O2 Op Amp Rolling

Discussion in 'Modifications and Tweaks' started by rtaylor76, May 18, 2016.

  1. rtaylor76

    rtaylor76 Can't wipe his tag

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    I know NwAvGuy's stance on op amp rolling. It's a subjective test, not objective, blah blah...however, I decided to see if different op amps could in fact improve the performance of the amp without any other modifications. I did this for many reasons:
    • Objective testing does not tell the whole story
    • Listening to different op amps can see if the design can sound better
    • Many people have the O2 and are either happy with it or moved on and stopped wondering if can sound better
    • Op amps are fairly cheap to buy to test
    • As long as you are careful, you can always go back to stock/unmodded
    Now there are three op amps total - input gain (U1) and one each L and R output buffering (U3 and U4).

    Original specs call for:

    U1 - NJM2068D
    U3, U4 - NJM4556AD

    Now I know NwAvGuy tested many of these for noise, current draw, and noise, so I started there with the following chips:
    • OPA2134
    • OPA2228
    • NE5532
    I am trying these chips in different combos. So far, my favorite combo is the 2228 in the input (U1) and the 2134 in the output buffer (U3, U4). This gives a very fast, detailed, and involving sound. It is very pleasant. The 2134 in all three positions is also nice and pleasant, but missing a bit of realism. I suspect due to the higher THD specs.

    I am keeping track of my progress and hopefully testing out some more op amps. You can view my progress and my notes here on my Google Docs file.

    I am open to suggestions to other op amps or I would love to hear any experiences any of you guys have had in testing out other op amps in the O2 amp. Other op amps already on my list to try:
    • AD8610
    • LM4562
    • AD8512
    • OPA2209
    And for reference, I am testing this with:

    Foobar2000 -> Schiit Wyrd -> Peachtree Audio X-1 (coax) -> Denon DA-500 -> O2 -> HD650 / Denon AH-D2000 / VSONIC GR07 Classic

    And my power supply for my O2 is a 15W / 1A

    (crazy audio chain for a work setup, I know)
     
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  2. frenchbat

    frenchbat BritishBat's arch enemy - Friend

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    LM4562 gets good results, as Benchmark media realized themselves. That's why they used it in the updated version of the Dac1, the HDR. But unless you're just having fun, get some better amp.
     
  3. purr1n

    purr1n Finding his inner redneck

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    I have LM4562 in the voltage gain position. NJM4556 are craptastic sounding (heh, good match for Grados), but put out a lot of current.

    If you don't need the power, a well executed battery (or well executed bipolar LPS) powered CMOY sounds better than the Objective 2. CMOY is a much simpler circuit without all the unnecessary crap.
     
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  4. rtaylor76

    rtaylor76 Can't wipe his tag

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    Thanks. I will try the LM4562.

    I plan on a better amp. And yes, I am having fun.

    I keep going back and forth on upgrading between: Vali 2, Project Ember, Asguard 2. With my dynamic headphones, I don't think I need anything too crazy. In just less than a year I have gone from nearly nothing to all this equipment. Just trying to eek as much performance out of this O2 as I can for now. Kids are expensive.

    Well, I think the idea behind the O2 was to create a CMOY without the floating ground. The only way to do that was with a current amp and buffering. The other bits are just for AC/DC conversion and battery charging. You also get way more gain. I SO wish there was a DIY version without the 9V batteries. I never use this thing portable. It is way to big for a portable amp. I'd rather have an E12, or C6, or even better an HA-2.

    Although you may be correct if you can get a better power supply for the CMOY like a batter or LPS like you said. Any battery or LPS will improve any piece of audio equipment.
     
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  5. purr1n

    purr1n Finding his inner redneck

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  6. rtaylor76

    rtaylor76 Can't wipe his tag

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    I have a CMOY. I built one from a board I got from Australia. A couple of traces were even bad, so I had to create jumpers. Building on a breadboard is a good option. It was just run on two 9 volts. It does not work much anymore since I pushed the power caps to the limit trying get it to push some planars. Those Alpha Dogs need some juice!

    I remember I liked the 2134 the best. I tested the 2228 and a couple of others I can't remember. I had one SOIC in a Brown Dog adapter that I can't find. I think it was an AD8610 and now I am kicking myself because I can't find it.

    But yes, something like a CMOY can allow you to test out the in-house sound of the opamps without going too crazy and easier to test. I get it. I am finding that you just get more of that sound when there are more of them - like in the O2.

    Have you seen this site:

    http://www.cycfi.com/projects/six-pack/op-amp-shootout/

    More for line output and not really headphones, but still applies.

    I see the LM4562 has a really fast Slew Rate (4th) - one of the highest...and low distortion too. One of my favorites, the OPA2134 is 9th in slew rate on this list. The 2134 has more noise...but it is last in the audio chain. The NE5532/NE5534A has much more THD+N than most of this list - it is no wonder I did not like it. It might have been the fastest chip in it's day, but I guess at a cost.

    Too bad the 2228 or 2227 is not on this list. I have already copied this list and I might put the specs in there to see how it stacks up. Also I read somewhere the OPA1612 is somewhat related to the OPA2211 and the 1612 is more the "audio" version of this amp. Note the OPA2211 goes for about $11 on Mouser and the 1612 goes for about $7 on Digikey - and both are SOIC.

    Too bad that LME49990 draws so much current.
     
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  7. logscool

    logscool Friend

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    Interesting might be some fun stuff to play around with. I still actually use my O2 for my sensitive IEMs (SE535, UERM) as most of my other amps have too high of a noise floor.
     
  8. rtaylor76

    rtaylor76 Can't wipe his tag

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    So thanks to manufactures willing to send free samples to try for builders (hehe), I have the following op amps coming to try:
    • AD8620 (x2)
    • AD746 (x2)
    • OPA1612 (x3)
    • OPA2107 (x1)
    It looks like TI is a lot more stingy with their freebie op amps, which is why I was only able to get one of the OPA2107s. I don't blame them as it is a $20 or so op amp when purchased as a single from distributors. You can only get 4 op amps at a time from AD (2 max each), per two week period. That's fine, these should keep me busy for more than two weeks as I am guessing. I am going to have to order some SOIC to PDIP adapters and some precision soldering to do. Only the OPA2107 and the AD746 are in PDIP packages. So that is at least 5 SOIC chips to put on adapters (for now).

    So far, the OPA2228 in the front end and the OPA2134 in the buffer end is working fantastically. It really brought my DA-500 and my AD-H2000s to life. I hear good things about the 1612 and the 8620, and the 746 is no slouch I hear.
     
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  9. Maxx134

    Maxx134 Friend

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    This is actually excellent news for me as I have an O2 for years catching dust in a drawer because I hate the dam thing.

    I used to love this unit,
    until I realizeded how harsh it sounded to me later.

    That's when the NwAvGuy's world collapsed on me.
    I felt like the guy from"the Truman show",
    Where all he had believe turned out to be a false world.
    I felt really deceived because I was so sure about all info his site had.

    That's when I vowed from them on always to trust my ears as the "final say "

    Sounding good or great , and sounding real, do not always go hand in hand.

    But this O2 goes have nice power & performance,
    And was my start into headphone amps.
    So It still not bad overall and the site did have a lot good info.

    But this op-amp rolling I never looked into so it really is great news I can change it's sound!
    :cool:
    Keep up the good work!
    :punk:
     
    Last edited: Jun 18, 2016
  10. rtaylor76

    rtaylor76 Can't wipe his tag

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    Thanks!

    The O2 is funny. In it's name is "Objective". As if testing for noise and current draw is the only real specs to worry about. And that of course can be done objectively of course. However, to not subjectively test for the best possible results is not a good design. What if car makers never tested their cars on a track or a master wine maker never tasted the final product? So who is keeping the original designers op amp choices? We question them when it comes to great name brand gear, why not a DIY builder's design? I digress.

    I too was not in love with the O2 when I first made mine. It certainly sounded better than the other consumer and pro-sumer headphone amps I had on hand that were built into other devices, but there was something missing. I heard this especially when I heard other gear at a fall headphone meetup. And when I started looking at mods for my DAC in changing the op amps, it dawned on me that the O2 might could also use some improvement.

    Everyone can follow along in my journey as I update my spreadsheet of notes:

    https://docs.google.com/spreadsheets/d/1j_dCCB9T959bZoy3REpW88tdqO05pqw9AIzNeA4JDM0/edit?usp=sharing

    If you dont't care to read the whole thing, my current love is:

    OPA2107 - input gain
    OPA2134 - output buffer

    The 2107 is really designed for critical applications, but I think its power in the fact that is a cascoded op amp in such a small package. AND it comes in a 2-channel PDIP package. The downside? It's $20 for such magic. However, the 2134 is only a few dollars, it is not a current monster, but two of them provide ample (pun intended) current for most headphones. Planars might be trouble, but they always were with the O2 - you need something more robust with a better power supply.

    I am having serious doubts if there are better 2-channel op amps out there than this combo for a simple headphone amp and I keep saying this, but then I do. However, in looking at things spec wise and also subjectively, I am having doubts if there is something better in a 2-channel package. Most of the better ones I am finding are single channel and in odd packages, like the LT1210 in it's odd 7 lead DD or T7 package. Plus, those have many more pins (Comp and Shutdown) that are not configured on this O2 design. You have to build a circuit board around it...not as simple and plug and play.

    So I encourage anyone to an upgrade. The easiest is the 2134, but the 2107 and 2134 combo are huge leaps in the quality of sound. I'd love for someone else to test. There is a small thread over at another forum site that speaks highly of the 2107. I just wonder why it is not in more circuits. My only guess is that for most designs it is cost prohibitive, and for many high end products that it would be designed for, buyers would rather see discrete designs, and for the same cost, I bet you could get the components needed for a discrete design. I also bet this is why the datasheet mentions medical and precision equipment where space and current draw can be an issue.
     
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  11. digitky

    digitky Rando

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    Thanks for suggestion of this combination opamp in O2. I have already tried it and feel better my current combination of ADA4637(input gain) + LME49990MA (output buffer)
     
  12. digitky

    digitky Rando

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    After testing with OPA2209 + OPA2134 combination, the sound is more balance than OPA2107 + OPA2134.
    I feel OPA2209 + OPA2134 is more suitable for listening the pop music.
     
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  13. rtaylor76

    rtaylor76 Can't wipe his tag

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    Try 2134 + 2209. Holy crap!

    Then try 2111 + 2209. However I would not have a 2111 if it wasn't for TI and their free samples. Expensive little chip.

    The 2209 is the best buffer so far of the ones I have tried in the O2.
     
  14. Maxx134

    Maxx134 Friend

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    OK, I am a bit confuse here.
    So, is it an agreement the best input gain is the 2209...?


    Is the 2111 better than the 2134?

    Also:

    So you reversed the chips and like that?
    So you like 2209 as buffer better than the 2134,
    And you like the 2111, as input gain,
    But still say 2209 is best buffer.

    So what about a 2209 + 2209 ??
    :)
     
  15. rtaylor76

    rtaylor76 Can't wipe his tag

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    I can't decide really. 2209 sounded great for awhile. It has detail, it has more current drive, but after a few days I put back the 2134's as buffer and it does not have as much "drive", but sounds more pleasant to listen to. It still has some grain in the mids that I don't like. Both are excellent. 2134 is just more classic laid back Burr Brown sound.

    I did try 2209 + 2209. It was too punchy. 2209 works okay in the input, but it really shines more in the output buffer. Most chips were the opposite.

    2111 is still best input I have tried. I still have to try:

    OPA1642
    AD797
    Maybe some LT's

    1642 seems to be a replacement for 2134, so I have high hopes even if it does not have as much current drive.

    You can check my Google Docs Sheet for the latest notes on my progress. Things have slowed lately because my oldest just stated Kindergarten. Also, had to replace sole parts on the O2. Mostly the op amp quick adapters and the LED. Apparently I blew out the LED when I put rechargeable batteries in when it was still plugged in the wall. Reverse voltage, and it died. That LED light is a crucial component to the operation of that thing. It's all fixed up now, so more testing soon. Time to get more op amps.
     
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  16. Maxx134

    Maxx134 Friend

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    Excellent info ..
    I just scratched the surface on opamp searched,
    and found there was over 500 opamps.
    So I had to look further,
    and I saw this post describing what are requirements for best opamps to use:

    Quote:
    "Although there are hundreds of families of op-amps on the market today, not all are suitable for DIY headphone amps. We can eliminate power op-amps, super-high-speed op-amps, high-voltage op-amps, low-frequency op-amps, and low-spec general-purpose op-amps. Audio requires a fairly high slew rate to maintain low distortion, flat frequency response from 20 Hz to 20,000 Hz, and decent output current if the chip is to drive headphones directly. A low supply voltage requirement is a plus for portable applications. We also ignore chopper-stabilized and CMOS op-amps as they're generally unsuited to audio. This eliminates the vast majority of op-amps on the market."

    It was an older article not so useful due to age here:
    https://tangentsoft.net/audio/opamps.html

    So I am looking around for best opamps regardless if they cost even 20 bucks , but I think the new ones are better and cheap.
    The only issue is the new opamps are not the old 8pin and are very tiny.
     
  17. rtaylor76

    rtaylor76 Can't wipe his tag

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    That is a good article from Tangensoft. I agree with most of his findings on the sound...well....for the most part I guess. Now remember he is using this in a CMOY, which means it is at a gain of 6 or so and driving headphones and with a less than adequate power supply (9V with a rail splitter).

    Although, that high slew rate is an odd one to me. I initially though I could look at the slew rate and say, "that one is about what I need,"but alas, it is not that easy.

    Case in point:

    One of my favorites is the OPA2111. That has a slew of 2 V/μS. Many say you need at least 20 V/μS for hi-fi audio. I am having my doubts on this. Why does the 2111 sound so good. Simple. It was designed as a precision instrumentation amplifier, has a Difet input, and has a GBP of 2. And this range is between 10Hz and 100KHz. No phase shifting in that range. So with this, a slew of 2 does not seem that bad. They even have circuit designs for phono preamps and instrument amplification applications and lists "Professional Audio Equipment" as one of the applications.

    It is true though that a high slew rate, say over 100, might not be the best option for audio. It is common to see higher slew rates for I/V converter op amps, but higher does not always mean better. Sometimes the faster chips are unstable at unity gains and/or not very suitable for audio.

    I used the TI finder and the AD finder for some of the op amps I tried. Just put in the parameters you are looking for and find what is available:

    TI Finder: http://www.ti.com/lsds/ti/amplifiers-linear/operational-amplifier-op-amp-products.page

    AD Finder: http://www.analog.com/en/parametricsearch/11070

    Warning...AD makes way more op amps that TI, so a lot harder to narrow down. I guess it is a good thing anyway that I lean towards Burr Brown designs.
     
  18. Poleepkwa

    Poleepkwa Friend

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    Once you tire of listening to opamps, try building the Butte. Not much money, much good sound and a really fun project.
     
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  19. Maxx134

    Maxx134 Friend

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    Hmm that amp amplifying section also uses just two opamps...
    Probably well chosen ones so no need opamp roll, as well as No 8pin sockets to opamp roll, but probably can be made.

    Also, here is quote about the O2 opamp choice:
    "Intuitively an amateur designer could easily be excused for believing ultra-low noise expensive op amps are the best way to design a silent amp. But the O2 doesn’t use ultra-anything."

    So looks like opamp rolling wasnt a priority , only price and practicality.
    So opamp upgrading is probably the overlooked thing to do.
    :)
     
  20. rtaylor76

    rtaylor76 Can't wipe his tag

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    I've seen the Butte. Looks very interesting.
     

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