B1 buffer DC at output

[blehmbo]

I originally posted this in another thread and it quickly got buried, so I will attempt to repost it here.

I recently completed my B1 build and I was wondering if it's normal to get fluctuating DC at the output (measured across R105 and R205) with music playing through it. With no signal running through my B1 the offset is steady around 5mV, but if I hook up a CDP and amp and play music the DC fluctuates to around 40.

I am using a 24v regulated linear power supply that is rated to put out 300mA if that matters. All components have been checked for proper placement and no cold solder joints were noted.

Thanks in advance

 

[clm811]

DC at outputs of B1

I recently measured my B1 and the DC on the outputs at turn-on ramps up to almost 3.5 volts!

Then it slowly decreases to 0 volts over about a 15-20 second period...

What could be wrong with my B1?

TIA

-Chas

 

[AndrewT]

Nothing wrong.
The capacitors need to charge up to half rail voltage.
They need current to do this and will pull current from anywhere they can find it. Even the input to the next stage in the audio string.

The big resistors that hold the inputs and outputs at near zero volts DC can only supply very low currents.

You need a mute/unmute on the output of the B1 if you want to do LIVE Power ON.

 

[AndrewT]

I originally posted this in another thread and it quickly got buried, so I will attempt to repost it here.

I recently completed my B1 build and I was wondering if it's normal to get fluctuating DC at the output (measured across R105 and R205) with music playing through it. With no signal running through my B1 the offset is steady around 5mV, but if I hook up a CDP and amp and play music the DC fluctuates to around 40.

I am using a 24v regulated linear power supply that is rated to put out 300mA if that matters. All components have been checked for proper placement and no cold solder joints were noted.

Thanks in advance

Your voltmeter is an average reading type.
It takes samples of the voltage at the test point and averages them.

If you have a combination of DC & AC voltages then the averaging will be taking account of the very variable AC Audio signal. The accuracy of the DC reading is being completely swamped by the variable and very large AC Audio signal.