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2) Operating outputs frequencies.
In the AN67 app note, the oscillator is made to operate at a frequency of 10 kHz.
The choice of this frequency is very relevant because non-linearity of modern audio equipment are very
low and so using 10kHz (instead of 1kHz often used as test frequency) ensure to reveal THD even for
high-end equipments.
Nevertheless, the EOSC10KV3 can operate at others frequencies than 10kHz, as 1kHz for example.
I built myself a 1kHz version of the oscillator, and checked with success same or better THD level than
the 10kHz version.
In addition, i provide with the EOSC10KV3 design folder a full bill of material for each 1kHz and 10kHz
oscillator version. There is only minors values change between us.
Of course operation at others frequencies are possible but not far above 10kHz, because loop gain
will decrease and THD will rise.
3) Instrument operation.
1) power supply requirements.
The EOSC10KV3 need only an external power supply to operate.
For optimal performance, low noise linear PSU is recommended (for example SSR01/SSR02 combo).
Using batteries is also possible ( 4 x 6F22 9V batteries for +/-18V operation).
Note that current consumption is about +/- 80mA, so batteries life time will not be high.
The EOSC10KV3 PCB have two internal voltage regulators options, and they have both their own
limitations :
The low noise regulators LT1761/LT1964 (default BOM values).
Maximum input voltage must never excess +/-20VDC !
If this voltage is excessed regulators will be damaged.
The standard adjustable regulators LM317/LM337 ( less expensive regulators)
Maximum input voltage must never excess 20VDC or 32VDC if inputs capacitors of regulators
(C50/C54 and C44/C45) are replaced by higher voltage rating.
(Regulators accept 32Vmax but inputs caps are 20V).
IMPORTANT NOTE :
In my design, input supply connector is a 3,5 stereo jack. The advantage is that you can use low cost
standard jack cable where you cut one side to connect wires to your own supply.
Care must be taken because +/-15V on the male jack connector will be shorted during insertion inside
the female connector ! You must avoid to insert the connector if you power supply is on, otherwise you
risk to destroy the power supply if it is not short-circuit protected !
2) Using outputs
After a complete adjustment (see chapter 4), the oscillator can be used.
The EOSC10KV3 provide two single-ended outputs .
Each of these outputs deliver same output voltage, but in opposite phase (180° shift).
This allow to get single ended signal using only one output, or differential one when using both and
taking only "hot" signal of each outputs. Note that in differential mode the output voltage will be twice.
For convenience, the amplitude control trimmer has been put on the front panel to allow easiest control.
The single-ended outputs amplitude can be adjusted using this trimmer between about 500mV to 3Vrms
(1V to 6Vrms in differential mode).
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