AKSA 100 N+ the hum the hum! - diyAudio
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Old 2nd February 2015, 12:42 AM   #1
Erskib is offline Erskib  Singapore
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Default AKSA 100 N+ the hum the hum!

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!)
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Old 2nd February 2015, 07:18 AM   #2
AKSA is offline AKSA  Australia
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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
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Old 2nd February 2015, 07:25 AM   #3
Erskib is offline Erskib  Singapore
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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
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Old 2nd February 2015, 08:10 AM   #4
AKSA is offline AKSA  Australia
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Glen,

You could do that, BUT, it didn't cause hum before, did it? Have you changed your source?

Hugh
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Old 2nd February 2015, 08:17 AM   #5
Erskib is offline Erskib  Singapore
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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. ;-)
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Old 2nd February 2015, 09:55 AM   #6
AKSA is offline AKSA  Australia
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Glen,

Do let me know your tests....... it is possible it is a filter cap because if you remove the input RCAs the hum is still intrusive. However, it is unusual for ALL caps to dry out at the same time, so I would expect one channel to be worse than other........

Let us know!

Hugh
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Old 3rd February 2015, 04:48 AM   #7
rabbitz is offline rabbitz  Australia
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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.
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Old 3rd February 2015, 06:57 AM   #8
AKSA is offline AKSA  Australia
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Thank you Pierre AND Ginger!

(Back to the future......)

Much appreciate both your advice to Glen......

Hugh
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Last edited by AKSA; 3rd February 2015 at 09:48 PM.
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Old 3rd February 2015, 07:08 AM   #9
Erskib is offline Erskib  Singapore
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thanks for the extra info and thoughts gents... I didn't get a chance to look at it last night. corrosion here is the norm - I'll clean it up and have a go tonight (with a bit of luck).

cheers,

Glen
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Old 3rd February 2015, 09:14 PM   #10
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I had a similar priblem on a 55N+.
Eventually found the 10 Ohm resistor which "isolates" the ground side of the input was blown open circuit. You might want to check that resistor with a multimeter before delving too deep.
Cheers,
Ian
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