Carver M-400 Amplifier Repair Keeps The 1980’s Alive

Carver is a famous name in audio equipment although they have been known to use odd names for things. For example, the 1980’s vintage M-400 magnetic field power amplifier that [JohnAudioTech] is repairing (see the two videos below). That sounds like something off a bad Star Trek remake, but, apparently, we weren’t alone in thinking that, judging by this 1982 review of the unit from a UK magazine.

Still, it is an interesting high-power amplifier and we love seeing gear of this age torn apart. The beast is rated at 201 watts — you have to wonder if the extra watt is another marketing ploy.

There were actually two units and they looked pretty good for four-decade-old boxes. One sounded pretty good outside of some noticeable buzzing. The other had something shorted inside. If you enjoy watching repair videos, you’ll appreciate this two-parter.

We have to admit — and it may be a personal bias — there is something more pleasing about seeing a PCB populated with a bunch of interesting-looking through-hole components. Modern boards with a sea of surface mount parts tend to look a little bland, aesthetically speaking. Of course, when it comes time to make our own boards, we are happy to use SMD and forego all that hole drilling!

We like watching computer repair videos, in particular. Or sometimes, something really exotic.

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3D Carver Makes Magnetic Fields Visible

The history of science is full of examples when a 3D physical model led to a big discovery. But modelling something that’s actually invisible can be tough. Take magnetic fields – iron filings on a card will give you a 2D model, but a 3D visualization of the field would be much more revealing. For that job, this magnetic field following 3D carving machine is just the thing.

What started out as a rapid prototyping session with servos and hot glue ended up as quick and dirty 3D carving rig for [Frits Lyneborg]. The video shows his thought progression and details how he went from hot glue and sticks to LEGO Technics parts and eventually onto Makerbeam extrusions for the frame of his carver. A probe with a Hall effect sensor is coupled to a motor spinning a bit that cuts into a block of floral foam. A microcontroller keeps the Hall sensor a more or less fixed distance from a rare-earth magnet, resulting in a 3D model of the magnetic field in the foam, as well as a mess of foam nubbles. Despite a few artifacts due to in-flight adjustments of the rig, the field presents clearly in the block as two large lobes.

Carving foam isn’t the only way to visualize a magnetic field in three dimensions, of course. If you’d rather have a light show based on the local magnetic field, try this 3D compass build we covered a while back.

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