I've come a long way: my modded crack build

[carlman14]

Hey all, I just wanted to share my modded-out crack build. I've come a long way from where I was at a couple years ago when I originally put this together. Building and modding this amp has become very addictive. I've learned so much about amplifier design in the process, and this has led me to take on other projects such as restoring vintage HH Scott amplifiers. So thank you to bottlehead for being the start of what is now my favorite hobby!

Here's a list of the mods I've done on it:

- speedball
- stained/finished base
- film output caps with bypass caps
- film cap for last psu cap
- 24 step goldpoint attenuator with vishay dale resistors
- Schottky rectifier diodes
- choke
- integrated khadas tone board with usb-c input on the top panel (It's an all-in-one unit now!).
- toggle switch for switching between onboard dac and an external dac.
- Rewire circuit for two 6J5 tubes instead of the 12AU7

Were all the mods worth their money in sound improvements? No. But did I have fun and learn a lot? Heck yeah!

[ALL212]

Nice!  Did the 6J5’s do anything for you?  Been tempted...

[Deke609]

That's awesome. Nicely done!

cheers, Derek

[carlman14]

Nice!  Did the 6J5’s do anything for you?  Been tempted...

I can definitely hear the difference between the different 6J5 pairs I have, but I'm not so sure about 12AU7 vs 6J5. There was a decent chunk of time between listening to the 12AU7 and the 6J5's, so I'm not 100% sure how different/better they sound. I'm considering wiring it up so I can use either the 12AU7 or the 6J5's (right now the 12AU7 socket is not wired up). If I do that, I could probably do a more direct comparison.

Honestly the motivation to do the 6J5 mod wasn't sound improvements... it was quarantine boredom and how awesome they look.

[Colonl_Charisma]

This is one of the coolest builds I have seen! Amazing creativity getting a DAC inside!

[carlman14]

This is one of the coolest builds I have seen! Amazing creativity getting a DAC inside!

Thanks! That's one of the things I love about bottlehead builds. Even after you're done with the stock build, there's still so much fun to be had adding mods to it!

[ipetruk]

Cheers, nice build,

I've also embedded Khadas, but vertically and using half of the third-party chassis for RF isolation. I've also put the coax out. I use Raspberry+Roon on USB, and my computer on coax.

The drawback of this design - heat from the Crack's chassis travels towardas Khadas, let's ee how it can deal with it. It is hot, but I can hold my hand on Khadas chips, so it should roughly be 70C.

Khadas is amazing, I cannot blind test distinguish it with any other DACs I have - Klipch Heritage Amp/DAC and SMSL M500. I have a switch to verify this statement  . I like how it autoswitches between USB and coax. Also this setup potentially allows me to plug linear power supply to Khadas and use only coax for data if I want.