Just need a bit of help regarding connecting my sound card to the output of my amp. I have an 8ohm 25watt dummy resistor. The amp works perfectly, however, when the sound card is connected, the dummy resistor starts to burn hot. When replace the resistor with a speaker, you can hear the amp get thrown out as soon as the output is connected to the sound card. The laptop is run off batteries. Sound card is a Behringer uca202. Do I need a DC blocking capacitor, or a massive 500k resistor in series with the sound card input?
Could it be a bridge amplifier? The laptop runs off batteries, but is there any connection to ground anywhere?
OK, it must be something else then. No idea what.
Is there a voltage divider between the amplifier and the sound card or just a direct connection? I wouldn't dare connecting a power amplifier straight to a sound card.
Is there a voltage divider between the amplifier and the sound card or just a direct connection? I wouldn't dare connecting a power amplifier straight to a sound card.
I'm using RCA connection. I haven't got a potential divider on it. Sound card and amp both still working.
It might, but it shouldn't. A sound card line or microphone input with or without plug-in power should not be so capacitive that it causes oscillations. Some weird things might happen when the sound card's ESD protection diodes are driven into conduction, though, or if plug-in power upsets the amplifier's DC protection.
The main reason why I wouldn't dare connecting a big amplifier straight to a sound card line or microphone input, or any kind of line or microphone input, would be the risk that you blow up the input.
The main reason why I wouldn't dare connecting a big amplifier straight to a sound card line or microphone input, or any kind of line or microphone input, would be the risk that you blow up the input.
OK...the sound card is faulty. The test input is giving out a voltage. Works fine on loopback. I used the other channel. Mind you, not sure if it was faulty before using it to test, as the first thing I did was a sound card calibration, which was rejected due to frequency response errors of more than 22db. The THD loopback test was good so went ahead with testing. The voltage divider, plus dc blocking capacitor didn't help. Anyway, all sorted. Thanks for your help.
There are lots of tips and tricks on sound card attenuators on this thread.
What you describe as the dummy resistor getting hot instantly sounds like the sound card input is driving the amp output - and this causes oscillation. If you connect an Oscope (make sure it is isolated from earth geound) if amp is bridged you can see the output go nuts.
I have seen this happen before and I think what you might need is use an external signal generator (separate from sound card).
Try adding a 600ohm resistor in series with the sound card input. Also you may have one of those cheap inductive wire wound resistors and they can also cause oscillation. Try a non inductive power resistor. Flat metal thin film EBG or special Mills audio-gradenon inductive wire wound (one of the windings is in reverse to negate induction).
What you describe as the dummy resistor getting hot instantly sounds like the sound card input is driving the amp output - and this causes oscillation. If you connect an Oscope (make sure it is isolated from earth geound) if amp is bridged you can see the output go nuts.
I have seen this happen before and I think what you might need is use an external signal generator (separate from sound card).
Try adding a 600ohm resistor in series with the sound card input. Also you may have one of those cheap inductive wire wound resistors and they can also cause oscillation. Try a non inductive power resistor. Flat metal thin film EBG or special Mills audio-gradenon inductive wire wound (one of the windings is in reverse to negate induction).