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|22nd December 2010, 11:20 PM||#1|
Join Date: Dec 2010
Location: New England
Sound Technology 1700a Voltage Calibration
I'm performance checking a Sound Technology Distortion Measurement system model 1700A. It is contending to be the newest member of my home diy bench. As owners know, the 1700A is part of the same mid-70s family and similar to 1700B, 1710A and 1701A models. My thought: this is more/less equivalent in specs and function to the HP 339A. But is physically big on my bench save my GR 1608A impedance bridge!
Questions follow background
I conducted a Voltmeter Measurement test and find that in ranges 30V and below (did not test higher ranges)...that as a voltmeter, this 1700A reads about 5% high across the scale whereas ST manual states to expect 2% accuracy. It is reasonably consistent across ranges (e.g. 3v on the 10v scale reads 3v on the 3v scale, etc.). While I'm no metrologist I believe the test was fair as it was cross-checked with good a behaving Keithley DMM and HP403B that were in close agreement.
In short, operationally, its all good per the manual. It passed the 8 performance checks in manual (section 3, 6-16). I am able to Set Level successfully, the Adjust CAL control works right and CAL is right on the line. I am able to make distortion readings (measuring itself, the internal oscillator THD+N comes in at .0015% at 1Khz). The Fast/Low light does come on with changes as it should, etc. FYI - the 1700B (AB) manual on the net applies here too (sans B model changes).
I did notice that the oscillator output looks noisy on a scope when *changing* the Oscillator Level (amplitude) control - the Fast/Low light comes on and then off as the waveform settles down and looks clean.
History: The unit was last calibrated in 1993 and is still sealed up. It went into private hands (non-commercial) at that time and probably saw very light use since then.
With the voltmeter slightly high (5% vs. 2%)
1a- will it through off Distortion measurement results? How much/which direction?
1b- will it through off Power level measurements (voltmeter error% squared)?
2a- Does this unit have a noisy oscillator level control pot or is this noise, when changing level, just a feature of these units arising from the design?
2b- if the pot, can one carefully spray with DeOxit or is it a sealed/replace-only type unit?
3 - In general, is it OK practice to use DeOxit on the Input & Ratio (rotary switch) controls and pot controls but not advised to use DeOxit on any of the pushbutton assemblies?
I know this is a big read - but wanted to put this out as there's not a lot of discussion on maintenance and evaluation of ST units.
Thanks in Advance!
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