bit close to the left channel of the board and to the output rca's. I worried about hum. But all I could do was put it all together and listen for the result.

Well, all went together nicely. I braced for the initial turn on, expecting some loud dissonant hum or sound or something. All I got was silence. The tubes were exposed and glowing. Amplifier and cd player on, volume all the way up. There was absolutely no hum, only silence from both speakers with ear up against each one. I listen a lot yesterday and nothing changed.

Here's how things went together:
AC wires kept seperate.
All signal wires 2 strand braided and sheathed in fibreglass cloth sleeving I got from Michael Percy.
Grounds all wired together.
NO shield around the tranformers. Trannies only about 35cm away from left channel of the board.

I only have GK-1 EL, so maybe some of the hum difficulties are from having more boards.

Felipe · « **Reply #44 on:** 9 Mar 2006, 11:10 pm »

I just discovered a great thing :

If i touch the body of the volume pot with my hand, the hum COMPLETLY disappears.
I remember i tested this once, before i shielded and connected this same pot to star earth and it didnt have the sme efect back then.
Maybe because i was wearing rubber shoes and today i was UN-shoed ?
Better earthing body flow ?

Nevertheless...i think its good knews. I just gotta now what to connect the pot to now...its already connected to BOTH channels GND .

Aurelius said he connected the AKSA STAR EARTH (negative terminal of speaker) to this GK1 star earth ??? Did i understood right ? Wouldnt this be connecting both SPEAKER (high level output) AND RCA (low level output/input) together???

Hugh,
I can get photos easily of 7Mp. But i only have the camera on te weekend.
I'll send you a couple of pics on Saturday. Thanks for the help.

You guys are GREAT

jules · « **Reply #45 on:** 10 Mar 2006, 12:39 am »

Felipe,

I'm very inexpert on electronics but I'd like to back up Rom's suggestion that you look at the copper shielding on your trafos. As I understand it, copper shielding around a fluctuating magnetic field works in the same way any self respecting copper wire does and converts the magnetic energy into electrical energy. This is fine as far as countering the magnetic field goes but it might mean you are creating an electrical feedback from the screening to the pot.

I don't know how hard it would be to do but you could remove the copper as Rom suggests or maybe isolate it from any earth that connects to the pot.

jules

rabbitz · « **Reply #46 on:** 10 Mar 2006, 01:18 pm »

Is the metal body near the thread of the pot grounded to the chassis or any other ground? I've found when using a non conducting chassis from plastic etc, I need a connection from the pot body to a ground to remove hum.

Worth a look.

Felipe · « **Reply #47 on:** 10 Mar 2006, 03:12 pm »

I have the pot body connected to the GK1 output RCA ground of both channels. NOT TO THE CHASSIS OR MAINS EARTH.

I can try to remove the copper and see what it does, but i suspect i must connect something to the body pot.

AKSA · « **Reply #48 on:** 10 Mar 2006, 09:19 pm »

Yes, Felipe,

I agree with you. The metal pot does need earthing and in fact I have connected the pot to star earth too through a small pcb on my Swift version.

I am sorry; I should have mentioned this.

Cheers,

Hugh

soitstarts · « **Reply #49 on:** 11 Mar 2006, 06:49 am »

Well, this'll be handy for when I finish mine off.
Dumb question time.....

Will just a metal barrier (plate) between the tranfos and PCBs be enough or do I need to encase the tranfos on all sides top and bottom???

AKSA · « **Reply #50 on:** 11 Mar 2006, 07:41 am »

Martin,

Rather than enclose the trafos, which in my view is probably not necessary because they are made of grain oriented silicon steel deliberately to constrain EM emissions, the best option is to mount the trafos on a piece of non-conductive material (plywood, hard plastic, etc) taking care to insulate the mounting screws so that you have the option of keeping the trafos OFF chassis earth. That way you have the choice of earthing the trafo directly to IEC ground, OR leaving it floating, whichever minimises hum best for your layout.

Cheers,

Hugh

soitstarts · « **Reply #51 on:** 11 Mar 2006, 08:16 am »

Thanks Hugh..
I like the way you know your customers, good to see you reiterated exatly what a non conductive material is..

That's our Hugh, he can communicate with Engineers, and he can communicate with peanuts...

fajimr · « **Reply #52 on:** 11 Mar 2006, 10:17 pm »

Quote from: soitstarts

communicate with Engineers, and he can communicate with peanuts...

HERE HERE... this audio peanut certainly appreciates Hugh's ability and patience to make things understood

Felipe · « **Reply #53 on:** 12 Mar 2006, 06:22 pm »

News from the East......

This one is going to put everybody with a big ? in their head :

BAD FINDINGS FIRST :

I disconnected the transformers and took them OUT of the box. Put them in a insolated wood stand, far away from the GK1 itself. Surprise or not...SAME HUM !!!!

So i assume this hum is not comming from the transformers as they have the same effect in our outside the case, with or without shielding.

Also, the Volume pot body was acting as the star earth. I tried to connect it either to GK1 GND or Mains Earth. No effect what so ever !!!

GOOD FINDINGS NOW :
What it does HAVE effect on the HUM is the following :

The very odd thing is that the bastard responds to my HAND touching in the VOLUME POT BODY. BUT no response to either of the earths ( GK1 ground and mains earth).

The left channel has coaxial and has LESS hum. The right channel is CAT5 unshielded. I will shield this one too. But the left channel still has some hum.

Now...... SUGGESTIONS ANYONE ???
I am out of options here, dont know what to connect the volume pot to ... unless i hire some dude to put his finger in the volume pot while i listen

Could it be the interconnect RCA cables ??? I think they are shielded but i am not 100% sure. Have been working fine without the gk1 in the path. Just CD + AKSA.

Well....i will put the trannies back in now. No need to have the copper either.
Cheers !

aurelius · « **Reply #54 on:** 12 Mar 2006, 10:40 pm »

Do you have any aligator clip leads? (These are real handy when trying to solve eathing problems). Try clip a lead between an earth point and the shaft of your volume pot (take any knobs off). See if it makes any difference.

Felipe · « **Reply #55 on:** 12 Mar 2006, 11:06 pm »

Maybe i am not being clear ....

I have connected the shaft of the volume pot to earth :
1st --> to the GND pin on the pcb.
2nd --> to MAINS EARTH

NONE have made a difference !

The hum only responds to my FINGER on the shaft !!!

AKSA · « **Reply #56 on:** 12 Mar 2006, 11:20 pm »

Felipe,

Put a 10nF cap from shaft of volume control to star earth.

That might do it!

Hugh

Felipe · « **Reply #57 on:** 13 Mar 2006, 10:26 pm »

What can i say.....Hugh is THE MAN, but everyone knows this already !

The cap worked like a charm. I now have about 1% or 2% of the HUM i inicially started with....but only hearable with my ear right next to the speaker....and i am being picky because the preamp is now really quiet.

The amazing thing is that the solution ended up to be so simple...
I started with copper plates shield, ES to mains, passing thru coax and thinking of mumetal enclosures..... NOT !!!!

2 things really made the difference :
- Remove all copper plates and isolate transformers from metal. Screw them to wood floor.
- 10nF cap between the Volume Pot body and Mains Earth.

Simple huh ?? Well...i had to try everything first....

I am thinking of putting the CAT5 back in. I cant tell the left from the right speaker now and only left has coax. CAT5 always sounded better to me.

ADVICE TO CONSTRUCTORS :

Start with the basics. Use no shield whatsoever. Not even coax. Isolate the transformers. Start from there and see what you get.
I ended up with extremely simple GK1 and very very quiet.

Thank you all that helped me with my quest. I never would have got it without you guys.

Now its to time to

Felipe

jules · « **Reply #58 on:** 13 Mar 2006, 11:16 pm »

Felipe,

thanks for sharing the experience to a hum free GK-1. Nice bit of persistance at the end there

Hugh, great analysis as usual. I suppose you could solve most of these issues in a few minutes flat if you had the offending equipment in front of you but it amazes me that you can figure out solutions at a distance online.

It's good to see this stuff happening in the open and I'll certainly be taking it into account when I do the layout for my own GK-1.

thanks

Jules