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Old 28th February 2004, 03:04 PM   #1
Freddie is offline Freddie  Sweden
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Default OPA549 amp

I'm going to build a cheap and simple 6 channel poweramp which is going to be used in my home theather.

Does it look ok?

/Freddie
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Old 28th February 2004, 03:14 PM   #2
mlloyd1 is offline mlloyd1  United States
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It will do.

I'd make R5 (the first input 20K) a lot larger, though

mlloyd1
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Old 28th February 2004, 05:53 PM   #3
Freddie is offline Freddie  Sweden
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Agreed R5 could be larger. I lowered the gain some too, I didn't need it.

I just did some calculations, after reading some datasheets. It appears to me that this device has got a pretty low Gain Bandwidth product of only 0,9Mhz.

If I have understood this right this means that I will have the -3dB point at around 59kHz. Is this correct? If this is true it makes no sense to have a lowpassfilter at around 100kHz, so I have removed it.

Can someone tell me If I'm right about this!

GBW=0,9Mhz (according to the datasheet)
Closed loop gain: (20k + 1k4)/ 1k4 = 15,3

900000 / 15, 3 = 58824Hz.

/Freddie
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Old 28th February 2004, 06:26 PM   #4
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You are obviously going to use a larger cap than the one on that circuit, right?

100uF is too small.


Carlos
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Old 28th February 2004, 08:55 PM   #5
Freddie is offline Freddie  Sweden
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Quote:
You are obviously going to use a larger cap than the one on that circuit, right?

100uF is too small.
What cap do you mean? All caps that are marked 100uF is going to be 100uF.
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Old 28th February 2004, 09:07 PM   #6
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my experience is 100u works well.

My OPA549 circuit is more simple:

20k between pin1 and 3

pin1 & 2 to speaker

pin3 1k to GND

input to pin 4, 47k from pin4 to GND

5 & 7 to V-

10 & 11 to V+

9 nc

pins 6 & 8 to GND

TIs datasheet shows this:
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Old 29th February 2004, 01:49 AM   #7
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Quote:
Originally posted by Freddie


What cap do you mean? All caps that are marked 100uF is going to be 100uF.

Any additional cap in external power supply?

Is this a power amp we are talking about?


Carlos
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Old 29th February 2004, 06:29 AM   #8
Freddie is offline Freddie  Sweden
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Quote:
Any additional cap in external power supply?
Yes, the caps shown in the schematic is just for decoupling close to the OPA549. I'm going to use something like 10000uF/channel in the powersupply.

/Freddie
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Old 29th February 2004, 08:51 AM   #9
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Default Hi Guys

I spent the weekend working on OPA544T and OPA548T,the first one was sufferring from high input sensitivity,so picking lots of noise when the closed loop gain was 30dB,I had to lower it to 26dB.But it didn't help that much...and the current capability is not that good....

The seconed monster was just great when worked at 30dB gain,and perfect when 26dB,the noise just disappeared because of the bipolar input stage.I used 15-0-15 transformer,3 Amp,to 4 Ohm speaker.

I want to ask about the transformers,when I use the following :

15-0-15 Volts
18-0-18 Volts
24-0-24 Volts

How many ampers I will need,and how much power it will deliver to 4 Ohm speaker when using OPA548T....

Thanks in advance
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