A Tom Evans ‘The Groove’ phono amplifier that blows the mains fuse when you switch it on.
This isn’t a mainstream piece of audio kit as it carries a very high price tag so it was interesting to see what made it tick.
It’s a funky looking unit in a very reflective black acrylic case. Shielding inside the unit is accomplished with pieces of unetched PCB connected to 0v. An unetched PCB is basically a sheet of copper that’s used as shielding.
If need your amplifier or phono amp repaired please email me.
The Groove has two independent power supplies and two audio boards. It’s in effect two completely separate turntable phono amplifiers (one for each channel) in a single case.
The fuse blowing was due to a faulty mains transformer. Also a failed op-amp on an audio board was pulling a lot of power from the power supply. That’s probably what took out the transformer.
In the photo below, the power supply board is on the right. It normally has two transformers. The faulty one has been removed and is awaiting a replacement.
There’s no circuit diagrams or any information on what any of the parts are so finding replacements took a bit of working out.
This isn’t helped by the fact that all the semiconductors have had their identifying numbers ground off and all the op-amps have heatsinks very firmly glued to them. They’ve probably also had their numbers removed!
To tell if an unmarked opamp is a single or dual package type the power pins are different. Obviously I had no idea what the part was so fitted a known good audio one in a socket.
The special design element of the The Groove is a very low noise voltage regulator shown below that Tom Evans calls a Lithos regulator. It provides +/- 14v for the audio circuitry.
Fortunately the Lithos regulator appeared to be working. A new transformer and op-amp for the audio section brought it back to life.
Note: After looking at another of these things with again a failed mains transformer that caused a big smoothing capacitor on the power supply board to fail, a massive burn out of the lithos regulator PCB due to melted and exploded capacitors I won’t take on another.
The removal of all the numbers on the semiconductors makes them difficult / impossible to repair to the original spec without a lot of reverse engineering (I’ve done some of it).
The main audio circuitry appears simple enough, the lithos regulator is more complicated as it appears to use a mixture of presumably opamps, transistors, regulators and loads of surface mount tantalum bead capacitors.