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AKSA 100 N+ the hum the hum!

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Hey all,

Well after an 8 (really!) year hiatus, I finally got around to hooking up my AKSA once again and while it was working like a charm previously, boy does it have some hum now! I went through all the setup diagnostics (yep, still have all the original documentation) and everything is within spec. So I can only assume one or more of the "factory original" caps in the PS has gone bad? Anything you guys can recommend I check before I pull out the soldering iron?

Glad to read you are still kicking and well on the mend Hugh, a lot of water has passed under the bridge for all of us in the interregnum!

Cheers,

Glen
(AKA EchiDna in a time long past!)
 
Hi Glen,

Welcome back, it's been a long time! Still in Singapore, ever coming home?

Yes, short the inputs to ground, turn on, and if the hum is evident, it's 90% chance it's been the filter caps. If you have a CRO, you will see, but it's almost certain.

Still upright, walking wounded, but not terminal!! (in the spirit of our PM just today in the media.......)

Happy New Year to you and your family!

Cheers,

Hugh
 
Thanks Hugh, yep still in Singapore but having spent a lot of time in the middle east in Saudi Arabia last year, I am very happy to be home and regaining some sense of normality again! I'l never say I won't return to Melbourne, but as per your previous news post on the webpage, the oz economy isn't in the best shape to be considering it right now!

Just to be clear, my star ground is not connected to mains ground, but is connected to the chassis. should I disconnect the RCA input wires (both) and run them to chassis?

cheers,

Glen
 
Hi Hugh,

The star ground was connected to mains ground when built, but disconnected after testing - I never removed the wire though...

Once I get home from work, I'll try connecting the input ground to the star ground and see what the response is. The hum is very loud even with nothing connected to the inputs at all. Sorry to say, I haven't got an oscilloscope...

The main reason for starting it up again was the gift of a bluetooth audio module I intend to integrate into my GK-1 (eventually), but for now, I just want the power amp to operate properly and phase 2 is to get the GK-1 back into service with the bluetooth as a source for network streaming experiments. ;-)
 
Had a similar problem with a DIY amp that wasn't used for years. Turned out it was some corrosion on the chassis so the ground connection wasn't making a good contact. Try a DMM at various points to the mains earth such as heatsink, speaker ground etc to ensure good continuity. I never run a signal ground directly to the chassis (power or pre) and I think on the AKSA there's a resistor for the signal ground.

I found on my AKSAs, connecting the star ground to the mains earth via a 10R resistor / reverse diode network worked the best for lowest hum but other builder do not use this connection with good results.
 
hum is on both channels and of similar/same volume - haven't had a chance to have a look at it yet, but the volume being the same (and Loud!) made me immediately think it should be a "common" source - ie earthing somewhere, somehow...

It might be 8 years on, but if there is one thing I know I can rely on in this world, its the network of AKSA owners (and the owner!) coming through with good advice! probably won't get to play with it until the weekend now unfortunately, but I will keep you all in the loop ;-)
 
Hi John,

Normally, the star earth of an amp would be attached directly to the chassis, and then the power IEC plug to the same bolt on the chassis as well. In modern mains systems, redolent with smps, electric motors and horrific spikes and even control signals, there is a lot of noise which can influence the sound at the speaker. This is the earth current issue which is worrying with many audio systems.

The idea is to separate the star earth from the mains and chassis earth (sometimes called power earth). A wire between them is cut, and a 10R resistor with two back to bad diodes is inserted into this wire. All the three components are in parallel. It means that nothing of substantial current goes through the resistor, it's through the diodes, one or the other, but the 10R resistor means that there is an impedance to the power mains to the signal earth (as we describe a star earth). Often, but not always, this can reduce the hum and noise to inaudible levels.

Cheers,

Hugh
 
Normally, the star earth of an amp would be attached directly to the chassis, and then the power IEC plug to the same bolt on the chassis as well. In modern mains systems, redolent with smps, electric motors and horrific spikes and even control signals, there is a lot of noise which can influence the sound at the speaker. This is the earth current issue which is worrying with many audio systems.

Cheers,

Hugh

Hi Hugh,

In all my builds, I actually keep IEC earth (which is tied to the case, for safety) completely separate to signal ground. IOW:
* RCA sockets are insulated from the case (using the red or white spacing washers that come with them).
* RCA earth tags on the inside are connected to amp module PCB earth plane.
* amp module PCB earth plane and speaker 'black' wires are connected back to the PSU PCB star ground.

Idid this precisely because of 'grunge' on the mains earth ... but is this a problem - iow do you recommend I instead use the old "resistor & diodes trick" to connect back to case & IEC?


Regards,

Andy
 
Aha, check all the rectifiers, particularly left side negative - might be blown, so just replace - then remove the nut Glen, and put in a large diameter metal washer.

Probably a simple repair! And yes, use a 10R with back to back diodes to IEC/mains chassis...... this should be useful.

Man, there is a lot of humidity in that environment in the tropics!

Hugh
 
well, the saga is done and dusted! and I'm happy to report that its all systems go - nothing but silence on both channels after the addition of a wide washer under the nut in the pic.The mystery of how that happened is unknown though. Yes Hugh, humidity is a killer here for exposed PCB's. Someday I must get around to re-soldering that board now I have a decent high powered soldering station, its got that whole cockie poo look ;-)

Terima kasih banyak pak Hugh et al ;-)
 
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