JMT CHA-47 = Fantastic!
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crymsonsunset

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A few weeks ago I posted an article detailing my impressions of the Headroom Airhead 4.5V portable headphone amp.

Overall, my negative review was not popular, but it was honest and my opinions about the AH have not changed from the original post.

I returned the amp to Headroom and after doing some searching and reading on this and the HeadWize forums, decided to commission JMT to build me a CHA-47 in a wintergreen Altoid tin with the following upgrades to his standard configuration:
  1. 470µF/16v PS caps
  2. Vishay/Dale resistors

Despite my dissapointment with the AH, I was optimistic. JMT was highly spoken of and highly recommended. After communicating with him through e-mail, it was clear to me that he understood what I was looking for, and he was willing to accomodate and explain the pros and cons of the customizations I inquired about.

After receiving the amp, I connected it to my PCDP's line-out (*NOT* headphone jack), plugged in my Koss KSC-35s and again selected Dream Theater's Six Degrees of Inner Turbulence Disc 2 for testing.

Immediately, I was impressed by the smooth, extended response. Every aspect of the music was represented with crystal clarity - from the lowest bass notes and kick drum beats to the highest cymbal crashes and synthesizer effects.

The sound stayed smooth as I turned up the volume. With a single 9V NiMH battery, the amp pushed my headphones to their physical limits of operation, and introduced no distortion. Loud volume was one of my goals in putting together a portable rig, and I got far more than I ever expected out of JMT's little amp. Unbelievable.

Now, I want to address a common misconception that some posters seemed to promote in my previous thread about the Headroom AH. I mentioned at the outset that I was looking for high volume. Not at the sacrifice of SQ, that was the number one priority. But overall volume was and still is important to me. I said that my benchmark for volume (and minimum benchmark for SQ) was the headphone output of my Yamaha RX-995 A/V receiver.

Because I made that comment, it seemed like a lot of people got on my case about hearing loss. Some even seemed to be suggesting that my hearing may have already been damaged, and that I therefore wouldn't be able to distinguish good sound. (If I've misinterpreted what someone intended, I apologize in advance). That's hogwash. I never stated that I intended to listen to the amp at excessive volume levels frequently or for hours and hours at a time. I do however, like loud music, and wanted an amp that had that ability when I really wanted it.

Back on track. The JMT CHA-47, in stark contrast to the Headroom AH, easily meets or exceeds the aforementioned A/V receiver in terms of SQ. It also has more volume potential than even I was looking for, not that this is a bad thing.

Most of the time, I listen to the amp at moderate levels at work, and I've spent a few weeks now enjoying it while being simultaneously amazed by it.

There is tremendous musical clarity, with excellent separation of instruments. Dynamics are good. The amp seems to faithfully reproduce the mix, never flattening it out but never exaggerating it either.

Another point that I was impressed by was the amp's silent operation. There is no audible hiss and no noise when operating the volume control.

The amp's construction is meticulous and solid. It goes without saying that portability is excellent. Incidentally, I took a trip recently and was curious to see, as some had joked or suggested, whether or not the amp would raise eyebrows at airport security. It did not. At one point, I was singled out for a random security check/bag search at the terminal gate. I thought for sure they would at least ask what the deal with all the electronic parts and wires inside the Altoid tin was. But they didn't.

All things considered, the JMT CHA-47 is a tremendous value. I was asked to keep costs confidential, and I intend to fully respect that wish. I will say, however, that the contribution JMT asks for is unbelievably reasonable. It is easily worth double the cost of the standard Headroom AH as it outperforms the AH hands down in every way.

To anyone considering the purchase of a portable headphone amp, you simply cannot go wrong with JMT CHA-47!
 
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mlchang

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I wholeheartedly agree with everything said. I love my penguin CHA47. And it got better after some "break-in" time. Smoother sounding after about 100 hours. So relative newbs (like me) if you are at all curious, it's worth it. Like the new Vanilla Coke commercials "Reward your curiosity."

Michael
 
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joelongwood

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Glad you're enjoying your wintergreen Altoid, crymsonsunset. JMT builds one helluv'an amp! I have 6 JMT-built amps in various configurations (cmoy, CHA47, and META42), including what I believe is JMT's first ever Altoids CHA47 amp. If you're happy with the CHA47 (and who wouldn't be?), then don't go any further. I share your impressions of the Total Airhead, so maybe we're hearing somewhat the same way. But if you want even more of what the CHA47 has to offer, if you can swing it, try the META42. To my ears, it simply sounds fuller, richer, with more dynamics and more effortless driving power than the CHA47. As in all things audio, only your ears will be able to tell if the extra expense is worth it. It was for me. Enjoy your new toy!
 
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jlo mein

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i noticed that the configuration of outside things on your amp is different than the configuration on Jude's amp that was made for him by JMT.

Curious, is there an LED on yours?

JMT has said that he completed my amp, so hes just waiting for my payment to reach him (damn slow canadian air mail
).....mine's in a Penguin Decaffinated mint tin (light blue)

do you plan on using rechargables or are you going to stick with alkalines?
 
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puppyslugg

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For you diyers, it can be improved. I have one from JMT and have changed the op2132's to ad8610's. If your source, such as an pcdp, you can remove the input caps and jumper them. (Check for offset first.) With a single 9v, it is an big improvement, but when powered by 2-9v batteries in series, it puts the amp into another league!
 
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crymsonsunset

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jlo -

My amp does have an LED. It is between the input and output jacks. If you look closely in the pic you can make it out.

Joe -

Not familiar with the META42. Is this another amp that JMT builds? Curious and intrigued...
 
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crymsonsunset

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Puppyslug -

Interesting. Is there any place with more explicit instructions on performing the mods you suggest?

Also, are you saying that you actually modified your PCDP?
 
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joelongwood

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Quote:

Originally posted by crymsonsunset

Joe -

Not familiar with the META42. Is this another amp that JMT builds? Curious and intrigued...


It's an amp designed by a number of Head-Fiers.........do a search for META42 and read all about it. For me, it takes portable listening to another level.
 
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puppyslugg

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Hi crymsonsunset,

No, I did not modify my pcdp. I did modify my JMT/CHA47. The only reference I made about a pcdp were in general terms, that is most (and home units) have caps at the output. If such is the case, then there is no need for the input cap in the cha47. If you plan to remove the cap, check the dc offset of the source.

There is 'no explicit instructions'. I just removed the opamps and replaced them with the ad8610/browndog adaptor mounted in machined IC sockets. Removed the input caps and replaced with jumpers. The ad8610 will work with a single 9v battery, but they sound better with more voltage. And if you haven't already done it, do the Apheared Ti rail splitter mod.
http://headwize.powerpill.org/ubb/sh...ays=20&stime=0
 
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post-156147
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The Quality Guru

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Joelongwood,

In regards to the META42: Have you tried any of the lower end META42's that Tangent says he can build for the same price as a CHA-47? I'm very interested in buying the META42- perhaps a lower end or mid-price one (in the $80-$150 spectrum). Have you heard any in the price range by any chance? Thanks for any help you can offer!

Regards, Luke
 
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joelongwood

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I believe the one I have is somewhere near the upper end of the price range you refer to. I don't have one of the higher end ones.
Luke, are you trying to tell me it get's better than this!?
 
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Joelongwood, that's all I needed to know. Thanks.
Hopefully after I get this META42 I can finally start updating my CD collection and listen to music, not bass, midrange, and treble!
 
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