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Chip Amps Amplifiers based on integrated circuits

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Old 14th September 2012, 05:59 PM   #41
tsiros is offline tsiros  Greece
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the two twisted pairs are indeed the input, two channels, but i use utp cable which i think is not a good choice, i should get coax perhaps.

the white pair from the pcb is speaker out, the orange is the ground. common for both speakers. no idea if this is acceptable, but the pcb only has one ground for both speakers.

the shielded going towards the bottom of the photo is the lightbulb tester.

the black square is a heatsink. the component with the two shielded wires on is the rectifier. its output goes to the pcb.

the remaining cable connected the pcb is the ground and is connected to the transformer middle tap.

what is 'MAG'? (edit: reading up on it in here )

Last edited by tsiros; 14th September 2012 at 06:03 PM.
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Old 20th September 2012, 02:35 PM   #42
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Er... call me crazy; but isn't this missing any form of rectifier on the power supply ? It's just transformer -> amp board ?
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Old 20th September 2012, 04:47 PM   #43
AndrewT is offline AndrewT  Scotland
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Sorry, MAG is my invention for Main Audio Ground. I usually reference fully at the start and refer to the acronym thereafter.

edit:
I take my sorry back. I have not used the MAG acronym in this Thread.
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Old 20th September 2012, 06:52 PM   #44
tsiros is offline tsiros  Greece
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stevehive: look below the amp board, the black square with a device on it, 4 wires (only three are visible from the angle i took the photo - two brown and one blue) sticking out of it. That's the rectifier bridge on its own heatsink. Overkill? maybe... but i didn't want to strain the amp heatsink not one bit. This way the amp heatsink is at ~40C. the rectifier bridge heatsink is dead cold.

andrew: no need for apologising. besides, i abrevviated it myself. you only said 'main audio ground'. i still am not exactly sure which ground it is. the power supply 'zero', the audio in ground or the speaker ground?

andrew: what about coax cable for RCA(amplifier case "audio in") to amplifier's (pcb's "audio in")?
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Old 21st September 2012, 08:23 PM   #45
AndrewT is offline AndrewT  Scotland
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The Main Audio Ground is just that. All the other "grounds" that need a voltage reference are all brought to this "point".

I keep with twisted pair for all audio frequency signals.
From what I read on this Forum, Coax is only good when the signals are into the MHz (or maybe, >10s of MHz). These high frequencies need transmission line characteristics with the resistive loading that a transmission line requires to attenuate reflections.
Audio interconnects cannot easily adopt those transmission line terminations? eg feed through 50r or 75 at the source end and ground with 50r or 75r at the receive end.
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Last edited by AndrewT; 21st September 2012 at 08:26 PM.
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Old 23rd September 2012, 07:44 PM   #46
tsiros is offline tsiros  Greece
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with the twisted pair cable i used from old utp cable, it had lots of interference

i removed it and in place i put a 2" long stereo coaxial cable, the standard thing you see usually with 3.5mm jacks at either end

now there is significantly less interference. I can not hear it at all from my listening position and i can just notice it with my ear next to the whizzer cone.

previously i could notice it from the listening position when the amp was idle (not playing music)
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Old 24th September 2012, 08:37 AM   #47
AndrewT is offline AndrewT  Scotland
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Then you must have corrected another mistake when you changed the cable.
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Old 24th September 2012, 08:48 AM   #48
tsiros is offline tsiros  Greece
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nope. i still have the connectors with the twisted cable, i can swap the cabling easily, the twisted pair is noisy

perhaps ethernet cable isn't appropriate? It was 8" long. from rca jacks to pcb
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Old 24th September 2012, 10:32 AM   #49
AndrewT is offline AndrewT  Scotland
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I have never experienced the deterioration that you describe !
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Old 24th September 2012, 01:48 PM   #50
tsiros is offline tsiros  Greece
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well, the amplifier is quite high gain, there is lots of interference in my house, its earthing is of low quality, the mains wiring equally so.

also, the amplifier is caseless, perhaps the twisted pair wire (look at the pic) i used isn't ideal for this?
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