The 'other' objective headphone amplifier: Presenting the C.H.AMP

[JoetheArachnid]

EDIT: Hooray for broken titles! Could a mod please fix it?​

 ​

​

The maw of the beast. Well, the headphone socket. And the other stuff. You get the idea...​

 ​

The Configurable Headphone AMPlifier (or C.H.AMP) is an objectively designed amplifier based around the idea that not all headphones or ears are created equal. Or the same. Or anything near alike. As many a seasoned Head-Fi'er will be able to attest, this is a truth much moreso than the idea that everybody should like the same sound and all headphones should behave the same way.
 
The C.H.AMP was designed by Frans de Gruijter who you may or may not have heard of: he designed a number of tweaks to the Bravo/Indeed amps that led to the recent Project Sunrise kits, which he also designed. Apart from that he's come up with a number of mods and filters for various Superlux and other headphones. He is thoroughly in the objective camp of things as far as audio goes, but still appreciates that some will prefer pleasant tube distortion or a tilted frequency response compared to a ruler-flat one. Hence the C.H.AMP - an amplifier that measures incredibly well but has the option to easily tweak the sound to your preference.
 

​

The innards of the beast. Like, once you go past the maw, this where you end up. Could be worse.​

 ​

The design is a dual-mono setup with (optimally) two transformers, an ultra-quiet PSU that uses 2xNE5534A and 2xBUF634P per channel, then 2xLM4562 (or op-amp of choice) per channel for current gain and 1xLM6172 (or op-amp of choice) for voltage gain. All components are through-hole except for a selection of SMD resistors used to set gain. Assembly isn't quite paint-by-numbers and requires referencing between a component layout diagram, a component list and the PCB.
The jumper configurations set gain, upper bandwidth, lower bandwidth/coupling capacitors, output resistance and DC servo connection. Adjusting the settings is very easy and has notable effects on the sound.
All of these settings are designed to accomodate certain headphones and tastes. Some headphones (believe it or not) may actually sound better on 100ohm output resistors than zero. Some higher-ohmic headphones might need more volume hence the gain. Some people might prefer a totally flat presentation or a lower treble rolloff for a warmer sound, or perhaps some want very deep bass and some want a slight rolloff for 'tighter' bass. It's all in the jumpers and can be experimented with easily.
This is essentially a very basic summary of the C.H.AMP's technical features and configuration - for far more in-depth discussion see the extensive 21-page manual. (It's just a PDF, it won't bite)
 

​

The populated PCB up close with jumpers visible on the left. Sadly they don't actually jump, they just sit there.​

 ​

[size=x-small]One thing to note about the C.H.AMP is that is presents soundstage incredibly well. This is the first time I've ever felt that there was really an element of space between instruments and the presentation is very wide in general. A downside of this is that music can often feel distant such that I turn up the volume only to find that the sound doesn't really change. Part of this might be that I'm very used to my other amp with a comparatively warm and intimate presentation.

In terms of overall sound the C.H.AMP is very sharp, almost to a fault. Every sound is rendered with great accuracy which can actually be somewhat detrimental to some of my less-well-recorded music, especially rock and pop-rock. I find that guitars especially seem to sound almost distorted because the edges of the notes are raw and sharp rather than being smoothed over. This seems to exhibit differently on different headphones, with some presenting is very well (HD 25-1) and some seemingly failing to keep up (HD 595).

The clean sound and lack of bass rolloff (at least with input caps bypassed) make this amp a good choice for electronic/techno music when paired with a good thumpy set of cans and the wide stage lends the amp to classical and orchestral music.

In terms of sources I've found that the FiiO E10's mostly neutral line-out leaves the amp a tad on the cool side, the C.H.AMP benefits from the slightly warmer and smoother presentation of the Marantz CD-50 SE. Obviously one can change the bandwidth and output resistance to get a warmer sound and I'm still experimenting with this, but for now I think that what I've said applies to all jumper settings I've tried thus far (mostly output resistance and bandwidth).[/size]
 
It's not a blow-your-socks-off powerful amp and this is quite deliberate. It could well struggle with the likes of HE-6s and K1000s, but should be able to power through the majority of dynamics and more efficient planars.
 
Overall this is a very good sounding amp, regardless of what I actually say (I'm significantly better at listing flaws than strengths). It blows away most of what I have to hand in terms of detail and presentation, and I shall be interested to see how it compares to other amplification at the 2012 UK Head-Fi meet.
 

​

'And as he sat on the great ridge of Ampedge and gazed out across the Peesibi plains to the looming mountains of Reservoir'kap and the twin settlements of Toroid-Trafo beyond, he was struck with a sense of wonder and delight.'​

 ​

So I hear you cry 'where can I purchase this incredible circuit board and build one of my own?' Well... you can't. At least not unless you get at least 9 friends who are interested in playing EUR30 each for a second run of boards. Beyond that, the up-and-running cost is about £180, then throw in whatever case you want. Obviously you can spend as much or as little as you like on components, I personally opted for 'good enough'.
 
If you have any sound or build questions ask away, for technical questions either consult the manual linked above or ask Frans (Solderdude) at Rock Grotto. Also see Frans if you're interested in buying a board yourself. Main C.H.AMP thread here.