[Rayvolution]

After reading the dramatic effect of the C4S upgrade I finally got off my butt and installed it. WOW you weren't kidding. The bass and resolution. I think the sound just jumped a couple hundred in quality. I'm blown away by listening to Queen and Nightwish in FLAC.
 
The C4S is a mandatory upgrade and its 2x easier if you install it before finishing the SEX. Desoldering and moving all the wires is a pain. 

 

[Loquah]

Good point about the component removal being slightly fiddly, but it's also fun to hear the difference it makes. Not sure which I'd recommend.

 

[tdogzthmn]

My CS4 is ordered!  I've spent several months with the stock amp so I have a good handle on it's abilities.  In addition to the increase in resolution and bass does the CS4 also increase the gain of the amp?  I don't have problems powering my traditional headphones but my speakers and especially the (SRD-7 >STAX) would benefit from some more headroom!

 

[Loquah]

  My CS4 is ordered!  I've spent several months with the stock amp so I have a good handle on it's abilities.  In addition to the increase in resolution and bass does the CS4 also increase the gain of the amp?  I don't have problems powering my traditional headphones but my speakers and especially the (SRD-7 >STAX) would benefit from some more headroom!

 
No change to gain (that I can hear and from what I understand of the circuit)
 
Have you got it wired with the 32 ohm tap? (or using the impedance switch?)

 

[Doc B.]

Yes, the gain increases a little, probably 2-3 dB.

 

[rx7mark]

Whats the gain and the max voltage on the Mainline for comparison?
 
Mark

 

[wewewho77]

Yes, the gain increases a little, probably 2-3 dB.

Do you think Mainline have enough power to bring the best out of HE500 or the S.E.X + C4S will be better?
Thanks Doc

 

[Doc B.]

I'd like to be sure of what is being asked about.
Gain is only going to matter with respect to the output level of your source and how much it needs to be increased. If the source output is low you need more gain in the amp.
Headroom is about having enough compliance at the input to handle large signal swings from the source. In a tube amp that is largely influenced by what the bias is at each gain stage. It's more of a concern if your source has a high output level. Neither if these has much to do with what amp will drive what headphone. That has more to do with the amp's output power rating into a given load. 
 
Mainline's power output is about 600mW and gain is, conservatively, about 12dB from the 32 ohm tap into a 32 ohm load. I have not tried HE-500s, though I think someone did at a Head Fi meet a while back and liked the result. I have heard LCD-2s and they worked well.

 

[skeptic]

With another day of listening under my belt, I figured I would offer up some further Mainline impressions - which I have also added into my post (#7) on the first page of the thread.  I've also really been enjoying reading all of your respective comments on the Sex + C4S and greatly look forward to Loquah's Mainline vs. Sex head to head once he's got them both sitting side by side.
 
To my ears, Mainline retains much of what I have come to think of as bottlehead's house signature (fast, dynamic and engaging - making your toes tap - with a hint of tube fullness and warmth - the tubes, in a sense, filling in for the room effects you don't get with headphones).  However, in the wake of several years of daily listening to my Crack, Mainline is just incredibly clean and refined in comparison, particularly in its excellent bass response and handling of transients.  This is no doubt the result of its ultra highly regulated single gain stage topology and excellent custom output transformers.  Based on my recollections from CanJam - I would analogize that mainline is as fast, detailed and dynamic as a Zana Deux (leaving slower "tubier" flagships like the Woo 5 in the dust), but with a slightly sweeter top end.  Trumpets can still scream when the source material calls for it, but I can't imagine this amp will ever be characterized as even slightly harsh or piercing - which criticisms are occasionally aimed at the Zana.  (I imagine this may mean that mainline has nice low high order distortion - sort of the antithesis of the disproportionate glare folks complain of in SS amps with lots of global feedback?)  In any event, these positive qualities essentially mean that the mainline is a perfect match for hd800's to my ears.  Even when listening to very simple music (i.e. the Wailin Jenny's - the Parting Glass), the incredibly clean separation between voices is an obvious improvement over other amps with which I am familiar and makes vocal harmonies that much more enjoyable.  The same obviously applies to fast complex music as well, where the mainline's control and handling of transients is consistently impressive.  The more I listen, the more enamored I become.
 
Hope more of you will have a chance to hear this amp in the near future. If possible, I will bring mine to the So. Cal. meet in March.  Also looking forward to receiving the balanced Alpha Dogs I have on order and reporting back as to how they pair with it.

 

[Doc B.]

Thanks so much for your kind words, skeptic! I would agree with what you are describing of the sonics. Mainline was a joint design effort of PJ, PB and myself. In some of our designs I let the guys pretty much dictate the way the amp will end up, for example PB's Crack circuit, or PJ's Quickie. However I kinda fussed and poked and prodded at this one to get exactly what I had in mind. I wanted an amp that was capable as a tool in a critical listening environment, that is to say something I could use for evaluations on my job whether they be equipment or recording quality evaluations. 
 
The OTL approach is very attractive because of its potential for great bass peformance. However OTL headphone amps tend to use cathode followers (including Crack). The CF is a great circuit, you get rid of the potential issues you have with transformers (expense being a big one) but I hear a certain quality to it that is identifiable as cathode follower sound. Same story for multiple gain stages like S.E.X. has, transformer outputs, etc. This also applies to DHTs vs. IDHTs and a lot of other things. Any design is a compromise, and what you are really doing in any design is deciding which compromises are acceptable to your personal taste. Hopefully one can find someone else out there who has the same taste...
 
In this case I felt that we could overcome the potential shortcomings of a single gain stage and having to use an output transformer more effectively than dealing with the sonic artifacts of cathode followers or multiple gain stages. This is the kind of thing you only pick up with experience, you gotta build 'em all and critically listen. I also knew from experience that - though I am still not sure why - the attenuator has a huge influence and needed to be the best we could find. We couldn't find what we wanted so we designed our own, as we did the transformers. Because of that kind of approach to the design Mainline will never be inexpensive like Crack or versatile enough to drive speakers like S.E.X., but I do think it is our best sounding headphone amp.

 

[JamieMcC]

   (i.e. the Wailin Jenny's - the Parting Glass),

 
Beautiful song I know it well, we all sung it at the end of a Cara Dillon's performance the other night.

 

[Loquah]

Yes, the gain increases a little, probably 2-3 dB.

 
Wow. I was having issues with only a limited available range on the volume pot before the C4S, but don't feel like this has reduced at all since adding the C4S. I know 3dB isn't massively significant, but I'm thinking that perhaps my volume issues weren't exacerbated because the quality improvements brought by the C4S offset the slight gain increase and therefore I can enjoy the music slightly louder than before because it's cleaner and smoother. Yet another benefit!

 

[brunk]

......
therefore I can enjoy the music slightly louder than before because it's cleaner and smoother. Yet another benefit!

I know exactly the sensation you are speaking of. For headphones, literally the only one I can do this with is the HE-6, and I'm no stranger to TOTL cans lol. All others give me a 'cringe' feeling.

 

[Loquah]

The C4S Experience

 
Hi Bottlehead fans. Due to a slight shipping "whoopsie" I've ended up with a C4S instead of the PJCCS for my Quickie. After discussion with the lovely Eileen at Bottlehead, we agreed that I could offer the C4S for free to an Australian Head-Fi'er who owns (or orders the S.E.X. kit).
 
What this means is that you can PM me and, for the cost of only the postage, get yourself a free C4S for an existing S.E.X. or an ordered S.E.X. (i.e. please don't ask for it in case you order a S.E.X. in the future - it'd be a shame if it went to waste).

 

[tdogzthmn]

What headphones are you finding work best with the SEX?  I certainly noticed the synergy between the Crack and the HD600 when I owned the pair.  So far the SEX has sounded great with everything and seems to have a particular synergy with my 120ohm K400 headphones.  I was also very happy the amp has been dead quiet with the music paused with no feedback even with the volume turned to max.  Also glad to see my CS4 board is coming in the mail.  Looking forward to hearing if my SR-507 is able to perform even better.