Ultimate Personal Headphone Amplifier

Simplicity with No Wall Wart

A really good headphone amp is something I’ve sought since I started listening with headphones when I was 17 in the late 1960s. My mother had acute hearing and was overly sensitive to stuff like Led Zeppelin.

Necessity is the motherhood of invention.

In response to Mom's yelling, I built a tube amp from two small tube-type TELEX magnetic tape playback preamplifiers that were often used with Viking loop cartridge tape decks. I combined the two and coupled the controls together with several dual pots.  I also rigged up a balance control. These preamps were not the broadcast quality ones most often seen on various vintage sites; rather these little things were used for industrial PA applications. Never the less, being of a tube design, the resulting amp had more than enough output to drive a pair of KOSS Pro 4AA headphones. It sounded very clean and had a rather good response.

Sometime after that, I purchased a receiver with a built in headphone jack. So, this headphone amp got…well I don’t know what happened to it. It was probably scavenged for parts.

It was after college when I stopped listening through headphones. I always had a set around though, and when I did listen, it was through a receiver’s headphone jack.

Then the dawning age of the portable personal music player came about. It was within the last 20 years when I again took an interest in listening through headphones. I primarily wanted to do this at work. I wanted to listen to stuff on my PC at work, but most companies disallowed this. So, I listen through a portable music player’s headphone jack.

The problem with practically all music players is a lack of controls like balance, bass, treble and such. So, I checked out a bunch of ready-made amps as well as several kits.

The problems with every unit I found included:

• Hiss,
• A deafening loud eardrum busting pop when powered on or off,
• No balance, bass, or treble controls, and
• Poor fidelity.

Even these hideously expensive units have no balance control. Maybe they think if someone spends $1,500 on an amp and headphones, they will only purchase media that is perfectly mixed; not to mention a person shouldn’t have a slight hearing loss in one ear.

Well, I…did go the Ramsey Kit rout and built the SHA2 Super Stereo Headphone Amplifier! It did have balance, bass, and treble controls. In fact, it’s the only one I found that did. But! It hissed and popped with the worst of them. In the end, I sold this thing on eBay for less than I bought it for.

So, now what?

I was at a buddy’s house where he had some homebrew studio audio stuff. He’s an amateur guitarist and often records his plunking. He was playing some of it for me rather loudly through his homemade pressboard studio monitors. He had a pair of rather expensive headphones setting on the table. So, to quiet the noise, I decided to use some hearing protection. I turned down the control on a box the headphones were plugged into and I put them on. I then turned up the volume a little and the sound was exceptionally clear. I later asked him where he got this box. He showed me the inside of this relatively large aluminum Bud Box and it just had a tiny circuit board with an 8 pin IC on it and several diodes and capacitors connected between this small transformer and the board. The small circuit card turned out to be a kit sold by PAIA. It was powered by a plus and minus 12V power supply.  It uses a ... 5532 op amp.

OK, I've heard it all before. "What, an op amp!"  The 9605K uses a 5532 op amp.  The specs and tests show that it rivals the most expensive headphone amps out there.  Besides, this op amp is used in many high end studio mixers.  So, if this op amp colors sound, then most music is colored.

PAIA 9605K Headphone Buffer Amp Kit

Well, for about $20 I ordered this amp. Now what do I do for tone controls.

K155 Stereo Tone Control Unit

I then remembered this little kit I picked up at the Dayton Hamvention. So, I assembled it. This small board had no synthesis or digital control. It is strictly analog. So, after a few tests, no pops and no hiss. I scoped it out and its frequency response and distortion levels were rather good. After combining the amp and the tone control together on the test bench, the results were full quieting with zero input. And the sound was excellent. This uses the 4558 ... yes, another op amp.

PAIA 9605K with Additions

I added two trimmer pots to the PAIA amp to set the proper output levels for the type of headphones I would be using and also to set top dead center the balance of the output level control.

K155 (can also be purchased at paia.com)

The K155 is powered from the Plus side of the 12 volt supply shown below. The above is the left channel only.

Plus Minus 12 Volt Power Supply

I wasn't going to drive the amp very hard, so the above was more than adequate. But if you are going to need more power for your listening, you should consider using a 12+12 24v CT transformer and two bridge rectifiers.

When I was at the Hamvention, I also bought several Ramsey enclosures and a bag of their knobs for various projects.  I took one of these boxes and I put everything in it. 

I did make a metal chassis to hold everything and I did add shielding around the preamp section. I also added filtering to the AC line.  And the power supply is regulated and has ample filtering. 

The resulting headphone amp is…well very good. I normally listen through a set of Sony MDR-V6s I bought in 1989. They’ve subsequently had a dozen or so replacement pads installed.

Look, I know; there are better headphones and better amps out there. But, I think mine rivals these. Besides, it cost me about 10% of what these others sell for.

The final critique was when a skeptical esoteric hifi nut listened to the amp through his Grado PS 1000 headphones.  Even I took a listen both through his 4 tube amp and my amp.  I think he had trouble.  I felt the tube amp added some...stuff to the sound.

Oh well.  He had paid nearly $425 for his amp.  Mine including case, transformer, and parts, cost me less than $100.