DIY 2-way switcher for Bottlehead Crack

[larcenasb]

Hello,

I'm planning on making a DIY switcher to select between headphone and preamp use, using spare parts I already have. A small ABS plastic box, a 3PDT switch, RCA jacks for the preamp out, 1/8" jack that'll go to the Crack's hp jack, and a 1/4" jack to connect HPs.

The thing is my 1/4" jack is switched (Rean NYS212). Will this work for a simple switcher? I tried looking up about switched jacks but am still confused. Am I able to just solder left, right, and ground to the left-side solder tabs? Or does something have to be done with the right-side solder tabs still for it to work? Forgive the crude Paint image and thanks for any help.

[Paul Birkeland]

This is doable with the stock Crack HP jack and a pair of RCA jacks mounted into the wood base.

You'd need some new 2.49K resistors.  One would go to the HP jack terminal where the red wire lands ,then wrap the other end around the stripped bit of black wire connecting the sleeve terminals on the HP jack.  The other would go on the HP jack where the white wire lands, then wrap the other end around the stripped bit of black wire connecting the sleeve terminals on the HP jack.

This leaves two empty terminals that are connected together and down to the sleeve in the stock Crack 1.1 build.  Remove the connections to the outer tip and ring terminals so they no longer tie to the sleeve terminal, then you can use these as your preamp outputs.  They will automatically activate when you unplug your headphones.

[larcenasb]

Ah, that'd be a much more elegant solution, no need for a separate box. Thanks, Paul!

[larcenasb]

But I'm still curious, is it possible to use a switched jack in the way I mentioned? Without soldering anything to the right-side solder tabs?

[Paul Birkeland]

If you have a 1/4" cable plugged into the Crack, then you could feed that into a switch box. The other terminals on the jack short the output to ground when there's nothing plugged in (which is why you have to get rid of that to make a preamp out).

Also do be aware that if you are feeding this to some giant DC coupled solid state amp, it will not be happy if it's powered on and you fire up the Crack, as there's a bit of DC offset while the coupling caps charge.  None of our amps, nor any tube amp that I've ever encountered is going to have fits with this, but a lot of the HiFi solid state stuff can't tolerate this kind of turn on behavior.

[larcenasb]

My plan was to--and I'm still considering it--to make a switch box that'll work like this (see attached photo).

I use the Bottlehead as a preamp going to my vintage Yamaha CR-1020 receiver, 70WPC. It is solid-state, but I've always turned on the Bottlehead first, to warm up the tubes, then the Yamaha. So, you're saying I should make sure to never turn on the amp first, then the Bottlehead? Or if the Yamaha is already on, couldn't I flip the switch to "HP out" on my switch box, then turn on the Bottlehead? Thanks for your speedy replies, Paul. You're a legend.

EDIT: Reworded to be more specific...

[Paul Birkeland]

There are plenty of coupling caps in old amplifiers (and especially receivers!), I wouldn't worry about that. 

[Mucker]

If you want a "one and done', "lifetime" preamp, consider a Moreplay. IMO it's a fantastic bargain and superb preamp! I too once considered doing the headphone jack thing with the Crack, but extremely happy going the Moreplay route.

[larcenasb]

Thanks, I'd love to build another kit as well. Steve Guttenberg's review of the Moreplay really had me salivating haha. When funds allow, I plan to pretty much have the ultimate Bottlehead room lol.

And thanks Paul, good to know I don't need to worry about the Yammie.

[larcenasb]

I slept on it and decided I don't really like unplugging and replugging my headphones whenever I want to use the Crack as a preamp, and I didn't want to drill into the Crack at all. So, I made the switch box with extra parts I had (1/8" Crack in, 3PDT switch, 1/4" HP out, RCAs preamp out). I think it turned out really well, and it's so convenient to just flip the switch.

[Happy Ghost]

This looks so cool.. btw what are the tubes you are saying in your Crack?

[larcenasb]

Thank you I'm using a 1950s RCA 6AS7G for the output tube, and a 1940s RCA 6F8G for the input tube. To use a 6F8G, you'll need a 6F8G-to-12AU7 6.3V adapter, which are available on eBay. Cheers

[Paul Birkeland]

The ground tabs on your RCA jacks are not in the right spot, and this could definitely cause some strange issues depending on what's connected to them.

[larcenasb]

Whoops! Yeah, they may not make good contact...with the plastic washer in the way. Thanks, will fix this today!