How to lock chassis to wooden frame?

[adamct]

I just recently built a Crack+Speedball. It was my first headphone amp build, and I am addicted. I found building the amp oddly relaxing. And as for the sound...wow! I'm in love.

I really only have a few complaints:

1. I use the Crack in a well-ventilated rack. But the power switch is way in the back, which is awkward for me to reach.
2. The volume control is pretty close to the front tube. Not ideal when fumbling in a dark room for the volume.
3. The power cord socket feels too plastic-y and a bit cheap.
4. The same thing applies to the headphone jack. This was the biggest surprise. I would have expected them to use something more robust.
5. The fact that the chassis lifts up everytime I remove a pair of headphones.

Any suggestions for 4 or 5? I'm particularly surprised I couldn't find anything to address #5 within the Bottlehead forum, but that may just be my inadequate search skills. I've picked up a couple of nylon tabs which I can screw into the wood frame surrounding the chassis plate, and which will then extend over the chassis itself, to keep it from lifting up. But before I drill holes in my frame, I thought I would check if anyone has a better, more visually appealing solution. Do you? I can't believe that I'm the only one this bothers or that nobody else has tried to fix it.

Also, any suggestions for a robus TRS headphone jack?

Best regards,
Adam

 

[jrebman]

Hi Adam,

Several of us have drilled out the chassis and used the switchcraft pro locking headphone jack.

I did drill 4 holes into the top plate on the long sides, glued two cleats to the bottom, inside edge of the base, drilled holes to line up with those in the top plate, installed some #8 threaded inserts and then used some 3" long #8 carriage bolts to bolt the top down to the chassis.

Another appproach, which Clark Blumenstein uses with his plyboo bases is a saw kerf slot that holds the plate in the frame itself.  This works great too

HTH,

Jim

 

[[email protected]]

I've never done it, but thought about securing the top a lot.  I figured the best way might be to fashion some flat triangular pieces of hardwood over each corner and secure them with a nice brass wood screw.  I always thought if I built amp to take to work I would want to do this for safety reasons.  Along with some kind of grate on the bottom.

Love to see what you come up with.

 

[adamct]

Thanks, Jim. I have an almost pathological hatred of locking jacks. Frankly, I just don't understand them. I've never had a pair of headphones accidentally become unplugged, and in any situation where I can imagine it happening, I would WANT the headphones to become unplugged, rather than yanking on the amp and risking damage. The only thing they do is make removing headphones more of a PITA, as it becomes a two-handed (or at best an awkward one-handed) operation.

I already felt this way about locking 1/4" TRS jacks, but my fury has been rekindled recently. I just bought a Woo Audio WA22. For reasons that I can only assume are related to colossal design stupidity, the damn thing uses a locking 4-pin XLR jack, but it doesn

 

[Paul Joppa]

I've never done it, but thought about securing the top a lot.  I figured the best way might be to fashion some flat triangular pieces of hardwood over each corner and secure them with a nice brass wood screw.  I always thought if I built amp to take to work I would want to do this for safety reasons.  Along with some kind of grate on the bottom.

Love to see what you come up with.

Over the years, I think this has been the most popular approach. Some have put in threaded inserts, since screwing into end grain is problematical if you unscrew it very often.  :^)

I think this comes down to the diversity within the Bottlehead family. It started with the hard-core DIY/eXperimenter crowd (of which I am a member), who flip their amp over to check things or make changes so often that any fastening is a hindrance and annoyance. I actually proved this to myself by screwing down a chassis plate on my original S.E.X. amp. Eventually I just threw away the screws ...  :^)  ... but I do understand the impulse!

 

[adamct]

My problem is just that I tend to switch headphones a lot. Right now, the headphone jack grips the headphone plugs pretty firmly, so when I pull on the plug, the whole chassis lifts out, which always shocks me. I don't want to damage the tubes doing that some day. Of course, the solution is to hold down the chassis when unplugging headphones, but my setup makes that a bit awkward. I think I will go with my original idea, and then post pictures when I'm done. Out of curiosity, does anyone know if it is possible to paint/color nylon screws/washers/tabs/etc.?

Best,
Adam

 

[VoltSecond]

In my other Bottlehead gear, after I got it painted and close to working the way I wanted, I used a thick bead of clear silicon glue.  I was careful to make it a surface only bead (not get it in the gap between the plate and the wood) so I could cut it if I needed to remove it.

After the silicon is there, you can't paint it over it.  The corner cleats sounds like a better idea if there is any chance you'll want to take the cover off.

 

[Grainger49]

Someone may have said this before but, you can glue a square cross section piece of wood in the four corners of the base.  Make them flush with where the top plate rests.  Then drill a hole in each corner of the top plate so you can screw the four corners down to the wood you just glued.

This doesn't give any support in the middle of the long side.  So you can glue two other pieces at the center of the long side and drill/screw them to the top plate too.  That is 6 screws and it will hold pretty well. 

Edit: I didn't know how tight the Crack back corner is.  That would make this suggestion less than optimal for Crack.

 

[jrebman]

I too thought about the corners/squares in the bocx corners but there is just so little room left to work with in the corner by the ac power inlet that I finally decided to do the 4 long bolts on the sides.  Clark's solution is the most elegant, though it reqquires removing one of the ennd panels to get the plate out.

Anyway, there are, lots of ways to approach this and as usual, BH folks are  pretty diverse and inventive in their creeativity.

Oh, another one I have planned on trying is to use a variation on the corner block approach -- epoxy some threaded hex aluminum standoffs in each corner and then use some #6 or #8 machine screws into them.

You can typically paint nylon parts with an epoxy based paint but it would probably help if you could scuff up the pieces a bit first.

HTH,

Jim

 

[Paul Birkeland]

A Blumenstein Bamboo base will keep the chassis plate from lifting up.  I generally rest part of my hand on the plate while lifting the plug out.

With some reasonably basic woodworking tools, you could build a base to do the same thing.

There are quite a few different choices of high end headphone jacks.  We chose a Neutrik jack that has a fair amount of flexibility; part of the fun of DIY is that you can change whichever parts you like.  We must also consider inventory when we select parts for a kit, and the Neutrik locking Jacks are not as consistently well-stocked as the other Neutrik jack we use.

There is also a grounding modification that would be impossible with the locking jack, and the stock jack allows for a preamplifier output to be added (if desired) that would cut out if headphones were plugged in.

I've never heard any criticism of the IEC inlet, they seem to have a death-grip on the chassis plate.

 

[2wo]

Not a very good picture but what I have done is drill a screw hole in the wood at the edge of the plate. The washers are i think called countersink washers, meant to be used with flat or oval head screws. Got them at Home Desperate. Or you could just use flat washers, or large headed screws...John 

 

[jrebman]

John,

I belive those are called cup washers.  Great idea though!

-- Jim

 

[STURMJ]

I prefer using silicone calking to "glue" the plate to the base.  The hold is sufficient for plugging and unplugging everything, and even moving the entire unit by grabbing the transformer (but I put a hand on the base ASAP when doing this).  When you want to mess around with the insides, you just push out the plate from the backside, can be a little tricky but never had a problem. Its easy to clean off the silicone and put a new bead in the channel. Also, when replacing the plate with new silicone it wipes up nicely off the wood base and top plate. 

 

[adamct]

The silicone sounds like a good idea. This is what I came up with. The nylon bits and screws were pennies apiece.

Best regards,
Adam

 

[2wo]

I like it. You got that quick disconnect action, perfect for the midnight mod  ...John

 

[ice9mike]

It happened. My top plate with tubes installed fell out of the frame while I was carrying it to my workbench. The 6080 tube was forced out of the socket and chipped the porcelain. The corner of the top plate bent and the 6080 is now unusable (unless you enjoy the sounds of an arching tube that is extremely microphonic).

I decided that a quick secure fastening system had to be developed. Being a mechanical engineer I have access to sample hardware from Southco. They make great fasteners including the quarter turn Dzus bolt. It comes in several styles and is often used on race car hoods and motorcycle fairings. I was able to install the hardware on the Crack frame and top plate.

Here is a picture of the finished product:

A closeup of the Dzus Fasteners with D-ring:

A closeup of the unsecured Dzus Fasteners showing self ejecting springs and plastic washer:

A closeup of the retaining washer under the top plate:

A picture of the frame with Dzus retaining brackets:

A closeup of the Dzus retaining brackets:

A closeup of how the Dzus retaining bracket is fastened to the frame:

Here is a parts list for one connection. Multiply by number of fastening points:

Dzus Bolt - D8-316-413-190
Side Bracket - D8-336-310-121
Plastic Washer - D8-376-001-049
Metal Retaining Washer - D8-326-101-200
Ejection Spring - D4-EHF5-3-950QA
2 wooden screws of your choice

The solution works great and I think it looks appropriate aesthetically. I would caution those with big caps or other components. Make sure the side brackets clear your hardware.

The biggest problem with this solution is that these fasteners are not easy to find. They aren't sold at Ace or Home Depot, and they can't be purchased directly from Southco. They are sold through distributors and may have minimum order quantities. There are some speed shops and online stores that sell similar versions, but they might be different from the part numbers listed above.

This post is really to just put out another possibility for securing your investment in time, money, and dedication. If you love you amp as much as I do, you will understand why I spent more time on this than might seem necessary. Good luck, and I will do my best to answer any questions.

ice9mike

 

[Doc B]

That is awesome. Takes me back to days I used to watch Trans Am racing and all the cars had Dzus buttons holding down the hood.

 

[Grainger49]

That is an excellent idea, and looks good too!

 

[Armaegis]

I decided that a quick secure fastening system had to be developed. Being a mechanical engineer I have access to sample hardware from Southco. They make great fasteners including the quarter turn Dzus bolt. It comes in several styles and is often used on race car hoods and motorcycle fairings. I was able to install the hardware on the Crack frame and top plate.

<snip>

This is slick enough that I would be totally willing to pay the extra few bones for it to be included in a stock kit.

 

[Grainger49]

Well, we are a DIY community.  Maybe someone can find a dealer who will sell pairs of them to the community?  Then on a future run Bottlehead might get the holes cut for those who want a secure top plate.