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Best Class A Amp Ever? Mark Johnson's T2 Class A Amplifier

Discussion in 'Headphone Amps (full-size)' started by adydula, Jun 8, 2019.
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  1. adydula
    I have build many, many DIY amps for headphones and have 10+ amps here to include several commercial amps, tube and solid state....so why build another headphone amp?


    Always looking for that special amp that really would remove that "veil"we all talk about, get new stuff and after a few weeks it seems the veil comes back and we are on to the next piece of gear....human nature for addicts of this pastime? :)

    Over at Diyaudio.com I am always looking for neat, different headphone amps that are affordable and straightforward. There are several choices but most have moved on the really small hard to solder at home parts.
    Some require hot air tools and sloder paste etc...a real pain in the axx.

    You could pick an O2 kit, CMOY, Butte, WHAMMY, Starving student, Bottlehead Crack etc..

    So why this amp?

    So along come this simple Mark Johnson design for a 2 transistor amp, with regular parts, a great pcb, easy to read and a big case to put it all in. Its all discrete, solid state, no IC's, no vacuum tubes. Its a single ended. Class A circuit operating at 150 ma bias current (exceptionally high for a headphone amp). There is no large transformer in the case, the power supply is a small 24vdc (500 ma) switching supply wall wart, safety rated followed by a 2-stage supply filter on the PCB. All parts are 100% thru hole parts, mounted on a single PCB with plenty of spacing between components, very easy to stuff and solder. Very suitable for first time DIY'ers! Its desgned to be a comfortable fit within a typical headphone chassis, like the Galaxy 1U from the diyaudio store ($49 includes shipping from Italy!). The pcb is 182 x 112mm. You can get the pcb and pre-made Galaxy front and rear panels silkscreened with lettering for $16.50, which IMO is a steal!

    To make it even easier to get parts, they have a mouser BOM link that has all the parts needed, except for the front panel volume knob. One of the issues with DIY is getting the parts, ordering only to find a needed part is on backorder. In my case the 10K dual stereo ALPS RK27 pot was on backorder but Parts Express had them for $15!

    Once you stuff and solder all the parts, they have three build and calibration docs available and many high res pictures as well. Final adjustments is setting the voltage for both channels to 5.1vdc across a resistor and adjusting a third pot to set the brigheness of the LED..imagine that...how many have you complained about the dang bright blinding led!! Its fixed here! LOL.

    But the real reason to build this amp is it really is that GOOD.

    Its a simple two transistor circuit, which has been around for ages, but this one has a few differences that seem to make a BIG difference in the outcome...the output stage bais is scaled up to 150 ma and uses high wattage resistors as the "collector" load of the output stage. One of the two semiconductor devices is a "darlington" transistor so you could argue its a three transistor amp, but there are only 2 devices in the design... one just happens to have a darlington pair. There is more "magic" in the design and its beyond my pay grade but you can read a detailed circuit description over at diyaudio.com

    So dont let all this scare you away! Its a really simple project and out of dozens that I have done..this is the easiest one so far to get right the first time.

    Really good? Remove the veil? ok yeah sure....

    Well the first time I fired up the T2 I knew this was a good amp...after a few hours I knew it was a really great amp.
    Aftere a few days its the best SS amp I have ever heard...and from me thats a BIG statement or diving board to climb out on.

    This is a chart Mark put together based on the excellent data from headfi. They tabulate the voltage and current (AC RMS) needed to make each pair of hedphones produce 110 dB SPL, which is very loud. I like this approach because it gets rid of intermediate variables like sensitivity, impedance, and so forth. The voltage & current data tells you exactly what you want to know: how to drive each of the 83 pairs of headphones to maximum volume.

    I've charted their data on the scatter plot below. Each red diamond is one datapoint from head-fi's table. Overlaid on the plot is measured data from the T2 headphone amplifier, plotted in blue. The blue line shows where T2's output just barely begins clipping: for X output voltage, T2 clips when output current exceeds Y milliamps. 80 of the 83 headphones in Head-Fi.org'sle, fall below the blue line. Which means that T2 will drive all 80 of them to 110dB SPL or louder. The ones T2 cannot push to 110dB are:

    HiFiMan HE-4, HiFiMan HE-6, HiFiMan H3-500 whose drive requiremnts border on the insane IMO. T2 is not insane and it cannot drive them to 110dB SPL. Sorry.

    The immediate thing was WOW its so dang clear, clean, crisp....like the sound presentation is so transparent. The articulation, the ability to hear all those micro details is there in spades...using all my headphones from 32 ohms to 600 ohms it was like holy cow how can such a simple design work do dang well? Its like this amp is screaming "here i am, here me roar!!" :L3000:.

    Most of the time switching between amps is not an order of magnitude change but more of a subtle one. Most of agree that getting a new set of headphones the change is really great. Well this is the first amp that has removed the veil and its like getting a new set of headphones. Its that GOOD.

    With live presentations its uncanny real....like being there or the closet to that I have experienced. I think the clarity and transparency of this amp allows for a stunning headphone sound experience.


    So the cost of all this sonic excellence is approx, $49 for the case, about $75 - $80 for parts, $10 for a knob....and your time..and some solder and soldering iron if you dont have one and a simple $10 voltmeter.

    Gosh I cant stop gushing how good this amp works...a truly "veil" remover....if your looking for your first DIY project this is the 'heat' you wont be sorry to have this amp in your collection.

    Any questions please fee free to PM me or comment.

    All the best
    Last edited: Jun 8, 2019
    JazzVinyl likes this.
  2. Spareribs
    Looks interesting. I like how it looks easy to build so it looks accessible for the average Joe
  3. adydula
    Yes it is really a great first time project with fantastic performance...folks will spend thousands of bucks for this sound and I am not kidding....

  4. adydula
    Here it is with its new aluminum knob all finished and working extremely well...one of the best performing amps I have ever heard!

    Alex WP_20190609_12_27_55_Pro.jpg
  5. Amish
    Not keen on the white lettering being so big and kinda taking away from the aesthetic of the case but looks cool otherwise. Seems to be a winner!
  6. adydula
    The case comes with blank panels you can do yourself...these came from mark.
    Amish likes this.
  7. adydula

  8. adydula
    After two weeks and rotating thru several other of my headphone amps I thought the newness would wear off like so many others...


    Its like its still absolutley "stunning"....the clarity and openess of this Class A amp is just wonderful.

    There is a depth to the soundstage that makes listening so very enjoyable...

    The clarity makes the articulation of instruments and placement easy to discern..uncanny.

    I can not state enough how well this amp works....

  9. viivo
    I may be missing something, but I'm unable to find any of these components at diyaudio's store or anywhere else. Do you have any links you can provide?
  10. adydula
    You have to order the parts from Mouser.

    Mark has sold out on the PCB's and front and rear panels.

    He is in process of getting the diystore to have these in stock for sale, sometime in the near future.

    He might do another GB if enough people are interested.

    PM him him over there.

    I bought my PCB and case panels from him, The case is from the DIYSTORE, the parts were from Mouser.

  11. tomchr
    Like many, I was intrigued by simplicity in design of the T2 and when offered to borrow one so I could measure it and have a listen, I jumped at the opportunity. It turned out to be about a week's worth of measurements, listening, and exploration of the ins and outs of the T2, which has led to one of my most thorough reviews. You can find my review (and measurements) here: DIY Audio T2 Headphone Amplifier Review and Measurements.

    attmci and starence like this.
  12. adydula
    Hello Tom,

    I just read your entire analysis and find it open, honest and straight forward.

    I am listening with the T2 right now.

    I have my build for about 2 months now and have a hundred plus hours of listening to all kinds of stuff on it and have compared it to several other amps.
    Senn HD600's, T90's, T1's, DT1350's, MSR7's, LCD2's etc.

    I was shocked at your analysis, I have a real hard time understanding how an amp that measures this way can sound so good to me and others.

    I have always been a technical guy and very objective, but my ground here is shaken based on your analysis.

    I have always looked at your work and HP1 as an engineering marvel to be sure.

    I do not doubt your measurements at all, but my hearing and experience is totally different for sure.

    The only thing I do agree with is the turn on thump....its there for sure, and this can be fixed, but its DIY for sure.

    The soundstage to me is wide, not congested at all.

    With all the IM, THD and other stuff you point out I am amazed that it does "sound" as well as it does!

    I think this was put out there as a easy first time DIY project to get younger folks into the electronics audio area.
    Easy to build and understand the circuit etc.

    That said when touting this the "best Class A amp ever" I can understand some folks wanting to have it "measured".

    But it doesn't take away the pleasure of building and using it at all.

  13. tomchr
    I was rather chocked that something that measured this bad could be listenable as well. But then again - as I also pointed out in the review - it's probably on par with a mid-fi vacuum tube amp. Many people seem to like those. In the end I just prefer a precise amp.

    I don't intend to stir up the sand vs glass debate. As you're probably aware, I used to have a 300B amp in my portfolio. It was a nice amp. I built two of them and rather enjoyed them. That lasted until I designed a vastly more precise amp. That amp and its successors have been my daily drivers since.

    We don't all have to like the same stuff. I'm a precision kinda guy. I hope that comes across on my website. :)

  14. adydula

    Totally understand. We all have budgets, at least I do!
    I would have loved to build your HP1 and have it in house as a real "objective" amp.
    But its cost to me was just way too much. Not saying it was not worth it...I understand when your a small business and the
    hundreds if not thousands of hours you put into making precision equipment.

    If you ever have a "review" unit or your next HP1 follow-on. I would happily review it!!


    Some of the amps comparing to:

    Last edited: Aug 6, 2019
  15. tomchr
    I'll keep that in mind. Thanks.

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