Originally Posted by zilch0md
You wrote this four days ago - well ahead of my e-mail to iBasso. Cheers!
What is "a heat sensor" (in the context quoted)?
yeah, I did didnt I hehe. ibasso's claim that buffers dont need bypass caps and that multiple AD797 used as a buffer is a good idea, with the only limit being the current, is confusing for such a technology company, i'd say the person who replied only looked as far as the line that says its unity gain stable and may not have actually used the chip.
the fact its in a FB loop doesnt mean its all of a sudden another opamp, we have demonstrated that it is proven mathematically to be unstable. Even chips designed to be buffers should have the rails bypassed/decoupled individually, they should also really have current sharing resistors. When all connected in parallel, there will be a tendency for some to hog the current more than others.
there is a reason Walt Jung stopped recommending AD797 for his super regulators, even though when stable its still pretty hard to beat even today. its plain to me they are not happy and they should not even be considered for this application in the first place, so continuing along this track even now seems ridiculous to me
as for the sensor, I mean not a camera, just an infrared heat sensor/thermometer rather than a camera if you want to save a bit. I cant find the link to the cheap thermal cameras I had, most on ebay are OTT for this, but the above will do
Originally Posted by kiteki
Thanks for the interesting posts I have to catch up on, some quick questions...
You mean like horse blinkers? The OPA2111KP seems pretty popular and I like it, IIRC it has a pretty low slew rate.
Interesting list, how come the 1611 and 827 aren't very popular?
What's the HD2? I sortof like the sound of AK4396 -> LT1028...
yes Horse blinkers, its a figure of speech, ie. pushing ahead at speed without looking around. The problem is, often massive slew rate is chased while thinking of it somehow being meaningful to having a responsive amp at audio frequencies, wide bandwidth and high slew rate are good indicators that the chip will be sensitive to layout and other conditions. These types will often need a lot of NFB and heavy compensation to be stable at low audio bandwidth, low gain applications, so any advantage can easily be lost.
if you like LT1028 in this application and arent able to check performance, try buffering or following it with a discrete follower, I like mosFETs, but some of the modern bipolars and definitely the power jfets are superb. I dont know why its not more popular either, personally I love opa827 and IMO its one of if not the best voltage feedback opamp for Dac IV stages, because of its stupidly low noise, high impedance jfet input stage and incredible AC performance, VERY low input bias current, which makes it great for the input of DC coupled circuits.
the opa1611 wont be very good without a buffer, has bugger all current, same with the opa1641, great chip and I love jfet opamps, but its like they forgot the output stage on this one, simply pissweak output power, so would need a buffer. I keep coming back to the lme49990 and I do like the 827 a lot, just dont have enough of them to throw around and its not a cheap one
IV stages are a bit of a different case, here I would champion the use of a very fast current feedback opamp designed for video mostly, as the glitch energy of delta sigma type dacs in particular is at very high speed, but you cant just drop current FB chips in place of voltage FB.
Originally Posted by AmarokCZ
Yes, lower gain certainly doesn't have lower bandwith.
On first line there is GBP at x1000 gain = 110MHz
Second line is just -3dB bandwith (not GBP) at x10 gain which is stated as 8MHz that means the GBP would be 80MHz.
It surely is odd and confusing since the first line is GBP and second line isn't, but it's not an error.
yeah youre right, the numbers make sense with that in mind, but its sure an odd way to present the info and has fooled smarter men than me. I just glanced straight past that as both being GBP until looking at it again when writing that reply above
Edited by qusp - 6/13/12 at 11:56am