Hagerman Cornet 3 Valve Phonostage Build

[Reffc]

As I'm pretty immobile with a bad back at the minute, I thought I'd finally get round to building the Hagerman Cornet Mk3 phono stage which I've had here for a while.

For those who followed the original Hagerman Bugle (Mk2) SS phonostage build, you'll already know just how impressed I was with the sound quality on offer and the elegent simplicity of the design, most especially the power supply smoothing.

Well, not one to rest on his laurels, Jim Hagerman launched a Kickstart project for the Cornet 3 because he believed it was such a good circuit offering a significant sonic upgrade on the already impressive Bugle kits. After conversing with Jim, I gave in to temptation and bought a kit.

The Circuit

Basically, it's a simple design which uses switch mode power supplies then smooths them, removing noise spikes etc with input capacitors and inductors. Unlike the SS version, this version also very cleverly uses an LM 555 op amp timer as an oscillator for a boost converter (in conjunction with a power transistor) to create the high voltage rail needed for the valve circuits.

The RIAA EQ is done passively. It's buffered by a single 12AU7 which is loaded by a (power) transistor current source, which is often beneficial in reducing distortion from valve stages. Overall, a simple but effective circuit.

The Build

This is what you get in the kit:



Closer look at component compliment:



A reasonable quality PCB measuring approx 180 x 115mm, substantially larger than the Bugle kit; Instructions (I would say "full" but they're not especially detailed and rely on some prior experience, although a stuffing diagram and component checklist along with a circuit diagram is provided); all components EXCEPT the UK to twin plug converter you'll need for the power supply.


First step is to attach some nylon posts to the PCB to help assembly:



It has to be noted at this stage, that this kit IS NOT suitable of you have no prior soldering experience as it requires a fair amount of dexterity and neat soldering due to the tightly packed components.

Next main job is to sort all resistors, test before bending legs to shape for insertion, then soldering in place along with diodes:



Following that, the other components follow with the Op-amp socket (DIP socket), power switch, LEDs, first Octal base (good quality gold plated contacts on ceramic PCB mount) and first of the capacitors.



The rest of the board follows before testing and building into the supplied enclosure (seen here with valves fitted):



Underside showing the considerable number of solder joints required:



Before final assembly, the circuit is tested to enshure that all LEDs light (the first one immediately showing that the 9V dc power supply is present, followed by the other two after a 20 second delay showing that the HV rail is operating).
Measuring across output, DC voltages should be 0v.

Input end view:



Powered up:



Close up showing gently glowing valves:



Sat on the rack atop the Albarry headamp which will feed it from the Zyx R50 MC cartridge on the Gyro. CD in foreground for scale and Hagerman Bugle can be seen to the right:



Side view:



I'll get round to building a timber sided Acrylic cover in due course but for now, will soak test it and will report back on initial sound quality.

All in all, a great value kit (about £240 delivered in kit form) and about an afternoon's work if you're handy with a soldering iron and multi-meter.