5 volts on Audio Input?!

[neo80]

Hi, I've been testing my new 2B for some weeks.

I was trying to use the Stereo mode, but when I connect the audio imput to the headphone socket on my computer speakers, I get a big noise on the speakers.

I have tested the input and it has 5 volts from ground to tip and middle conection.

photo_2015-12-09_20-39-37.jpg

If I turn on Commander option, then I get 2.8v to tip and 5 volts to middle.
I'm not sure about damaging a mp3 player, or even my phone if I connect it

[admin]

If you are running any audio device at the same time, as a 2B you are bound to get some interference, adding speakers into the audio loop, or any other amp will probably produce some noise, and is a bit pointless as the 2B is can process audio that sounds rubbish most of the time.

I am a bit confused - audio input to a headphone socket on speakers - should that not disconnect the speakers?

If you switch Commander on then you cannot use audio mode, as this the digital link interface shares a connection with the audio input.

The audio input has capacitor isolation on the inputs to isolate the audio input from the digital interface. As you are effectively trying to measure the voltage on one side of a capacitor, with the other connect to the input of an amp, the voltage will be indeterminate, it could be 0V it could be 5V, it depends on the state of the charge on the capacitor. It's not an issue and won't cause any damage to any input device.

Si

[neo80]

I am a bit confused - audio input to a headphone socket on speakers - should that not disconnect the speakers?

Yes, plugging headphones doesnt disconnect the speakers, this model has an independent switch to turn them on and off. I usually send from this output music to kitchen and bathtoom, without disconnect the speakers on the computer room.

If you are running any audio device at the same time, as a 2B you are bound to get some interference, adding speakers into the audio loop, or any other amp will probably produce some noise, and is a bit pointless as the 2B is can process audio that sounds rubbish most of the time.

I know, it's an anoying interference

If you switch Commander on then you cannot use audio mode, as this the digital link interface shares a connection with the audio input.

Agree. (and note to future updates: Stereo mode should disconnect digital link when selected)

The audio input has capacitor isolation on the inputs to isolate the audio input from the digital interface. As you are effectively trying to measure the voltage on one side of a capacitor, with the other connect to the input of an amp, the voltage will be indeterminate, it could be 0V it could be 5V, it depends on the state of the charge on the capacitor. It's not an issue and won't cause any damage to any input device.

Well, that's ok in one channel. After some minutes, voltage between base (ground) and tip conector (audio left) became almost 0 (There's a capacitor, indeed).
But from ground to middle (audio right channel) I still have 5 volts, and the interference is on the right channel. Connecting an amperimeter, I have constant 34.1 mA

[admin]

Agree. (and note to future updates: Stereo mode should disconnect digital link when selected)

The audio input has capacitor isolation on the inputs to isolate the audio input from the digital interface. As you are effectively trying to measure the voltage on one side of a capacitor, with the other connect to the input of an amp, the voltage will be indeterminate, it could be 0V it could be 5V, it depends on the state of the charge on the capacitor. It's not an issue and won't cause any damage to any input device.

Well, that's ok in one channel. After some minutes, voltage between base (ground) and tip conector (audio left) became almost 0 (There's a capacitor, indeed).

Yes because you are discharging it too ground.

But from ground to middle (audio right channel) I still have 5 volts, and the interference is on the right channel. Connecting an amperimeter, I have constant 34.1 mA

Not a good idea!!!

The level you see is DC, probably from the Digital Link Interface transmitter (I'll check why its not switched off). The capacitor on the input to the amplifier blocks DC, so only a AC signal will get to the amplifier and the proceed to the rest of the 2B circuitry, However by shorting the digital link input to ground through your meter you have just exceeded the limits on the input - its only rated at 25mA and you have just shorted it through your meter and measured 34mA, so if you now find that the digital link no longer works, you know why.

would it cause interference to speakers? - it shouldn't as i) speakers also run on AC signals (the varying signal caused the electromagnet and thus cause the speaker cone to move in and out, and the level is far too low to offer any effect over that of the driving amplifier.

I also noticed from your images that your largish crock clips appear to be capable of shorting across channels, again something that we would not recommend.

Question : do you get the same interference on 2B.010??

Si

[neo80]

Not a good idea!!!

The level you see is DC, probably from the Digital Link Interface transmitter (I'll check why its not switched off). The capacitor on the input to the amplifier blocks DC, so only a AC signal will get to the amplifier and the proceed to the rest of the 2B circuitry, However by shorting the digital link input to ground through your meter you have just exceeded the limits on the input - its only rated at 25mA and you have just shorted it through your meter and measured 34mA, so if you now find that the digital link no longer works, you know why.

would it cause interference to speakers? - it shouldn't as i) speakers also run on AC signals (the varying signal caused the electromagnet and thus cause the speaker cone to move in and out, and the level is far too low to offer any effect over that of the driving amplifier.

I also noticed from your images that your largish crock clips appear to be capable of shorting across channels, again something that we would not recommend.

Made it carefully, and tested before conecting not to short across channels.
About measure, made it quickly, but I know, I can burn something inside.

When I connect the phone as a player, it works ok.
Opened the speakers case and found a TL074CN who multiplexes the audio from the computer. No capacitors between headphones socket and the TL074CN, so the DC from the 2C goes to this chip and makes the interference, replicated on the speakers channel.

Connecting directly to PC (no speakers), works well too.

Aparently, there's no damage from the quick mA measure. Digital link and audio input works.

Question : do you get the same interference on 2B.010??

Si

Tested in 2B011, and same interference. I can test in 2B010 later.

Anyway, it's not a problem with 2B, only with my speakers. I'll add them a small capacitor to each chanel, to fix this problem.

Thanks for your help and patience