On 23/05/2019 1:20 PM, Scott Dorsey wrote:
In article , Mike Rivers wrote:
On 5/22/2019 1:17 AM, geoff wrote:
Looks like the unit natively runs on a RC-based local oscillator.
The 60Hz mains frequency (x2=120Hz) is only used for the 'Calibrate'
function, and the unit can be calibrated equally well from a precise
musical-note tone.
Did you find a schematic somewhere? I seem to remember mention of a
synchronous motor driving the strobe disk, but that might have been
another model. Seems reasonable, though, to be able to adjust the speed
of the strobe disk so you can "zero" it on an off-pitch piano or an
orchestra that likes to play to an A different from 440 Hz.
Yes, the ones I have worked on have a synchronous motor, both the tube
ones and the earlier solid state ones, but I haven't worked on any of
the current models. I'm a bit worried about how much an RC oscillator
would drift, but as long as you check it every time you use it, why not?
You could still cal against a 50 Hz signal, it would just be a different
note.
--scott
Motor driven by the local RC oscillator.
The dedicated CAL function expects a 60Hz mains, but it can be
calibrated from any known source without switching to 'CAL'.
Schematic and parts list are in the user manual ( !!! ).
https://www.dropbox.com/s/bytbnzbvt0...anual.pdf?dl=0
Stability is/was good enough for many significant studios and
musicians/bands/orchestras. But they do warn to calibrate for every
session....
If the mains transformer can't be jumpered for 220vac, I will get a
replacement (available) and find the Rs and Cs to change for 50Hz. And
may as well change all those old resistors with 1% all around, and recap
for good measure.
geoff