Mainline vs legacy Smack kit

[larcenasb]

Back in 2010 I believe is when I first met Doc, at a headphone meet in some Seattle library. He had set up at a table the Crack, SEX, and Smack, as well as Paramount monoblocks running the AKG K1000 headphones. I brought my AKG K501 headphones and tried them with each amp except the Paramounts.

I remember reading somewhere on this forum that the Mainline was a successor to the Smack but obviously upgraded substantially, is that correct? At the meet, I remember Doc turning over the Smack and setting some impedance switches to best match my 120-ohm headphones, and it just sounded so controlled and sublime. Very smooth and warm as the volume got louder. Zero listener fatigue--just seductive hi-fi. Now, I have heard the Mainline, but not with my AKG K501, so I'm wondering how the Mainline might drive them, what differences can one expect from the Smack to the Mainline? Anyone with experience with these amps, I'd greatly appreciate your impressions. A Mainline build just might be my springtime project. Thanks!

[Paul Birkeland]

So back in the day when the Crack was pretty new and it was the only headphone amp we sold other than the SEX, PJ cooked up the idea of the Smack to make a dedicated headphone amp that didn't have the constraints that the dual purpose SEX amp had.  The Smack ultimately suffered from a few changes in the market that were hard to see coming. 

The first was that the typical output level from source components dropped rather substantially as iPod and phone DAC chips started replacing what one would otherwise find in typical consumer electronics.  The 2V "Redbook Standard" output became more like 300mV, and the Smack really worked best with that 2V source and didn't quite have enough gain to be happy on those 300mV sources like iPods, phones, and some USB DACs.  Nowadays this has become less of an issue again, but the timing with Smack was rather inconvenient. 

Beyond the source voltage issue, balanced headphone amps eventually all migrated from dual 3 pin XLRs to a single 4 pin XLR, and this would have meant starting completely over with the kit to stay complaint with what our customers demanded. 

Lastly we also saw some disappointment with the impedance switching arrangement being mounted on the bottom of the amp.  For people who wanted to listen to six different pairs of headphones in the span of an hour, turning off the amp and flipping the switches was a bit cumbersome.  This switching kit functioned better on the SEX and Stereomour where typically switching the impedance configuration wasn't done all that often, but on the Smack it just wasn't quite a good fit. 

That's how we arrived at the Mainline at the end of the day.  It has the impedance and balanced/unbalanced controls mounted up top so they are more usable, higher gain tubes to work better with lower level sources, and connectors that are more in line with market expectations.  Ultimately I would suspect that A/Bing the two amps would reveal a lot of similarities, with the Smack being a bit on the warmer side but the Mainline being a touch quieter and cleaner. 

[larcenasb]

Oh, it was from the Mainline product page, ha! Thanks, Paul. Interesting about the Smack being a bit on the warmer side....that was what really drew me into the listening back in 2010. It matched so well with the sometimes thin-sounding K501. A lot to think over for me and my next project.

[Larpy]

To my ears, the Mainline does not sound warm.  Indeed, it doesn't sound "tubey" at all to me.  And there's no way to tube roll, so you can't use different manufacturers or different tubes to tweak its sonic signature.

[Doc B.]

Peebs is pretty right on in his description. The Smack was good enough to be used by the duping engineers who monitored the making of Tape Project albums for many years (though Paul Stubblebine recently requested a couple of Stats, as they have transitioned to ES headphones for monitoring). That said, I personally would not go back to a Smack from a Mainline.

[larcenasb]

Thanks Larpy, thanks Doc!

I am listening to Spendor Classic 4/5 speakers right now and they don’t sound bright, nor do they sound warm….just very lifelike tone coming from them. The Mainline gave a similar quality through my AKG K240 Sextetts when I listened at Bottleheadquarters. I guess there’d be no reason to think the K501 won’t also be handled in just as a composed and lifelike way. So perhaps, like the Spendors, the Mainline is beyond the need or urge to tube roll. I’m considering the Mainline now and thinking of build possibilities.