O2 Op Amp Rolling

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

  1. Maxx134

    Maxx134 Friend

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    Looking at specs it uses 15v suppy and my two 9v so I would assume so, but after checking further,
    I am also now in opinion of Marv...

    I have been out of loop on prices and so I just checked,
    And for value, I realized I am wrong.

    I only had to check the schiit site to see they have FOUR AMPS that will beat the O2 in power alone...

    Then checking online, the O2 STILL sells for around $129.

    So yeah, the only reason to roll opamp is if your stuck with this unit already..

    Taking a look at what's available on ebay with cmoys and small Chinese units,
    they all seem to be much better than the units I tried 6 years ago..

    So yeah, I will have to concede that this endeavor with op-amp rolling is pretty much like a "bandaid" in terms of sonic value.

    I personally rather have a small Vali for my own "headphone burn in" purposes.
    Anyways I will pop these new op-amps in to see what happens,
    but now my enthusiasm is gone after this reality "bitch slap" of what's out there.
    I shouldn't have looked at all the nice stuff on schiit site and ebay...
    :oops:
     
    Last edited: Oct 22, 2016

  2. Cspirou

    Cspirou Friend

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    Curious how a discrete op-amp would workout, like Burson audio.
     
  3. Kattefjaes

    Kattefjaes Mostly Harmless

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    If you must have a small rollable amp, a Vali 2 with an EH6CG7 would almost certainly make you smile- and the price isn't outrageous.
     
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  4. Maxx134

    Maxx134 Friend

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    O2= 129 = opamp roll
    Vali2=169 = tube roll
    Project starlight = 159 = tube roll / opamp roll..
    Rolling tubes may also serve as a new tube burn in amp as well..
    :)
     
  5. Kattefjaes

    Kattefjaes Mostly Harmless

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    Never had a chance to play with those little Garage1217 things, they're not common here, so I was hesitant to mention them; I'd be guessing. BTW, the $159.99 one is a kit, it's $189.99 for a pre-built acrylic Starlight.
     
    Last edited: Oct 22, 2016
  6. rtaylor76

    rtaylor76 Acquaintance

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    First off, you guys are right to say to throw it in the trash. It is what it is.

    For all those wondering if why an O2, it was because it was a cheap DIY DAC. I am on a serious budget with two kids and don't have discretionary income to speak of. I am handy with a soldering iron, so when I can build something for half I can buy it for built, I get to have fun with a project and a product too. Not for everyone. Trust me, I don't want to DIY everything.

    Anyways, if you read my first post in this thread, you might understand. A cheap improvement that does not require any soldering.

    Might I remind everyone briefly that this thread and search began before the Vali 2 even exisited...it was still just a Vali with that vibration sensitive micro tube.

    So are you saying that you swapped out the chips and now the left amp went out? Or the left side starting going out before you swapped anything out?

    Either way, it is probably the seating of U3 or U4 (I can't remember which one is L and which one is R). The swap DIP-8 mounts on the part list are pretty cheap and the pressure pins that hold in the legs of the op amps can go wonky on you after a while. Try re-seating the op amp or bending the legs of the op amp. Word to the wise...don't try this with a pair of headphones you like...you can spike the voltages and pop the drivers like I did with my Vsonic GR07's. I had to replace all my DIP-8 mounts after swapping all those preamps. Well...mostly because my SOIC adapters had the huge legs that just pushed those spring clips out of the way, so they would not even hold the DIP 8's in place. But then again, it could be an input issue. Chips can die on you too, but that is probably more rare

    The 2228 is warm. The 2227 is also warm. You guys also might try just three 2134's for a more balanced sound. The 2111 is still my favorite, although I know $20 for one op amp is kind of nuts. For most it will not be worth it and I understand (unless you can get TI samples). I also hear the OPA2111KP is even better than the PA version. That one is not available for sample, so I'd have to buy to try.

    I am still most interested in trying out the OPA1642 that is supposed to be the replacement for the 2134. I would also like to try the OPA2141, although that one is more for portable applications, I think that would kind of fit the requirements here. The 1642 uses call more for high end audio applications.

    Yes, the JRC4456 has tons of amps available (70mA), is quiet, but I'd argue that you don't really need all that current for some headphones, not just Grados. Yes, higher end Senns and planars need many amps and I hope anyone with a real set of planars has a way better amp. The OPA2134 has nearly half the the amount of mA swing (40mA) as the 4556, but sounds way better if it does not get quite as loud. The 2134's also draw nearly half the current as well (4mA vs 9mA), so it's actually kind of a win...that is if you have headphones that are power hungry. Too bad you can't use the BUF34U in this amp.

    And on the point on voltage swings and gain, my gain settings are 1x and 2.5x, instead of the 2.5x and 6x of the standard. The power supply on this is pretty weak and can't handle huge amounts of current draw. To be honest, the circuit would probably be way better with more robust power rails and dump the 9V batteries and charging bits. I never had issues with driving issues, but then again, I tend to listen at lower levels.

    So some of you guys can not be concerned with op amps, but even I was surprised the improvements that could be had for so little.

    And don't worry...the O2 isn't my only amp anymore. I have upgraded a few things...and going back to the O2, even with the op amp changes, does not even compare to a real amp. I get it. I am still going to search for better sounding op amps.
     
  7. Maxx134

    Maxx134 Friend

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    Ok , I have inserted these opamps,
    And I have to happily conceed that my O2 finally NOT sound like a POS that I tossed away in closet.
    It is finally now a decently musical toy.
    :)
    These should be standard recommend op-amps for this amp.
    But all is not perfect.
    I did a bit notice less power and some overload on high gain.
    This exactly happened..
    On high gain setting, loud passages would clip/distort.
    It is now only good for low signal input sources.
    That's exactly what happened again.
    The pure turd nicely heavy opamps were replaced and I lost what sounded in "db" to about one third less power..
    Yet the loss came with a huge boost in sound quality,
    So the trade off was well worth it,
    For those stuck with this unit.
    This happened to me..
    I threw this thing in a plastic bin and stored it away for years Before pulling it out again,
    Only to be let down with harsh sound.
    So maybe I can somehow trick @thegunner100 to listen to my unit again...
    :p

    When no one makes things the way you want them to be, DIY , or "ordering custom" is the way to go.
    ;)

    Edit: I am not sure which side(L/R) output opamp I may have killed,
    But insertion of the new ones solved it.
    I not sure yet so I saved the opamps.
     
    Last edited: Oct 23, 2016
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  8. rtaylor76

    rtaylor76 Acquaintance

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    Awesome!

    What is funny is that some op amps you need to run in high gain to be stable. A 2228 has already has about 6x gain out of the box. So 6x would be like 12x, and I would not doubt clipping would occur. I think op amp driven guitar amp pedals run around 20x to 25x gain.

    Either way, there are op amps on the list that are rail to rail:

    • OPA2209
    • OPA1612
    • OPA1602
    • LME49276 (not tried yet)
    • OPA1642 (not tried yet)

    The 1642 being JFET and R2R has me really wanting to try them, although it does have less current output, but also draws even less. So, it's a trade off. You could almost stack two of them on top of each other with the amount of current it draws (1.8mA)...just thinking out loud.

    I will also admit all the ones I listed are SOIC. That is the trend. DIP-8 is becoming more and more obsolete. There might be some good AD or LT designs...and those boutique Muse. AD has a really good op amp finder...once again, thinking out loud.

    I cannot thank you enough for verifying my results. I'll be glad to send you some of my samples to borrow to test out for yourself if you like. All except my 2111....that one is staying in my O2.

    But I agree...it is a tradeoff. Less gain and current drive for a huge increase in SQ.

    Not the best design for sure. You can certainly see and hear the limitations of this amp design, but pretty cool you can improve the quality somewhat.

    I know it is a little a few years ago, like the iBasso P4, or the Fiio E12 DIY...I guess I just like tinkering with stuff.
     
  9. Marvey

    Marvey Loves sex and records

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  10. Maxx134

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    I was OK with the opamp roll with O2 but just not portable enough for me.
    Plus I hate the ocillating pop sound on low battery.

    Anyways it's back in the closet and I been looking for another amp to spark my motivation and interest,
    And I have found it in this mini tube amp:

    Gemtune APPJ PA1502A

    It is a Class A Single Ended Triode(12AX7)front end,
    driving a pair of Triode Strapped,6v6 Power Tubes.
    The amp uses quality Japan output transformers,
    And is capable of up to one watt at 32ohm.

    It has upgrade potential as I will replace the coupling caps and upgrade the cathode bypass caps.
    It uses modern compact switch mode PSU so it is very small with surface mount parts on top side,
    and uses DC for heaters.
    With old stock tubes this unit really supercedes anything in the $200 price range,
    and once upgraded, should compete with some big boy amps
    :)
     
  11. rtaylor76

    rtaylor76 Acquaintance

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    This would would be a better design with as a low powered speaker amp rather than an headphone amp. I do like 6V6 tubes - very efficient and quick. And I do like the DC on the heaters.

    And not sure it would best anything in the $200 range. I think that would depend on your headphones. My Darkvoice 336SE was that price and is killer on my HD650's. Although anything over 150 ohm headphones and just forget it, unless you really hate bass.

    And no worries on the O2 is kind of not well built for portable use. The design is also pretty long in the tooth, as well as being kind of big for portable as well.

    Actually, I have found a very great sound in the Fiio A3. This may sound suprising, but I say this for a few reasons
    • It uses an OPA1642 as the input - which is the replacement for the OPA2134 that I and everyone likes so much.
    • The current output buffer is an AD8397, which is clear and detailed, and powerful - great for portable use
    • Lithium Ion battery with 1400 mAh.
    • It's constructed well, small, and strap to the back of most any DAP.
    • The bass boost is well suited for hi-fi (only if you want some extra "oomph")
    The AD8397 is a bit aggressive, but not quite as aggressive as the AD8210, but matches well with balanced armatures - very clear, quick, and detailed sounding amp. It lacks a bit of refinement of the A5, but the A3 sounds better than the stock O2.

    I love having analog volume control on my portable headphones. I also like a dedicated amp. I would not use the A3 for desktop use, unless for low impedance heaphones.

    The O2 is still a bit half cocked for desktop use. I think NwAvGuy was on a quest for the cheapest and best measurable DIY amp available for build. I love the DIYaudio place, but there are better designs/circuits/op-amps out there.

    I think I have learned quite a bit about op amp circuit design and different op amps. I realize how useful, and yet how limiting they are. This journey has been invaluable. So I am on to my Darkvoice and have swapped op amp rolling to tube rolling. I will still have my O2 around for checking out different op amps and for general use.
     
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  12. Maxx134

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    Very nice
    :punk:
     
  13. rtaylor76

    rtaylor76 Acquaintance

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    I finally got around to replacing the LED. I got tired of waiting for Mouser to have the legacy part in stock, so I just ordered one of a similar specifications from Digikey. I had to get one with straight leads and just angle it in the correct place. Took a bit of patience, but it looks stock now. I have no idea why that legacy LED is so back ordered from Mouser. So many people and companies making O2 amps? Anyway...

    With the OPA2111 and the OPA2134's as buffers, it still could not sound better. I did a little A/B comparison with my Fiio A3...the O2 sounded cleaner, more detailed, and better separation. Then I realized the O2 was in low gain (1x), and the A3 was in low gain (2.5x). Once both set to 2.5x gain, things got a bit more even. The A3 had a little more low end presence, but the O2 still had more detail and separation.

    I got some OPA1642's finally...except I did not pay attention too close when ordering samples from TI's site and I got four in the MSOP package. Darn those things are small. Then I found, or thought I found, a MSOP to PDIP adapter. I was super careful in soldering and amazed myself I got them both on...then I noticed the boards are too wide for PDIP. Darn you sparkfun! Although their SOIC to PDIP adapters are great as well as cheap.

    So back to TI for ordering.

    Although I am on to op amp testing on my DA-500 DAC, and that is for I/V conversion from PCM1702's, filtering, and output buffer. Those are different requirements and a different circuit, and not the same requirements as an O2. Not suprising though that the OPA2134 is pretty great in the filter circuit.
     
  14. Grattle

    Grattle Rando

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    Disagree. The O2 performance, as you know, is dependent on board layout. The chips may not react the same way in a more simplified circuit. Just my 2 cents. I have built 3 of them. The opamps and buffers are easy to swap, and cheap if you screw one up. I recommend you try a 16 VAC powesupply instead of the standard 12 VAC.
     
  15. Grattle

    Grattle Rando

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    I have a spare red led you are welcome to free of charge. Not an exact match, but electrically, its close.
     
  16. trl

    trl Rando

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    Hello,

    I've rolled lot of opamps inside my O2 headamp, but sound was about the same in most cases. Anyway, changing the default 2068 opamps will increase O2's performance by being able to increase the voltage gain for more than 6.5X (if anyone's interested). Usually LM4562 or LME49720 would be a good opamp to drive the voltage gain stage for such an amplifier, though measured noise is no better than 2068.

    However, I've noticed that MUSES8820 is a "not-so-expensive" wire-with-gain opamp and I've used it for over 1 year in my O2. I've also tested the MUSES02 and I've noticed an improved soundstage. Also, soundstage did improved even further with Burson SS V5 I'm using right now (took the batteries out to make more room for this little beast). Of course, for the price of the V5 or 02 opamps I can't recommend them, but it worth a listen if you can borrow from a friend to AB test it against another O2.

    For the output buffer, MUSES8920 could be an upgrade, thought the output voltage is clipping a little bit faster than using the default 4556 opamps. Some said that changing the two 4556 opamps did improved the sound; perhaps I haven't spent much time on testing this, but I couldn't tell a difference yet. Anyway, who really needs a real upgrade from 4556, then OPA1688 seems to make a difference, at least based on its specs and based on the first reviewers from DIY forum.
     
  17. rtaylor76

    rtaylor76 Acquaintance

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    Thanks. I appreciate that, but I already got an electrical equivalent to work as well. Although the forward amperage was 10mA...I should have went for the 2mA one. The stock is a 10mA though.

    And to @trl, I have always wanted to try some MUSES op amps. The stock 2068 op apms, sure, can drive voltage, but at what SQ. Everything through that sounded dry and very lean on bass.I am sure the MUSES sounded better. And yes, you will not get enough drive power out of some different op amps, so there is kind of a trade off.

    Without the 9V batteries for portable use, you could really build something. Thinking along the lines of a "Butte" or something. http://www.pmillett.com/butte.htm

    I like the fact the Butte has input power caps. Something the O2 is very much missing. The switching power supply is also much simpler because there is no comparitor op amp to match the batteries voltage output or trickle charge them either. However, this is only a single op amp design.
     
  18. rtaylor76

    rtaylor76 Acquaintance

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    Most of the time I use a 15V 1A AC wall wart supply. It is actually a wall wart to a another product I hardly use anymore. It has more to do with the available amps. The incoming voltage is regulated by the MOSFETs....albeit rather simply. Either way, I never saw a change in the voltage rails to the op amps with either supply.

    There is a slight more detail and more "focus" with a better supply. To some it might even sound a tad brighter. Different op amps made a much bigger change.

    The sound does drop just a tad as well when going fully battery operated. I use rechargables. Others may have a different experience with standard 9V batteries. I have never tried. I hardly use mine portable anyways.
     
  19. gertu

    gertu Rando

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  20. rtaylor76

    rtaylor76 Acquaintance

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    The OPA2107 is my favorite dual channel PDIP-8 o.o amp ever. It is the closest to discrete without going exotic.

    I've now have 2107's in my DAC in the I/V and buffer with a OPA2134 in the filter.

    I have also discovered the dangers of op amp swapping and op amp instability. If the circuit around it was not designed with that op amp in mind, they can sound exciting at first, but then you realize there is missing bass and a fatiguing sound, such as the THS4032. It has awesome specs, but never work in the simple O2 as it is way too fast and hard to keep stable at low gain.
     

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