Crack;Bottlehead OTL
Aug 23, 2016 at 9:57 AM Post #7,846 of 11,276

Bacci

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  Hi. 
 
Did anyone do this mod: 
 
http://bottlehead.com/smf/index.php?topic=2946.0
 
Who would mind photographing it, as I can't really understand exactly what is required. 
 
Also sorry I haven't read through the 523 pages of this thread, but is there a consensus on what valves to buy as a must-do upgrade. I am not particularly budget sensitive but also don't want to spend stupid money either. I guess max $100?
 
It would need to be plug and play though, I am done soldering my unit for a while.


It's not really an upgrade mod, just a precaution to avoid DC offset on your headphones in some situations, like when you plug them in right after turning the amp on. 
Solder the three pins on the outside of the headphone jack (facing away from the 12AU7, the side where there are 2 unused pins), together.
 

 
Aug 26, 2016 at 5:39 AM Post #7,847 of 11,276

audiojun

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Does anyone have an 5998 tube for sale? I am mainly interested in a tube that will lower the output impedance of my crackatwoa.
 
Sep 2, 2016 at 4:58 PM Post #7,850 of 11,276

buke9

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Anyone looking for an unassembled kit, pm me!
If you would have posted it a day earlier I would have bought it . Bought a already done one really wanted put it together myself.
 
Sep 8, 2016 at 3:47 PM Post #7,852 of 11,276

audiojun

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I built the crack sold it and built T3 then bought a crackatwoa.

The crackatwoa sounds just like the crack, but it is a much lower in noise with the tube shunt regulator and with a better power transformer. Like the crrack it gots a good midrange harmonics easy to listen to, but the treble is a veiled and the bass is too bloomy (in comparison to T3). Although I can change the sound with modifications, but I found it sounded that way with all the tubes I had. I have a 7802 tube coming, higher transconductance than a 5998, 3 times higher than 6080, it should lower the output impedance from 120 to 42 ohms with the 7802 tube which would probably make the crack sound much better.

Currently I am trying to get the Crackatwoa to sound like my Torpedo III while preserving that midrange musicality, while I am trying to get the Torpedo III to have a rich musical tone like the crack.

If it was my money I would modify the HD800 (super dupont resonator with absorber) and get a Torpedo III it is much more linear, powerful dynamics, fast transients, tight bass, crisp treble. The crackatwoa though still has the musical midrange which I prefer over the Torpedo III. Although I heard the T3 isn't available no more as a kit. I haven't fully modded my crackatwoa yet so my impressions may change. Though if never heard the T3 I would be very happy with the crackatwoa.
 
Sep 8, 2016 at 4:09 PM Post #7,853 of 11,276

NightPhotograph

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I built the crack sold it and built T3 then bought a crackatwoa.

The crackatwoa sounds just like the crack, but it is a much lower in noise with the tube shunt regulator and with a better power transformer. Like the crrack it gots a good midrange harmonics easy to listen to, but the treble is a veiled and the bass is too bloomy (in comparison to T3). Although I can change the sound with modifications, but I found it sounded that way with all the tubes I had. I have a 7802 tube coming, higher transconductance than a 5998, 3 times higher than 6080, it should lower the output impedance from 120 to 42 ohms with the 7802 tube which would probably make the crack sound much better.

Currently I am trying to get the Crackatwoa to sound like my Torpedo III while preserving that midrange musicality, while I am trying to get the Torpedo III to have a rich musical tone like the crack.

If it was my money I would modify the HD800 (super dupont resonator with absorber) and get a Torpedo III it is much more linear, powerful dynamics, fast transients, tight bass, crisp treble. The crackatwoa though still has the musical midrange which I prefer over the Torpedo III. Although I heard the T3 isn't available no more as a kit. I haven't fully modded my crackatwoa yet so my impressions may change. Though if never heard the T3 I would be very happy with the crackatwoa.


Thanks for sharing your opinion on Crackatwoa. I was worried that Crackatwoa would loose that warmness of Crack that HD 800 really needs for the sake of a blacker background. Now, I think I will go for it. I believe T3 is quite bright which might not be a good match for the HD 800 though very resolving.
 
Sep 9, 2016 at 9:09 PM Post #7,854 of 11,276

audiojun

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Thanks for sharing your opinion on Crackatwoa. I was worried that Crackatwoa would loose that warmness of Crack that HD 800 really needs for the sake of a blacker background. Now, I think I will go for it. I believe T3 is quite bright which might not be a good match for the HD 800 though very resolving.

 
Crackatwoa is a good choice actually, for people who care about mids and musicality. Torpedo III will beat you up with the dynamics it throws at you. When matched with the HD 800 it's playing to the strengths of the HD 800, showing off it's dynamics and transient response just something that needs to be experienced imo. Probably need to be paired with a modded HD 800 because of brightness like you said.
 
My Crackatwoa sounds amazing right now, rolled a 7802 Tung-Sol and wow it's flexing it's muscles, it's probably getting closer to the T3 in dynamics. Tighter bass, more crisp treble, beautiful mids, sound stage is big, vocals are beautiful and come to life. Also I have an output impedance about ~42 ohm thanks to that 7802 tube. Still need to replace the stock output capacitors, should be able to get the parts by next week. Also no twoquiet stepped atteunator yet.
 
Sep 10, 2016 at 11:28 AM Post #7,855 of 11,276

Doc B.

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I suspect your output impedance is not quite that low. The current in the Crack circuit is low enough that CF output impedance calculations using the published tube data tend to be too optimistic. My SWAG would be it's probably more like 70-80 ohms. That's still a nice improvement from a 6080 and certainly should be audible, especially on lower impedance cans.
 
You have the dubious honor of now having contributed to driving the price of 7802s into the stratosphere like the 421A and 5998. Welcome to the club, I've done that with 5998s, 6DN7s, NOS mesh plate tubes, reel to reel tape decks, prerecorded tapes, and a few other things over the years. Unfortunately I have never been smart enough to stockpile the item I have been enthused about before announcing my enthusiasm.
 
Sep 10, 2016 at 3:20 PM Post #7,856 of 11,276

audiojun

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Yeah probably not that low, but it does have triple the transconductance of 6080.

My 7802 was cheaper than an 5998. Probably would be good to stock pile a few 7802 since I could see these are going to be very expensive in the future since I could only find one seller with it in stock.

Doc I am wondering if it's possible to drop the impedance even more? I know its possible to lower the impedance by lowering the cathode resistor value, but crack is CCS loaded so I am not sure what to do on the CCS.
 
Sep 12, 2016 at 3:23 AM Post #7,857 of 11,276

NightPhotograph

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Crackatwoa is a good choice actually, for people who care about mids and musicality. Torpedo III will beat you up with the dynamics it throws at you. When matched with the HD 800 it's playing to the strengths of the HD 800, showing off it's dynamics and transient response just something that needs to be experienced imo. Probably need to be paired with a modded HD 800 because of brightness like you said.
 
My Crackatwoa sounds amazing right now, rolled a 7802 Tung-Sol and wow it's flexing it's muscles, it's probably getting closer to the T3 in dynamics. Tighter bass, more crisp treble, beautiful mids, sound stage is big, vocals are beautiful and come to life. Also I have an output impedance about ~42 ohm thanks to that 7802 tube. Still need to replace the stock output capacitors, should be able to get the parts by next week. Also no twoquiet stepped atteunator yet.

Eventually, I decided to get Crackatwoa for my HD 800. Doc says this kit is not recommended for inexperienced builders and they are better off with Crack. Since Crackatwoa would be my first DIY project, I'd like to know whether it's just going to take more time to build or its soldering needs better techniques. 
 
Cheers
 
Sep 12, 2016 at 11:52 AM Post #7,858 of 11,276

Doc B.

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It just takes more time to build than a Crack, and some PC board soldering. So it's sort of like a Crack with Speedball, but with more parts. I've seen guys who never picked up a soldering iron build stunning amps, and guys who brag about being experienced technicians completely screw them up. A successful build is much more about exercising patience and following instructions than having any particular skill or level of experience.
 
Sep 12, 2016 at 10:32 PM Post #7,860 of 11,276

jamesino

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I currently have an HD 650 with Magni/Modi 1 and am looking to purchase a used, pre-built BH Crack + non-installed Speedball.
 
I have zero soldering experience and no tools.
 
If upon audition I find that the BH Crack works, how likely is it to break several months down the road?
 
Is there anywhere in NYC where I can bring the BH Crack and ask someone to install the Speedball upgrade for me? Any idea how much this typically takes and how much it would cost?
 

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