Basically you have to just lump together as many primitive shapes as you need to make what you want to make what looks like one object. So you make the basic shape and then add-on other primitive shapes to it which you have re-sized and squished into different versions of themselves and plaster them onto everything else. Like the amp would be a cube (hard or round edged) stretched to the exact shape size and proportions you want, the knobs would be cylinders which you have made small, the lines on the end of the knobs would be even smaller objects which you have made out of more cubes, re-sized to make them tiny flat strips and then made white, and say for a backing behind the knobs you would use yet another hard edged cube to make it flat and the right size and add the stainless steel texture to it. Adding the various textures to each item makes it come alive and to make lights use the texture which glows static and change it with the colour picker. To add things like the knobs and make them exactly stick out at 90 degs and not be on messy angles, use the snap rotate function, bent arrow with a magnet on the top toolbar, you can change the degree settings in the settings panel, I use 45 degrees as it allows me to snap things around and not have my mouse move off the circular lines before it snaps. I found that 90 degs was too much and the default of 15 was too many snaps and I would lose count, but 45 allows me to count easily and get things perpendicular or opposite in the best amount of moves without the cursor leaving the line. So yea, you have to look at what you want to create, break it into it's separate parts and you usually can find a shape in primitive shapes which will work when you alter it, glue it to whatever you are working on and add the correct texture to get the effect you are trying to achieve.