Monday, January 2, 2012

Sample & Hold Complete!

Although I finished this (and the Voltage Follower) before I got the VC Trigger Generator working, I decided to wait until the latter was functioning before I posted these.  Here's my completed banana-fied S&H!

Things are a bit crowded on the front panel with the switches, but I figure that the switches & knobs on the S&H aren't used a whole lot once a patch is set up.  (At least based on my experience with other S&H units.)  I took off the large tabbed washers from the NKK switches, because they protruded just slightly from the edges.  Obviously I could've ground them down, or just made sure to put the S&H in the cabinet first, but they aren't critical, so it didn't seem worth it.

No calibration is required on this module, and both circuits worked just fine.  I've tried triggering it from the VC Trigger Generator, and even just a banana cable connected to ground.  The grounded banana was a bit wonky, since the input isn't debounced, and you'll accidentally trigger it 2-3 times - but it worked!  I initially tried testing it with my DMM, but the output wasn't steady at all (I'm not sure why) - everything showed up fine in the oscilloscope, though.

You'll notice on this (and the VC Trigger Generator) some of the MTA headers are unused - those are for the V-Triggers that I'm not using.

The boards are designed to be used with switching jacks for the inputs, with the switch lug attached to the internal "noise" generator.  I've used a SPDT switch instead, with common attached to the signal input, and the ends attached to the internal "noise" generator and the jack, respectively.  I didn't try it with an external signal, but considering it works from an internal source, there shouldn't be a problem.

I've called it the "internal 'noise' generator" because (to my surprise) it isn't actually a noise generator!  Instead, it is actually a ramp oscillator (based off of a UJT) running at approximately 12kHz. It is going fast enough where you'll get something that is effectively random. There's two of these on-board, with one for each S&H, which is nice, so you won't have the output correlated between the units.

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