hardnrg Posted July 12, 2008 Posted July 12, 2008 Ok, so as some of you may know, around my birthday this year I bought myself some AKG K 701 headphones. These are regarded as the best headphones in the world by many, and amongst the best by pretty much everyone. Trying to play music with the K701 plugged into the headphone socket of my Technics SU-V620 New Class A amplifier resulted in slightly disappointing results, with a feint, but noticeable warbling distortion when listening at moderately loud levels and especially when the bass was turned up at all. Turns out the K701 is very inefficient and consequently very hard to drive without the signal being distorted. Now, let's be clear here, this isn't clipped or overdriven distortion, this type of distortion is the result of inadequate amplification, like trying to drive a 200W speaker with a 10W amp. So, hmm, the headphone output just wasn't going to cut it, and taking a look at a the various headphone amplifiers available, I quickly found out that most of them are devoid of any tone controls, and the price of high-end headphone amplifiers is quite astonishing! I started looking at a few DIY amplifier designs and found the M Share this post Link to post Share on other sites More sharing options...
Andrewr05 Posted July 12, 2008 Posted July 12, 2008 Pretty neat NRG! I saw a mod the other day where someone built a headphone amp into an old chunky SCSI tabletop cd-drive, they used the existing headphone out jack and kept the front bezel. It looked pretty cool... Share this post Link to post Share on other sites More sharing options...
hardnrg Posted July 12, 2008 Posted July 12, 2008 This project didn't really have an exciting progress. It was a case of buying a load of components from all over the world and soldering them to the pre-made PCBs, and them wiring them all up in the case. Also, I just didn't have the time nor the patience to piss about with a camera during the build, so here are the final photos of the completed amp. Here's how it looks from the front: Part of the options in the Front Panel Designer program is the ability to plot out text to be engraved and then filled with paint. I really like black and red together, my main computer has a black/red theme (YES, I *am* going to finish it this year lol). So, I went with red filled-engraved text. Turned out nicer than I expected. The accuracy of using a digital caliper and having the panel CNC milled really paid off and the knobs and headphone jack were exactly how I wanted them, inset into the panel. With the amp turned on, the red ring of the switch lights up and completes the black/red theme magnificently. I sanded down the 3mm blue LED with fine grit silicone carbide paper so that it was flat and also frosted instead of clear. This gives it diffusion whereas it was clear and narrow beam to begin with. I even had the back panel CNC milled because I didn't fancy taking handheld power tools to the anodised surface. It would be highly likely that the surface around the holes would be scratched if I attempted this with a drill and jigsaw or something! The phono/RCA holes are like an athletic track shape, and the IEC socket is a rounded rectangle with a tight radius, there's no way I could do this with the tools I have. Right, so enough about the case, here's the inside! As with the earlier internal layout design, the locations of the PCBs of the PSU and amp haven't changed. The main toroidal transformer is also roughly in the same place, but what has changed is that I needed a smaller transformer to provide standby power for the switch circuit, and then I moved the switch circuit and power relay to the side panel when I realised I could attach standoffs to the extrusion. At the front you can see the inset volume pot, and also you can see where I had the headphone jack holes milled in the wrong positions! I was going on the reverse-side cutout drawings on Neutrik's site, but luckily it's quite easily to cut straight through holes even on 10mm aluminium. So I made my own. Near the front, up on the side panel is another relay, mounted on a simple circuit that delays when the headphone output is connected to the amp, which eliminates turn-on thumps and the strange turn-off squeal I was getting with the headphone output connected to the amp directly. That's it really, I wish I had time to take more pics but I haven't. Also this is my first amp build, so I got quite stressed a lot of the time trying to make things work, so I probably would have thrown my camera at the wall or on the floor in frustration a lot of the time, especially with the heat of 2x500W halogen lights beaming down on me! Gotta get my thread in quick because I know Greg (Fueler) is gonna bust out his crazy media case real soon and make this effort look a bit lame in comparison Share this post Link to post Share on other sites More sharing options...
jammin Posted July 12, 2008 Posted July 12, 2008 This project didn't really have an exciting progress. It was a case of buying a load of components from all over the world and soldering them to the pre-made PCBs, and them wiring them all up in the case. Hey, if it's good enough for companies that actually build amps.. The red filled text gives it a bit of a retro Hi-Fi feel for me. Nice. Do I even want to ask how much it cost to get everything bought and shipped to and from various locations? Share this post Link to post Share on other sites More sharing options...
Andrewr05 Posted July 12, 2008 Posted July 12, 2008 That machining really does "make" the case, it looks prfessional with them being inset like that... Awesome job! What was the total build cost if you don't mind me asking? Share this post Link to post Share on other sites More sharing options...
Farva Posted July 12, 2008 Posted July 12, 2008 Damn steve! Looks awesome, very clean work! Share this post Link to post Share on other sites More sharing options...
hardnrg Posted July 12, 2008 Posted July 12, 2008 Do I even want to ask how much it cost to get everything bought and shipped to and from various locations? I'm not sure if *I* want to really know Nah, I probably could work out the total cost... let me tot it up... Case, 10mm panel, knobs: €77.40 = Share this post Link to post Share on other sites More sharing options...
SMeeD Posted July 12, 2008 Posted July 12, 2008 Thats a sexy looking amp. What I would give for that setup! That looks clean and professional. For a first anything that is nothing but awesome. Share this post Link to post Share on other sites More sharing options...
hardnrg Posted July 12, 2008 Posted July 12, 2008 Thanks Here are some old quick photos I took that give a better sense of the size of the amp. Share this post Link to post Share on other sites More sharing options...
Silverfox Posted July 12, 2008 Posted July 12, 2008 Nice Though for Share this post Link to post Share on other sites More sharing options...
Compxpert Posted July 12, 2008 Posted July 12, 2008 Really nice setup. Makes me wish I had more money for things like that. I barely have enough for a set of AKG headphones let alone what you paid to make that amp. So this Technics amp I have here at home with its headphone jack and 100W/channel can't power them properly? How many W/ch do they require? Share this post Link to post Share on other sites More sharing options...
hardnrg Posted July 12, 2008 Posted July 12, 2008 haha... yeah... same old mess... it's not much better now The Graham Slee Solo and Woo Audio 6 SE are about the same price and have been recommended to work well with the K701... It really would be a gamble me buying any pre-made amp though, unless I went over to Manchester or somewhere to audition some (Liverpool has nowhere near the city centre, I think there's one HiFi shop in the whole city, Richer Sounds doesn't count lol) I guess in a way it's like building a kit car, buy all the parts, tweak the design a bit, put it all together and add a few bits... if anything goes wrong I can fix it which is a bonus the problem with the headphone output on my speaker amp is not the volume as such... I think maybe the headphone output has it's own amplifier... it's not like I have 150W coming out of the headphone socket lol... anyway, for all my other headphones the headphone output is fine, but the K701 I have to turn the volume to about 50% instead of 20-25% for normal listening, and it's already sounding slightly distorted... Basically, the headphone output on almost every speaker amp is an afterthought, so it can't drive all headphones with a clean signal... Share this post Link to post Share on other sites More sharing options...
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