Audio: low THD two tone generator

@2012/9/14

these 2 weeks i play the 2 tone generator with good THD performance, I had build one audio generator with THD around 3%, and had a factory Rig built long away ago with NIXIE frequncy display, that's cool and very Big. THD about 0.3%.

Wein oscillator stable by JFET, i can get total THD < 0.1%, output amplitude around 50mV, relatively low, a additional gain stage is needed.

simple design plan

1. use mica 6800pF as bridge capacitor for best performance

2. match 5% resistor: get close value as you can

700HZ: 33K + 6800pF

1800HZ: 13K + 6800pF

Power supply

use op-amp to provide a +VCC and -VCC. a additional LDO stage is suggestion.

LOW THD WEIN oscillator

quick built

following section is added @2011/11/25

696Hz THD: 0.03%

1.856Khz THD: 0.01%

Buffer and gain / selector

@2012/11/25

buffer following the oscillator and a additional gain stage provide amplifier for the signal cause the oscillator output level is so low. (50mV-- 100mV).

then use a double 3 position switch select the A , B or A+B signal. and use a 2k pot as balance adjust.

after mixer, a extra gain stage is added to get 500mVpeak level signal. (note finally i have only a high output, 0.47uF series with a 560R resistor).

buffer build block:

balance and Attenuator:

Balance borrowed from F2DC's 2 tone generator. (low impedance driver + high input impedance buffer)

Mixer of audio use this one:

here is my combination quick prototype:

all done in Box

@2012/11/25

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