My latest subwoofer - a bridge opa549 built onto a piece of plexiglass - Page 2 - diyAudio
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Old 22nd December 2004, 10:00 PM   #11
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Looks good to me.. for some reason the pictures wouldnt load in firefox, but worked fine in IE.


What layout did you use for bridging, was it in the datasheet?

How does the power compare to a pair of 3886s?

Also what voltage are you getting out of the transformer?


oh and any hum at all, its kinda annoying when there is 60hz hum for a subwoofer :/


thanks
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Old 22nd December 2004, 10:55 PM   #12
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I used the bridge schematic from AN-1192, but used 470k feedback resistors on each amp for enough gain to work with my reciever's output.

I have never heard a bridged 3886 amp, but I have never been impressed with any of national's chips in a subwoofer. The opposite goes for a full range speaker. national's chips are designed more for hi-fi audio, unlike TI's chips, which aren't really designed for audio at all.

But when comparing to commercial subs, I have noticed it performs better than them. This sub easily overpowers my infinity 600W 10 inch sub, and thats even a ported one. I have also compared it to a velodyne sub, with an 8" woofer and a 10" radiator, and found the velodyne to be a little too thuddy, while this seems to have much tighter, more controlled bass. To me, it sounds much better.

The power from the transformers is 36VCT 175W, but after the rectifiers, I never measured the voltage.

And, yes, there is a slight hum because I went for a standard transformer instead of a torrid and I think it's a little too close to the magnet of the speaker. But the hum is inaudible when sitting 10 ft away from it.

The only complaint I have with this is it does very well with running bass lines, but not so well with quick booms. Then, it gets a bit thuddy. I dobut it's the amp, but instead the speaker. I remember hearing this one in the store and it doing the same thing.

Other than that, I'm still suprised at how good something I made turned out. It's about time for me though!!
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Old 24th December 2004, 12:13 AM   #13
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hm that seems like a fairly high voltage to be running the chips at.. maybe it drops a bit under load though? Datasheet says +/- 30V as "max".


So did you use the AN-1192 schematic straight, other than the change in feedback resistors?

You must have added the current limit and Ref voltage connection though right? I tied both of mine to ground and for some reason I cant get the amp to work..


Thanks
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Old 24th December 2004, 02:50 AM   #14
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Well, carlosfm and I were talking about these chips in a subwoofer a while back, and he said how his sub, using 2 opa549 in parallel running at a regulated +/-29VDC, which is 1V below the max, and they seem to run happily at that voltage.

I believe mine is running at about +/-25VDC, which is plenty enough below the max for them to run fine.

Yes, I used the exact schematic from AN-1192, and changed the feedback resistors as I said before.

I have also tied the ref to current limit, then connected them both to ground. Be sure the pcb connection is good (use a multimeter on resistance mode, touch to the main gnd trace and touch the other side to the ref and current pins). I spent about an hour trying to figure out why another amp I built using an OPA549 wouldn't play anything. The trace on the PCB had split (small enough to not be visible easily), and the chip was stuck in off mode.

Are you using a split or single supply?
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Old 24th December 2004, 06:38 AM   #15
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Hi soundNERD,

It is really a very simple and effective way to use AN-1192 for bridging GCs, mine used a balanced line driver because all my GC modules were setup'd in a NI fashion. It really feels good to built something worth your time.

BTW, here's a pic of what I built for a sub amp.

JojoD

Click the image to open in full size.

Click the image to open in full size.
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Old 24th December 2004, 12:41 PM   #16
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Very nice!

Did you build the metal plate yourself or recycle it from a subwoofer?

Looks like 4 chips? probably bridge / parallel? What chips did you use?

Have you connected it to a speaker yet? If so, how does it sound?

The only thing I may worry about that is the size of the heatsink. My amp uses only 2 chips, and the heatsink on it gets hot enough to hurt you if touched. 4 chips puts out twice the heat, and, from my view, the heatsink on your sub looks almost a little too small for how much it's cooling.

Other than that, very well done!
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Old 24th December 2004, 01:05 PM   #17
markp is offline markp  United States
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You can get pure black stain from www.rockler.com and look at the 'dry dyes' for black.
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Old 24th December 2004, 01:12 PM   #18
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markp,

Thanks. I'm suprised I never saw it there before. I've looked at their store for it before.

I have tried black dyes in the past, and it pretty much ruined my speaker. The results were terrible. If I touched it I would get a bunch of black powder on my hands, so I had to clear coat it, making it glossy, which I ddin't want, to stop it. And the color was more of a dark gray than black.

But I found a black stain at rockler, next time I'm there I will look at it.
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Old 24th December 2004, 01:14 PM   #19
markp is offline markp  United States
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I've used black analine dies with good results too. I also put a clear coat on top of them too.
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Old 26th December 2004, 01:57 AM   #20
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Quote:
Originally posted by soundNERD
Very nice!

Did you build the metal plate yourself or recycle it from a subwoofer?

Looks like 4 chips? probably bridge / parallel? What chips did you use?

Have you connected it to a speaker yet? If so, how does it sound?

The only thing I may worry about that is the size of the heatsink. My amp uses only 2 chips, and the heatsink on it gets hot enough to hurt you if touched. 4 chips puts out twice the heat, and, from my view, the heatsink on your sub looks almost a little too small for how much it's cooling.

Other than that, very well done!
Hi,

I built the plate myself, i mean cut, drill, sanding, etc.

Those are the same chips as the one you used and is trully in a bridge parallel config. It's already been working for weeks now, very good indeed.

I don't worry about the heat too much, when I build bridge parallel, I make sure that all the 4 separate amp sections have the lowest possible dc offset so that when connected in BP config, current will not conduct hence no extra dissipation.

Oh btw, I did subject the 549s in a torture test by clamping a 100W soldering iron on the heatsink just to test the thermal protection and it really works thereby protecting the chips.

The plate during painting....

Click the image to open in full size.
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