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Old 2nd September 2011, 07:36 AM   #1
diyAudio Member
Join Date: Aug 2011
Default Audio Buffer for 8Ohm speaker

I need to drive 8Ohms speaker from the output of a PGA2311.
The datasheet for PGA2311 mentions that it can directly drive a load of 600Ohms.
Can i use a series resistor to match up with the load ? (would that be a right approach)
Or would it be better to build some unity gain audio buffer to drive the 8Ohms headphone speakers ?
The output of PGA2311 is a zero-crossing one (no DC offset).
LM380 and LM386 have a fixed internal gain, which is undesirable for my application.
Also, I'd like to use a dual rail supply OPAMP instead of a single rail supply to elimitae the bypass capacitors which create a click and pop when i turn the signal on/off.
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Old 2nd September 2011, 09:20 AM   #2
jaycee is offline jaycee  United Kingdom
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Join Date: Apr 2004
Location: Norwich, UK
To drive an 8 ohm load you will require current gain. If that's all you need, something like a BUF634T would work. If you need voltage gain, then you could simply use an opamp in front of it with your desired gain, or you could program the needed gain into the PGA2311
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Old 2nd September 2011, 09:30 AM   #3
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Join Date: Aug 2011
Hey jaycee, ya i need some current gain, i am changing the voltage gain on PGA2311 and don't want it further amplified by some opamp..
I will check with BUF63T
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Old 2nd September 2011, 10:22 AM   #4
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Join Date: Aug 2011
BUF634T seems to be exactly what i need !
Is there any similar buffer with 500mA output current ?
Also, can you point to any buffer which has a control input ?
So i can turn the output on/off using a controller ?
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Old 2nd September 2011, 02:43 PM   #5
jaycee is offline jaycee  United Kingdom
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Join Date: Apr 2004
Location: Norwich, UK
If you want higher than 250mA you are probably going to have to do it with discrete parts. For example a diamond buffer arrangement (same as what the BUF634T has internally) with BC639/640 outputs.
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Old 8th September 2011, 08:17 PM   #6
tonal is offline tonal  Greece
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Join Date: Apr 2007
PGA2311 works with +/-5 Volts and, according to the datasheet, it will deliver +/-3.75V on its output.
If a buffer (no voltage gain) is to be used to drive a pure ohmic 8Ω load then the buffer should be capable of delivering something less than 0.47A and an average power of 880mW.
If that works for you then go ahead, but if you need more power then you must consider using a power amplifier and not just a voltage buffer.

BUF634 is not capable to deliver that much current, because 550mA is what it takes to activate its internal short circuit protection and not a sustained output current which is about 250mA.
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