Just completed work on the Burr Brown headphone application with the OPA2604.: 1k &10K, giving a gain of about 11. 10K shunted with a 100pF cap. and a 47nF/10R Zobel on the output. Works well with various types of headphones.
Unfortunately, the 2604 is now obsolete, the OPA1688 is recommended as a replacement.
This design relies on the high output current capability of the device, so BEWARE of non genuine parts!
Unfortunately, the 2604 is now obsolete, the OPA1688 is recommended as a replacement.
This design relies on the high output current capability of the device, so BEWARE of non genuine parts!
Are you sure about that, because the short circuit current of the OPA2604 is 40mA which is definitely nothing to write home about - especially not when the OPA1688 can manage 75mA?
What's probably more important is that the OPA2604 was pretty much the only "audio-grade" opamp that would tolerate more than a +/-18V supply voltage. Also, I don't see which design you mean, but if you are referring to a standard CMoy type circuit (which is sounds like) then you are unlikely to need full supply voltage or full output current anyway
EDIT: And if you are concerned about output current capability then any of the new OPA16xx audio opamps in combination with the BUF634A will easily fix that.
What's probably more important is that the OPA2604 was pretty much the only "audio-grade" opamp that would tolerate more than a +/-18V supply voltage. Also, I don't see which design you mean, but if you are referring to a standard CMoy type circuit (which is sounds like) then you are unlikely to need full supply voltage or full output current anyway
EDIT: And if you are concerned about output current capability then any of the new OPA16xx audio opamps in combination with the BUF634A will easily fix that.
AD8656 can manage +/-220mA from 5V single supply... More realistically with signal swing +/-100mA. So it can drive 30 ohms nicely upto about 1.5Vrms, and its a lot lower in noise, important for sensitive headphones/earbuds. The 5V will limit the power of course, but its worth knowing CMOS opamps like this usually have beefy outputs as current gain is easy with CMOS.
The OPA2604 is not rated for less than 600 ohm loads - that 10 ohm Zobel network must be pushing it towards instability.
I suspect you could use something like the AD8656 with bootstrapped supply rails (BJT emitter followers on each rail) to good effect for more voltage and retain the low noise and high current.
[ Ah, Analog Devices seem to have a Spice model for the AD8656, perhaps I should see if it works in LTSpice ]
The OPA2604 is not rated for less than 600 ohm loads - that 10 ohm Zobel network must be pushing it towards instability.
I suspect you could use something like the AD8656 with bootstrapped supply rails (BJT emitter followers on each rail) to good effect for more voltage and retain the low noise and high current.
[ Ah, Analog Devices seem to have a Spice model for the AD8656, perhaps I should see if it works in LTSpice ]
Well according to the model the AD8656 distortion increases with load, so that high current ability isn't as wonderful as it seems. No such thing as a free lunch..
Perhaps the best approach for headphones and opamps is paralleling the opamps for higher current.
Perhaps the best approach for headphones and opamps is paralleling the opamps for higher current.
The application note effectively parallels up the 2 sections of the dual op amp. :Burr Brown Application Bulletin by Morgan Monks. Unfortunately, no reference number.
Cmoy was built with opa2134.
https://diyaudioprojects.com/Chip/CMoy-Grado-RA1-Headphone-Amp/
Opa2604 will not drive headphones. Its a wonderfull low distortion opamp though, when used correctly.
Nice, didn't know of the AD8656 before. Could it be the same chip as the OPA1656?
I did that with OPA275 a long time ago... to drive my HD600 straight from the DAC output.
Now I do the same (no preamps/headphone amps...)... but now I use Holo May DAC and its XLR out to drive the HD650 in balanced mode. Stunningly beautiful and real...
Now I do the same (no preamps/headphone amps...)... but now I use Holo May DAC and its XLR out to drive the HD650 in balanced mode. Stunningly beautiful and real...
Analog Devices are not Burr Brown / TI, and the supply voltages are very different