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Old 27th October 2003, 08:49 PM   #11
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I don't know if it matters that the DC offset is positive or negative. I have about -9mv on both of my channels; perhaps this has something to do with my ground loop hum, or perhaps it's coincidence.
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Old 27th October 2003, 09:23 PM   #12
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As long as it is smaller than few tenths of millivolts offset is not a problem.

I'm glad I could help..

Cheers

Andrea

BTW You made me curious... especially the cheap sources...
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Old 27th October 2003, 09:23 PM   #13
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Well...there is no buzz now. Silent. Everything runs well, so i'm just wondering if - offset is bad. It used to be positive....so....

if its not bad....I'll leave it Later!

-Matthew K. Olson
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Old 27th October 2003, 09:43 PM   #14
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The polarity of the offset isn't important, maybe the new R9 shifted the balance from +3mV to -3mV but I'd rather take care of the output wires (sorry.. couldn't resist.. hey noo.. I was joking )

Cheers

Andrea / always looking for a cheaper place to buy things
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Old 27th October 2003, 10:08 PM   #15
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Well...beats crap outa me. Ok...here's the real scoup on what happened. I made a gainclone custom for a guy ....i've never met him until this last weekend when I finally met him and we listened to my sym 400's. During setup...since he doesn't believe in banana's....he had his gainclone connected to his speakers via solid core which was just screwed to the terminals of the gainclone. Well...so I figured...I'd just keep the gainclone off and plug the sym's into the terminals ...because I had bananas and it'd make it easy. Dumb me. The gainclone is an inverting amp, and the + terminals on the gainclone are really tied to ground. THEY ARE BOTH TIED TO GROUND. So when I went to plug in both amps into the gainclone...pop...pow...icky. I'm lucky I didn't destroy his speakers. Ok, long story short...I developed a buzz in my mono's....we went...huh...well its probably the cables or something...who cares. We cranked it for about half an hour...everything was fine except for the buzz. Man did we have it cranked and the amps didn't even heat up. Ok...so then I was like, uh, lets plug in the gainclone and see how it sounds compared to the mono's. Well, haha. uh...we plug it in...turn it on...and snif...snifff......something smells. I open the gainclone case and poof...a puff of smoke comes out :-D DOH!!!!!

So now I've finished fixing both...and my wife prefer's the mono's :-D Later ya'll

-Matthew K. Olson
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Old 27th October 2003, 10:19 PM   #16
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Well that is an interesting story, I will keep that in mind when working with inverting circuits.

While you're here, I might as well ask, how did you mount/connect the output devices? I used Holton's suggested method using aluminum angle-brackets and the temp drop is just too much, I want to re-do it with the devices mounted directly to heatsink somehow (except his PCB isn't designed to allow under-board direct mounting a la Pass DIY). I have these huge heatsinks, 0.28C/W per channel and the transistors still heat up a good bit (45C idle to 60[?]C) from music over 90db. This would merit fixing before I decide to really crank it anymore. I didn't get a close enough look at yours on Saturday.
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Old 27th October 2003, 10:35 PM   #17
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Ok, this is really simple. Have a look at holton's other amps. If you notice he has his outputs mounted via an aluminum bar effectively bolting the heatsinks right to the main heatsink without individually bolting each output right to the heatsink.

http://www.aussieamplifiers.com/avamp.htm

I thought it was a good idea...I bolt down w/ 1/8" aluminum bar and brass #8 screws...works well...nonferrous etc. Time to get working on dinner and listening :-D Laters!

-Matthew K. Olson
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Old 28th October 2003, 06:02 AM   #18
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Quote:
Originally posted by Kilentra
Well that is an interesting story, I will keep that in mind when working with inverting circuits.

While you're here, I might as well ask, how did you mount/connect the output devices? I used Holton's suggested method using aluminum angle-brackets and the temp drop is just too much, I want to re-do it with the devices mounted directly to heatsink somehow (except his PCB isn't designed to allow under-board direct mounting a la Pass DIY). I have these huge heatsinks, 0.28C/W per channel and the transistors still heat up a good bit (45C idle to 60[?]C) from music over 90db. This would merit fixing before I decide to really crank it anymore. I didn't get a close enough look at yours on Saturday.
I mounted my devices directly to the main heatsink, look

here

Cheers

Andrea
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Old 28th October 2003, 10:22 AM   #19
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Dang andy you stole my idea on the caps! haha! looks great Hope you are enjoying those caps...I know I am. Pics of guts will be up soon. Actually, I think Kilentra got some pics of my amps this weekend. We'll see if he posts them. Later!

-Matthew K. Olson
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Old 28th October 2003, 10:32 AM   #20
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Did I forget to mention that I also used Stealth 30A rectifiers?

These caps are really good (Q/P is almost unbeatable)...

Cheers

Andrea
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