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Old 13th Dec 2022, 12:04 am   #45
Jolly 7
Octode
 
Join Date: Feb 2018
Location: Southampton, Hampshire, UK.
Posts: 1,049
Default Re: Noise issue with DIY variable PSU and audio amplifier

My problems with audio distortion and extraneous noise while feeding the amplifier are now solved. Here's what I did:

1. Installed my own amplifier board based on a TDA2822M chip. There was nothing wrong with the Grundig board, but my DIY board is smaller and was easier to customise

2. Instead of tapping of the power transformer AC secondary, I took two parallel taps off the rectified 21V DC, one for the regulator circuit and another one for a Mini 360 buck converter. I then set the output voltage of the converter to 5V DC to feed my amplifier circuit. This outputs audio that's loud enough from a 4 or 8 ohm speaker.

3. Some enthusiasts elsewhere have reported success by using mains stepdown transformers as audio input transformers. I used an old 6-0-6 volt mains transformer from a Reader's Digest tape recorder, with the primary connected to my external audio source via a 3.5mm mono jack and the secondary to the amplifier input. The audio is now crystal clear and there is no attenuation of audible frequencies.

There is still some hum which may be from the close proximity of my new 'audio transformer ' to the mains transformer, but this can easily be made inaudible by increasing the volume of the audio input signal.

Here are some pictures.
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