On the topic of opamps and running temperature, somewhat discussed earlier in this thread (here relating to current-feedback (CFB) models such as AD844 and THS3001) …
It was already said before (Chad in post 16, etc...), but it worths checking anyway:
Did you remove those 3.3n across the feedback resistors?
In my overzealousess, I jumped the gun here, and didn't carefully check this thread
While I haven't listened to DAC, I can say that the AD844s are now only slightly warm to touch. This is comparitively warmer
than any other IC on this PCB, but no way near the temps encountered before removing those caps.
...I am now noticing heat issues with non-CFB models (e.g. AD797 and especially AD843), and specifically used in the MF A324 I/V stage, as noted in this schematic:
(Note the use of the 3300pF capacitor C(L), and 620 ohm resistor in the IV feedback circuit.)
The MF A324 I/V stage was designed pretty much based on the PCM1738's datasheet suggestions (page 23 here: http://focus.ti.com/lit/ds/symlink/pcm1738.pdf
When using AD797, I inserted a 100 ohm resistor in series with C(L), as recommended in the AD797 datasheet …
Using this config, the maximum running temp I recorded was 97F (36C). Note that C(L) was kept at 3300pF per orig. design, not 20pF to 120pF as in schematic above; the sheet says: "The value of C(L) depends on the DAC and again, if C(L) is greater than 33pF, a 100 ohm series resistor is required."). Note: the AD797 is a single-channel opamp so the application requires two per stereo channel.
When using AD843 (no changes to stock I/V in first image above) the maximum running temp I recorded was 112F (44.4C). Although this is puzzlingly "hot", it is still within spec (max datasheet temp: 70C). I heard no obvious distortion during listening tests. Note: the AD843 is a single-channel opamp so the application requires two per stereo channel.
I've also used AD825 (single) and AD827 (dual) -- both are cool-running models. My Questions/Comments:
Is the stock IV circuit (show in first image above) not "optimized" for AD797 and especially AD843? If so, is that causing the heat "issue"?
If not, and if these opamps are behaving normally, should one heat-sink them?
While the running temps may be high, both these opamps are the best-sounding models I've used in this I/V circuit.