I recently bought a Korg Monotron Duo. To record with my laptop that lacks an internal mic I also accquired an external USB soundcard with one mic and two headphone jacks (rather cheap device). The latter device works quite well in regard to hear music from laptop and recording with a mic/headset. But what comes in from the synth is too quiet. And in addition although there is a cable plugged in the headphone jack of the synth, there is quite aound from the internal speaker of it! If I plug in headphones directly to the synth the output is well and the speaker is quite. That's why I assume the external soundcard to be the weak part. Any opinions or knowledge on this issue? Thanks in advance.
It's possibly an issue related to the driver settings of your usb sound card. There is likely to be a microphone gain parameter somewhere in the configuration screens related to the sound card. Try and adjust that to increase the microphone input gain.
You ideally need a sound-card that has a "line" level input port. this would be the correct port to use with a device such as this.