Future high current upgrade?

[Dr. Toobz]

From what I've read, it sounds like there is a modification to the Crack that makes medium impedance headphones sound much better. I'd love to hear from the Doc himself as to whether or not Bottlehead is planning on making this an upgrade kit for the Crack, whether this would be a worthwhile mod for those of us with "maxed out" Cracks, and how low of impedance headphones will work following the mod. Was the mod using a 5998, or a regular 6AS7?

I'm still curious about K702's. I love my HD650s, but I would be open to getting another pair of phones that has better sound staging - and the K701/2 are always mentioned as the ultimate "soundstage" headphone, if a bit bass shy. Talk of this mod has my interest piqued......

[Doc B.]

So far the mod has worked well, we got a lot of very positive comments about the Crack at RMAF. I need to get our gear back from RMAF before I can further evaluate the mod, and the gear is still in transit. We have quite a few projects on the table right now, so I can't say if or when it might become available just yet.

[Dr. Toobz]

I'll be waiting with bated breath :-)

In the interim, the K701/2 should work well with my SEX amp, if I get too impatient. I've been "grado-ed out" for years, so the AKG's seem to be a logical contrast from the HD650's. Too bad the HD800's are so much money!

[Dr. Toobz]

As luck would have it, I found a pair of like-new AKG's for about $200. Once these arrive, it will be interesting to compare them on the SEX amp vs. the Crack (with Speedball, 5998 output tube and 100uF film capacitors). Having to temporally part with the Speedball isn't a deal-killer to me, so I will likely be first in line for the high-current upgrade kit, if and when it is released.

If the AKG's end up not being to my liking, at least they have good resale potential!

[Dr. Toobz]

Any updates on how the high current modification is holding up? Still curious to hear what the AKG's would sound like with an OTL amp like the Crack....

[grufti]

I sent Doc B email about the higher current version a couple of weeks ago, but haven't heard back. It's something that I'm on the verge of trying by myself, but I would prefer to benefit from the Bottlehead know-how, wisdom and testing.

It should be possible to have a modified version of the Speedball upgrade in a higher current Crack. Let's wait and see what will happen on this front.

[Doc B.]

Ah, project Crack-a-two-a. It will probably become a Rev2 kind of thing, as we will also replace the power transformer and maybe do some other stuff to adjust layout and such. As far as the prototype is concerned, it is still holding up very well, but it doesn't really have that many hours on it yet. It's done most of its cooking at Head-Fi meets.

[lextek]

So what headphones would thi be aimed towards?

[Paul Joppa]

I don't think the recommended headphones would change much.

[BNAL]

Here is the $64, 000 question.  Will there be an upgrade path for the current Crack?

[Doc B.]

Here is the $64, 000 question.  Will there be an upgrade path for the current Crack?

PJ and I just had a meeting about this last week. The high current prototype layout is a bit of a kludge on the existing Crack chassis. When we started to look at the way the layout would need to be changed to better accommodate the parts required for the new design we realized that we should probably revise chassis to the 8 x 10 format, change over to the PT-7 as used in S.E.X. 2.1, and design a new board for the Speedball that will accommodate the larger heat sink we use in the Eros power supply. So I think this will be a Rev 2 kind of thing.

It may end up being possible to install the new high current Speedball board in the existing kit, but I'm not sure as we haven't gotten that far yet. It might be so big as to interfere with beer can sized output caps on the current chassis. I've seen a few of our very early Bottlehead kits come across the bench this year, that got chopped and channeled and lowered and louvered as we offered mod after mod over a several year period. It can get pretty scary under the hood, and sometimes it think it might be better to start fresh as we did with Foreplay III.

[Dr. Toobz]

If you do end up testing the Speedball for the Rev2 unit on the original circuit, I for one would be more than willing to give up the "beer cans" for more current with medium-impedance cans when using a 5998 as the output tube. My AKG's, which I've turned out to like better with time, just need a bit more "oomph" to sound good on the Crack, even with the 5998 and presumed 70 ohm output impedance.

The HD650's I usually paired with the Crack started to bore me after about a year and a half, and have been sold. But, this leaves me with no headphones that match well with the Crack, at least for now.

[grufti]

The way Doc describes it bodes well for me too. I already have a second transformer for the filaments taking some heat off the Crack's iron. The extra power supply circuit takes up some real estate under the hood, but a lot less than most "beer can" capacitors. The Speedballs' territory is still wide open. So yeah, I'm definitely looking forward to the extra oomph. I hope it comes soon.

[Paul Joppa]

I spent part of today working on the layout. There may be just enough room for the new boards, with new holes to mount the larger output board. But it's wide, leaving room for caps that are no more than 1.5" diameter. (Hence the larger chassis, for up to 2.5" beer cans.) Anyhow, this is all preliminary and subject to change.

Personally, I would start with bypassing both the output caps and the last cap in the power supply - bypass caps can be smaller, and I think the PSU cap is equally important.

Stock layout is looking very similar - I don't want to stray too far from an already very successful design. The new cathode resistors (if you don't get the Speedball) are going to be big, and hot!

I gotta say, now that I'm digging into it, kudos to PB (Caucasian Blackplate) for a robust and flexible original design!