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Old 30th May 2002, 12:45 AM   #21
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nick,
when the input ground comes in contact with the star ground, the hum/buzz is quite a bit LOUDER.

any other ideas?
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Old 30th May 2002, 04:04 AM   #22
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Default wire size

I'm afraid I can't provide any direct ideas for you, but I noticed your comment about 22GA vs. 14 GA wires on the input common.

Yes, there is a big difference between 14 and 22.

Cross sectional area of 22 GA is about 1/64th of 14, and resistance is about 6x greater.

I would think that it should not matter since there shouldn't be any appreciable current flowing in the input ground circuit. But that may be a clue, since the hum increases when you increase the wire size (if I understand you correctly).

I got the info from http://www.tpub.com/neets/book4/11c.htm

By the way, if you're in the US, consider a scope from ebay. You can get one that will do the basics for under $100, and a very good one for $200 or less.
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Old 30th May 2002, 07:26 PM   #23
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sounds like a ground loop. have you tried connecting 10 ohm resistor to leave the ground. i can't remember where is best to connect the resistor. try connecting at signal ground to mains earth. Can't really remember. On the scope to cure hum, a scope might do some help. The main thing that can cure a hum is patience and guidance and luck. Great combination. Try out different solutions and hope for the best.
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Old 31st May 2002, 12:47 AM   #24
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WOW!!
I HOPE SOMEONE READS THIS, I WOULDN'T BLAME YOU ALL IF YOU'D GIVEN UP ON ME.

HUM GONE
MUSIC GREAT
ME HAPPY

I USED THICKER WIRE FROM THE INPUT GROUND TO EARTH AND ALSO A CONNECTION TO THE PCB GROUND.

SORRY IF THAT HAD ALREADY BEEN SUGGESTED AND I'D NOT CAUGHT IT.

I REALLY WANT TO THANK THIS FORUM, THE PATIENCE AND ATTENTION THAT HAS BEEN AFFORDED THIS NEWBIE THAT, AS MENTIONED BEFORE IN OTHER THREADS THAT WAS IN OVER HIS HEAD!
I'VE REALLY LEARNED ALOT HERE, MORE THAN I THOUGHT POSSIBLE.

THANKS AND I'LL TRY TO FORWARD SOME PICS WITH PARTICULARS ONCE I GET THIS BEAST REASSEMBLED.

CHEERS,
SCOTT
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Old 31st May 2002, 01:17 AM   #25
fcel is offline fcel  United States
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Quote "............ AND ALSO A CONNECTION TO THE PCB GROUND"

Scott,
Are you saying that you did not have the ground wires to the main pcb all this time? Or you're saying you're using thicker ground wires to the main pcb?
I do remember there wasn't a ground "plate" for the Aleph 2 main board and thus requires two (input & output?) ground wires to the board ... or something like that.
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Old 31st May 2002, 01:42 AM   #26
Apogee is offline Apogee  United States
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Here's a pic of the board.

Scott - Did you have GND wires from each of the two GND vias tied to your star ground? It sounds as if you ran your input grounds only to your star ground and not also to the board. It shouldn't have mattered unless the GND wire on the input side didn't have a good connection or your star ground was floating... Is this correct? Lastly, was your star ground also earth (chassis) grounded?

I'm unclear on exactly what you changed????

Thanks,

Steve
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Old 31st May 2002, 01:52 AM   #27
BrianGT is offline BrianGT  United States
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Scott,

Can you post some pictures of your working amplifier? or e-mail them to me at: gte619j@prism.gatech.edu

I am interested to see your finished amplifier.

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Brian
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Old 31st May 2002, 02:03 AM   #28
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Lightbulb AND ALSO A CONNECTION TO THE PCB GROUND

Hmmm...... there seem to be two ground traces on the PCB with pads that would connect standoffs and/or mounting screws to the chassis ground. These grounds would only be tied together by
the mounting hardware unless delibrately and correctly wired together . Ground loops? Yes I think we can say that is a very real possibility......... Brian you want to help us out on the correct ground connections?

H.H.
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Old 31st May 2002, 03:13 AM   #29
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well,
it's never so simple is it? one channel was working so i replaced C7 on the other channel and hooked up the wires and fired 'er up.
HUMMMMMMMM

so, i made dinner and calmed down to give it another go.

here's the current, and very quiet setup: (i don't know if it's correct, but if it's quiet it's good, no??)

- both ground busses on the main pcb are ganged and connected to the star, along with the cap ground, center taps.

- the negative, or ground on the amp input is tied to the board ground AND to the mains earth ground with a heavy cable.

this is for one channel, the other channel is wired the same.

and it is crystal clear. with only a slight hum with my ear to my test speaker.

hope that helps clear it up.

brian, i'll get some pix over to passlabs diy this weekend.

not really sure why it's working well. i do think that the thick ground going to my mains earth is helping rout any crap out, back into the plug ground.

thanks,
scott
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Old 31st May 2002, 03:28 AM   #30
BDP is offline BDP  United States
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Scott,

Glad to hear that you have resolved your oscillation and ground loop hum problems. Way to stick with it. I guess this means your amp isnt for sale. There were many good suggestions and yes a solution was suggested in the e-mail I had sent you.

"As far as grounding goes let me see if I understand how you have it configured. The input ground is isolated from chassis and attaches to the PCB ground. There is only one ground wire going to your star connection from the PCB. Your speaker ground, isolated from chassis, is connected to your star connection...."

You might give a summary of your trials and solutions so others may benefit from your learning.

BDP
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