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Old 13th April 2012, 03:20 PM   #1
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Default Vintage Heathkit Electronic Switch as soundcard interface

I had been looking at a Heathkit ID-101 electronic switch just for an idea to add a third channel to my 2 channel oscilloscope. However after looking at the circuit I ask myself if this thing could be used as a soundcard interface. It has one output (which may be enough) but It probably can be modified to use the two sync outputs for L and R of the soundcard.

I purchased one that is on the way. I will play with it and post my findings.

I wonder if it has good enough specs to be able to do distortion measurements with the PC.
Attached Images
File Type: jpg ID-101_1974.jpg (416.8 KB, 63 views)
File Type: jpg heathkit id-101_0000.jpg (758.8 KB, 54 views)
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Old 24th April 2012, 12:54 AM   #2
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So I received the unit, calibrated it and did some tests with it.

It does what it is supposed to do and it definitely works as a two channel attenuator for the PC using the sync outputs. The main output can be used but it only puts the signals together in the same channel or one at a time. The sync output is ac coupled only.

I ran some tests with Right Mark Audio analyzer (have never done this before). I tested my EMU PRE USB in unbalanced loop mode. Then the output of the EMU Tracker USB to the Heathkit input and then its output to the EMU Tracker USB. I have attached a report from RMAA .

I am confused as to why the noise floor is reported around 30db less that what the graph shows. Possibly I am doing something wrong.

In any case, I think it is an inexpensive way of attenuating signals to use a PC sound card as an oscilloscope. The one thing I noticed with the EMU soundcard is that as soon as I connect the common to ground (rather than floating) the noise floor in the realtime FFT goes to around 100db. The outputs of the Heathkit have common to ground (chassis).

Any Solid State gurus think the noise performance can be improved by performing some simple mods?
Attached Images
File Type: jpg Heathkit comparison.jpg (74.7 KB, 31 views)
File Type: png dr.png (19.7 KB, 26 views)
File Type: png fr.png (12.1 KB, 27 views)
File Type: png ns.png (18.1 KB, 9 views)
File Type: png thd.png (18.7 KB, 10 views)
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