Bottlehead Crack - Coppermine Edition

[4krow]

    Surely, I dont have to tell you how impressive this is to me. That is bec ause, I think that copper and brass are two of the best to use for  making a statement. First, I just have to know how long this project took to build, and I would beIbeInterested in knowing where you sourced the copper plate.

 

[HF9]

    Surely, I dont have to tell you how impressive this is to me. That is bec ause, I think that copper and brass are two of the best to use for  making a statement. First, I just have to know how long this project took to build, and I would beIbeInterested in knowing where you sourced the copper plate.

Agreed, copper and brass are attractive metals, aren't they? I actually went through this project a little faster than typical as I had all the parts on the ready. It took a month and a half in total. In regards to hours, I'm afraid I didn't keep track. Maybe 30-40?

If I recall correctly, the copper plate was either a third party seller on Amazon or eBay. It was 12" x 12" x 0.1". I based the design on 12x12 so I wouldn't have to cut the metal plate in a straight line, although I'd imagine that could be done by the average metal shop.

 

[4krow]

If I were a rich man,  I would have the copper plate machined with all of those little maching circles that you see in watchmaking. But I guess that his would never end. A little is good too much gets goofy fast.

 

[vikingtap]

Hi Hf9:
  A quick question if i may. Can you let us know exactly what resistors you substituted and with what values? I see you replaced ALL with Kiwame/Koa 2 w. But some of the resistors in the speedball i cannot find a direct/equivalent replacement. I dont want to blow something up by inserting a resistor with either TOO little or TOO much resistance as i dont know what might happen?
  Any comments would be very much appreciated.

regards

 

[HF9]

I have a number of koa speers that I bought back when they were cheap at Mouser, so I don't really think much of using them, but as they are hard to come by now and the cost is $1+ each, I may not have used them so indiscriminately. As Koa's have a 2% or so variance, I measure the ones I have and pick out ones that are closest to the value in the kit. An example is that the kit might have a 237ohm resistor, but I have some koas rated 240ohm, so I measure a few and get one that's the closest at 238.5ohms, and all is well in the world.

 

[vikingtap]

Ah i see. So lets say i want to replace a 33k resistor and i have one that measures 32.1k and one that measures 33.9k, which one would be more suitable? is it better to go with LESS resistance or MORE resistance?

Thanks in advance.

 

[HF9]

There's no set rule of thumb. I personally like to make sure my resistors are within 1% of whatever the kit calls for, however you have to speak with someone from Bottlehead to find out which resistors can vary within the circuit. It depends on the position and their purpose. Generally tube amps can have greater variances in resistor values. Back in the day, carbon comps were as much as +/- 10% of their marked value. Now, with high speed op-amps/transistors in solid state designs, the values need to be much closer.

I'm pretty sure someone already asked about each resistor value position varying in the Crack, it may be worth a search first.

P.S. Bottlehead selects ideal resistors depending on their purpose, (e.g. carbon comp, carbon film, metal film, etc.), so unless you've GOTTA have boutique resistors in there, the ones that come in the kit are already very suitable

 

[Paul Joppa]

Best to ask on the forum if you want to use different or lower precision resistors. For example, I specify metal film for a lot of resistors, but sometimes it's because they are 1%, and sometimes it's because they are quiet even though 5% would be fine.

 

[Shappers]

Really inspirational build again, beauty and performance all wrapped up together.  8)

I would love to hear what you think of the sound once you have some hours on it. I really love the big oilers but my choice of bypass was perhaps not the best I made.

Glad I logged in today, lots of great projects to catch up on 

 

[4krow]

  I looked at your project in DIY site. You are as good a writer as a builder. I enjoyed reading about different parts of the process. In the layout of the top plate, do you find it a challenge for things to line up properly, or is some amount of fudging ok? Also, I would think that a milling machine would be the ultimate for this process.

 

[HF9]

Hi Greg, glad you think the writing is okay. I've never been the greatest writer, but I get by

I like to use a ruler and a thin sharpie to try and line everything up on the chassis as best I can. Sometimes, even with a drill press, things don't line up perfectly, but I chalk that up to the "beauty" of hand-made electronics, where things aren't perfect, but you can visually tell that a lot of work went into them.

 

[adamct]

HF9,

I saw that you used GreenLee punches for the Neutrik plug, and Dremel cutting disks for the rectangular holes for the IEC and transformer. Can you provide a little more detail around your choice of tools for these tasks?

I will be building an amp where I am creating the chassis plate out of 0.08" aluminum.

I bought a Proxxon rotary tool and have cutting disks for it.
I bought these drill bits for smaller holes.
And I was planning on using these hole cutters for larger holes (Neutrik jacks, etc.).

Any thoughts on whether these are appropriate tools? I am also hoping to do some engraving on the chassis plate, using the Proxxon tool with engraving bits. Any advice/tips/watchouts you have would be welcome. This will be my first time attempting a task like this.

Best regards,
Adam

 

[4krow]

Adam,

    I think that the Proxxon tool is a very good idea. It is a heavier duty version of the Dremel. Using a thin cutting disc, you can cut square holes as long as you don't let the disc get away from you. Also, for small holes, a good drill bit with proper bit geometry is probably your best choice. I am curious about the Greenlee punches having the effect of deforming the metal after it has been punched, but I have never tried one. When it comes to engraving, you will find out quickly whether that is your thing or not. It has never been my forte' with tools.

 

[adamct]

I suspect engraving won't be my forte, either. I thought about giving it to an external service, but I figure that if I'm going to build an amp myself, then I want to build the amp myself.  ;D

I picked up the Proxxon Flexishaft, which should make things a little bit easier on the engraving side. And when I ordered my chassis plate, I bought two extras to practice on...I'm about 99.99999% sure I'll need them.

Any advice on: (a) how to avoid letting a cutting disk get away from me, and (b) "proper bit geometry"?

Also, is there any reason by the GreenLee hole cutters can't be used on wood? I know they aren't really designed for wood, but...

Best,
Adam

 

[HF9]

The GreenLee punches are great if you plan on using them many times in the future. Basically you drill a pilot hole, then put the draw stud in the hole (the punch is on one end and the die on the other), then the ball bearing nut is tightened until it punches a nice clean hole in the metal.

A hole punch on a drill press (or a step bit) can be used, but it's not quite as clean or precise. I've found that the D Flange jacks like the Neutrik locking don't have a lot of room for error, a hole that is slightly too big will be visible from the front.

The real drawback re: Greenlee Punches is they are so damn expensive ($60-90 each for typical tube amp sizes). They also make an IEC inlet size (#60031) but if I recall correctly it was $350 bucks  That's why I use a Dremel with cutting disc

GreenLee tools are only for metal. They would probably separate the plies in wood and make a mess if you tried to use them on a thin board. With a thicker board they would likely just get stuck.

This article may help you on tool decisions.

 

[4krow]

I will shoot in the dark as to why I wouldn't think that the greenlee cutter won't work on wood. I will guess that it may splinter the fibers significantly. Seeing how it wasn't designed for wood, I think you should try it on a thin piece first to see how the wood reacts.
  The best advice that I can give about cutoff wheels is not to be in a hurry! Skim the cut line with it a few times, and watch out for when the disc cuts through the metal. Find a position that you can steady your hand as you work the cut, and remember to stay 'straight' on your cut. If you start to arc your cut, that's the most likely time for the disc to grip the sides of the cut and take off.
  As to bit geometry, make sure that you have a sharp bit, and that the cutting angle of the tip is 85 degrees. More importantly, don't use a bit with outrigger teeth as these are designed for wood only. The side flutes of the bit don't matter as much, but there are some designs that are raised and really like to grip the sides of the hole, making the bit climb into the hole quickly. I suspect these bits are designed more for drill presses that you would have the object clamped down in the first place. In some cases, I would use a cutting wax to help the drilling process, but no for aluminum. Brass seems to be it's own lubricant. Steel may need a little more patience to drill.

 

[adamct]

HF9: Thanks. I just read through the article and it looks like I have most of what I need.

4krow: Well, I can't figure out what the cutting angle of those DeWalt bits linked to above is. And what do you mean by outrigger cutting teeth? In any case, thanks for the tips.

I picked up a drill press last weekend on Craigslist for $125, so I'm hoping I'll be in OK shape...

 

[adamct]

I just realized I can use my spade bits for drilling the larger holes in wood...so no need to try the GreenLee hole cutters.

Thanks,
Adam

 

[Grainger49]

I hadn't posted before, sorry life is busy.  This is a beautiful execution of the Crack.

Your finish was so smooth that I thought it was a copper top plate.

Congratulations on a beautiful build.

 

[4krow]

  The typical angle for a metal bit is 85 degrees. There are some used in machine work are 105. I actually like those best, but they are not so common.

  Let me try to steer you away from the spade bits, unless you don't care waht the edges of the holes look like. They are great for plumbers, electricians and carpenters, but a no no for woodworking.

  The outrigger teeth that I was mentioning are used on some brad-point bits designed for woodworking. If you go to Lee Valley tools, they have a great selection of quality bits of all kinds. Worth the time to look. They also have an explanation for each type of bit that is useful.