I searched and didn't find an announcement thread on this (not-yet-released) amp. I have a Crack and am excited to see that Doc is making more awesome headphone-amp kits.
Here is Doc's description from the Bottlehead website:
Two Bottlehead headphone amps have left an indelible impression on the headphone industry over the past few years. The S.E.X. amp opened the way for someone with efficient speakers to make the transition to the ever growing range of great headphones available, having the best of both worlds in one Single Ended Triode amp. Meanwhile the Crack OTL (output transformerless) headphone amp has set a new standard for exceptional sonic performance from high impedance headphones at budget prices.
Last year we retired the premium Smack headphone amp kit. There were a lot of really sophisticated aspects to that kit- adjustable output impedance to handle a wide range of headphones, both single ended and balanced headphone output, a single gain stage circuit with active loading and hybrid shunt regulation, and very good transformers. And very good sound - I thought it was clearly our best sounding headphone amp at the time. Unfortunately for Smack we revamped the S.E.X. kit and in doing so came up with an amp that pretty closely matched Smack sonically and offered enough power (2W!) to run tough cans like LCDs, HEs and K1Ks, that had become very popular.
Smack's lower gain and 1/10 the power output was a compromise in the name of greater resolution and speed and more quiet operation. And we somewhat compromised the kit with a very functional but standard stereo volume pot to keep the price down.
So we decided to rethink the concept of a more premium headphone amp. We wanted to keep the positive aspects mentioned above, and we wanted a bit more gain and more power, and a better attenuator up front for increased resolution. We also had heard a lot of customers ask for extra inputs and a reworked impedance switching setup that avoided turning the amp off and going inside to adjust output impedance and balanced/SE output.
And so here you see a photo of the functional prototype of Mainline, our new premium headphone amp. It uses 6C45pis as the power tubes and a 12AU7 as the two channel hybrid shunt voltage regulator, which is fed by a CRCRC power supply using Cree high voltage Schottky rectifiers . The 6C45s and the shunt regulator are both loaded with C4S active loads. The circuit has Zero global negative feedback as usual and parafeed transformer output using the same OT-3 transformer we used in Smack.
There is a switch which sets the output impedance for low or high impedance headphones, one that sets the output to single ended or balanced, and a source selector for two sets of single ended RCA inputs. Output jacks are both from Neutrik - the fancy locking TRS jack that tweakers seem to fancy for their Crack kit, and a four pin XLR wired in the standard AKG K1000 pinout for the balanced jack. The attenuator is the same as used in our Submissive 36 step attenuator with six coarse 9dB steps and six fine 1.5dB steps for a total of 56 dB attenuation. The production version will have a cool acrylic overlay for the controls like our BeePre 300B preamp.
Output power is about 600mW. Input impedance is 25Kohms minimum. We have used the amp with everything from low impedance Grados to high impedance Sennheisers and even power hungry Audeze phones. They all sound great.
We plan to have the kit shipping by late June. The regular price will be $1199. However we are going to do an initial run of just 25 units, and these we will sell at a pre-release price of $999. Bear in mind that this is essentially the same concept that we used in a custom $7500 headphone amp that we built 10 years ago. The difference is that Mainline uses high quality current production components like Vishay resistors, Panasonic electrolytic capacitors, Cree Shottky rectifers, rather than super rare and exotic vintage parts. The fact that we've added a few circuit improvements that we've developed over the past ten years to that over the top amp design of ten years ago makes it all the more worthy of your consideration for a headphone amp to complement the quality of your high end headphones.
Edited by dsound - 5/22/13 at 11:06am