The Beta22 Amplifier

Introduction to the Beta22

To start with, the Beta22 amplifier is a design by AMB Laboratories. It is a fully discrete, high current, class A headphone amplifier that’s considered by many to be the best of the best in solid state headphone amplification. To quote AMB Labs:

The all-discrete (no integrated circuits), fully complementary and cascoded topology, high-current MOSFET output stage, full class A operation and carefully tuned operating points provide vanishingly low distortion, high speed, wide bandwidth, low output impedance, and high output power. All elements of the design were critically examined to create an amplifier that performs as well on the test bench as it does with music.

A Beta22 PCB.

 

The default power supply for the Beta22 amplifier is the Sigma22 which is specially designed to provide high quality, dual rail, regulated power for the Beta22.

σ22 (“sigma 22″) is a high-performance DIY dual-rail, tracking, linear regulated power supply (PSU). Originally designed as a companion PSU for the β22 amplifier, the low-noise, high-current, excellent line/load regulation, wide-bandwidth, and stability characteristics makes it also ideal for other DIY stereo headphone amplifiers, preamplifiers, power amplifiers and other applications requiring a dual-rail regulated PSU.

A Sigma22 PCB.

 

Since the Beta22 is a do-it-yourself (DIY) amplifier, build quality will vary from amp to amp, and so will the sound properties. Ultimately, the sonic signature of an amplifier depends on the design, and so if you follow the guidelines from AMB, it should be relatively easy to achieve the reference-class sound output. In solid state amplifiers, op-amps and capacitors often provide the biggest tuning capability to the sound. On the Beta22, no op-amps are used (since it is fully discrete), and none of the capacitors are in the signal path, so that takes out a lot of the variables in the sound properties.

The Beta22 is modular, and you can shrink/expand the size of the amplifiers as such:

  • Two boards build, sometimes referred to as a “two channels”, is the cheapest and simplest build. It requires two Beta22 amplifier boards (one for each stereo channel), and one Sigma22 power supply board.
  • Three boards build is the default configuration. Where in addition to the two boards, another board is added to provide an active ground channel. This requires three Beta22 amplifier boards, and one Sigma22 power supply board.
  • Four boards build, often referred to a “Balanced Beta22″, one board for each of the four channels in a balanced stereo configuration (L non-inverting, L inverting, R non-inverting, R inverting). The four boards build can be powered with a single Sigma 22 power supply, or dual Sigma22 power supply to have a dedicated power supply for each stereo channel. The four boards can also be wired for handling a regular unbalanced headphone, in which only two boards will be used.
  • Five boards build gives the benefit of having a four boards for balanced operation, as well as a three boards configuration for an unbalanced operation with active ground. (The active ground board requires a different configuration, hence you can’t have active ground in a four board build)
  • Six boards build gives the benefit of having four boards for balanced operation, as well as two sets of single ended amplifier outputs with active ground on both.

Clearly, the number of boards will add to the total cost and complexity of the project.


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  • buz

    How far away from the BCL would you place it? (Going by the description, I think I’ll made a good call in getting my M-Stage, because this sounds a little dull to me :)

    • http://www.headfonia.com Mike

      Hi Buz, the BCL wins in speed, but overall the Beta22 is still superior.

  • xnor

    The "lack in bass" your friend heard was most likely just due to the (very) low output impedance (= good) of the b22. And the layered bass you've mention is the logical side-effect. This has nothing to do with the amp itself. Add two 100Ω resistors in series, or just connect your bass heavy headphones to a receiver and you'll get a "punchy" bump in the FR (depending on the headphone).

  • xnor

    About soundstage: moving the headphones even millimeters on your head will cause more drastic changes than what you'll ever be able to hear between most, if not all, amps that are well designed.

    (Check out headphone measurements from HeadRoom expert Tyll posted at headfi, if you don't believe me.)

    So this is a moot point for me as well.

    As for "treble that sparkles", "less neutral", "more PRaT and impact" … why not use the E7 with bass boost plus some equalization instead. t_t

    Note: I'm not defending the b22 or amb here, I don't even (want to) own one.

    • http://www.headfonia.com Mike

      Thanks for the comments, xnor.

      As an experiment, I have tried adding a resistor on the headphone out on another amplifier, and the higher the resistance at the output, the bassier the sound is. I don't remember it adding bass punch though. Perhaps you can share the particular amplifier and headphone combination you've used for your experiment.

      I know that Tyll is a measurement expert (we talked about headphone measurements before), but I never realized if he has made such remarks about headphone positioning being able to replace soundstage characteristics inherent in an amplifier design.

      About soundstage: moving the headphones even millimeters on your head will cause more drastic changes than what you’ll ever be able to hear between most, if not all, amps that are well designed.

      Lastly, I don't understand how using an E7 can alter PRaT and impact, besides the fact that it's a very inadequate source for something like the Beta22.

      • xnor

        Punch is a matter of accentuating frequencies around 100 to 200 Hz, where many headphones have an impedance peak. Combine that with high Zsource and you're likely to see more punch (again: it depends on the headphones). It doesn't have much to do with the amp itself, except that some amps might roll-off sub-bass which could result in the punch sticking more out of the music.

        Maybe the resistor value was too high/low.

        Slightly different positioning will result in big differences – peaks and nulls especially at higher frequencies. That's what he measured.

        Now think of playing a mono signal, you should hear the same on both ears but you don't because of positioning differences. It might not be so easily noticeable with a mono signal, but has an effect on stereo imaging nevertheless.

        I'm sorry about the e7+bass boost+eq joke, but that last paragraph was just too much.

        • http://www.headfonia.com Mike

          Hi Xnor,
          I understand what you're trying to say, and I'll try to experiment with what you just shared.

          Cheers,

          Mike.

  • glac1er

    Thanks for the review Mike. This B22 makes all headphones sound good, even the ibuds.

    • xnor

      An amp does NOT improve the signal.

      Yours seems to be quite broken if even ibuds (!) sound good.

      • http://www.headfonia.com Mike

        Thanks for the information, xnor.

      • Brian

        Nah, I think Glacier brought up a very important point in a sense that all these cool devices only serve as a bridge between your ears to sweet, delicious music.

  • Shahrose

    Very informative reviews. Instead of merely gushing, you've provided a balanced view with pros and cons and great detail within each section. I also felt your comparisons to other amps in the price range (or even to lower-end amps) was helpful as it gave me reference points to gauge the Beta with.

    If you ever get a chance Mike, do post a review of the Dynahi/Dynamite/GS-X/GS-1. I think some of the shortcomings you've found with the Beta might not be present in the Dynahi or Justin's well-designed Dynalos. (I know some who feel the bigger Gilmore amps are superior to the Beta).

    • http://www.headfonia.com Mike

      Hi Shahrose,

      I'm glad you find the review useful.

      A review of the Gilmore designs would be really hard to pull off. They're not very common around here, and HeadAmp is not the type that gives out loaners.

      I felt that even a first class design like the Beta22 has weaknesses, and so it's only logical that the GS-X/Dynamite would do better in some areas than the Beta22.

  • Frank

    as an audio mastering engineer i deeply prefer the HPBA-2 by Qes Labs

    here you can read my review:

    http://www.head-fi.org/forum/thread/479300/review

    no sound coloration.Plenty of dynamic.

    A true balanced reference monitoring system through headphones

    highly recommended!!

    • http://www.headfonia.com Mike

      Thanks, Frank. Doesn't hear much about the HPBA-2, but you're welcome to post some impressions on it. :)

  • Jehan

    Hey mike, how much is the total cost of a 4 board Beta 22 inclusive of a case? thanks

    • http://www.headfonia.com Mike

      Budget roughly $1200-$1500 depending on the case you use.

  • Jehan

    $1200-$1500 for a 4 board? Where can I get the case custom made? Lastly, how much will assembly of 2 boards Sigma 22 be? Thank you very much.

    • http://www.headfonia.com Mike

      $1200-$1500 should be enough for everything, including 2 S22s with two toroids, case, attenuator, knobs, wiring, jacks, etc. There is no standard case, and so you need to find your own enclosure, design the layout and holes and get a shop to get the holes made.

      Please visit the amb.org/beta22 site, under their parts list page, they have a list of suppliers for the enclosure.

      I personally got the case for this built @ Kaichin at Sim Lim Tower (top floor) for SGD ~$40 each. It works well enough. The front panel is black anodized aluminum, but everything else is plain sheet metal. The paintjob is a bit thin and scratches easily though.

      The audio store in Taiwan (check the link under amb website's parts list) makes nice looking cases, but the cost is quite prohibitive for me.

  • Jehan

    Thanks Mike. Keep up the good work.=D

  • http://blog.cheetahdeals.com CheetahDeals Blog

    Is there a company that sells pre-made Beta22s?

  • Brian

    So Mike,

  • Ferdiansendjaja

    Hi mike

    I just bought beta 22 2ch from the local forum and when i test it with NAD RP 18 ortho, i spoted a noise comming from the driver (like the rp18 drivers broken). Is these caused by damaged mosfet like you mention before? Or the gain (gain 5) is to high for rp18??

    The setup : ipad – b22 – rp18 via lod2rca

    Thanx mike 4 d input

    • http://www.headfonia.com Mike

      Maybe grounding issue.

      • Ferdiansendjaja

        Ooo the grounding issue eh, do you know where the place to fix this issue in jakarta??

        Thanx again 4 the info

        • http://www.headfonia.com Mike

          You have to find a builder. Talk to the guy who sold you the amp?

          BTW welcome to the world of DIY.

  • Gibran

    Hi Mike. A noob question. How much improvement will I get from CMOY to Beta22 if I am using HD650? Will amp upgrade improve my listening experience by a big margin? Thanks in advance :).

    • http://www.headfonia.com Mike

      Gibran,
      The difference will be HUGE!

      • Gibran

        Hahaha, I’m decided ;).

  • http://www.facebook.com/chmarques1 Caio Henrique Gonçalves Marque

    someone tried the b22 with the audez’e lcd 2 ?

    • http://www.headfonia.com Mike

      Pretty good but not really worth the hassle IMO. I’d just go for a Burson. Similar price and you get much better build quality.

      • http://www.facebook.com/chmarques1 Caio Henrique Gonçalves Marque

        thanks again mike, i am thinking which amp i will use with the lcd 2 ”closed”

        • http://www.headfonia.com Mike

          Nice.

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