Archive | March 2014

Farmhouse Table

This one’s just a quick post to show off my experience with the Farmhouse Table plans from Ana White’s page. It’s a nice, straightforward design which goes together reasonably quick and uses affordable lumber (in our particular locale).

The one tip I’d have for building this table in Ontario is that if you’re buying box store lumber (Home Depot, Lowes, etc) be careful about selecting the right stuff. The cheap framing lumber that works for this table is usually “SPF”, which means it’s a potential mix of spruce, pine or fir. When I bought the stuff for this table it was all quite nice pine, but I know that in previous years they’ve had lots of ugly, cantankerous spruce. Haven’t run across fir yet…. in any case, I’d recommend purchasing some samples before you get started and ensure it’s the good stuff, and that it’ll retain it’s shape well.

Another thing I would consider if I was building again, would be to trade the 2×6 table top for a 1×6 or some other 1xX wood. The 2×6’s are extremely solid but man does it ever make this thing heavy! The table top alone it over 100lbs. It was quite a job getting this thing in from the garage.

 

Anyhow, here are some pictures.

Joinery

Table Top Being Joined

Table Top Pre-Finish

Table Top Just Prior to Staining

The stain I picked was Minwax Jacobean, it was a nice dark stain that matched the decor in our dining room reasonably closely. It does a really good job of disguising the cheap lumber in this piece, although the more woodworking I do the more I am learning that what adds the most value in a piece is the amount of time spent on the finish. An unfinished version of this table can be whipped together easily in one day, but to get this looking like something I would want in my dining room took well over a week of sanding, coating, and drying cycles.

Top Stain

Table Top With First Coat of Stain

Legs

Table Legs Being Stained

Table

Finished Product In It’s New Home

 

Bench Amplifier

I’ve been working with some AD9850 ebay modules that are serving well as function generators, but they’re a bit limited output power wise. I needed something to boost its signals into the 1/4 to 1/2 watt range and the designs at SM0VPO’s page look to be pretty close to what I need.

Building off the design posted at the very bottom of the page, I’ve come up with my own board based on SMT parts because apparently I have a masochistic need to work with 805 components, but also because it would meant that even with the clumsiest layouts I could still fit it into the small die cast aluminum project boxes that I like.

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Using the toner transfer method and the HCl+H2O2 DIY etchant process I had the PCB laid out in just a couple hours, it’s not the prettiest board but it should do the job. I’ll post the eagle files at some point for anyone who’s interested… though it can very likely use some optimization… 🙂

Part placement went not too but there was one rather significant hangup. I had two types of transistor on hand, some BC847 and some 2SC4081. I thought I was placing the 847s, which would line up with SM0VPO’s design, but it turns out I was actually placing the 2SC4081s. This might have been a waste of time but I figured it was worth a go.

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When the board was fired up and fed a 1Mhz signal it did manage to amplify but it had a pretty distorted output. With the biasing set the way it was it seems like these little chips weren’t able to do what I was asking of them.
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I ended up swapping out these little guys for some higher power capable 2n4401 chips that I had to scrounge around for. I also added a pot for the biasing on the input transformer to see if I could tune in a little better. The emitter resistor also needed to be changed out. The value stayed the same but it turned into a 1/4W axial style in order to better deal with the power dissipation, even if only during my messing around with biasing values. Perhaps on revision 2 I might actually get a full SMT version of this amplifier, but this will do for now.

Here’s the whole package put together and in it’s new home.

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With a 0.5 Vrms input I get about 3.3 Vrms output (both into 50ohms), so that’s not a bad performance for a rev A boards I’d say 🙂