Another bride of zen completed!

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Kermit

Kermit

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Joined 2002
#1
It has been more or less finished for some time to be honest. It just takes some time to do the last finishing touches. Once sound comes out, the will to finish the last bit on the exterior tends diminish by the joy of listening. But with the rainy summer we have had in Oslo so far, there has been plenty of time to finish the last 5 % one some long overdue projects.
I’m attaching a few pics if anyone care to see.
 

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#2
On the inside there is a relay volume control based on that discussed in the “constant logarithmic volume control” thread. It’s controlled with BCD that also controls the display. It’s a bit “prototypish” but it works very well.
 

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#5
Last picture. From the making of the front panel. All cutouts made with router. It doesn’t show well on the pictures (poor camera, even poorer photographer), but the knobs are countersunk in the front panel.
 

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#7
Kermit,

Just... Wooow.

Very nice looking preamp for a lush sound...

And nice idea for the router. What type of "mill head" did you use ? A one made for wood, or a special one ? And what about the rotation speed ? AFAIR, wood routers spin far too fast for milling aluminium, no ?

BTW, very very nice work. Hope you will have some more rain to complete other nice projects 😀
 
#9
You can make a template and use bearing tipped carbide cutters to make the final pass with the router. And it leaves a very nice edge if your template is smooth. I freehanded a cutout in 1/4" aluminum with a 3/8" carbide mortice bit with beautifull results, then used a chamfer bit to relieve the edge. It take big balls and a steady hand, but the lack of grain makes it quite predictable.

Beautiful work by the way.
 
#10
Like Brian says, a template or straightedge and bearing tipped bit is the way to go. Any bit of decent quality works, but the router must have variable speed, as it needs to be set to a slow speed. Use some scrap pieces to find the speed that works best. Use WD-40 or similar as lubricant. Wherever possible I remove most of the cutout with drill and hacksaw. If working with thicker pieces I screw the template to the backside to make sure it stays where it is suppose to. Clamping the workpiece securely is very important, as any slip can make the bit “dig in” to the aluminium and snap off. Don’t ask how I know..

Alain, here are some details about the preamp:
Chassis is 3mm aluminium except for front witch is 6mm. Top and sides painted with etch primer and spray painted with black acrylic auto paint. All parts finished with clear auto top coat. Separate 9 and 12 volts power supply for logic and relays. The heart of the controller is 3 bcd counters. 1 for input selector and 2 for volume control. Display is made up of 2 dual 7-segment displays. The relays and resistor network is arrange like described in this tread http://www.diyaudio.com/forums/showthread.php?s=&threadid=21198&highlight=

If you want to know more I could try and post schematics, just have to dig them up and perhaps clean them up a bit.
 
#11
And don't try it with a POS 1/128 HP 2 amp Black and Decker toy router from Wallmart. You need a real tool with 8 A or better motor. If you don't have variable speed, you can use a variac and run it at 75% voltage, and let the speed droop a bit. Give it some cool down time while running too.
 
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