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Old 22nd Apr 2017, 7:51 pm   #13
Silicon
Nonode
 
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,152
Default Re: Bush DAC 90A Conversion

Have you modified the wiring of the 'ground' end of the volume potentiometer?

In the original circuit the ground end of the resistive track in the volume control is connected to the cathodes of V2 and V3.

These are about 1V positive with respect to the chassis.

The output signal ground of the Bluetooth device may not be isolated from its negative power supply connection.

If you connect the power supply negative to chassis you will probably change the biasing of V2 and V3 and alter the AGC behaviour.

There will be a small amount of IF frequency at the cathode of V2. It may find its way into the audio amplifier, get rectified and turn the Bluetooth device into a crystal set.
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