Grado RA1 Headphone Amplifier Clone

This headphone amplifier project started when my colleague offered me a candy. It is actually a candy inside a tin. Well, I asked politely if I can take the tin instead of the candy. This quite awkward and she is confused why I am asking for it, but she give it to me anyway. So let's this project begin.

I am trying to make this project as a low budget headphone amplifier. I have already few op-amps on hand and I just using one of them in this project.

The original Grado RA1 headphones amplifier use the JRC4556D but what I have right now is the JRC4558D. As I check to both datasheet, they can still be use for substitute in this headphone amplifier circuit.

I found the Grado RA1 headphones amplifier schematic online. Somebody has open the unit and try to figure out what is the components inside this headphone amplifier.

The schematic is basically a non-inverted amplifier schematic. The resistor for feedback based on the clone schematic is 470k ohm and the inverted input goes to the ground is 100k ohm. The non-invert input have bleeder resistor goes to the ground using 100k ohm.

The input capacitor from original Grado RA1 using Solen 5uF and it wouldn't fit inside this tin. So in this project, I will using my favorite capacitor is the Elna Silmic II. The capacitor value that I use here is 4,7uF. This capacitor is small and very famous for good sounding capacitors.

The filter capacitor for each voltage input are 100nF WIMA. This is also the best film capacitor for audio.

Others components required are the power switch, input-output jack terminal and ALPS potentiometer. All of those parts are cost not more than $10.

As usual, I will make this headphone amplifier by point-to-point connection between components. I still using a small PCB just to make sure all components are in well arrangement.

The first resistor is installed on PCB. This is the feed back resistor.

After that, I am continue to install the other resistors and capacitors.

Look how simple this headphone amplifier. This is all finish and ready to put inside the tin.

The next step is making few holes on the tin for mounting the input output socket and the potentiometer. This tin is super thin. Using the big drill like this is a bad idea. The holes finished are in bad shapes. I think I should use only the manual grinding for this kind of work.

Before I install the sockets, I attach the signal cables to the socket pin out. This would be easy for me to attach between the socket to the PCB later.

The input socket cable goes first to the potentiometer as the volume control before going to the PCB input signal.

Continue to the battery input, in this headphone amplifier, I will do the same as the Grado RA1 use. The dual differential voltage is using from 2 battery. This small tin is fit enough to put 2 pieces of 9 volt batteries.

After all finished, there is a miscalculated on the switch location. When the nut put into the switch, the tin cannot close properly. I have to cut the tin a little bit to make this fit.

I make some cut and bending the tin, Once it all done, the tin can be close properly. But it looks quite ugly now.

I put the fresh battery and this Grado RA1 clone is ready to perform.

I am using this amplifier very often. This amplifier is never absence at my working desk or during my serious listening session at home. What I like from this amplifier is the music presentation is natural, uncolored with keep presenting the dynamic of the music. It is just like the original music from the source amplify to drive the power demanding headphone connected to this amplifier.

One thing I notice there is little hiss when no input signal present into this headphone amplifier. This hissing is occurs when I using the low impedance earphone. But when I change to the Audio Technica ATH-M50X, this hissing is un-noticeable.

The battery life is outstanding. This is because using 2 pieces of battery. This configuration give double the battery lifetime compares to using only one. When the batteries need to replace, they should be change simultaneously with the brand new batteries. This to make sure no voltage different between those two batteries which can lead to the large DC offset output to the headphone.

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