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Old 11th January 2005, 09:34 AM   #21
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Quote:
Originally posted by paulspencer
Isn't that dangerous?
It could be if none of the other gear attached is safety earthed. I'm certainly not recommending you leave it that way.

The safety earth's main purpose is so you can attach the chassis and other exposed metal parts to it, ensuring the mains fuse blows in the event a live wire touches the chassis. You do not have a chassis!
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Old 11th January 2005, 10:44 AM   #22
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Quote:
You do not have a chassis!
good point! lol
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Old 11th January 2005, 11:30 AM   #23
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Quote:
Originally posted by paulspencer
Here's a pic of what it looks like ... still needs work to try out all the suggestions ...

YES I KNOW ... it's messy, but please don't tell the electons! Hmmm the word has got out I think ... someone has told the hum electons that my wiring is messy, so they are complaining loudly!
Hi Paul,

Looking harder at the pic I can barely distinguish power ground wires, but it seems that you are makin' a common mistake.
Are you routing the power ground of each channel to that "0V" point you identify in the pic? (that plastic-thing-with-screws, what's the english word for that?).
That is too much distance.
Hum is a question of centimeters.
Run a thick (and as short and direct as possible) wire joining both channels' power grounds and from a mid point of this, run a wire to the PSU ground (that "0V" connection you have).

Tell us later.
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Old 11th January 2005, 01:06 PM   #24
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Quote:
Originally posted by carlosfm


Hi Paul,

Looking harder at the pic I can barely distinguish power ground wires, but it seems that you are makin' a common mistake.
Are you routing the power ground of each channel to that "0V" point you identify in the pic? (that plastic-thing-with-screws, what's the english word for that?).
That is too much distance.
Hum is a question of centimeters.
Run a thick (and as short and direct as possible) wire joining both channels' power grounds and from a mid point of this, run a wire to the PSU ground (that "0V" connection you have).

Tell us later.
Ok I will go through it all since it's not easy to see what's going on...
Sorry it's not a bit more clear ...

Plastic thing with screws? ... I think you mean "terminal block" where wires are joined.

By power ground do you mean star earth?

In between the caps there is that 0V point which I understand is star earth. A single wire connects to the terminal block centre position that I've used as star earth. I have the following connected to this point:

* heatsink
* -ve wire on each of the speaker outputs
* ground on each of the input RCAs
* braiding on the input cable that is shielded on one end - connected not on the PCB end but the end near the inputs
* ground on the PCB

I have just worked out the case I'm going to build for this. I'd like to put the heatsink on the front and have a fairly simple box the height of the heatsink (75mm) x 420mm wide x 350mm deep. I will put the power supply parts close to each other and make all cables as short as possible, separating the input cables as much as possible and putting AC power lead on the opposite side to input cables.

Should the heatsink be insulated from the rest of the case?

Is there anything else I should consider in laying things out?
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Old 11th January 2005, 02:09 PM   #25
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Paul,

The RCA (signal) grounds should go directly to the PCB, not to the terminal block.

So, do you have one or two ground wires from the PCB to the terminal block?
Is it one per channel or a single common wire?
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Old 11th January 2005, 03:12 PM   #26
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Quote:
The RCA (signal) grounds should go directly to the PCB, not to the terminal block.
right ...

So at the end that is connected to the input on the PCB, the shielding should go to the ground pin (one point) on the pcb ... on the other end, the shield should be connected to the ground as it is now

Quote:
So, do you have one or two ground wires from the PCB to the terminal block?
Is it one per channel or a single common wire?
Just one wire from the PCB ground pin to the terminal block (star earth)

The PCB has a single earth point, as does the power supply as there is just one transformer with one star earth point.
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Old 11th January 2005, 03:27 PM   #27
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hi
This is the way I have connected my (humfree) chip amp:
Click the image to open in full size.

And in real life it looks like this (not so good pic):
Click the image to open in full size.

protective earth (greenish) is connected to case(s) not to power ground but I have connected it near in case I would like to connect them. Input signals runs in seperate coax with shield as signal ground connected to each input ground.
I dont know if this is best way to do it but it is working.
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Old 12th January 2005, 03:54 PM   #28
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I was hoping to have another go at fixing the hum today, but instead I ended up working on another project - modifying a case I'm recycling to hold my active xo. I made a rear panel to suit the RCA inputs of my xo and power cord, now I have to tweak it a little and make a nice looking front panel and paint the thing black (it's a wussy looking silver thing)

Keld,

I don't understand that green line fully - what it is and how it is wired. Is it connected to mains earth on AC mains lead?

I had a look on your site and there were a lot of things I'm interested in, you have a lot of interesting projects ... some of the links were VERY slow to load (I have a very fast internet connection, so if it's slow on mine... then it's slow!), I wonder if the images have a higher resolution than they are actually displayed as. It left me wanting more info (ie text, description, a bit about what you did, how you did it, why etc ...) in particular about how you built things, as is looks like you have some ability to build things that most don't build, working with metal etc, which is of particular interest, especially since I've just for the first time today had a go at making a metal case! ... I look forward to seeing what you come up with on your site
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Old 12th January 2005, 09:42 PM   #29
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Hi
The green/yellow wire is the protective earth from the mains and is connected to each case. sometimes you connect it to your power ground but I have chosen not to. Read more about earthing here: http://sound.westhost.com/earthing.htm

And yes I have some projects on my homepage and most of them are not finnished Why it is slow to load I dont know, it must be the ISP (comhem) server that s**ks. All my pics are heavely compressed average size is something like 25kB. And i have (almost) no scripts so they really should be loading quite fast, but it doesnt I have also noticed a decrease lately in download speed when browsing my pages . maybe its time to call Comhem

I know there ought to be a lot more text on my pages -- but it is a low priority project.

PS I have some big pics (200kB) a 1911 from 1916: http://web.comhem.se/~u33113170/1911.htm
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Old 13th January 2005, 02:12 AM   #30
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Keld, sounds like it's the ISP, you aren't paying for it are you? I'd hope not if the ISP is making it that slow. I don't like the ads on geocities, but they seem to run fast.
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