A laptop supplies a low voltage DC power source from it's input socket to power a cheap headset type mic. Frequency response and hiss don't feature high on the design list. It is also what's called an unbalanced connection, as it has to squeeze left and right signals into one connector. Decent microphones use two conductors for each input which has more benefits, and your preamp supplies a very different powering voltage to any mic connected. The preamp then connects to the recording system using a different system too. I guess you have the MP? which is a kind of beginners device with a tube as the active component. It does have jack outputs as well as XLR, so you are just using one of them to go to the computer with a ¼"to 3.5mm cable? It worked OK at one point? If so then something has gone wrong. Your job is to find out where. Try these ideas.
Disconnect the microphone from the preamp. Connect and power up the preamp. set both knobs about halfway. Start Audacity in the normal way. Meters should be off - no indication at all. Connect the jack to the computer and is this when the meters suddenly read red and you hear noises? If so, then the interface is oscillating. A fault, and the valve (sorry, tube) is feeding back. Sometimes a result of being thumped and the internal structure collapses. If it is silent, then connect the microphone and see off that starts off the noise and over-level indications on the meter. This suggests that the mic is unhappy. You don't say what it is, but is it a condenser needing phantom power? Try turning that on and off and see if the noise comes and goes too. It is possible but rare that the mic has gone faulty, but mic issues are often due to the phantom power supply doing strange things. Inside a tube preamp are some quite high voltages, higher than phantom power and quite able to give a shock. Banging them about can mean the HT supply can appear in other places where it isn't welcome. It could even be sent to the mic, which might make that oscillate. You need to be systematic. I suspect you probably got advised to buy the pre-amp, but it really isn't the right thing for a recording setup using a bog standard computer. Most folk would select things like the Behringers for cost effectiveness or the Scarlets - which connect to your computer and replace the internal audio system with something better. You then connect your inputs to it and the outputs to your monitor system. Even the cheap ones are streets above the internal ones - and so many PCs have hums, buzzes and whines inside the box which you don't want. Your preamp gets low level condenser mics up in level, and lets you use it as a DI - getting things up to line level, with the distortion some but not all people believe sounds nice. I happen not to. You need to buy a USB audio interface to record with any real quality.
This all said, I suspect that it's one of two things. The preamp is faulty - most likely. Or you have accidentally changed the audio input on the computer from expecting line level input to mic level input and the tube preamp is vastly overloading the input.
Like most things - substitution is the only fault finding device that may be available to you as a newbie. Will your mic and preamp work on a different computer? If it does, it's your computer. If it's identical, it's probably the preamp. It could be the mic, but a swap to almost any other mic will sort that question. The only other thing could be the cable between computer and preamp. It's unlikely, but cable do go open circuit or short circuit. Open can produce all kinds of weird noises, and short is normally silent.
There you go - some ideas to try, but realistically you do need a proper audio interface if you want to record the best quality. even at the budget end, low noise and high quality NEVER come from the mic socket on a PC.
My equipment is about 4/5 years old. It did work properly in the beginning, don't know what changed. Anyone who can help or should I buy new gear?
