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Old 8th January 2005, 06:52 AM   #11
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Quote:
Originally posted by paulspencer
Not yet, I've got a lot of diy things happening, but its high up on my list. I'll post when I have got some more progress.
If you get stuck, give me a call or an e-mail.

Quote:
Originally posted by paulspencer
That's a shame. My main interest in the club was meeting diyers. I organised a diy speaker event at my place a few months ago with a good turnout from this forum, and if I had been with the club a bit longer, I might have been up for running the diy section.
DIY experience isn't really required. You just need to have the enthusiasm to organise the gatherings. There are plenty of guys in the club that like to show off what they've built.

Jeff
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Old 8th January 2005, 02:17 PM   #12
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I hooked this amp up to my speakers (not test speakers) for the first time and I like the sound. In fact I'm quite impressed, it sounds a little better than I expected. Also there are no thumps on turning on/off - the first thing I've built I can say this about. I'm not sure why as there is no special relay switch or muting.

I've hooked it up with everything connected to star earth ... -ve input and outputs as well as the ground on the PCB itself.

Hum persists.

When I had just one input (unshielded) I thought I had removed the hum. So I wired up inputs and outputs of both channels, hum was back! Did I fix it then mess it up? As far as I'm aware I did nothing different, except shield the input to the other channel. The shielded braid I wired to the -ve input which goes to star earth.

Out of time tonight (it's late) ... I will have to look at things again tomorrow.
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Old 9th January 2005, 11:09 AM   #13
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Paul

The -ve input (or shield if that's the -ve) should go to the amp PCB only and not the star earth.
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Old 9th January 2005, 11:58 AM   #14
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I hooked it up today along with my active xo ... turned it on for 1 sec but the hum was really bad and I got another sound that was ugly ... hmmm .. I have to look into it all again and make sure I didn't get something horribly wrong :O

I had this idea that the hum on the chip amp would be cut out by the tweeter protection (passive 2nd order @ 800 Hz) ... in the RTA the hum is centred around 50 Hz.

I'll have to fix up the wiring and do it a bit better, shield both inputs and get them right ... so do I hook up the shielding at one end?
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Old 9th January 2005, 01:08 PM   #15
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If your cable has one wire plus shielding connect both ends

If your cable has two wire plus shielding you connect one for the signal(both ends),one for signal ground(both end) and the shielding is connect at one end(close to the amp where all signal ground connect)
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Old 9th January 2005, 01:24 PM   #16
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Paul

50Hz....... you've got a ground loop.

If you are using a single screened cable like Jaycar WB1500, then the centre wire is connected to the RCA +ve and the PCB input +ve and the screen is connected to the RCA -ve and the PCB input -ve.

If you use a mic cable like Jaycar WB1530 that is 2 core screened, then you use the 2 core wires for the +ve and -ve as above and the shield is connected at one end only. I tend to connect this to the input end but others do it the other way...... sort of like a balanced cable.

Ground loops can be fun to track down and it sometimes helps to do this with a jumper lead connecting it to the -ve input on the PCB or -ve on the input and a 10R resistor on the other end and trying different locations. Even connecting the L & R grounds on the RCA input can help.

If it's not in a case yet could be part of your problem.

Rod has some info on his site to help track down these suckers and sometimes a complete rewire can help as it could be as simple as a bad crimp or solder joint.
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Old 9th January 2005, 01:36 PM   #17
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Thanks for all the tips guys ... I'm going to have to sort out all this stuff and go through all that's been posted and try it all, as well as get my diy mic preamp going, set up my active xo right and recalibrate via ultracurve and see how this active xo really works!!!

I must say, even with a bit of hum I like the sound of this amp so far!
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Old 11th January 2005, 08:39 AM   #18
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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!
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Old 11th January 2005, 09:01 AM   #19
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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 ...
To get more meaningful suggestions other than "try this" or "try that" a clearer picture is necessary. Or better yet, a wiring diagram of every wire connection.

Easy question - is your circuit earth tied to mains safety earth anywhere? If it is, try it without this connection.
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Old 11th January 2005, 09:29 AM   #20
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Isn't that dangerous?
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