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Old 3rd February 2003, 04:46 PM   #1
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Default not a gainclone, but...

I want try LM3875 as a subwoofer amplifier which will drive 8" subwoofer. So, it will be a small subwoofer system, not a monster scale one. Plus, I want to make an active crossover for it. Could anybody let me know where I can start from? Is there any website with DIY PCB for subwoofers? Any comment would be appreciated. Thanks.
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Old 3rd February 2003, 04:58 PM   #2
halojoy is offline halojoy  Sweden
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Default Re: not a gainclone, but...

Quote:
Originally posted by JAZZ2250
I want try LM3875 as a subwoofer amplifier which will drive 8" subwoofer. So, it will be a small subwoofer system, not a monster scale one. Plus, I want to make an active crossover for it. Could anybody let me know where I can start from? Is there any website with DIY PCB for subwoofers? Any comment would be appreciated. Thanks.
JAZZ2250

Subw-amps have lower demand for speed.
Makes it easier.
On the other hand they Need High Current Peak capacity.
Makes it harder to make a good sub-amp.
Trafo must be be strong enough.

To use a IC-power amp for sub can be done.
But such chips can not compete with a
discrete with the right Output Stage.

ICs are often limited in there current output,
sometimes EVEN protected by a current/power limiting cicuit.

For normal demand you can use a Power IC for SUB.
For best performance with LOW LOADS IMP,
I should go Discrete.

halo - not too discrete or moderate
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Old 3rd February 2003, 05:00 PM   #3
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If you need more than 50 watts for your sub, you might want to read this. It was written with the lm3886 in mind, but it also applies to the lm3875...

If you read through the bigger gainclone thread, I think you'll find a few links to pcbs.. Here's one such link (pcb on bottom of page):
http://home.triad.rr.com/scottnixon/dac.htm

--Jordan
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Old 3rd February 2003, 05:04 PM   #4
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Default Re: Re: not a gainclone, but...

Quote:
Originally posted by halojoy
ICs are often limited in there current output,
sometimes EVEN protected by a current/power limiting cicuit.
Case in point, from the LM3875 datasheet:
Quote:
Over-Voltage Protection: The LM3875 contains overvoltage protection circuitry that limits the output current to approximately 4Apeak while also providing voltage clamping, though not through internal clamping diodes. The clamping effect is quite the same, however, the output transistors are designed to work alternately by sinking large current spikes.
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Old 3rd February 2003, 05:24 PM   #5
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Default low output

Thanks, guys. Well... mine will be a small sub with low output. 50W will be more than enough. So, I guess LM3875 is still OK. Then, how about the active crossover? Thanks.
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Old 4th February 2003, 09:45 AM   #6
Hamish is offline Hamish  Australia
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what about trying burr-brown's OPA549? 75W and 10A peak current output. they dont sound too bad either. ive got a couple i tried in "gainclone" setup.
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Old 4th February 2003, 10:25 AM   #7
halojoy is offline halojoy  Sweden
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Quote:
Originally posted by Hamish
what about trying burr-brown's OPA549? 75W and 10A peak current output. they dont sound too bad either. ive got a couple i tried in "gainclone" setup.
I think that can be interesting.
There are some other, not so fast Power Ops,
that very well can used as SUBwoofer amps.
That can put out a lot of power, TO3 case.
And would have enough speed for SUB-amp.
OPA549 is one of them.

halo
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Old 8th February 2003, 06:09 AM   #8
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Quote:
Originally posted by Hamish
what about trying burr-brown's OPA549? 75W and 10A peak current output. they dont sound too bad either. ive got a couple i tried in "gainclone" setup.

Thanks, Hamish. I checked the datasheet of OPA549, and it seems to be a good choice power-wise. I don't think I need more power than that. Did you try it in gainclone setup using a hard-wiring? How does it sound compared with LM3875?

BTW, is there any pcb layout available online for 2-way 2nd-order L-R crossover? Something like P09 in "Elliot Sound Products" (uing TL072 or compatible) would be fine. I'm thinking to put it in front of amplifier section and to send the HF (> 300 Hz) to LM3875 and the LF (< 300Hz) to OPA549. A crossover point of ~300Hz seems to be ok.

Thanks.
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Old 9th February 2003, 03:11 AM   #9
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Default pcb.....

please.....
nobody?
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Old 9th February 2003, 06:46 AM   #10
Hamish is offline Hamish  Australia
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don't worry about the pcb, just do it point to point. not enough parts to bother.

the opa549 sounded fine. i don't really know enough to compare them. should be terrific as a sub amp though.
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