| soundNERD |
I want to build a single supply opa549 to run off of 12VDC.
I tried using the schematic provided by TI for single supply operation of any opamp, but when turned on, I got instant, unbearable distortion at any volume level. I thoguht it was from running at only 12V, but I tried 40V and got the same problem.
Does anybody know how to make these things run off a single supply?
Thanks! |
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| zagisrule! |
Are you using a suitable capacitor in series with the ouput to block DC? Generally over 2000uF or so....
-Matt |
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| soundNERD |
yep... even input.
At first I forgot to, but there was no DC output. When I added it, nothing happened.
Was it right to tie the Ref and the other pin (can't remember it's name) that normally ties to ground to the negative supply pin, which is connected to ground, along with the signal and speaker ground? |
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| peranders |
Can you show us the schematic?
Do the inputs float at half the supply voltage?
You must be beware of that there are special single supply opamps and there or "common" ones.
Please show us how you have done becasue this is real simple to solve.
EDIT: To your last question, no it was not right.
+U is connected to positve supply pin and ground to the negative. |
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| soundNERD |
Here is the schematic.
Thanks for all of the help. |
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| thomas997 |
Let us know how it sounds if you get it working. I want to build a sub amp with a ~26V standard transformer I have here..
thanks |
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| soundNERD |
Thomas,
That schematic doesn't work. It's the one I built that does not work.
Almost forgot, I also tied the Ref and I/LM to ground, as they would be in a normal split supply circuit. |
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| zagisrule! |
Use a voltage divider on the input of the op-amp to bias the + input to 1/2 the supply rail.
Otherwise you will only get half the audio signal out!
When the input is connected like peranders suggestion it will work, but it is vital to have input and output DC blocking caps or you will fry your source and your speaker! :eek:
Use resistors of 1K to 10K or so (even higher would work, just remember the two resistors you use must be the same value.
-Matt |
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| zagisrule! |
And by the way this will barely make any power at all, 2W or so into 8 ohms at 12VDC.
At 26VDC you would hardly have enough for a sub amp at 9W or so into 8 ohms.
-Matt |
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| soundNERD |
With peranders circuit, I also connect 12VDC to the power pins not just where it shows right?
And I still don't know what to do with those ref and I/lm pins |
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| mod_evil |
Hi friends, can i use the OPa549 to amplifier my headphone amp? How much ampers this chip need?
thanks for attention. Mod |
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| soundNERD |
11A current for a headphone!!! :hot: :hot:
I highly dobut you would need that much, and I highly dobut your headphones would take it.
The 549 can power an 8-ohm load at around 60-80W and headphones run at under .5W. I also dobut it would sound good with a headphone as headphones are from 32-64ohms, which is too high for the chip to handle.
For a headphone, something like an LM4881 works very nicely. It puts out stereo .25W, which is more than enough for most headphones. |
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| joensd |
| quote: | | With peranders circuit, I also connect 12VDC to the power pins not just where it shows right? |
Youīd connect it also to V+;
ground will be connected to V-
The rest as per P-Aīs schematic.
| quote: | | which is too high for the chip to handle. |
Donīt think so...
Higher resistance=smaller load.
It certainly canīt compete with a OPA627/BUF634 or the like headphone amps (noise-wise) but if you have the chip lying around (=frugal-phile (tm))and handle it carefully I canīt see a reason not to use it.
greets |
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