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Bottlehead Kits => Crack => Topic started by: Shamsyrup on January 09, 2021, 08:09:59 AM

Title: Audio signal on B+
Post by: Shamsyrup on January 09, 2021, 08:09:59 AM

Hope everyone is doing fine. I am getting audio signal on my B+ line. Is it normal ? I have also taken some measurements on the DC filtering stages. Attached all the pictures. All measurements were taken when the amp was fully cranked up. Are these measurements normal ?

Thank you.

Title: Re: Audio signal on B+
Post by: Tom-s on January 09, 2021, 08:23:56 AM

You're watching power supply ripple.

Edit. That how i interpret the power supply filter results. But i can't explain the 1khz tone you have on the B+?

Title: Re: Audio signal on B+
Post by: Shamsyrup on January 09, 2021, 08:27:38 AM

What about the audio signal on B+ ? That is not power supply ripple.

The 1khz tone was fed to the input of the amp through a function generator.

Title: Re: Audio signal on B+
Post by: Tom-s on January 09, 2021, 08:29:58 AM

That's your amplifier functioning.

Title: Re: Audio signal on B+
Post by: Shamsyrup on January 09, 2021, 08:32:29 AM

So it is totally normal to see audio signals on high voltage DC B+ power rail ?

Title: Re: Audio signal on B+
Post by: Paul Joppa on January 09, 2021, 08:59:15 AM

The output signal current flows through the power supply, and the impedance of a 220uF cap at 1000Hz is about 0.7 ohms, so there will be some signal.

What was the signal level? And what was the load (i.e. headphones plugged in? what impedance?)

Title: Re: Audio signal on B+
Post by: Shamsyrup on January 09, 2021, 09:56:19 AM

Signal level was 1 volt and the load impedance  was 300ohms.