| Tomo |
Hi,
I am thinking about using LM1875 or equivalent power opamps to drive Grado headphones. I am hoping that it might well be operating in Class-A at ear-splitting volume.
The main concern is that it might blow the cans. But what if I operated the opamp at fairly low gain such as 1 ~ 3. I found a following schematics in LM675 specs.
I am wondering if I can use this with LM1875. Also, I am wondering if I were to attack another resistor to the feedback resistor to fix up gain other than 1.
Thanks,
Tomo |
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| Tomo |
Oh,
And, I would be appreciated if you can tell me how this is proper when the chip is not unity gain stable?
Seems like snubber inserted between the inputs ... am I wrong?
Tomo |
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| crown300 |
| For 8 Ohm headphones, put a 330 Ohm resistor in series with the headphone. |
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| Bill Fitzpatrick |
| I'm wondering why it's OK to put a series resistor in line with 8 ohm headphones. Won't this screw up the damping? |
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| crown300 |
1) Per the datasheet, the minimum gain for LM1875 & LM3886 is 10. Then the fastest and easiest way to drop power is to use resistor in series with headphones. For 8 ohms, use 330.
There may be a more "correct" or eligant way, I don't know of one.
1) It may "technically" screw up the damping.
2) Try it, and let us know if it does. |
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| GregGC |
| quote: | Originally posted by Tomo
Hi,
I am thinking about using LM1875 or equivalent power opamps to drive Grado headphones. I am hoping that it might well be operating in Class-A at ear-splitting volume.
The main concern is that it might blow the cans. But what if I operated the opamp at fairly low gain such as 1 ~ 3. I found a following schematics in LM675 specs.
I am wondering if I can use this with LM1875. Also, I am wondering if I were to attack another resistor to the feedback resistor to fix up gain other than 1.
Thanks,
Tomo |
It should work. You can add a res between -In and GND to change the gain. R2/R1 should be bigger than 10 (so that LM1875 is stable). The cap, use someting like 1uF. |
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| Tomo |
Hi,
I don't want to be limited by the guidelines. Besides according to this schematics, you can have it operating at UNITY gain.
I want to know how the snubber connected across the inputs will bring stability to opamp which isn't unity gain stable.
Tomo |
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| SY |
| Rather than dropping things with an output series resistor, why not use a 10:1 voltage divider at the input? |
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| Tomo |
Hi,
Thank you Greg!
I found the section. Time to study it in close details.
Tomo |
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| Tomo |
Hi,
I read the paper and I realized something. Appearently, this method reduce the actual "signal" gain to unity, however, noise gain stays at the minimum gain within some certain bandwidth.
That means G=10 applied to noise, but the signal goes through without gain. I am worried that such increase in noise level may be very bad ...
Help me, oh so great ones of the hall of wise!
Tomo |
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| carlosfm |
Tomo,
The OPA power op-amps from Burr-Brown are unity-gain stable.
No fuss.
You can try the OPA548.;) |
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| Tomo |
Hi,
Thanks, Carlo. I will go for those. Very cool that I can adjust current.
Tomo |
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