INTRODUCTION
After building a OPA2134AP CMoy / Grado RA1 headphone amplifier in a timbre box, I wanted to try this high performance OP amp in a line stage / preamp. Rod Elliott's High Quality Audio Preamp (Mk II) which is a two stage preamp with balance control seemed like a good choice.
DIY PREAMP AND POWER SUPPLY
Two small pc proto boards (Radio Shack 276-159 / Dick Smith H5601) were used to accommodate all components. Metal film polypropylene capacitors were used in the signal path. It would have made the whole project easier by using physically smaller caps but for me the sound was a priority. For the power supply I used a 1.2A 18V regulated SMPS wall wart. I definitely do not need 1.2A, but I wanted a gutsy supply. Two 1k 0.5W resistors make up the "virtual ground" split supply. 220 uF low ESR capacitors and 0.1 uF decoupling capacitors are used for channel. This simple supply configuration works very well and is dead quiet.
PREAMP ENCLOSURE
The case only measures 115 X 90 X 55 mm (same size enclosure that I used for my Nanoo LM3875 Gainclone) and placing all the components in this tiny space, including a dual gang volume control and balance control was going to be tough. Unless you enjoy working in ridiculously small spaces and/or you are masochistic, build this preamp in a bigger case. Even a slightly bigger enclosure would be better. For the finish I use an acid etch primer, allowed a few days drying and then the spray color over the top. This was the same technique used with the big red caps on the Synergy Roasting Pan LM3875 Chip Amp / Gainclone. 
RESULTS
I have used the preamp as a front end to my S-5 Electronics K-12 Tube Amplifier. The test setup comprised a NAD C542, modified bookshelf speakers and DIY Silver Interconnect Cables. The preamp added nothing and took away any CD player/ Valve power amp miss-match. For that reason I have named it Neutrino. The balance control has a very wide sweet spot and the volume control was non-twitchy, linear and easy to use. A very inexpensive project but it feels odd to build something that adds and removes NOTHING audibly in a cute box. Try it.
Mark Houston 
Other DIY Audio Projects by Mark:
31 March 2008
DIY OP Amp Based Preamplifier
03 December 2007
DIY Class-T Amplifier Kit (AMP6)
It has been a long while since I added one of my own projects to the diyAudioProjects.com website. I had actually finished this project back in the summer, but never got around to pulling together a web page for it until now. Over the past few years I have read a lot of good things about Class-T Amplifiers (T-Amps). For those who are unfamiliar with T-Amps, the chip manufacturer (Tripath) describes the Class-T amplifier chip as one that can offer both the audio fidelity of Class-AB and the efficiency of Class-D.
I decided to try a kit from 41hz.com as they are priced very well and I have read several good reviews of their T-Amp kits. I opted for the AMP6 kit which uses the popular Tripath TA2020 chip. The kit was only $39 and fairly simple to put together.
For the enclosure, I used a prefabricated aluminum chassis. The results are a little industrial looking, but heck, I am interested in the sound quality, not the enclosure.
A lot of people describe T-Amps as having a "warm tube like sound". I didn't think so. I did not like the sound when mated with high efficiency fullrange speakers. However, with more traditional speakers (2 and 3 way) I was very pleased with the performance of the little AMP6 (about 12W into 4 ohms and only 7W into 8 ohms). It provided accurate tight bass and detailed mids and high. While I prefer the sound from my DIY LM3886 Chipamp (gainclone) Kit, the AMP6 is a solid preforming small amplifier with an excellent price to performance ratio.
Full details of my experience with the AMP6 and additional photographs are available at the AMP6 (T-Amp) - DIY Class-T Amplifier Kit project page.
What's Playing: New Order -Vanishing Point (instrumental)
05 October 2007
Synergy - LM3875 Gainclone Amplifier
Mark has been hanging out in the kitchen and has put together the Gainclone amplifier shown below.
For the enclosure, Mark has used a heavy cast aluminum cooking pan and a massive wooden cutting board. The amplifier is based around the LM3875 chip (power opamp) and uses point-to-point wiring. The amplifier follows the "rigid and compact" approach of the 47 Laboratory Gaincard amplifier. A rigid enclosure is used to reduce resonance and vibration while a short signal path, feedback loop and minimal parts (compact) are used to preserve information. The schematic of the three resistor amplifier is shown below.
Keep cooking Mark, as I look forward to more of your projects. See the project page for full details of Mark's Synergy - LM3875 Gainclone Chip Amplifier Project.
Related DIY Gainclone Projects:
- Mark's Nano LM3875 DIY ChipAmp (gainclone)
- Bruce's LM3875 DIY Chip Amplifier (Gainclone) Kit
- Gio's LM3886 DIY Chipamp Project Kit
- Mark's Point to Point LM3875 Gainclone / ChipAmp instructions
13 August 2007
Grado RA1 Headphone Amplifier
A while back I got the headphone bug and purchased a pair of Grado SR80 headphones. I am very pleased with these headphones and consider them to be great bang for your buck. The Grado SR80 headphones have an impedance of 32 ohms, so I built a CMoy Headphone Amplifier in an Altoids mint tin to drive the demanding headphones. The results were surprisingly good, especially when you consider that one can easily build a CMoy Head Amp for about $20. The CMoy easily outperforms the built-in headphone amplifiers on my NAD C162 and NAD 1020 preamplifiers.
A while back, I was showing off the Grado SR80 headphone / CMoy combination to a friend. He is the Walkman, Discman and now iPod type who typically lives with the factory supplied headphones until they die, replacing them with similar light travel headphones. He was stunned with the amazing sound quality, so I let him live with the Grado / CMoy combo for a while. Not surprising, he loved the sound quality, but found that the Grado headphones were too bulky and leaked too much sound for use on public transit.
While he found that the combo was not suitable for his daily commute, he was in love with the amazing sound quality and decided to spoil himself. He purchased a pair of Grado SR225 headphones and a Grado RA1 headphone amplifier for use at home.
For those of you who are not familiar with the Grado RA1 headphone amplifier, it is well regarded, runs off of two 9V batteries, is housed in a beautiful mahogany enclosure and retails for about $350US. A stock photograph the Grado RA1 is shown below.
Recently I had the opportunity to visit and listen to his Grado SR225 / RA1 combination. Of course I brought along my CMoy headphone amplifier! :)
We both did some blind listening and in the end we pretty much had the same listening impressions. We thought that both the CMoy and RA1 amps sounded excellent and fairly similar, but we both gave a slight edge to the DIY CMoy amplifier. We were both a little surprised, considering you can build a CMoy for about $20 or buy an already built one for about $40 on eBay, yet the Grado RA1 rings in at $350.
Schematic - CMoy Headphone Amplifier (above)
As you can see, both of these designs are based around a operational amplifier (opamp). For my CMoy, it is a OPA2132PA (Burr-Brown) which retails for about $5 and for the RA1 it is a JR4556 that retails for less than $0.50!!! Despite the fact that the JR4556 is a low cost opamp, the RA1 sounds pretty good. Not as good as a properly implemented CMoy headphone amplifier, but it should keep most people happy.
While I consider most Grado headphones to be a great purchase, $350 for a Grado RA1 gets you a $20-$40 headphone amplifier in a $300+ mahogany case.
Related Post:
- DIY CMoy / Grado RA1 Headphone Amplifier Project
- DIY CMoy Mint Tin Headphone Amplifier
- DIY Class A MOSFET Headphone Amplifier
What's Playing: Peter Gabriel - Solsbury Hill
25 April 2007
The "Beast" - A LM3875 Chip Amplifier
Bruce has put together a LM3875 based Non-Inverting Chip Amplifier using the LM3875 kits available from audiosector.com. He has affectionately named his project the "Beast". For the enclosure, Bruce used plastic and aluminum project boxes from Radio Shack. The power supply consists of a 200VA toroidal transformer and is housed in a separate enclosure.
Consistent with what most are chip amp kit builders have been finding out, Bruce has found out that these gainclone kits result in a great sounding amplifier at a reasonably low cost. For more information about this project, see The "Beast" - LM3875 Chip Amp.
Related Posts:
18 December 2006
Nanoo Chip Amplifier (LM3875 Gainclone)
Here is another one of Mark's projects which has been added to DIY Audio Projects website. His latest creation is the compact DIY Nanoo Chip Amplifier (LM3875 Gainclone).
The enclosure for the amplifier is a tiny aluminum box that measures 119 X 94 X 34 mm. The amplifier is based around the popular LM3875 chip using point-to-point wiring. Power to the amplifier is provided via an external power supply which is also housed in an aluminum enclosure.
See the project page for more pictures and information about the Nanoo Chip Amplifier (LM3875 Gainclone) Project.
Related Projects:
- Bruce's LM3875 Chip Amplifier (Gainclone) Kit
- Mark's LM3875 Gainclone Chip Amplifier in a Roasting Pan
- Gio's LM3886 DIY Chipamp (Gainclone) Project Kit
07 November 2006
CMoy Mint Tin Headphone Amplifier
Originally Posted: 21 June 2006
A while back I purchased a nice pair of cans ... Grado SR80 Headphones. When I bought them, I knew that they would drive me to build a DIY headphone amplifier. Well, here are the results ... A CMoy mint tin headphone amplifier.
The CMoy is a very popular and easy to build headphone amplifier that can be fit into a mint tin. It can be used to drive demanding headphones, produce thunderous volumes and most importantly, it sounds excellent. The original article A Pocket Headphone Amplifier by Chu Moy discusses all the fine points of the amplifier, while How to Build the CMoy Pocket Amplifier provides excellent and easy to follow building instructions.
My version of the CMoy headphone amplifier uses two nine volt batteries, the OPA2132PA (Burr-Brown) operational amplifier (opamp) and a gain set to 9. Since I will be using this with a portable MP3 player, I elected not to include a potentiometer as the volume will be controlled through the MP3 player.
The CMoy headphone amplifier sounds pretty darn good when you consider the simplicity and low cost. It provides excellent clarity, even at high volume. The headphone amplifier does not seem to add its own colorations to the sound and there is a lot of detail. The amplifier is very well behaved and there are no pops when powering up or hiss during operation. Overall, this is a very nice little performer and it considerably increases listening pleasure with a good set of headphones.
Related Posts:
- Grado RA-1 Headphone Amplifier
- DIY CMoy / Grado RA1 Headphone Amplifier Project
- DIY Class A MOSFET Headphone Amplifier
06 November 2006
LM3886 Chip Amplifier (gainclone)
Originally Posted: 3 May 2006
After several months of planning and acquiring parts, I finally got down to constructing a chip amp (gainclone). The amp uses the National Semiconductor LM3886 chip with printed circuit boards (PCB) purchased from chipamp.com. I finished the amp late last night, so I only have about 3 hours on it and I don’t think it is burnt in. So far it sounds pretty good. It sounds much better than it should given the simplicity and low cost of this amp. There is a lot of power available and the bottom end is very good. It sounds a little bright and tinny to me right now, but I will reserve judgment and make a comparison to my S-5 Electronics K-12M tube amplifier kit after several more hours. More information about this project is available at the LM3886 Chip Amp (gainclone) project page.
Related Projects:
- Bruce's LM3875 Chip Amplifier (gainclone) Kit
- Nano LM3875 ChipAmp (gainclone)
- Mark's DIY LM3875 Gainclone in a Roasting Pan
