Love the green on the top! Great aesthetic touch!Hi there! I finished building my Crackatwoa last weekend. I can say now the temp isn’t a concern for the sound-deadening material. The top plate gets warm after hours of use, but never hot. I use NVX 90 mil butyl sound deadener.
Also, I wouldn’t worry about the anti-RFI sheeting unless you have serious problems with RFI where your audio gear is. The amp is dead quiet. Separate issue, but it even silences my USB DACs when other amps amplify the hash and buzzing at louder volumes.
Loving the Crackatwoa so far though. I’ll write a detailed comparison between my heavily-modded Crack and the Crackatwoa after a few weeks. Cheers! Oh, and here are some photos in the meantime.
Crack;Bottlehead OTL
- Thread starter ironbut
- Start date
Hi there! I finished building my Crackatwoa last weekend. I can say now the temp isn’t a concern for the sound-deadening material. The top plate gets warm after hours of use, but never hot. I use NVX 90 mil butyl sound deadener.
Also, I wouldn’t worry about the anti-RFI sheeting unless you have serious problems with RFI where your audio gear is. The amp is dead quiet. Separate issue, but it even silences my USB DACs when other amps amplify the hash and buzzing at louder volumes.
Loving the Crackatwoa so far though. I’ll write a detailed comparison between my heavily-modded Crack and the Crackatwoa after a few weeks. Cheers! Oh, and here are some photos in the meantime.
Very nice customization touches, the color, the volume knobs, on/off switch. Well done!
Galapac
1000+ Head-Fier
Well thought out customization. I like how you routed the wires from the RCAs, nice touch!Hi there! I finished building my Crackatwoa last weekend. I can say now the temp isn’t a concern for the sound-deadening material. The top plate gets warm after hours of use, but never hot. I use NVX 90 mil butyl sound deadener.
Also, I wouldn’t worry about the anti-RFI sheeting unless you have serious problems with RFI where your audio gear is. The amp is dead quiet. Separate issue, but it even silences my USB DACs when other amps amplify the hash and buzzing at louder volumes.
Loving the Crackatwoa so far though. I’ll write a detailed comparison between my heavily-modded Crack and the Crackatwoa after a few weeks. Cheers! Oh, and here are some photos in the meantime.
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Gosh, that's so beautiful! Well done. I wish I had the skills...Hi there! I finished building my Crackatwoa last weekend. I can say now the temp isn’t a concern for the sound-deadening material. The top plate gets warm after hours of use, but never hot. I use NVX 90 mil butyl sound deadener.
Also, I wouldn’t worry about the anti-RFI sheeting unless you have serious problems with RFI where your audio gear is. The amp is dead quiet. Separate issue, but it even silences my USB DACs when other amps amplify the hash and buzzing at louder volumes.
Loving the Crackatwoa so far though. I’ll write a detailed comparison between my heavily-modded Crack and the Crackatwoa after a few weeks. Cheers! Oh, and here are some photos in the meantime.
larcenasb
100+ Head-Fier
Thank you, CaptainFantastic, Galapac, and warp2600
A couple members pm’d me asking about what mods I did, so I should’ve posted that here from the get-go. Sorry hehe, but here you go….
- Audio Note balance and volume pots
- Multicap PPFXS 0.1uF 600V RC filter film caps
- ASC LTI 4-5 60uF 500V output film caps (60uF is okay because even with 33uF output caps, 250 ohm headphones will still play down to 20 Hz at -3 db, and below 200 ohm headphones really shouldn’t be used with an OTL amp. Also, these caps are 91% off on partsconnection.com, so at $5 a pop, it was too good a deal to pass up for film caps. Keep in mind these are very large and would need creative mounting to fit in the smaller Crack.)
- Output cap rolling mod: Velcro straps instead of zip-ties, and then spade connectors and flexible cable from an old RCA composite video cable that has been unused for over a decade (I’m going to also use this as a preamp, so caps as small as 2uF will work fine for that… it’ll be fun to try some nice caps at the lower-cost capacitance)
- custom control overlay (quickly designed it in Paint (the Art Deco font is called DK Otago) then had someone on Etsy make a proof, laser-cut the acrylic, then engrave and powder coat the text/numerals. I was surprised it all only cost $25 plus shipping.)
- NVX 90 mil butyl sound deadening to underside of top plate (to reduce user-handling microphonics)
- heavy-duty toggle power switch (with custom-cut hard plastic as a washer to cover the corners of the original square cutout …. plastic was from a container lid)
- Wood base has 4 inner posts for way-more-than-needed sturdiness
- 4 coats of Tried & True varnish oil to wood base, inside and out (lol, this was a labor of love!)
- Power transformer bell cap has 4 coats of automotive-grade Rust-Oleum Custom matte emerald green spray paint
- top plate has 4 coats of Rust-Oleum Universal hammered silver spray paint
- custom rear info badge (for anyone in the future who gets this when I’m gone, at least they’ll know what it is, what tubes are needed, and a little of the company’s history)
- knobs are from AliExpress, solid aluminum, so many to choose from….
- DIY 3.5mm-to-RCAs Canare cable (for preamp use)
- Octal adapters: 6SN7GT-to-12AU7 & 6F8G-to-12AU7 (both 6.3V)
And I think that’s everything….lol, I’m just on my phone and going off memory. Still, not nearly as many mods as my Crack + Speedball. The Crackatwoa really doesn’t need much (only pot and output caps really), the circuit is fantastic and let me tell you the weight of that power transformer is seriously serious. Cheers
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larcenasb
100+ Head-Fier
I think you can get there with practice! If there’s something else stopping you though and you want one of these amps, PM me and perhaps I could build you one for a reasonable fee.
buencamino
100+ Head-Fier
Hi, relatively new owner to a crack... been liking it so far with my HD800S... and gaming with it is great too... maybe just that lately it's been giving me cracks/static at random moments, and I may need to check the solder joints with chopsticks for any incorrect joints... but looking forward to learn in this thread...
larcenasb
100+ Head-Fier
Congrats, you’re getting so much for your money. And many before you have loved what the Crack’s smooth sounds does for the HD 800. Enjoy!
Also, if you’re unable to find out the problem, don’t hesitate to go over to the Bottlehead forum and post in the Crack section. The Bottlehead team are very active there and quick to help. Usually you’ll just have to post your voltage/resistance checks and attach some photos of your wiring/solder joints. Hope you get it all fixed up. Cheers!
Until recently I was having static/squeaking problems in my Crack.
I reinforced all the welds and the problem was solved.
Total silence, even using valves with adapters.
Guys, I'm thinking of modifying my Crack, changing the output caps for the film ones and adding a choke.
Which ones do you recommend and where can I buy them?
Which ones do you recommend and where can I buy them?
larcenasb
100+ Head-Fier
Hey, I was going to let someone else answer, but since you haven't gotten a response yet, here you go:
The brand and model aren't so important here, the main thing is to have film caps, in general, handling the audio signal. The Crack is a simple circuit, so no need to spend crazy amounts. Just make sure the diameter of the caps doesn't exceed 54mm, otherwise you'll have to get creative with mounting. For reference, my Audyn Q4 68uF 400V caps are 52mm in diameter and fit nicely on each side of the chassis (see attached photo).
Here are some of the usual suspects:
Mundorf MKP 100uF 250V 46mm-diameter ~$120/pair (partsconnexion.com)
Dayton 100uF 250V 51mm-diameter ~$80/pair (parts-express.com)
Audiophiler 100uF 250V 50mm-diameter ~$60/pair (eBay)
Panasonic EZPE 100uF 500V 35mm-wide (rectangular cuboid shape, so mounting may be a little odd) ~$44/pair (newark.com)
Also, you can get away with lower-capacitance caps (see attached chart). This will save you space and money. If you follow Bottlehead's recommendation and only use headphones that are 200 ohms or greater, then output caps as low as 47uF will still allow frequencies just below 20Hz to pass at -3 db. Again, I use 68uF caps and notice no bass roll-off with the 300-ohm Sennheiser HD 600 or 600-ohm AKG K240 Sextetts.
Here are some more options:
Mundorf MKP 68uF 250V 43mm-diameter ~$72/pair (partsconnexion.com)
Audyn Q4 68uF 400V 52mm-diamter ~$53/pair (parts-express.com)
Solen PB 68uF 400V 49mm-diameter ~$51/pair (partsconnexion.com)
Audiophiler 68uF 250V 39mm-diameter ~$36/pair (eBay)
Just in case, remember it's recommended that you drill holes to secure zip-tie mounts with a screw and nut. If you just use adhesive zip-tie mounts, eventually the weight of the caps and the heat of the top plate will cause the adhesive to let up and the caps can fall.
For a choke, the Triad C-7X is a common choice .... ~$12 (digikey.com)
If you are wondering more about upgrading, I wrote a whole guide that's gotten buried deep within this thread: https://www.head-fi.org/threads/crack-bottlehead-otl.476650/post-16152725
Hope this helps. Cheers.
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Another option that I used was the KZK white line capacitors 100uf. Very good value for the caps based on their price...BUT...they ship from Russia. I checked on ebay just now and it mentioned the seller is out through dec 31st. Great caps, bad timing. 
larcenasb
100+ Head-Fier
Never saw those before, thanks for the info. I like the clean look of them. But whoa, it says seller is away till Dec 31st, 2030!!Another option that I used was the KZK white line capacitors 100uf. Very good value for the caps based on their price...BUT...they ship from Russia. I checked on ebay just now and it mentioned the seller is out through dec 31st. Great caps, bad timing.
https://www.ebay.com/itm/332678750938
I liked them in my first crack build; inexpensive, clean sound, and weren't so big I had to make a mess of everything. For the already warm crack they're a good choice.
But, again...getting them from Russia...
But, again...getting them from Russia...
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