Easter breaks in Denmark are quite long and as the weather cooperated part of the time, I did manage to squeeze in some audio-related activities 🙂

A while ago when I launched the version 1.5 of my “mini-pre” a reader asked if I had done any comparisons of the different opamps I suggested and I replied I hadn’t. On one hand I’m surprised that I can even hear differences between opamps, but on the other hand when you think about it it’s a bit like replacing a whole amplifier and then it is of course a bit less surprising that changes are audible.

Now, I am always a bit hesitant to make recommendations for opamps based on just my own sound preferences and my limited testing, but on the other hand I have done opamp comparisons in the past and my impressions haven’t been far off what I have been reading elsewhere. I also found the comparisons to be very useful for myself and since it has also been a while since I’ve really tried the newer opamps on the market I started thinking it would be worthwhile to try comparing a few types again.

Actually doing comparisons in practice is a different matter though as the newer ICs are only available in SMD packages and so I had to pick a more “brute force” approach than the usual method of just swapping DIP opamps. I could have used DIP adapters, but I wanted to be sure that there were no oscillation issues etc. and so I decided to build an extra preamp instead with a different IC. These two boards are therefore completely identical except for the choice of IC – even the two Alps pots come from the same supplier so nothing is left to chance (well, sort of, anyway – plenty of variables left still 🙂 ).

The original amp has the OPA1656 and the other has the OPA1642. From what I know the OPA1656 is currently the highest-spec audio grade standard opamp that TI offers. The OPA1642 is “one step down” but still very highly rated, and it is JFET-input which should give a low enough DC-offset to be used directly in this kind of application. The bipolar input “equivalent” to the OPA1642 is called the OPA1612 as far as I know.

Not quite ready to post my listening impressions of these two ICs yet, but it’s been quite a good exercise to try comparing opamps again – and yes, I can still hear some differences 🙂

12 Responses to Comparisons…

  1. ksjung88 says:

    Long time ago, I purchased a little 3116d amplifier.(it was a real phenomenon here) But whenever I touch the volume knob, a kind of noise is generated. Some say it’s because the ground of this device floats( I must admit I can’t figure out this meaning.). Anyway, to solve this problem I searched and came to this conclusion. Put a pre circuit to adjust the volume! That’s what I mentioned in the email. =) Anyway, I am pleased with this post, the pre board is very similar to one of many pre boards I searched a few days ago.

    • theslowdiyer says:

      The hum when you touch the volume control can be because the pot itself should be grounded but isn’t. if you look at some of my builds with the Alps blue pot, you’ll see a wire going from a “PG” (= pot ground) pad to one of the screws on the back of the Alps. For the smaller pots you’ll have to connect the ground wire in a different way, but you can at last try to see if doing this fixes the problem 🙂

  2. Foppe says:

    I’m curious what your opinion of these opamps will be. I’ve been swapping opamps in my whammy headphone pre amp, and while the differences between opamps are subtle, between opa2132, opa1642, opa627, opa2210 and opa1656, my favorite two opamps are opa1656 and opa627.

    • theslowdiyer says:

      We are very much in agreement I think 🙂 For dual opamps the OPA2107 sounds a bit like a dual OPA627 IMHO and I like that one as well. Sadly, all the “old favourites” are either discontinued or so ridiculously expensive that I couldn’t justify buying them 🙂

      • Foppe says:

        Same here, I would not consider buying opa2107 or op627 because they are way over the price I would pay for an opamp.

        But somehow, TI allowed me to order all the opamps I mentioned as samples on my gmail email address at no cost, which was very nice of them.

        It’s amazing how close opa627 and opa1656 are. Especially considering one is over 10 times more expensive, and you need two of those…

      • Foppe says:

        This back and forth caused me to test out the remaining opamp in my sample stash: The OPA827. I’ve been going back and forth between these three opamps, and my final conclusion is that, in Whammy, with my sources, and with my headphones (Senn. HD560S, a pair of open back headphones with a neutral, flat sound signature), OPA827 is the best sounding of them all.

        OPA1656 is maybe the most “composed” of the three to my ears, but OPA827 just a little more authority in the lower regions, and a tiny bit more “open” sounding.

        For what it’s worth. All three sound absolutely fantastic.

  3. sjariev says:

    Hi Uffe,

    Just a post I was waiting for, thanks. I am searching for some volume pots for some amps, your mini jlh amp and two chipamps, one by Tom Christiansen the LM3886 DR and one from the open source files for a lm3886 amp on diyaudio.

    I have some questions: I want to use your boards for the mini-pre, because I want to use the discrete Burson opamp. Can I use this board for the amps mentioned above, will it work, and will it be difficult to wire it, is the alps a special one, or just a 10kOhm log one?

    Can I get your permission to use your boards?

    Hope to hear from you.

    Bye from Deventer, the Netherlands



    • theslowdiyer says:

      Hi sjarief, that should work. However, the Burson discrete amps are very large, so I’ve never actually checked if they will physically fit the v1.0 board – do that first 🙂 The Alps pot is a standard blue RK27 type, with a value between 10k and 50k.

  4. Pingback: A modern take on the CMoy Headphone Amplifier – (mis) Adventures in Hi-Fi

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