What values and circuit did you use for a paralleled pair?
0.33ohms seems very low - is that inside or outside the feedback loop? I assume outside given the unity gain. I am planning to try 10R inside the feedback loop with a gain of 7.5 in a 47 Amp circuit.
> post 225, 247, 255, 270, 297 ?
I've been asked per PM about our boards in various configurations.
I regret to tell you that we have discarded all remaining prototype boards some time ago already.
It was just a series of quick experiements, with no intension to follow up.
If I am not wrong I think you can get an adaptor PCB from TI to make it DIP8 compatible.
Thanks for your interest anyhow,
Patrick
I've been asked per PM about our boards in various configurations.
I regret to tell you that we have discarded all remaining prototype boards some time ago already.
It was just a series of quick experiements, with no intension to follow up.
If I am not wrong I think you can get an adaptor PCB from TI to make it DIP8 compatible.
Thanks for your interest anyhow,
Patrick
What a bummer it only comes in this package, I take it that's a ground plain heatsink on the bottom, suppose that can be hand soldered using the tabs at each end and having the ground plane pre soldered with a layer of solder and sweating the two together, need some serious heat though.
http://www.ti.com/lit/ml/mpds117l/mpds117l.pdf
Cheers George
http://www.ti.com/lit/ml/mpds117l/mpds117l.pdf
Cheers George
I checked those posts again - didn't find anything about paralleled pairs aka 47 Amp. There are OPA1622 on dip adapters with resistors/caps available too, and they would work in a 47 amp. ??TI OPA1622 ??? 145ma??? ??? ?????DIP8 ??-???
If I would like to use the OPA1622 or the INA1620 EVAL board driven by a symmetric source for a HP amp, how to best incorporate sort of volume control with a standard pot?
> I checked those posts again - didn't find anything about paralleled pairs aka 47 Amp.
We never considered it to be necessary.
Especially considering the stability problem we experienced in post #255 even with a gain of >>1.
But what do we know.
We were asked about our boards shown in those posts specifically.
And hence a public answer for anyone else who might have the same interest.
Hope that it is now clear,
Patrick
We never considered it to be necessary.
Especially considering the stability problem we experienced in post #255 even with a gain of >>1.
But what do we know.
We were asked about our boards shown in those posts specifically.
And hence a public answer for anyone else who might have the same interest.
Hope that it is now clear,
Patrick
What if I use a LT5400 4x1kohm array in front of the INA1620 EVAL and shunt those by a standard pot of say 10k?
Any drawbacks of such an arrangement except for a slightly higher noise figure?
Any better ideas?
Last edited:
Killer current noise and really good voltage noise and really, really good distortion are, to date, mutually exclusive, are they not? Is there another opamp that has come close to what the OPA2156 is delivering? It really does seem to bring something to the party that hasn't be available before.
You hinted about an audiophile version coming next. Now that the OPA2156 is available at Mouser can you share anymore on the audio version?
I appreciate the positive feedback on the OPA2156. The audio version should be sampleable on ti.com this quarter. I believe February or very early March. And then it will officially release to market a couple of months after that. I will update this thread when it's on ti.com.
Hi John. How 1622 makes for Adc buffer? Is there a best vssop opamp suitable for adc input buffer? I was looking at opa1642 and opa1602 Thanks.
OPA2156: Is there a THD vs. output voltage plot/measurement into 200R (or so)
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.
I'm wondering if the OPA2156 would make a good (maybe improved in an area or two) replacement for the NwAvGuy O2 Headamp NJM4556A output chips:
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.
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.
I'm wondering if the OPA2156 would make a good (maybe improved in an area or two) replacement for the NwAvGuy O2 Headamp NJM4556A output chips: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.
Last edited:
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).
When i get back to Australia, I'll try opa2156, opa828, njm4580 along with opa827 opa1612 in o2 circuit with 32 and 16 ohm load.
IMO choosing audio opamps based on specs an sales blurr brings you nowhere.
Given my findings on the stellar spec'd INA1620 on their evaluation board being a variant of the OPA1622, I wonder if those guys at TI ever audition what they tout as "High-Fidelity Audio Operational Amplifier" or if those guys are close to deaf?
don't trash your TEAC UD-H01 DAC, pimp it!
don't trash your TEAC UD-H01 DAC, pimp it!
In short, the stock INA1620EVM board is crap in terms of sonic performance!!!
On top of that the PSRR and channel separation figures by no means reflect real world behaviour in the audio realm.
There is no other way than to try and audition by yourself.
Last edited:
I bought two 1622evm and it's not bad at all. Very organic and clean sound. It sure needs good power supply. Have you done measurements? I did, and it's not surprisingly good but pretty good. O2 with opa827 and 0.1 output resistors will be better than the evm. But opa1622 gives more possibilities. Also the opa2156 should be pretty good too. Very low ol output impedance and enough output current. And cmos input stage can be used directly after volume pot without issue.
Seriously, I don't need any more measurements if auditioning brings up such a bunch of crap. And I already traced it down to a fair degree if you have read my postings.
To add on the above list of shortcomings, the INA1620 isn't even capable to directly drive a AKG K701 without issues.
You will have to add output resistors to make that happen. Not what's advertised and no good in terms of audio performance as well!
Frankly, I'm not after "not bad at all" with a chip that is stellar specd and said to be for audio, but after outstanding sonic performance right away.
The INA1620EVM board doesn't do that any justice at all.
All in all I've come to the conclusion that pairing the TPA6120 with LT5400 to form a "audio grade" symmetric IN / symmetric OUT instrumentation amp for driving cans would possibly be the route to go.
Sure, for the O2 headphone amp not being a symmetric design this point is mute.
To add on the above list of shortcomings, the INA1620 isn't even capable to directly drive a AKG K701 without issues.
You will have to add output resistors to make that happen. Not what's advertised and no good in terms of audio performance as well!
Frankly, I'm not after "not bad at all" with a chip that is stellar specd and said to be for audio, but after outstanding sonic performance right away.
The INA1620EVM board doesn't do that any justice at all.
The INA1620 with its matched resistors for me were the main reason to give it a try.
All in all I've come to the conclusion that pairing the TPA6120 with LT5400 to form a "audio grade" symmetric IN / symmetric OUT instrumentation amp for driving cans would possibly be the route to go.
Sure, for the O2 headphone amp not being a symmetric design this point is mute.
Last edited:
I have used k701 on several actually good measured amps. jds el amp, violectric v200, artemis It just doesn't sound right. k701 needs high distortion and higher low frequency noise to mask it up to sound good. Bad headphones will sound bad from a clean amp.
1622evm is not the best performing evaluation board of 1622. The original one has opa1612 in the front and let 1622 do a better job. More over you can use 1612 so sum the differential signal and set 1622 at +1 unity gain so reduce distortion even more.
On the resistor side. 0.1 output resistor is low enough for the resistance from interconnects to be prominent. Let along your long cable which is very likely to have 0.5ohm impedance.
I beg to disagree.
The AKG K701 is a beautiful sounding headphone that does stand the test of time.
Admittedly it needs a very long break in time of weeks, month even and is picky about amps as those with low phase margin easily are pushed into oscillation or at least to the onset of.
But even a very cheap NuForce uDAC3 is capable to drive them nicely, the TPA6120 in the UX1 performs even close to excellent.
No contest to the INA1620!
That may well be.
But the INA1620EVM is the evaluation board available from TI.
What good should it be for if not for evaluation of its sonic performance?
Who needs learning of instrumentation amplification nowadays?
What is "the original one"?
Possibly have a link?
Sorry, I do not understand what you mean?
By the way, what was it that the NJM4556A fell short in the O2 HPA, that you feel forced looking after replacement?
Last edited:
Let's forget about k701 now. I think we will get no where by discussing that.
Another evaluation boaed is High-Power High-Fidelity Headphone Amp for Current Output Audio DACs Ref Design (Rev. C)
http://www.ti.com/litv/pdf/tidu672c
Higher gain from opa1612 allows more feedback of 1622 allowing lower distortion.
If you use 1622 in unity gain configuration, distortion can be lower. Tested on o2 platform, very good.
4556 has 0.001% at 1khz but much higher distortion at lower and higher frequencies like a smiley curve. i won't talk about audibility of such distortion, but it's much better with opa827 the distortion goes under 0.0001% full spectrum 32ohm.