[Felipe]

Hi there,

So i finally found the time to build the LF55, every test worked flawlessly and when connected to speakers appears to be noise free.  I didn't let it burn in decently so i will not comment on the sound just yet.

I introduced my GK-1 in the chain, because i needed the volume control.
Bad news...the bastard is showing HUM again. Damn... and i thought i got rid of it !
I am in a new house, this may be the reason for the humming, different AC mains. In the old house i had some hum...but now its showing up some more...

Nevertheless i will have to open it up and try to find the cause. It sounds much like the old initial problem that i had...a strong low volume HUM in the 50/100 Hz region. The problem of this HUM is that it can be heard in the entire living room as it echoes a lot...

Does anyone know how to measure my DC in the mains and filter it ?

Regards,
Filipe

[AKSA]

Felipe,

I'm pleased you have your LF up and running!!

Now, hum is most unlikely to be DC on the mains.  Check you have a connection between amp star ground and amp chassis;  if not, try it with a croc clip.  Then, if the hum is present only when the GK1 is connected, I'd be looking at the GK1.  There's an earth loop and the voltage difference across this loop is being amplified somehow.  If you run a croc clip from GK1 chassis to amp chassis, does it increase or decrease the hum?

That's the first test sequence.......  Try this, then come back again to the forum!!

Cheers,

Hugh

Second test is another croc clip from GK1 chassis to source chassis.

[Jens]

Hugh is absolutely right - it is very unlikely that your hum is caused by DC from the mains. DC on the mains usually just makes toroids hum a bit (and it's easily cured with a very simple DC blocker).

I just recently finished my LF and had no difference in hum level between the 55N+ and the LF. I have a very small amount of hum, partly because of a little too much unshielded wiring inside my GK-1R and partly because I use and an unshielded interconnect between the GK-1R and the LF. But even though my speakers are 96 dB efficient, I still have to get my ear all the way up to the speaker units to hear this hum.

If you have a tuner connected to you GK-1, try removing the antenna cable. That's a classic for hum issues!

And make sure the various components in your system are in phase on the mains (it's very easy to reverse the plug in the wall socket for one of the components.

[Felipe]

Ok...short time analysis last night lead to some conclusions :

- I have a little bit of a buzz noise coming from the LF55 amps. This i am sure is being picked up by the short unshielded CAT5 in line level input wire. I will shield it...i solved it this way in the past on AKSA100.
This is not serious though....

- I am picking up more noise in the DIY interconnects GK1-->LF55. They are shielded but still induce some noise. I will replace them with a lesser quality commercial product to block the noise and deal with them later on. So far so good.

- I have the 50Hz HUM coming from the GK1. Don't know how to deal it yet, will try earthing connections. I have 100% WOOD BOX so i can not "earth" the chassis....and don't need to of course.
This HUM is quite annoying, i can hear 2 to 3 metres aways from speakers so must eliminate it.

So...1st shield interconnects...2nd try to reverse phase in the amps....3rd open up the GK and try some shots.

Only have time in the weekend. Will post results then.
All the best,
Filipe

[andyr]

Ok...short time analysis last night lead to some conclusions :

- I have the 50Hz HUM coming from the GK1. Don't know how to deal it yet, will try earthing connections. I have 100% WOOD BOX so i can not "earth" the chassis....and don't need to of course.

Filipe

Hi Felipe,

Don't forget at the weekends you also have to shower your new wife with extravagent attention, otherwise she might wonder why she married you!!   

You have mains hum in your GK-1 and you have a wooden (unshielded) box ... I wonder if these two things are related?   

Maybe you have to completely line the inside of the box with Al or Cu foil and make sure all these sections are earthed?

Regards,

Andy

[Seano]

With a 100% timber box on the GK-1, I suspect you'll need to connect the earth back to the amp.  Problem is I can't think from where.  You'll need better brains than mine for that one.

I recall something from Hugh saying that the the GK-1 was reliant on a earth connection to the amp.

Also I know that my volume pot chassis required an earth connection to the GK-1 chassis to rectify a hum issue. 

And all my internal Cat5 wire has to be binned because it is picking up hum too.  Hugh apparently now uses sheilded microphone cable or some such for internal signal wiring in the GK-1 to manage hum.

Best of luck...

[andyr]

And all my internal Cat5 wire has to be binned because it is picking up hum too.  Hugh apparently now uses sheilded microphone cable or some such for internal signal wiring in the GK-1 to manage hum.

Seano, your Cat5 cable may not be the problem (causing the hum) if you have a metal earthed case?

My GK-1R uses twisted pairs from input/output RCAs to the PCBs and twisted pairs/single 'hot' wires between PCBs (as instructed by Hugh).  The only place I've used shielded wire is the place where the instructions say you should ... from the vol control, I think?

And I get zero hum.

Regards,

Andy

[jules]

Felipe ... you got a good photo we could scratch our chins over? This has to be a case of a a pictue being worth a thousand words as far as analysis goes.

jules

[AKSA]

Felipe,

I'm a bit crippled at the moment - nasty case of food poisoning.  I should be back to assist tomorrow.....

Cheers,

Hugh

[Felipe]

Hi Felipe,

Don't forget at the weekends you also have to shower your new wife with extravagent attention, otherwise she might wonder why she married you!!   
...

Lets put "extravagant" on that! One should never neglect the wifey to 2nd ...! 
And one thing is for sure, she didn't marry me because of my amp building skills! 

Hugh,
hope you get better soon, nasty sickness the food poisoning one. sometime it gets really serious. hope to turn out well for you.

Last night i reversed the plug on the GK1. It seemed that it made a difference. But i should shield the interconnects and see whats left of it. I think i won't be able to eliminate all the HUM...but if i could get it quiet enough NOT to hear it from my listening position, it should be OK.

Cheers all,
Filipe

[PSP]

just in case you haven't, there is some simple stuff you could check before doing all the work of shielding your chassis or digging into your GK-1:

Do you have hum when the inputs to your power amp are shorted (solder a wire from center conductor to ground pin on the cheapest male RCAs you can buy)?  No?  Then we know that the amp is OK.  In one of my AKSA amps, an input RCAs became just loose enough so that the signal ground had weak and intermittent connection to the amp's chassis ground... this produced sudden and quite audible hum on the scale that you describe... not enough to threaten the drivers but clearly audible 15 feet away from the speakers. 

Now put shorted RCAs all the inputs to the GK-1... do you have hum now?  If yes, do you have some coax cable from which you can make a set of temporary interconnects to see if shielding your interconnects will help?  Make sure that your male RCAs are making good connections from the signal earth of the GK-1 to the signal earth of the amp... use contact cleaner, perhaps.  If your interconnects use really fine wires, maybe--in your new environment--you need a larger wire (or a second small one) for the earth-to-earth connection.

Good luck,
Peter