Mainline vs. others

[mete]

I have a Crack without Speedball, and I only modified the volume pot (replaced it with Alps RK27). I really like it but I wonder when I want an upgrade what I should get. Is Mainline better than all others for all (high and low impedance) headphones ? or is it better to build Crack with Speedball or S.E.X (with C4S?) before Mainline for some reason ?

I have both high and low impedance headphones but because I like Crack I mostly use HD600 (I may get an HD800 if it matters). I have two sources, an R2R DAC and Phono amp, I mostly listen digital/DAC.

[Larpy]

Crack and Mainline are very different headphone amplifiers.  Very different.  The Mainline does not share the Crack's tubey lushness.  Instead it sounds extremely clean and detailed.  In fact, to my ears, it doesn't sound "tubey" at all.  It's definitely the better amp for low impedance headphones.  There is no question about that.  The Mainline will drive just about any headphone on the market (though you might have to turn it up almost all the way for inefficient 'phones).

Though they're both Bottlehead products, the two amps are apples and oranges. 

If forced to choose only one, I'd go with a Crack with Speedball.  But my preferred headphones are high impedance Sennheisers.  Sounds like you're the same (the 800 will work just as well with the Crack as the 600).

I guess I'd put it this way:  if you find yourself listening to your Crack and feeling it sounds a bit opaque (to use an optical metaphor, as though it's just slightly out of focus or showing you an image that's been filtered to make the colors look just a little oversaturated), then you should look into the Mainline as an upgrade.  It will give you a more accurate depiction of the recording.  You will hear more details.

But in comparison to the Crack, the Mainline can sound a little clinical, a little bleached.  The Crack trades resolution and accuracy for a more syrupy (a thicker textured midrange) sound that many find, well, addictive.

That's how my ears hear it anyway.

If you find yourself wanting to upgrade your Crack beyond the Speedball, there mods you can try like adding a choke to the PS and changing the driver tube from a 12AU7 to a 6SN7.  But these mods wouldn't come as kits from BH.  However, there's a ton of info on them in the forum archives.

[Doc B.]

If you want something that falls between the two sonically get the S.E.X. amp - warm but less "tubey" than Crack while not as resolving and clean as the Mainline.
My preference is to Mainline. But understand that my preference is influenced by having been involved with mastering engineers and by the need for high resolution to evaluate recordings being considered for reissue. That's a somewhat different requirement than one might have for casual, relaxed listening.

[mete]

Crack and Mainline are very different headphone amplifiers.  Very different.  The Mainline does not share the Crack's tubey lushness.  Instead it sounds extremely clean and detailed.  In fact, to my ears, it doesn't sound "tubey" at all.

Great answer, thanks. You actually understood my question better than how I asked it. Maybe first I should say that Crack is the only tube amp I have ever heard. I have listened two hybrids before, and plenty of solid state ones. I think among all I prefer Crack. The reason I did not get the Speedball upgrade is also I wanted to hear first -not sure if it is right words but- a very classical tube amp.

If forced to choose only one, I'd go with a Crack with Speedball.  But my preferred headphones are high impedance Sennheisers.  Sounds like you're the same (the 800 will work just as well with the Crack as the 600).

I am not very good with adjectives in general, but if clean and detailed is also mostly associated with solid state amps. then yes, it sounds like I would prefer Crack then.

[mete]

If you want something that falls between the two sonically get the S.E.X. amp - warm but less "tubey" than Crack while not as resolving and clean as the Mainline.
My preference is to Mainline. But understand that my preference is influenced by having been involved with mastering engineers and by the need for high resolution to evaluate recordings being considered for reissue. That's a somewhat different requirement than one might have for casual, relaxed listening.

I was going to ask about the S.E.X. amp. and good you mentioned about the high resolution and mastering. I think I listened so called resolving or transparent etc. amps (Stax and some studio equipments etc.), and I find myself going back to Crack after listening them (for casual listening as you said). So if I understand your and Larry's reply correct, maybe I should try a Crack with Speedball first (and maybe also with hd800) before even trying S.E.X. amp.

Is being "tubey" related to OTL or can a transformer coupled amp sound similar in terms of tubeyness to Crack as well ?

[Larpy]

I don't think using the output tube as a cathode follower and dispensing with an OTL necessarily makes for a tubier sound (though I could be wrong).  Plenty of tube circuits with OTs sound plenty tubey.

Doc's recommendation for the S3X is a good one.  It does indeed occupy the midground between Crack and Mainline.  And it will drive any headphone you'd care to throw at it. 

Given its relatively inexpensive cost, the Speedball seems like the obvious next move.  It will nudge the Crack's sound in the direction of the Mainline: a little more resolution, a little less lushness.  It's possible you'll decide you prefer the Crack without the Speedball.  If so, it's easy enough to undo the mod.  And then you'll know that you're a fan of old-fashioned tubey gooeyness.  Well, maybe "gooeyness" is going too far.  Good old-fashioned tubey richness.
 

[hmbscott]

Regarding the speedball upgrade, I built my Crack and listened for several months before upgrade to speedball. I was immediately put off a bit because Speedball sharpens it up and moves it on the spectrum towards Larpy's description of the Mainline (less tubey more resolving), but after letting my ears get used to the new sound I find Crack+Speed ball very satisfying, although I am on the fence as to whether I like it better than the basic Crack. Speedball is a clear improvement if a high resolution is your thing. That said if the rich tubeyness of the stock Crack is your main draw to it you might want to keep it stock, and look for something like the SEX for a cleaner sound and broader drive capability.

[mete]

Regarding the speedball upgrade, I built my Crack and listened for several months before upgrade to speedball. I was immediately put off a bit because Speedball sharpens it up and moves it on the spectrum towards Larpy's description of the Mainline (less tubey more resolving), but after letting my ears get used to the new sound I find Crack+Speed ball very satisfying, although I am on the fence as to whether I like it better than the basic Crack. Speedball is a clear improvement if a high resolution is your thing. That said if the rich tubeyness of the stock Crack is your main draw to it you might want to keep it stock, and look for something like the SEX for a cleaner sound and broader drive capability.

Even if I do Speedball, I am not going to modify the Crack I have. So because of that, and also to have something more different, getting S.E.X. amp makes sense.

I thought Crack+Speedball moves Crack in the direction of S.E.X., but it is not that simple I guess, so if one prefers Crack to Crack+Speedball, he/she can still prefer S.E.X. amp to Crack ?

Also, is it better to install C4S from the start or better to try without first ?

[Larpy]

I think it's accurate to say that the Speedball pushes the sound of the Crack in the directions of both the S3X and the Mainline.  The Crack's circuit is about as simple as can be, and that plays a big part in why it sounds as it does.  The S3X's circuit is more complex (plate chokes, OTs, DC heaters) and perhaps because it's higher powered and a parafeed circuit instead of a cathode follower, it sounds more authoritative than the Crack.  The sound is clearer.

I've heard a Crack but don't own one.  I have both a S3X and a Crack-like OTL headphone amp based on Pete Millett's Wheatfield HA2 amp from the late 1990s (a circuit that I suspect influenced BH's development of the Crack). They sound different enough that neither makes the other superfluous.  You ask if someone could prefer the S3X to the Speedballess Crack (Slowballed Crack?) and I think the answer is yes.  The Crack-like OTL amp I built sounds sweeter than the S3X, but the S3X sounds snappier, more dynamic.  I like having both options available, but if I could only keep one, I'd keep the S3X, if only because I have low impedance Audezes as well as Sennheiser 800s that I occasionally like to listen to.

And, yes, you definitely want to build a S3X stock first before adding the C4S upgrade.  In fact, if you want to keep the S3X's sonic signature closer to the Crack's, you might want to forego the C4S upgrade. 

[Paul Birkeland]

Yes, part of the reason I started making OTL amps was because I couldn't afford an HA-2!

[mete]

Yes, part of the reason I started making OTL amps was because I couldn't afford an HA-2!

I checked the circuit of HA-2 as far as I can understand. Is there something particular that exists in HA-2 and would be good for Crack but it is not implemented due to cost or complexity for a kit build ? Is there a reason HA-2 has (I think) grid stoppers in both stages but Crack does not have for 6080 (I guess the volume pot works as grid stopper for the input?) ?

[Paul Birkeland]

Is there something particular that exists in HA-2 and would be good for Crack but it is not implemented due to cost or complexity for a kit build ? Is there a reason HA-2 has (I think) grid stoppers in both stages but Crack does not have for 6080 (I guess the volume pot works as grid stopper for the input?) ?

Grid stoppers won't hurt on the 6080 but aren't all that critical on the 12AU7.  I definitely consider stoppers mandatory on a tube with more than 10,000uMhos of Gm, optional/probably a good idea on tubes from 5,000-10,000uMhos, and not really all that useful below 5,000uMhos.  For the Crack in particular, decent layout practices make it not much of an issue, but stoppers can help if you're running a 5998.

I'd say really this is the other way around in terms of applying HA-2 design details to the Crack.  The HA-2 and the first couple of OTL headphone amps I played around with suffer from using a tube rectifier.  This forces the first cap in the power supply to be relatively small compared to what's necessary and you end up really needing a choke with a good amount of DCR or a lot of RC stages to knock the power supply ripple down.  Using a solid state rectifier frees you up from those constraints.  The HA-2 also runs quite a bit more B+ voltage to help increase the value of the cathode bias resistor in the output stage, but the larger Speedball board eliminates the need to do that and keeps the power dissipated inside the chassis reasonable while maximizing available signal current in the output stage for the intended load (rather than burning it off in that resistor).  Looking at the HA-2, each 2K cathode resistor dissipates 18W and that's a huge challenge to deal with inside a chassis. 

We also provide larger coupling caps for the output while I think Pete was using smaller valued film caps.  I think the smaller film caps would definitely be a better choice for 600 ohm headphones, but maybe a bit more debatable as the impedance decreases below 300 ohms. 

[mete]

Grid stoppers won't hurt on the 6080 but aren't all that critical on the 12AU7.  I definitely consider stoppers mandatory on a tube with more than 10,000uMhos of Gm, optional/probably a good idea on tubes from 5,000-10,000uMhos, and not really all that useful below 5,000uMhos.  For the Crack in particular, decent layout practices make it not much of an issue, but stoppers can help if you're running a 5998.

I'd say really this is the other way around in terms of applying HA-2 design details to the Crack.  The HA-2 and the first couple of OTL headphone amps I played around with suffer from using a tube rectifier.  This forces the first cap in the power supply to be relatively small compared to what's necessary and you end up really needing a choke with a good amount of DCR or a lot of RC stages to knock the power supply ripple down.  Using a solid state rectifier frees you up from those constraints.  The HA-2 also runs quite a bit more B+ voltage to help increase the value of the cathode bias resistor in the output stage, but the larger Speedball board eliminates the need to do that and keeps the power dissipated inside the chassis reasonable while maximizing available signal current in the output stage for the intended load (rather than burning it off in that resistor).  Looking at the HA-2, each 2K cathode resistor dissipates 18W and that's a huge challenge to deal with inside a chassis. 

We also provide larger coupling caps for the output while I think Pete was using smaller valued film caps.  I think the smaller film caps would definitely be a better choice for 600 ohm headphones, but maybe a bit more debatable as the impedance decreases below 300 ohms.

Great information, many thanks Paul.

[Larpy]

The HA-2 used a 6SN7 as the input tube.  Personally, I much prefer the sound of the 6SN7 in this position to the 12AU7 that the Crack uses.

Pete Millett made fewer than 40 HA-2s before pulling the plug on Wheatfield Audio back in 2000 or so.  He's admitted on other forums that he was “the world's worst business guy.”  I believe he sold the rights to the HA-2 to HeadRoom Audio back when it was Tyll Hertsen's company, but AFAIK no more were made.

I bought one of those original HA-2s from Headroom.  I was shopping for a headphone amp and was looking online at the Headroom amps (made in house) when I noticed they also had the HA-2 for sale.  I don't think anyone else ever sold Wheatfield amps.  Given Headroom's generous return policy, I ordered both a HeadRoom Max and an HA-2, thinking I'd return the one I liked less.  I returned the Headroom Max, even though it had way more resolution and power than the HA-2.  The HA-2 just had something magical going on, the kind of component that sucks you in without drawing attention to itself.

As I recall, the HA-2 sold for $799, $899 for one with upgraded tubes.  I got one with upgraded tubes (Mullard CV378 rectifier, GE 6SN7, TungSol 5998--boy, those were the days).  It was kind of ugly, but very well built.  Almost all of the resistors were Rikens.

I gave away my HA-2 to a friend who now lives across the country, so I've never heard a stock HA-2 next to a Crack, but I have made 4 or 5 of my own versions of the HA-2 circuit over the years.  The latest one uses solid state rectification but keeps the choke.  As much as I love glowing tubes, I have to admit the solid state rectifier sounds better (I tried it both ways).  And I use blue LEDs to bias the input tube (instead of the resistor plus bypassed cap array Pete used on the HA-2: he bypassed the electrolytic bypass caps with 1uF Solen caps).

It sounds really, really good.  Not better than my S3X, but different.  A friend brought his modified Crack over to compare it my own modified HA-2 circuit, and he thought it was a draw.  I wasn't so sure.

I think the 6SN7 plays a big part in why I like the HA-2 circuit so much.  Plus, the 6AS7/6080 tube is pushed harder: 2K cathode resistors instead of the 3K used in Crack.  As Paul points out, that makes for one toasty chassis, so I have a hefty heatsink in mine.  I also decided to use a toroidal PT and choke because I just could not get the Hammond iron I'd been using to be quiet.

[Paul Birkeland]

If one wire is moved in the Crack, the 6CG7 can be used in place of the 12AU7 (the 6CG7 is a 9 pin 6SN7).