Just increase the gain to 6.5X. I have some 121-122dB KZ IEMs to test it.
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Opamp Rolling, Does It Work?
- Thread starter jackenhack
- Start date
I wouldn't, it was just to test opamps for lowest possible noise. I've also did the same for Conductor 3X that has almost 15W, so you can call me crazy if you want.
AnalogSteph
Major Contributor
Oh, I'm not doubting that one bit. I'm just saying it's basically an academic exercise, that's all.
You can turn the O2 gain stage into a pretty decent input voltage noise / current noise / unbalanced current noise / input bias current tester if you want, just by socketing 4 resistors per channel and having something to short the input when needed.
Interesting - I always thought that the '860s were merely selected for higher Vcc. I am aware of some issues with high popcorn noise that are said to be resolved by now. Is this happening in the O2 as well? If not, you wouldn't happen to have a schematic of the opamp's surroundings? I see you've been inside the HPA-3B extensively.
That's interesting. In a way I'm not terribly surprised, AD's customers (including industrial, medical and military) are likely to be a bit more picky when it comes to actually sticking to datasheet specs compared to consumer electronics manufacturers.
It's still odd that some bipolar input types like OPA1602/1612 would stray this much - usually input offset voltage for bipolars is within a mV without too much effort, and these are using input bias current cancellation as well, so unless their surrounding are seriously high impedance (not an ideal match with these particular types to begin with)...?
Not really, sorry, but you could try spotting something here perhaps" https://cdn.head-fi.org/a/8179590.jpg.
The input DC was also measured for I/V stages as well and identical opamps gave me different results (measurements done after few minutes, when opamps where warm enough). I wasn't expecting myself differences that high, but maybe this is why so many manufacturers don't wan't to use direct coupling.
Output offset voltage is not only caused by input offset voltage and gain. The input bias current can also be the cause. Some designs like to use high value resistors where it can easily cause issues.
Personally in the all amplifiers I built using opa1656/2156 or opa2111/opa1612 all have offset under 1mV. With gain it may be a little bit higher. But have not seen any crazy numbers yet.
In I/V stage and dac output stage things can get a bit tricky. Many DAC output stage needs biasing to cancel the output offset. There are a lot of things can go wrong. But still haven't seen any number higher than 5mV.
AC coupling is a good practice. It's just a lot safer. Regardless of the amplifier having DC detection or not.
Personally in the all amplifiers I built using opa1656/2156 or opa2111/opa1612 all have offset under 1mV. With gain it may be a little bit higher. But have not seen any crazy numbers yet.
In I/V stage and dac output stage things can get a bit tricky. Many DAC output stage needs biasing to cancel the output offset. There are a lot of things can go wrong. But still haven't seen any number higher than 5mV.
AC coupling is a good practice. It's just a lot safer. Regardless of the amplifier having DC detection or not.
TOOdamnFRANK
Member
Did you ever end up testing the opa1656?
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