By Xin Feng [08/16/02]

"A Headphone Amplifier That Shoots the Moon" - David J. Weinberg, editor of The BAS Speaker and Widescreen Review magazines, in his recent review published in Vol 25 No2 of The BAS Speaker.

History and Technical Details

You can always buy the cool stuff including the latest version of this amp.

[03/28/04] Benchmarks, you can see how great this tiny amp truly is:

[02/08/04] V7.0. Separated output channels, higher class-A biasing current and significantly better battery life. Warmer sounding.

[08/12/03] Official release of V6.2C.  This version summarizes all the improvements introduced after V6.0:

Overall, the sound is more transparent, detailed, punchy and sparkling with lower distortion and thorough removal of veil.  See below for details on CCS and XinFeed.

[07/20/03] Added a new option: symmetric class A biasing via current source.  By maintaining a small amount of constant bias current, small signal distortion (crossover distortion) is minimized.  Sound is improved while battery life is almost the same.  The CCS technology is invented by ppl (you can find this great diyer on headwize) and I implemented it in a unique symmetrical scheme.  The current source parts we use are the Vishay SST502 series which are very expensive but the performance is exceptional.  For example, the SST503's capacitance is only 1.5pf and its current is super flat within .45-45V range.  Here is my test data:

By cascoding two SST503, the current is even flatter.  Here is the test data:

For 2N5484 that's used in many other amps, I tested two versions of them: Vishay and Fairchild.  The Vishay ($0.48) is totally useless for this purpose - the current goes from 1.68mA@0.5V, 3.09mA@1V to 4.13mA@10V.  Meanwhile, the current is not steady at all.  By cascoding two of them does not help much: 0.9mA@0.5V, 1.38mA@1V and 1.78mA@10V.

The Fairchild 2N5484 ($0.07) is much better than the Vishay 2N5484, but still no compare to SST503, especially when voltage is low as in the case of this amp.  For a single 2N5484: 0.97mA@0.5V, 1.33mA@1V and 1.57mA@10V.  When cascoded:

As you see, much more expensive parts must be used in our amps,  to achieve the smallest size and longest battery life without losing performance.  Even though, we still try our best to keep the price as low as possible.

[06/18/03] XinFeed external add-on module.  I did not make an external xfeed module for earlier XIN amps because the Linkwitz xfeed causes volume loss.  Now my XinFeed is perfect - no volume loss and fully bypass able; therefore it is time to make such an external add-on for all amps that have no xfeed built-in.  It is so small (tiny), it will never be hassle to use.  Gold-plated contacts, high grade PPS film capacitors and precision resistors ensure durable and good sounding.

[06/07/03] "XinFeed".  The Linkwitz crossfeed (left side of the picture) works very well.  However it has two shortcomings.  First, the 400 Hz bass compensation is remained even when SW5/6 are set to bypass position.  Although it is ignorable but few people do hear the difference.  Second, the crossfeed circuit causes volume loss no matter it is enabled or bypassed.  Thus, the amp needs a higher gain to compensate this volume loss.  There is an alternative crossfeed circuit in headwize library - the "Natural Crossfeed" by Jan Meier.  However, it is not thoroughly bypassed neither - the crossover resistor (s) always connects the two channels.  In my test, I can still hear channel crossover when I set the switch to bypass position.

Therefore, I, as a perfectionist, had to create a perfect crossfeed circuit that eliminates these shortcomings - it must not cause volume loss and must be entirely bypass-able.  The resulted circuit is "XinFeed".  It works very well with my amp.  The amp no longer needs a higher gain to compensate the volume loss caused by Linkwitz circuit.  When the bypass switch is set to "bypass" position the entire crossfeed circuit is removed out and there is nothing left to touch the original sound.  Bass enhancement can be added or not with XinFeed.

[05/07/03] V6.0 - with built-in crossfeed!  We did it again, in less than one year after the first release of this very unique Xin Super Mini Amp.

The built-in crossfeed circuit is a full implementation (fine tweaked) of CMoy's modified Linkwitz crossfeed.  Please check CMoy's www.headwize.com website for technical details.  Without adding noticeable effect to original music, crossfeed reduces fatigue caused by long-time listening.  Just the sound image is moved slightly and pleasantly away from your head to the front.  If you don't need this feature at all, just don't add this option when you order.  Even included, it can still be easily bypassed.  The slide switch on the left corner of the amp case is for crossfeed bypass (to left to bypass).  Crossfeed effect is very subtle (otherwise it would be a bad thing).  You can download this test audio and check the difference.  This test audio produces white noise to left and then right channel.  When you enable crossfeed (move the slide to right), the sound position moves slightly from very left or very right towards the center, which you'll feel is more pleasant and less pressure.  When you bypass the crossfeed, the test sound pushes to very left or very right, which is not so pleasant and puts some pressure on your ears.  Such effects, shown clearly by this test audio, are not so noticeable when you listen to normal music, but they are there and, especially, will show up after a long period of continuous listening.  Therefore, the crossfeed circuit in our amps is very well implemented - it does not ruin your music but makes your joy better and longer ;).

The two buttons are for up/down volume control. Analog pot version are also available.  Still the same tiny size as before, much smaller than a credit card.  Still weighs only 2.5 oz including 3 AAA batteries.  Still consumes very little power (only 12.5 mA) and batteries still last 120 hours continuously.  Can still use external power and batteries with an optional booster connector.  The optional super blue power light looks very cool and consumes almost no power (only 1 mA).  It has no any side effect on sound and is meanwhile a rough battery level indicator - it becomes dim when battery is low.  This super bright LED is very visible under direct California sunlight!!!  I did not include this light as a default because a light annoys some people and the super blue LED is very expensive ($3) and is difficult to mount.

Compared to V5.18, there are some more improvements in this version in addition to the added crossfeed.  Uses fully SMD components (all high-grade type), except the two large low ESR power filter caps, to ensure superb audiophile level audio.  All the resistors are 1% precision type.  All the caps are very expensive high-grade PPS film type (costs $1 each!).  There are four expensive ICs (one more than V5.18, most of them are $7 each) used for digital volume control, FET-input amplifier, hi-current output buffer and power buffer, respectively.  There are totally five op-amps in these ICs, and they work together under Walt Jung's multiple feedback loops for the best audio amplification.  Yes, the power buffer now uses a separate IC to avoid any potential crosstalk.  Also added are two film caps to the two power caps for even better sounding.  SMD components are hard to see in headphone amps because of high cost and production difficulty.  I saw few such amps and they are priced at $$$$!  I have my own secret that allows me to do SMD devices easily and quickly; actually I do them much faster than conventional through-hole components.  Therefore, my amp does not cost you an arm and leg while providing you the best sounding that the latest technology can offer.  Due to these improvements and better SMD components used, this version sounds better than before, with crossfeed enabled or bypassed.

Much less wires inside for solid reliability.  It is even smaller and thinner than the new iPod and it makes the iPod sound better.  The best use is to attach this tiny amp to the back with Velcro.  Once I find the iPod connector, you can also use the new iPod's line-out (a true one) for much better sound quality and use this amp to power the iPod for doubled or longer play time.  Until then, you can use the lineout port in the docking station.

Available immediately for online ordering.  Older versions cannot be upgraded to this version as it is a thoroughly new design with new casing.  There is no extra space in earlier versions to add the Linkwitzs crossfeed circuit.  But don't worry and we offer something even better.  In order to show my appreciation to my dear customers, current XIN amp owners can purchase this latest and greatest amp with crossfeed for a special upgrading price.  I think this is better than offering an external module which has more cost and is hassle to use.  Also, to help poor students, now we offer academic discount.

[04/05/03] V5.18.

With these improvements and changes, now the amps are truly optimal for both portable and home.  I keep my promise - smaller and better and do my best to keep the low price.  I don't forget my old customers neither.  All earlier versions owners can add the internal active power module for $30 or upgrade entirely to this latest version for $60. Free shipping for 1st class mail or international airmail.

Above pictures show the PCB board.

 Looking at above tiny PCB board, you should understand why I don't sell kits - not everybody can do such micro soldering.

[02/21/03] Amps that have no booster connector should not be used with external power, because a protection circuit is also added together with the connector.  Without such a protection circuit, the amp could be easily fried.  Therefore don't try external power if your amp does not have a booster connector.  If you do want to use external power, please send your amp back to add a connector together with a protection circuit.  This circuit also detects external power automatically and make the best use of internal and external power supplies.

For amps that have a digital volume control, they can only stand with 7.2V.  Therefore use only 3 AAA internally (alkaline or rechargeable), 6 AAA (rechargeable only, with a booster) or 1 7.2V (rechargeable only or a 6V walwart, no internal batteries).  For amps that have an analogue pot, the maximum voltage is 12V.

[02/01/03] Let's remember today - the Columbia Space Shuttle disappeared.  As a former rocket scientist, I feel very sad, especially that I just added Space Shuttle boosters to the amps only 10 days ago.  In memory of the seven great and brave astronauts, I added a 2-button volume control version (up/down) and both 1 and 2-button control now can remember its position even when the power switch is turned off.  Let's remember.

[01/28/03] Don't be scared, not another version, just some answers to some questions regarding versions.  V3.1 has the most significant sound improvement so far.  V3.0 can be upgraded to 3.1 (free).  V4.0 doubled the output voltage, which is not upgradeable from V3.0 or 3.1, but the improvement is not so important if you never heard of clippings.  The booster connector of V5.0 can be added to V3.0 or 3.1, which makes the doubled output voltage of V4.0 even less important because of the much higher power voltage can be added through the connector.  Therefore, if you have a V3.0, it can be upgraded to V3.1 (free) and, if you like, to V5.0 (i.e. add the external connector, $20 fee apply, due to the significant cost added to parts and labor).

The ER4P-to-4S adapter built into V5.0 makes ER4P sounds equally to ER4S and it does not hurt other headphones including ER4S.  Such an adapter has been built into all earlier versions, just the value was not optimized for ER4P.  So, don't worry about it if you don't have ER4P.  For ER4P users, now you no longer need to carry the adapter to get the optimal sound.

While new versions keep coming out, we do have been doing our best to keep the value of the earlier versions and the price for the newer versions.  It's not perfect, but most customers agree that it is the best.

[01/22/03] V5.0. Added a booster (-b version) and built-in ER4P-to-4S adapter.  Like the Space Shuttle, that can use boosters, now the Xin Super Mini Amp too has a booster!  The amp still works like before without the detachable booster.  With the booster connected, its working voltage is doubled (from 4.5V to 9V), which lets it to drive hi-impedance (300 ohm or higher) headphones with more headroom.  Because op-amps, which are used in our amps, perform better at higher voltage, this booster should improve the overall sounding also (In fear of being blamed of bragging, I leave this to my dear customers to test it out).

As you can see from the pictures, even with the booster, this amp is still world's smallest and lightest.  Wanted an amp for both ultra portable and home?  Here it is, still, $99.99.  Who really needs a booster?  Those who listen very loudly with very high impedance cans.

With a booster connector, you can also use 9V batteries cautiously.  If you use both the internal AAA batteries and a 9V external battery (as showing in left picture), make sure they are ALL rechargeable (Ni or Ni-MH, not the alkaline type).  If any of them is not rechargeable (1.5V/9V instead of 1.2V/7.2V), the total voltage will be too high and the amp is in danger.  If you use only one external 9V battery (the right picture), then it can be any type - rechargeable (7.2V) or alkaline (9V).  The amp automatically detects the internal and external batteries and make the best use of them.

With a 9V battery interconnect cable, you can mount a 9V battery nicely as showing in the below picture.  If you cannot make such a cable by yourself, you can buy it on the Cool Stuff page.  Yes, you can also use a AC adapter, but make sure its output is 7.5V or lower.  Note that many AC adapters, such as those from Radio Shack, are not regulated and a specified 7.5V is actually as high as 13V!  Therefore, for such AC adapters, use a 4.5V one.  A 200mA or higher AC adapter is adequate and a regulated or switching AC adapter like those sold by Wal-Mart is highly recommended.  If you are not so sure which AC adapter you should buy, just buy one from us on the Cool Stuff page.

I would like to say it clearly again, all these are optional and the amp always works with just the internal 3 AAA batteries.

BTW, I too hate this endless upgrading, but I don't want let anybody be able to criticize my amp (I welcome any complaint) and I want everybody be happy.  This time they said the voltage was not enough and it was not rocket science, so I gave it a Space Shuttle booster!  As I said before, I do these amps and everything you see in this website in my spare time only, so I cannot make it perfect overnight.  Customers cannot wait until it is perfect neither.  If I didn't sell the amp, I would be (I was) flooded with email asking when available.  So I chose this versions route. Whenever I hear a big complaint, there'll be a new version right after.  What's the next?  The crossfeed and the in-line amp, but I cannot give a time table as always.  Neither does president Bush, he cannot give a time table on Iraq war neither, but just keep saying "time runs out".  So don't count on the optional (not critical) features, at least after the "time runs out".

[01/08/03] V4.0. Re-designed output buffer stage which provides almost doubled dynamic range than earlier versions.  When battery is 4.5V, the amp is able to output  4.42V before clipping, or 3.52V when battery is 3.6V.  Yes, the amp can deploy almost all the battery's supply with only 0.08V offset!  With the maximum output of 110mA and 4.42V, this latest super mini amp can drive flawlessly either hi-impedance (such as Sennheiser HD580/600) or low-impedance (such as Grado 60 headphones) using only 3 AAA batteries which lasts up to 39 hours (based on 700mAh Ni-MH rechargeable batteries).  Together with the power supply improvement since V3.1, the sound has been significantly improved and this amp, not the only one though, has reached the highest level an op-amp based amp could offer regardless its smallest size.  The sound is incredible.  If there were anything missing in the sound of earlier versions due to size limit, there is no more because all the circuitry that's necessary for the best sounding have been included in V4.0.  I spent most of the recent holidays to re-design the circuit board to put all the necessary components into the same tiny case.  As you can see in the following pictures, wiring is also significantly simplified.  The V4.0 will be available in a week in both digital or analogue volume control types at an introductory price of $99.99.  For the first time, we'll also offer samples to reviewers (upon request).  Yes, this latest amp is by no means ashamed to any other amps on market or from DIYers.  Thank you all, especially to the early adopters of my amps, for your very valuable feedback, otherwise this amp would have never been as perfected as it is today.  Unfortunately, earlier versions cannot be upgraded to V4.0 due to a re-designed circuit board.

A tip: if you still cannot imagine how small this amp is from the pictures, please go to your local Radio Shack store and look at the 4-AAA battery case (270-411).  Another tip: does these pictures give you any new idea?  How about putting such an amp into a single-AAA or AA flash to make an inline amp for, say, iPod?  That's exactly my next step. Thank Eliot Jacobs for this great idea and I'm making the first Xin Inline Amp exclusively for his beloved iPod.

[01/01/03] V3.1.  Improved power supply circuit, which contributes to better bass, more details and more spaciousness.  Burn-in time should be reduced significantly.  I knew, but still amazing, what a difference a better power supply can make.  Amps shipped today or later have this new circuit.  V3.0 (digital) and V3.0-a (analogue) owners can send their amp back for free upgrading (1st class mail, fees apply for other shipping methods, see products page for shipping fees).  You'll love the new sweet sound.  One-day turn around.

[12/01/02] V3.0-a.  Same as the V3.0 but with an analogue volume control.  The same neat circuit design (the left IC is not present in this version).

[10/31/02] V3.0.  One-button digital volume control - no more that bulky knob or any mechanical part; line-in jack - no more that tethered plug and use any of your favorite connection cable; large power caps - 470uF (vs. 220uF before) and should sound as good as a full meta42 if not better.  Battery life is the same as before.  My first impression is significantly better bass and lots of juice.  I.e., this tiny amp is the world's smallest, most featured and first-class sounding.  As you can see, it is even smaller than a mini disk, but the caps in it are huge - no compromise on sound!  There is no any extra fat to ruin the sound neither.  A truly audiophile-level amp but in the smallest size.  Even myself cannot believe this is true, but we are talking about rocket science, right?  You can buy the latest amp on our products page.

[10/18/02] Now the gain is set to 10 by default.  If your amp sounds not loud enough, you can send it back and we'll change the gain for free (free for 1st class mail, $4.99 for priority mail).  Now both the super mini and mini can drive well almost any headphones including HD-580/600 and ER4S. Those that have order # equal or greater than 30630638 already have gain of 10.

[10/09/02] V2.0. Now the super mini has the same feedback loops of the mini.  This is another milestone in super mini's development.  The sound is now transparent and detailed.  Super mini owners can send their amps back for this upgrading.  Because more expensive parts will be added and the work is very difficult, a $20 fee will apply - well worth it.  Now I challenge you for hearing any significant difference from a full meta. Those that have order # equal or greater than 30606083 already have this latest improvement. $80

[9/16/02] V1.0. AD823 + Buffer + Volume Control. Global feedback. $60

[8/26/02] V0.1. AD823 + AD823. $50

[8/16/02] V0.0. AD823 only. $40

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Last modified: June 22, 2005