This is an article about my new PCB design for CMoy headphone amplifier. Main feature is that the new PCB fits exactly to the classic Altoids tin-can. This new CMoy incorporates moreover bass-boost circuit and constant current charger for 9V battery.

The amp is based on the Project 19 PCB, so uses a pair of LM3876 (or LM3886) power opamps, run from a ±35V supply. I used a cut-down P88 preamp PCB because I only wanted one preamplifier stage, but the entire board can also be used. Alternatively, the P19 amp can be run at higher gain than normal, alleviating the need for a preamp at all. The down side of this is that the noise level will be higher, and background noise may be audible with efficient speakers and/ or very quiet surroundings.

This simple amplifier shows the LM386 in a high-gain configuration (A = 200). For a maximum gain of only 20, leave out the 10 uF connected from pin 1 to pin 8. Maximum gains between 20 and 200 may be realized by adding a selected resistor in series with the same 10 uF capacitor. The 10k potentiometer will give the amplifier a variable gain from zero up to the maximum.

I was in my final 6 month work term with an electronics company as a trainee. Within this company there are a few audiophiles who are tube lovers and spend astronomical amounts of money on their audio equipment. My training supervisor had found Mark's Class A MOSFET Amplifier Project and suggested that I design a PCB and build this project as part of my training. I followed the Class A MOSFET Amplifier Schematic with the following exceptions. Instead of the 2SK1058, I used the 2SK2221 mosfet which I had on hand. I compared the datasheets of the 2SK1058 and the 2SK2221 and the differences between the two were very small. The other change was to use a 6800 uF capacitor on the output instead of a 4700 uF capacitor.

This article descripts, how I built amplifier from Mr. Marshall Leach known like "The Leach Amp". I built amplifier from the original instructions on these pages: http://users.ece.gatech.edu/~mleach/lowtim/. Article about bulding of this amplifier I found later in journal A_Radio Praktická elektronika 11/2002. For many years I looked for construction of HiFi amplifier wit a good parameters, enough power reserve and simple construction. I built a couple of amplifiers with integrated circuits MBA810, TDA2005, LM3886, but I was disappointed by their output quality and noise. I decide to built a classic construction with discrete components and bipolar transistors. Construction from Mr. Dudek was interesting, but I didn't like used components and complexity. All of my requirements satisfied construction of the Leach Amp. Circuit author publicates in a February 1976 in american journal. From these days circuit was not practically changed. Little changes are descripted on authors page.

This a LM3886 amplifier that features both balanced (XLR) and unbalanced (RCA) audio inputs. I've changed the internal circuits of this ChipAmp or so called "GainClone" to use premade circuit boards. The reason for this is that the bass/ low frequency response of the prior version was not as powerful as I would have liked. It is said that simply adding more capacitance to the power supply improves this, but worsens the high frequency characteristics. Boards use a noninverting amplification scheme, versus the inverting circuit I had used previously, I have heard some people mention that noninverting is better in some respects so wanted to try it. At the bottom of the page you will see the different schematics for the inverting and noninverting designs. In addition, Images will now load in a new window.

Gainclone in the inverted mode with the pot at its input is great amplifier, so it will work fine without any preamp or input buffer. However, here is a suggestion for the further improvement of some parameters of the sound of the inverted gainclone. During experiments, I paid special attention not to loose the good sides of the original, unbuffered inverted gainclone.

CMoy is very simple portable headphone amplifier. I assembled CMoy during one hour. Instead of R5 and R25 is used only wires. These resistors are assembled only in case of oscillation. The value should be few ohms. Now I have to find some good box, and put my CMoy inside. It will be maybe most difficult part of building CMoy amplifier :-). The sound is very good for so easy and small device. It can improve the sound of MP3 players, mobile phones and other portable devices. I would like to make some measurement of frequency characteristics, THD and also try to use different OpAmps, but unfortunately I don't have enough time to make it now.

Musical Fidelity would let you believe that this is a Class A design. However, in common with most commercial amplifiers, it is a class AB amplifier - it simply has a rather high standing current in the output stage, which results in the first 8 watts or so being class A.

GainClones have VERY few components and this one is based on the National Semiconductor LM3875 IC. The PCBs and components are very simple and quick to make, only took about 20 mins to assemble both amps and rectifier board. DC offset was about 80mV on one channel and about 40mV on the other. I used the optional Ci capacitor in the national datasheet for the IC which reduced it to between 0-4mV: This is the capacitor I chose, its an Elna Starget (expensive). The case was MUCH more time consuming and difficult to make though. I bought all the aluminum from a scrap metal yard including the heatsink. I got my aluminum panels cut at a sheet metal shop as I cant make straight cuts with a hack saw.

This is a Chu Moy headphone amp I made. I got the PCB design from Guzzler from Head-Fi and the original design is very popular and is here. I changed Guzzler's layout so I could use a Taiwan Alpha pot on the PCB. These pots a high quality (some say better than ALPS blue velvet) and are available from Jaycar. You can see the thread here. I also made a DIY Brown dog adapter so I could use two OPA627 single opamps in a dual opamp socket.

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