Headphone Amplify me!
Amplifier For Headphones? What, like to make it go louder?
Ever since I had gotten my Grado SR-125 Headphones I have always wanted to get an amplifier for them to see how it sounded. Of course there are cheap options like the Ramsey SHA-1 and that 100 dollar job from headphone.com but i really wanted something a bit higher quality that i knew would work well with my grado phones. And more importantly, something Affordable!
I built the Ramsey amp which uses dual LM386 OP amps and, while it only costs 30 dollars for the kit, I wasnt at all impressed. Even at 30 dollars the way it sounded was simply unacceptable. Too much hiss in the background, and the dual stereo pots make it a bit hard to get the balace between channels correct without spending some time at it.
I had always known about this clone and had come very close to ordering the parts more than a few times but everything would have cost around 40-50 dollars when all is said and done. Alot to spend on something i dont even know will make a difference. So when the time finally came that i could fabricate my own case, and get many of the parts from my college electronics lab I seized the oppotunity. Introducing the well suited for Grado headphones amp Clone. The picture above is version two of the amp, which includes more precise fabrication, better PCB layout and better parts than my first stab at the amp.
The case, i designed and fabricated from scratch using simple metal working tools and some old aluminum sheet. Once it was done i painted it with a silver/grey Hammered paint and from there it was coated with some clear lacque for gloss and durability. It is a one peice design that uses two seperate cases, one for the amplifier portion and the other smaller case for the batteries and switch. They are then connected with a wire harness going from the power side to the amp side through rubber grommets near the rear. The inputs are high quality gold Rear mounted RCA jacks which I decided to use over something like a headphone jack because the main purpose of this amp is to be used with something like a computer or home cdp or tuner.
The OP amp the grado amp uses is a 4556, dual op amp in one package. Some will say that it is not the best sounding chip around but it does a great job delivering the high current needed to drive the grado line of headphones which are all 32 ohms. The PCB artwork is a heavily modded version of what grado uses in their amps, I changed the layout to suit my case and parts. The curcuit is very simple as can be seen in the picture, and most of the folks who pay $350 for the real thing are dissapointed to find out what they really paid for (a nice mahogany box) The coupling caps I use are the Clarity Caps PX series 5.0uf, they are not pictured but are by far the most expensive part in the circuit at around 4 dollars each. I use them for their sonic properties and since they are in the signal path i dont mind spending a few bucks on them. The resistors are all 1% with the exception of the brown ones which are 5% tolerance. And matched to as close as I could get.
The sound is pretty decent, And the difference between using the amp and not is definetly there. The sound is much fuller, more powerfull and more lifelike. And the amp is dead silent, my first amp has some hiss in the background that is audible (yet low) from about halfway up on the volume. I was pleased to find that this one is absolutely quiet. I'll be honest, i would not pay the retail price of these amps to get the difference that i am getting with my clone but thats just me. Total money in parts came to around 30 bucks on this amp but keep in mind that i fabricated everything from scratch which saved alot of money. Your results may vary if building this amp but overall i would rate it at a 9 out of 10 for being fun to build, usefull and worth the price of parts.
Heres another amp I fabricated which is basically just the first one torn apart and remade with an all new chassis modeled after version two. However I decided to go "all out" on this one as far as the case goes and the attention to detail. The piano black finish consists of 7 coats of paint and the accent peices down the side are stainless steel. The performance of this version three, which i believe looks the best by far is about the same as the second amp if not identical.
Since building the Black one pictured above, I have built two more. The first, my "No holds barred" version is pictured below. The second which is a gift for a friend I am finishing now. I am NOT building these and selling them as a buisness. Each one of these that I make is better than the last one, I suppose thats why I have made more than a couple of them.
This Version uses Solen coupling capacitors, Metal film 1% tolerance resistors, a better pot, the Neutrik 1/4" jack, Along with Bulgin Battery drawers and all in a custom made case of African Mahogany and Copper sheetmetal. And i have added an LED for power on indication.
Total Current draw for the amplifier is only 11ma
Parts List
- 100k ohm stereo pot
- DPDT switch
- Headphone Jack for output, 1/4 inch is best
- 2) 121k Ohm Resistors
- 2) 464k Ohm Resistors
- 2) 100k Ohm Resistors
- 2) .12uf Polyester Film Capacitors
- 2) 5.0 uf Audio grade capacitors such as solen,clarity cap, auricap etc.
- 1) 4556 OP amp. commonly seen as JRC4556AD
- 2) RCA jacks for input
- 2) 9v batteries with holders and clips or drawers
Heres A picture of the Finished Amp I made for a friend. It was hard to see this one go because I like it the most out of all the ones i've made so far. Practice makes perfect!
Componet Side Layout
Various Notes on Construction
There are a few things to remember when building this amp, First of all your switch MUST be a DPDT or DPST, if you do not switch both the neg and pos wires you will not be turning the amp completely off and your batteries will drain. The batteries are wired up in series and the point at which the negative and positive of the two batteries is connected is going to be your ground. Make sure you connect everyting to this ground, inputs, output and volume control.
The coupling caps will go from the rca inputs to the input on the pot. make sure you keep everything in order so that when the amp is done your left and right channels will be where they are supposed to. If not, just remember a a quick fix is to simply chage which inputs you plug your cables into. The inputs to the board are going to be your outputs from the 100k pot.
The PCB layout I designed to fit what kind of case i am using and what configuration i wanted. Yours may need to be chaged.
Copper Side Layout
Heres the Copper side of the PCB layout. This is what you will need to either copy into a PCB program or print out and use to etch with. When your etch the board your text should be as it is in the picture to avoid putting it on backwards.