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Old 23rd June 2005, 08:45 AM   #1
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Question Simply 3x gain preamp for OPA549

For the subwoofer channel on my 5.1 surround amp, I'm planning on using a single OPA549 (the other 5 channels are LM1875) as it will provide around 70-75w rms for my subwoofer.

However, upon searching the forum, people say that a gain of around 10 is the maximum you should use with the OPA549. But having said that, I'm only going to be using this chip for frequencies lower than 200Hz, so would using a gain of around 20-odd affect this region?

If it will, does anyone have a schematic for a simple circuit that will increase the gain from between 2x and 3x to use before the input to the OPA549? I've done searches of the forum, but they all seem much more complicated than I actually need (OPA627 buffers etc etc).

Thanks.
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Old 23rd June 2005, 11:14 AM   #2
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Default Re: Simply 3x gain preamp for OPA549

Quote:
Originally posted by mangrovejack
For the subwoofer channel on my 5.1 surround amp, I'm planning on using a single OPA549 (the other 5 channels are LM1875) as it will provide around 70-75w rms for my subwoofer.

I dont think you will get that much power.


Quote:
Originally posted by mangrovejack

However, upon searching the forum, people say that a gain of around 10 is the maximum you should use with the OPA549. But having said that, I'm only going to be using this chip for frequencies lower than 200Hz, so would using a gain of around 20-odd affect this region?

It should work with no problems


Quote:
Originally posted by mangrovejack


If it will, does anyone have a schematic for a simple circuit that will increase the gain from between 2x and 3x to use before the input to the OPA549? I've done searches of the forum, but they all seem much more complicated than I actually need (OPA627 buffers etc etc).

Thanks.

Try this
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Old 23rd June 2005, 04:36 PM   #3
PKS is offline PKS  Norway
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Default Change.

Nice circuit, but change R1 to 2k. Non inverting so you have a 3x gain. then use 7.6x on the 549.(sorry bad english)
Use two 549 paralelled for more real power
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Old 23rd June 2005, 05:39 PM   #4
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Default Max gain of OPA549

Hi: In response to the previous concerns regarding the max gain of OPA549 chip amplifier,after reading the TI datasheet i do not see any problems with using the chip with a voltage gain of 20+.TI does not mention any possible instability problems at higher gains.If someone has info to the contrary,please post a link to that information. Thank You Robert Cottiers
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Old 23rd June 2005, 08:20 PM   #5
PKS is offline PKS  Norway
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Default Re: Max gain of OPA549

Quote:
Originally posted by RCBandwidth
Hi: In response to the previous concerns regarding the max gain of OPA549 chip amplifier,after reading the TI datasheet i do not see any problems with using the chip with a voltage gain of 20+.TI does not mention any possible instability problems at higher gains.If someone has info to the contrary,please post a link to that information. Thank You Robert Cottiers

It's not a problem... But it sounds like ****... Max 10!
Make an amp, and test it out...
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Old 23rd June 2005, 10:21 PM   #6
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Default Re: Re: Max gain of OPA549

PKS

Have you heard it used as a subwoofer amp?
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Old 23rd June 2005, 11:01 PM   #7
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Default Re: Re: Simply 3x gain preamp for OPA549

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Originally posted by jaudio



I dont think you will get that much power.


From the other threads discussing the OPA549, I was under the impression that was what I could get (I guess as a maximum rather than an average figure)?

I'll be using a 18-0-18 transformer and will be using a 4 ohm subwoofer, so what do you think the realistic power output would be? Either way, I think it will be enough for my fairly modest system.
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Old 24th June 2005, 12:04 AM   #8
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Im not sure what the internal voltage drop is but my rough estimate is about 50watt rms.
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Old 25th June 2005, 08:18 AM   #9
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hi
you know RCBandwidth was right me myself tried OPA549 bridged parallel power amp for subwoofer and it sounds great
and very very loud
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Old 26th June 2005, 03:18 AM   #10
AJT is offline AJT  Philippines
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opa549 can be supplied with max of +/-30 volts, whereas the opa541, +/-40 is allowed. these chips have a fixed bandwith, so that increasing the gain decreases the high frequency corner. but if you are using for subwoofer, then i see no problem with decreased bandwith, as you will not be needing it any way. i say go ahead and do it.
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