Conn tuner
On 20/05/2019 12:08, geoff wrote:
Anybody know the power/current consumption of an ST-11. I have a USA
version coming and will need to build or source a 110v 60Hz
inverter/whatever supply to run it from 230v 50Hz.
Doesn't mention the power spec in the manual, though it does have
schematic and component list !
geoff
I've just looked at the circuit diagram, and it seems the unit works by
using a local RC oscillator, which is divided in frequency under the
control of the diode matrix and ICs according to the settings of the
note selector knob to drive a synchronous motor attached to the strobe
disc at a variable speed. The light is flashed at audio frequency by a
transistor driven into saturation once per cycle of the input frequency.
The combination of the differing strobe disc speeds and the audio
frequency flashing of the neon gives stationary patterns at the various
note frequencies, with the differing rings being more clearly visible at
different octaves.
As such, the tuning is independent of the mains frequency, and the only
time the mains frequency is relevant is when the unit is being calibrated.
So, the disc and all the electronics are exactly the same for 50 and 60
Hz machines. The only caveat will be that the power transformer *may* be
designed for 60 Hz, and you may need a different one for 50 Hz, even at
110 Volts, as the lower frequency may cause it to overheat. Subject to
that caveat, use a 60 Hz reference tone for calibration fed in to the
mic input from a signal generator, and you'll be fine. To get the right
voltage, use a site dropper transformer, which gives 110 Volts at the
output from a 230 volt input. Available ex stock from any builders'
merchant in the UK for about seventy pounds sterling plus twenty or so
for the plugs and sockets needed to connect it.
Another alternative is to import a 110 V 60 Hz inverter as used in many
American RVs and boats, and power that off a lead acid battery which
will give about 10 minutes of use per amp hour of capacity. A 150 watt
inverter should be big enough, but make sure it is pure sine wave, not
modified, as the modifoed sine wave will generate interference on the
electronics, and may damage the power transformer.
--
Tciao for Now!
John.
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