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Old 12th August 2011, 03:21 AM   #1211
cersepn is offline cersepn  United States
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Quote:
Originally Posted by AndrewT View Post
Twisted pairs are missing.

Remember for every flow there must be a return route.
Electrical/electronic circuits are approximately what it says. The electricity flows around in a loop (circular route = circuit) all the way back to the start (the source of the emf).
Oh, okay. For the output, i understand the wiring. But i'm a little confused how to do a twisted pair at the vol pot <=> input section and the proper GND-ing scheme at the volume pot.

Because i need to connect the GND to two sides (RCA GND and DCB1 IN GND), how should it be done?

1) Each RCA IN's GND connects separately to individual (L and R) attenuator GND, then attenuator GND -> dcb1 GND?

2) Or attenuator GND does not -> DCB1 GND; instead, each RCA GND -> DCB1 GND (so there's two GND wires connected at the DCB1 GND)?

How should the twisted pair be implemented here?

Twisted pair for (RCA IN -> DCB1 IN) + (RCA GND -> attenuator GND)
OR
(RCA IN-> DCB1 IN) + (RCA GND -> DCB1 GND)?

Sorry for the novice questions. I read most of the grounding articles online but i still don't understand how to do it properly.

I tried these two methods and now i don't have the 60hz hum anymore when the source is plugged in without any volume level. But now there's some sort of funny high frequency noise and when i turn the volume up a little, the hum comes back. The higher the volume, the louder the noise
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Old 12th August 2011, 07:47 AM   #1212
Cobra2 is online now Cobra2  Norway
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Check the RCA-connectors ground...you put the "ring" between the isolating plastic?

Arne K
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Old 12th August 2011, 08:19 AM   #1213
cersepn is offline cersepn  United States
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Arne, do you mean the washer ring? Yea i did
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Old 12th August 2011, 11:06 AM   #1214
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Originally Posted by johnwmclean View Post
Iím building a balanced DCB1 hot rodded @ 600ma. Iím using a 111 x 222 10mm thick al anodized blocks to sink to the 3mm base plate 435mm x 353mm of the chassis.

This is my set-up internally:

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John,

That seems a lot tidier than bulky heatsinks. I am surprised that a block of aluminum can do the job as well as a heatsink. Is your unit running yet or is this a build in progress? Once it is built, please let us know how well it cools. Thanks for sharing.
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Old 13th August 2011, 11:32 PM   #1215
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Michael,

By design fins are always a better option than a solid block for heat transfer. Fingers crossed my blocks work effectively, there’s certainly a large surface area for dissipation, I also plan to treat the surfaces between the base and al blocks with grease, avoiding any air pockets.

I’m still awaiting some parts, once up and running I will let you know the outcome
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Old 14th August 2011, 12:01 AM   #1216
Salas is offline Salas  Greece
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Quote:
Originally Posted by cersepn View Post

I tried these two methods and now i don't have the 60hz hum anymore when the source is plugged in without any volume level. But now there's some sort of funny high frequency noise and when i turn the volume up a little, the hum comes back. The higher the volume, the louder the noise
Is it like a whistle? Could be oscillations. Change your 220R series input/output resistors to 470R ones if the symptoms persist. Your now ones are they 220R for sure?
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Old 14th August 2011, 01:49 AM   #1217
cersepn is offline cersepn  United States
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Originally Posted by Salas View Post
Is it like a whistle? Could be oscillations. Change your 220R series input/output resistors to 470R ones if the symptoms persist. Your now ones are they 220R for sure?
Sounds like a whistle. Yea they are 220R. Will order some 470R to try out and see if it's the problem.

When the source is not plugged into the input, the speakers are quite quiet - very very slight high frequency hash. The moment the source is plugged in, that whistle thing starts.

Can i say with certainty that it's not a ground loop problem anymore?

There's also this strange phenomenon: when the left speaker is ON and right speaker is OFF, unplugging the power cord from the right speaker causes a hum in the LEFT, even though the right side is OFF

And sometimes when both speakers are on, and i turn off one side, the other side will make some crackle/pop noise. I'm quite lost as to what to do now. Any help is really appreciated!
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Old 14th August 2011, 02:06 AM   #1218
Salas is offline Salas  Greece
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Ground loops sound like hum and buzz. Zzzzz with some roar underneath. Whistle can be sign of oscillation between components. About your speakers power chord plugging/unplugging it certainly changes the mains ground route relationship to the common channels ground on the pre. Nothing is certain without expert data, but we try guess so you will not walk alone.
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Old 14th August 2011, 03:46 AM   #1219
bkdog is offline bkdog  Australia
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Originally Posted by cersepn View Post
There's also this strange phenomenon: when the left speaker is ON and right speaker is OFF, unplugging the power cord from the right speaker causes a hum in the LEFT, even though the right side is OFF
!
This could be an earth issue, and as Salas pointed out, without expert data diagnoses is difficult at best. Do you have all of your gear running from one power socket via a power board? If not, maybe there is an earth issue with one of your power sockets and running everything from a single power outlet with a verifyable earth will at least eliminate that from the potential list of problems.

Good luck!
BK
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Old 14th August 2011, 04:48 AM   #1220
cersepn is offline cersepn  United States
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Ah, i was looking around every part of the PCB to make sure i didn't miss out anything. Turns out one of the transformer wire wasn't secured properly to the terminal and it was loose.

The whistle/high frequency hash is gone - but the hum's back.

I've tried every conceivable way of wiring up the GND but i can't just get rid of the hum; the hum gets louder as i turn up the attenuator volume. This is even without any source plugged in.

Is it possible that i overheated any of the parts during soldering? Are the FETs particularly susceptible to overheating? But if that were the case, then wouldn't my measured values of the voltage, offset etc be weird/wrong?
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