paradigm shift

i was able to accomplish two main things over the 2009-2010 holiday season. one was to build an ampeg b-15 preamp for use with a tube power amp that was just lying around. the other was to learn a bit of 3d mechanical design.

when i build the b-15 preamp, i had made a few mistakes. once again, i failed to plan enough clearance between the turret board and the input jacks (circled in green). i had to chisel away part of the circuit board board to get it to fit.

i had it all roughly sketched up on graph paper. this has been my quick and dirty method for laying out an amp chassis, except when i want to change anything i need to take a new piece of graph paper and start all over again.

3d mechanical design is changing all of that for me. i signed up for a 30 day evaluation of alibre design, a low-cost ($97 usd for the standard package) 3d design and 2d drafting solution. this 30-day evaluation is actually of alibre professional which includes sheet-metal capability.

i started by creating a sheet metal version of the chassis i used for my ga5f1 build and punched all of the mounting holes in it. then i started modeling each of the parts that went into the amp and assembled it. cool. now i have a 3d model of an amp that i have already built.

now when i did my layouts for the ga5f1, i used a graphic aers program as a 2d cad program. it was very time-consuming it took me hours to create the parts and incorporate them into a layout.

i took my sheet metal chassis model and created a 2 dimensional drawing from it of the front panel layout. i printed it off and it was precisely to scale. it took me only a few minutes to do this. i could easily use this template to drill a front panel on a new amp with accuracy.

nex,t i thought i see just how much time this software might save me. i recently bought another vox pathfinder amp to build a 5w version of the vox heritage amp line into. i looked for a chassis that would fit without modification, but i could not find any. so i took some dimensions from the original pathfinder chassis, translating all the mounting holes to a 3d sheet metal model. now i had a 3d model of the blank chassis i needed. i imported this model into the 2d design, added dimensions, hole centers and callouts as needed. now i had all the information a metal shop would need to fabricate the chassis for me. this entire process took me 10 minutes and 35 seconds!! (yes i timed it)

in the meantime, i've had an opportunity to take a 3d modeling training class at work and i've been applying what i have learned on the design of a 100 watt(ish) b-15 that i am helping a coworker build.

this has been an amazing experience. i am using a blank jtm45 chassis for the build and have to do all the chassis work myself. i modeled up the chassis and have been modeling up parts as needed. this has been a complete lifesaver! i have identified many mistakes that could have been disastrous to the amp build. now as i find these, i can make adjustments to eliminate them. here are two examples:

1. over the holidays, i had my coworker build and stuff the turret board for his amp. i had provided 4 mounting holes on the layout for the turret board. when i modeled these mounting holes and placed them in the blank chassis, it became clear that two of these mounting screws would interfere with the output transformer. now, i could have simply offset the transformer from the chassis using an extra nut. instead we identified 2 alternate locations for the mounting holes which, after adjusting the position of the output transformer gave us enough clearance.

2. the power transformer we are using is quite large for a jtm45 chassis. the transformer was modeled to be mounted near the power and standby switches. after inserting the models for the switches and power transformer into the assembly there was clearly going to be interference, and in a bad way. i moved the power transformer more near the power tubes until there was about 1/4" clearance between them, but the switches wouldn't fit. Looking closer at the switch datasheet, there was a switch available with solder tabs that were shorter than the quick disconnect switch contacts. i updated the model to reflect this and gained the clearance i needed. tragedy averted again!

i would highly recommended taking the time to install and check out the trial version of alibre design. if it saves you time as well, buy the standard version. i did and i feel it was well worth it!

here is the current (not completed yet) design of the b-15-100:

once the mechanical design is completed i'll just need to print out drill templates, order parts and start building!

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