[Audio-Me]

[size=xx-small]expect initial response later on...[/size]

 

[Audio-Me]

First, I'd like to say that it was a pleasure to hire the services of Jon, great guy (polite, doesn't talk ********).

I receieved the amp in a small box coushined in peanut fill (he shipped it via USPS Priority Mail on Saturday, I got it on Wednesday, the package went from far west to far east of US)

The little amp reminded me of a handheld 2-way radio.
The case is a black plastic PacTec model# HML-9VB-ET. (2.7x4.6x1.5)

I asked Jon to optimize this thing to drive Sennheiser HD600 (yes, I'm using this for portable rig). I specifically asked for the smoother sounding 470µF caps (no idea what the hell they are, just read in a thread they sounded smoother than the regular ones), and ¼" headphone out jack. This is exactly what I got, in addition to two 9V battery power supply for more juice to feed the Senns, and a gain of +8.5db for volume adjustment.

I've ordered a custom mini-mini cable by Bolder. It's .5m made of two runs of Belden 89259 wire terminated with Canare F-12 plugs. I haven't gotten it yet, and I couldn't find my Markertek mini-mini cable, so I just hooked this upto my home cd player using Monster Cable Interlink Portable 400 MkII (used to use it to connect pcdp to HeadRoom Supreme).

It sounds great, have the volume knob @ 9 o' clock (zero is seven o' clock). If I can recall back correctly, the sound is comparable to the Creek OBH-11SE. I'm very pleased so far, but there is one quirk, it sounds bright at the moment. I'll post a follow up after some serious burn-in. Melt away them nasty highs!

 

[pedxing]

What is the 8.5 db gain volume adjustment for?

 

[Audio-Me]

JMT, would you care to explain this for us please? Because I honestly don't know (only slight idea), lol.

 

[Audio-Me]

Notes

Reference music: Richard Clayderman - Brahms, Beethoven, Mozart: Clarinet Trios

Batteries used: Maha 9V 160mAH rechargeable NiMH(2)

After 12 hours of break in, the sound is still bright, audible grain, but it's opened up a little. Soundstage is very small, and channel separation is a bit too much (don't know if that makes sense or not). This is particularly evident in Jazz pieces where the saxophone comes exclusively from the right, piano middle, and trumpet from the left. This is bothersome for me when using headphones, as I'm hearing things from one side to the left (panning is torturous as there's hardly any blending). I wish I had asked for crossfeed to ease the wide stereo imaging. The strong points are that hi-hats and snare drums sound excellent, instrument separation is very accurate.

 

[jona]

Audio-

You might try fresh 9V alkaline batteries. The rechargables sometimes do not put out quite the voltage as alkalines (esp. older NiCad's). Just for grins, check the voltage with a voltmeter when you have your amp on. I have noticed my Cmoy (twin 9V power with Meier x-feed) sounds much brighter and less open as the batteries get old & drained.

Jon

 

[Audio-Me]

From prior experience, I've always thought alkalines worked better than rechargeables. I've read up on NiMH and it supposedly outputs full voltage for 80+% of its capacity. These batteres that I'm using are actually rated at 8.6V, and are brand new. I'm sure they'll get better after a few charge/discharge cycles. So I'm giving these a try for efficiency and cost saving sakes.

I always buy boxes of alkalines, plenty of Varta 9Vs.

 

[Audio-Me]

Well well, after an initial 24 hour break in period, and a change of batteries, the sound has calmed down, no harsh grain what so ever. I'm surprised how much more refined it is now, it sure sounds smooth.

Portlable satisfaction here I come.

I got an email telling me that my custom Bolder mini-mini cable is done, and will be shipped today. I paid same price as the amp, lol, it damn well better be worth the money. I was told that the two runs of the Belden stranded 89259 wire wrapped in heatshrink would be very stiff though, doh! As long as it bends enough to be stuffed in a large pocket, I should be okay.

 

[pedxing]

Anyone wants to take a wild shot what a 8.5 db gaine adjustment is?

I have to replace my 9v batteries inside my JMT CHA47 amp too. I am glad mine came with an DC line input too - save money on the batteries. However, my amp is almost twice as large as Audi&Me's.

 

[Audio-Me]

I know this isn't even really a review, just a brief. But I don't think anyone really needs an in depth review of this neat affordable entry level amp.

I tried it with my sound card (128x oversampling, upsampled to 24bit/96khz prior to analog convertion) and it sounded even better. I believe I'll get similar results through the line out of Panasonic SL-CT570 when I get the Bolder mini-mini cable.

At the request of kelly, I have taken a few b&w shots of the thing, and will have them scanned next Friday (hopefully).

I miss crossfeed, but the channel separation is not too bad now, I think I can deal with it.

Would the owners of JMTs amps care to comment and/or add to my initial findings?

 

[Audio-Me]

Jon, could you please tell us what you think about your amps? I'm sure many of us would be interested to know.

 

[Vertigo-1]

The 8.5db gain is simply how fast your amp gets loud. 8.5db is definitely for Sennheisers. For low impedance headphones you typically would want a gain around 3-4, which is what all my JMT amps are set to right now. The higher the gain, the easier and faster it will be to push your headphones to loud levels...the problem is with low imp high sensitivity 'phones, you would have absolutely no control over the volume knob. At 8.5db, I could literally just touch the knob off from zero point and it'd be way too loud. At that level you're also likely to run into pot mistracking problems as well. At the same time, for Sennheisers, setting a gain of around 3-4 would suck because you wouldn't have enough room to spin your knob before maxing the knob out. At 3-4, you'd probably have to keep the knob well over 1/2 all the time. Basically, you might end up hitting the end of the knob before getting to sufficiently loud levels/sufficient levels of power, depending on how loud you listen.

I can't really speak for JMT, but I can imagine what'd he say about his amps already. A simple case of credit where credit due. While he does make the amps, keep in mind the very way the amp sounds is in reality a refinement of several people's circuit board design, which includes Chu Moy, Hansen, and Apheared, hence the intials CHA. If you love the way the amps sound, you're loving the work of those three people in reality, alongside JMT's meticulous work of putting together the amp. It's oftentimes that we praise the amp based on who made the amp, but forget about the underlying designers of the circuit that really delivers the sound. I think that's all JMT would ask of us as well, that we keep in mind those who designed the circuit board.

Without a doubt though, JMT very rightfully gets to strut his feathers about how handy dandy neat and clean his amps are, and just what a great guy he is.

 

[Audio-Me]

Well, the Bolder mini-mini cable arrived in the mail today. I anxiously fired up the portable rig (Panasonic SL-CT570 w/ Nexcell 1800mAH AA batteries - JMT CHA-47 w/ Maha 8.6V 160mAH batteries - HD600)....

My goodness, this thing is freaking huge (thick)! Stiff as steel wire. Wayne was right when he warned me two runs of the Belden would make things super non conforming. They do bend though and stay bent. The Canare F-12 plugs are gigantic as well. The plugs seem to be all silver, but I haven't noticed any coloration (particularly brightness). This is built like industrial cable, good qualities for an interconnect, but NOT portable. =\ I'm afraid I'll have to order a Markertek mini-mini cable (unless someone directs me to a better flexible one) since I seem to have lost mine. Well anyway, this cable definately holds true about needing burn in. It sounds neutral, but lifeless . The bass isn't there, and the highs well, clip, midrange is boring, it is smooth however. At this moment, the Monster Cable out of HK cdp and my sound card sounds better. Better cable + weaker source = can't compare with weaker cable + better source. I notice that with the Bolder cable, I need to turn the volume knob a little higher to get normal volume. I have faith that it will vastly improve after a few days of constant use.

 

[Audio-Me]

Ok, after running through two CDs, I can already notice improvements. The bass has tightened up and is on the warm side.

Midrange is just beautiful. Highs are soft, but all there, just the way I like it.

This cable rocks. I tried it out of the monitor out (3.5mm stereo mini, outputed from upsampled 16bit 48khz signal) of my sound card, and it sounded even better. I don't miss the HeadRoom Supreme anymore, I'm thinking about the Cosmic Reference though.

 

[Audio-Me]

Ahh the hell with a more flexible cable, I love this cable.

I'm just going to stuff everything into a backpack anyway, so off I go into portable bliss...

Even though it's quite early, I can honestly say that I prefer the custom CHA-47 w/ Bolder cable over the Supreme w/ monster cable. The Supreme performs better, but the smooth tone of the cha-47 just steals me away.

Hopefully, I'll be able to A/B for sure at the Boston HeadRoom tour stop with DanG as witness and correspondent.