CMoy headphone amplifier version 3

After building my Mark II CMoy headphone amplifier I decided to make a version which resembled more of a desktop model.

The differences for the Mark III are both internal and external. Although the schematic still follows that of Tangent, I decided to have a go at laying out a board by myself. This is part of my continuing, slow education in that as well as building equipment from detailed instructions, I hope to start understanding what it is I am doing by altering elements of the build.

I had a stripboard already, so I downloaded a template and designed the layout on that. Once I was satisfied it would probably work, I cut the board to fit into the slots of the enclosure, but also made sure to cut the tracks of the rows where components were placed. This was to ensure that they weren’t connected electrically to the chassis.

As usual, I tested the power supply before building the amplifier section. I did continuity checks with the multimeter at all of the connections on the board and all seemed fine, so I wired up the chassis parts, which included a full size 6.35mm headphone jack and RCA input sockets.

I tried to be consistent with wiring colour but I’m slightly hampered in that I don’t have enough variety of said wiring colours! I suppose I could buy some at some point. I’ve used yellow for ground so the layout should make sense in that regard at least.

The first test produced no sound. Careful, detailed analysis showed me that I am an idiot and had forgotten to install the op-amp in the socket. Once installed everything worked fine. I powered it with the 19V laptop charger that came with the ACA, as I have changed that for the 24V Meanwell version as recommended by Nelson Pass. The sound as tested through my HD650 was again very good with no hum present. I am very pleased with this build, to my eyes and ears it looks and sounds good and the cost of building is negligible.

For those wishing to replicate this I’ve included the bill of materials I drew up. For more information on the this version of the CMoy, see my earlier builds here and here and you should read the Tangentsoft website first.

Bill of materials for the Enjon CMoy MKIII as built.
CPC=CPC Farnell (minimum order £5 for free delivery)
RS=RS Components (no minimum order for free delivery)

Description	Quantity	Supplier	Supplier part number	Price
4.7kΩ metal film resistor x2 0.25W 1%	2	CPC	RE03757	£0.67 for 50
10kΩ metal film resistor x3 0.25W 1%	3	CPC	RE03723	£0.67 for 50
1kΩ metal film resistor x2 0.25W 1%	2	CPC	RE03722	£0.67 for 50
100kΩ metal film resistor 0.25W 1%	2	CPC	RE03724	£0.67 for 50
0.1uF capacitor Vishay (Class X2)	2	CPC	CA07136	£1.46 for 2
220uF 35V Nichicon electrolytic capacitor	2	RS	739-4453	£0.72 for 2
OPA2132PA Op-amp	1	RS	218-8281	£6.34
Winslow 2.54mm Pitch 8 pin DIP socket	1	RS	813-115	£0.46 (£2.28 for pack of 5)
3mm green LED	1	CPC	SC08014	£0.10 (£1.00 for pack of 10)
Stripboard 64x95mm	1	Amazon		£0.50
Alps RK0971221Z05 potentiometer (includes power switch)	1	RS	729-3521	£2.89
DC power input socket	1	CPC	124-3247	£1.26
RCA inputs (shielded)	2	CPC	PSG01717 PSG01605	£2.72 for 2
6.35mm headphone socket Clifford Electronics	1	CPC	CN02262	£1.44
Volume knob 22m diameter to fit 6mm shaft	1	CPC	SW02901	£1.98
19V laptop adaptor	1
Hammond 1455 series enclosure	1	CPC	EN84145	12.84