Agree.
Nice board, thanks for the link.
But there are two IMO major issues not addressed
- possible common mode errors of DAC chips
- different impedance seen at the OUT of the transimpedance amp stage
ok
I'm not after specs at all, so that point is mute for me.
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Agree.
Nice board, thanks for the link.
But there a two IMO major issues not addressed
- possible common mode errors of DAC chips
- different impedance seen at the OUT of the transimpedance amp stage
ok
I'm not after specs at all, so that point is mute for me.
On the last part. I wasn't talking about spec sheet. I was talking about real world measurements. If you want I'll show you.
I don't doubt any of your measurements.
Its just I don't care about distortion figures that much, at least not as a solely basis of decision making.
In audo there are always two questions to answer IMO
- how does it measure
- how does it sound
More often than not those answers do not go hand in hand, at least that's my experience so far
Its just I don't care about distortion figures that much, at least not as a solely basis of decision making.
In audo there are always two questions to answer IMO
- how does it measure
- how does it sound
More often than not those answers do not go hand in hand, at least that's my experience so far
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Sorry for quoting an old post, but didn't find a dedicated thread for OPA2156.
Just wanted to say a colossal thank you to you and your team.
2156 is an excellent part, the best non-discrete dual I have heard ever.
Popped these in my Topping D50 I-V and LPF stage and one in FiiO A5.
Amazing tonality - such a sense of air, richness and sweet mids!
This was a lesson I had to learn when I first rolled to the OPA1622. Those are available for cheap on DIP8 adapter boards for plug in replacement.
Occasionally the OPA1622 at the plug in adapter board got into distortion mode with my AKG K701, some oscillation I guess.
Was not able to trace it down because it worked ok as soon as I hooked up my oscilloscope.
There are two measures one can undertake against oscillation / low phase margin
- decoupling capacitive load by adding OUT resistors
- http://www.ti.com/lit/an/slyt630/slyt630.pdf
Adding OUT resistors did the trick both for the OPA1622 and later on for the INA1620 and was the first choice for lazy me
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Has anyone happened to measure the OPA2156's THD vs Output Voltage into something around 200R at gain = +1? The datasheet graph only goes to a load of 2K.
I have something specific in mind.
NJM4556A datasheet
The 4556A's big claim to fame is high (70mA) output current per half into fairly low impedance loads (headphones, in this case) with relatively low distortion. This new chip has the whopping 100mA, curious how it stacks up to THD vs. Output Voltage graph on page 3 of the NJM4556A data sheet. The O2 parallels 2 NJM4556A per channel for the output. NwAvGuy's dScope plots from years ago take the THD vs. output voltage of the whole O2 down to a headphone load of 16R, worst case (what the paralleled NJM4556A's are driving on each channel).
Another cool thing: since the O2 has the (10K) pot-in-the-middle design the input impedance the NJM4556A looks back into can he high, something I've worried about (source impedance op amp distortion). But Matt at QuantAsylum just showed
https://www.diyaudio.com/forums/equipment-and-tools/231401-quantasylum-qa400-qa401-52.html#post5690467
that the CMOS OPA2156 can beat bipolar in some areas on situations like that. At mid-volume the NJM4556A looks back into 5K||5K||40.2K = 2.35K (AC signal, there is a coupling cap to the pot wiper to keep DC out). Matt showed the knee is around 1K (see his paper in that link above for details).
--> cat emo just because.
I just got my opa2156 directly from ti.
test was directly in to 16 ohm real earphone load instead of dummy load
250mvrms.
An externally hosted image should be here but it was not working when we last tested it.
http://oi63.tinypic.com/2ds2q01.jpg
Now comparing opa2156 to opa827 subjectively.
This could all be in my head so keep in mind.
opa2156 sounds a bit fast and dry sounding comparing to opa827. Opa827 sounds a little bit more liquid and robust sounding. Will it change over time? Idk. Do i like it? As long as the headphones don't suck.
Technically two opa2156 has higher current than opa827 but higher voltage noise. Would the noise affect the sound? Maybe. Because the distortion at normal listening volume will be way lower than the noise. So if there's sound change it's probably the noise. (there are only two 0.1ohm resistors in the signal path of the testing circuit)
Thank you Ti for creating excellent opamps.
This could all be in my head so keep in mind.
opa2156 sounds a bit fast and dry sounding comparing to opa827. Opa827 sounds a little bit more liquid and robust sounding. Will it change over time? Idk. Do i like it? As long as the headphones don't suck.
Technically two opa2156 has higher current than opa827 but higher voltage noise. Would the noise affect the sound? Maybe. Because the distortion at normal listening volume will be way lower than the noise. So if there's sound change it's probably the noise. (there are only two 0.1ohm resistors in the signal path of the testing circuit)
Thank you Ti for creating excellent opamps.
Hi!
You did not have any series output resistors on 2156 output?
Just double-checking.
Do you have 1622 to compare 2156 by any chance?
Thanks!
It depends on your application.
I personally prefer direct parallel(add resistor). This way I can lower the noise by sqrt of 2 and adding capacitive load driving capacity. The other way can have very low output impedance. The first method also may have lower distortion at high frequency irl.
Add another stage in the front before potentiometer for the gain. You don't sacrifice any distortion and noise performance.
Direct parallel also lowers output impedance .
Yes I am thinking on adding a prestage opamp for the gain and make the paralel ones at unity gain .
It lowers the physical output impedance yes. But there is ballast resistor outside the feedback loop. Unless there is another opamp wrapping around the 1622s there will be substantial output resistance after all. Sure it's possible to use values like 0.33 ohm and parallel more than 2 to keep output impedance low. But theoretically it's still higher. The example of 1ohm will result in 0.5ohm output resistance will is much higher than what could be done. You may argue the audible difference. You may but objective speaking there is difference.