Wednesday, 14 December 2011

Mystery Project update 2 "The Time Vampire"

"ta da" another Headphone Amplifier/Pre-amp it took way too much time to make.

If you have been following the previous posts what you have been looking at is.... as someone posted in the comments section and i quote..

" A double-ended power supply that takes a single-ended input and splits it with a voltage divider. The space on the right could be for some op-amp circuit that requires +/GND/- instead of just +/GND."

 What this basically means is the power input for the Burr Brown OPA2107 Operational amplifier  or Op-Amp needs -Volts and +Volts the T shaped wire which runs down the middle is the ground or in this case a "virtual ground" produced by the voltage divider it never comes into direct contact with the main power ground incoming from the power jack.

To create the power buses I used solid core 1.10mm wire taken from mains twin and earth cable used for the internal house wiring.

Here's the Schematic for the Amp it follows the classic Cmoy design.You can find more info here

The two 4.7k resistors near the back are the voltage dividers,the supply to the power jack in this case is 12VDC is then halved by the voltage divider producing -6v and +6v on both of the outer copper wires or you could call then buses.

The +V for the LED is fed straight out of the back of the power jack and uses the -6v copper wire for Ground through a 1k Resistor ,as this all comes before the voltage divider as far as the LED is concerned -6v is normal ground.

The two large silver Nover 470uf 40v capacitors are for the power supply rails followed by the two red bi-pass capacitors for Op-Amp stability just in case of any oscillation which strictly speaking should be attach as close to the Op-Amp legs as possible .Having said that i haven't had any stability issues with this IC in other Cmoys i have made.

 Now to start adding the Resistors

Here you can see the the  Turquoise Resistor legs (R4) sticking out from the top of the Op-Amp IC this is where they loop round from the output to where R5 should be on the Schematic.R5 is optional and i never install it but it still needs to be connected to the output with or with out the resistor this also cuts down on additional wires.The turquoise resistor (R4) sets the gain along with R3.

you can see the loops better in this picture

The bottom 4 Leads can now be connected to the virtual ground

Time to add the Input caps these stop any DC voltage (Direct Current) entering the amplifier from the source (iPod ETC) through the input jack socket as this would also be amplified by a factor of the gain. Audio signals work on AC (Alternating Current).The gain is set quite lower as the input source in this case the PC has high output and there will be no volume potentiometer to physically adjust volume.

The legs from the turquoise resistors are bent to form the output connection which will be hooked up to the headphone jack socket.

To hook up the Input and headphone jacks I used enamelled wire from an old transformer to give a consistent look but it also has a good amount of insulation against shorts.

Tested ,working and sounding great!

After you consider how much I had to handle this thing to construct it and wore nothing to counteract static there was always an outside chance it wouldn't work.
Looks like these Op-Amps are pretty robust.

Next for the fun stuff !

Continued here..