Conn tuner
On 5/23/2019 3:03 PM, geoff wrote:
On 24/05/2019 1:09 AM, John Williamson wrote:
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.
Yep - all ofÂ* the above already.
Might be worth considering as a simple project popping in a stable and precise
oscillator.
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.
That power side of things already thought of and considered too messy. Marginal
gain through having 60Hz power as a target. Will see if the xformer is, as the
schem suggests, in reality strappable for 220v.
geoff
Nobody uses tuning fork anymore? The battery lasts forever.
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