CMoy Headphone Amp

A while ago I came across a picture of a headphone amplifier in an Altoids tin. Even though I don’t have headphones that necessarily require an amp (Audio-Technica ATH-M50) I decided to go ahead with the build. It’s an easy enough project to build in a weekend. I followed this excellent tutorial with a few modifications. I built the single 9V battery version. I ordered all my components except the pot from DigiKey. I ordered the pot from Mouser. I still had a bunch of perfboards lying around from previous projects and used one of them. The total cost for the parts came to around $30. Unfortunately DigiKey doesn’t show you the shipping cost on checkout and to my surprise they charged me $30 for regular UPS ground shipping. I contacted their support and apparently there is a shipping cost calculator link somewhere during the checkout process. Seriously DigiKey, it’s 2015, update your website.

The CMoy tutorial has last been updated in 2009 and not all the components are available anymore. Please see my parts list below for alternatives that are available today.

Parts list DigiKey:

Count   Part No.        Desc.                                   Price
2	P5552-ND	CAP ALUM 220UF 35V 20% RADIAL	        0.84
2	338-3417-ND	CAP FILM 0.1UF 200VDC RADIAL	        6.06
1	10.0KXBK-ND	RES 10K OHM 1/4W 1% AXIAL	        0.1
2	4.75KXBK-ND	RES 4.75K OHM 1/4W 1% AXIAL	        0.2
2	100KXBK-ND	RES 100K OHM 1/4W 1% AXIAL	        0.2
2	1.00KXBK-ND	RES 1K OHM 1/4W 1% AXIAL	        0.2
2	10.0KXBK-ND	RES 10K OHM 1/4W 1% AXIAL	        0.2
1	OPA2132PA-ND	IC OPAMP GP 8MHZ 8DIP	                6.96
1	160-1708-ND	LED 3MM HI-EFF RED DIFFUSED	        0.33
2	CP1-3513-ND	CONN JACK STEREO R/A 3PIN 3.5MM	        3.42
1	ED90032-ND	CONN IC DIP SOCKET 8POS GOLD	        0.97
1	2238K-ND	STRAP BATTERY 9V I-STYLE 4"LEAD	        1.11
2	47.5XBK-ND	RES 47.5 OHM 1/4W 1% AXIAL      	0.2
1	226-2092-ND	KNOB CLR GLOSS .50"DIA 6MM SHAFT	5.36

Parts list Mouser:

Count   Part No.        Desc.                                   Price
1	RK0971221Z05	Potentiometers Flat 15mm 10k	        2.94

In the tutorial’s schema the power LED is placed before the switch. This configuration makes sense if you go for an external power supply. If you go for the battery version make sure the LED is connected after the switch. If I would build this again I wouldn’t built a version with the pot anymore. The Alps pot has a built in switch which is nice but it has it’s lowest resistance right after you switch it on. So when you turn the amp on it starts with maximum volume. If you have a source with volume control, I would just install a regular switch to turn the amp on/off and regulate the volume at the source (that said the volume knob looks pretty cool :).

Test setup:

Wired inside the tin:

Finished product:

Some notes on the sound quality. With the ATH-M50s the difference is not huge, but noticeable. You can listen at insanely high volume and even at very high levels the sound is very crisp and free of distortions. I would say it packs a bit more punch into treble and base and changes the sound more towards the warmer end.

All in all a fun project and a cheap way to get a nice sounding amp for your cans.

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CMoy Headphone Amp

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