Wednesday, 10 March 2010

CMoy for Altoids box

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.


Few weeks ago I decided to modify my first version of PCB for CMoy amplifier. I wanted to implement following improvements:

+ use new nice small stereo potentiometers with On/Off switch
+ increase capacity of input coupling capacitors
+ add possibility for bass-boost circuit
+ add blocking capacitors for opamp
+ add constant current charger for 9V battery
+ add power jack connector for charging
+ use double side PCB with ground plane
+ modify the shape of the PCB

After few hours of thinking new schematic have arrised.

Schematic of the CMoy with battery charger

P1 is the volume potentiometer with On/Off switch. C2 is coupling capacitor. R2 defines the input impedance of opamp. R3 and R4 define the gain of the amplifier (5x in this case). Rb and Cb form bass-boost circuit. These components increase the gain for low frequencies. For the low frequencies the gain is 14. By increasing the Rb resistors you can increase the gain for low frequencies and vice verse. You can decrease the cutting frequency by increasing the Cb capacitors. Bass-boost can be deactivated by shorting out Rb resistors. As a opamp I use OPA2132, but many others can be used as well like OPA2134, OPA2227, NE5532, ... C3+ and C3- are blocking capacitors for power supply for opamp. R5 is optional, but to avoid some bouncing at the output the value should be around 22 ohms.

V1 is a Rail Splitter which creates virtual ground. C1 is high quality blocking capacitor with low ESR. Resistor R1 limits the current through LED. The value should be modify according the type of LED. D2 limits the maximum voltage in the input to 12V. U2 together with resistor R0 create constant current source for charging the 9V battery. In my case the R0 has value 47 ohms and then the current is around 25mA. Cin is tantalum blocking capacitor for U2. D1 is Schottky diode for avoiding any damage when the voltage with opposite polarity is connected.

I designed the PCB with two rounded corners. The PCB fits exactly to the Altoids tin (see pictures below). On the PCB are also nice pictures of input jack and headphones. The resistors and diodes must be assembled vertically to reduce occupied space.

Assembly diagram (top side).

Assembly diagram (bottom side)

PCB (top side)

PCB (bottom side)

Assembled PCB (top side)

Assembled PCB (bottom side)

As you can see on my first prototype there are some mistakes and modification:

1) pins 1 and 3 of volume potentiometer P1 must be exchanged, otherwise if the amplifier is switched on the volume is set to maximum

2) polarity signs for battery clip are opposite

3) only one TLE2426 Rail Splitter should be used, I wanted to increase the maximum current by putting two rail splitters in parallel. I have seen in one forum that it is possible. But finally I observed very high current consumption, probably because the voltage splitters are not exactly same. If only one is used everything is OK.

Last step was to mount the amplifier to the Altoids tin. I made the holes according the position of components on the PCB and than I covered the bottom of the tin with insulation to avoid some short circuit, because the tin is from conductive material.

Mechanical drawing of holes in Altoids tin

Holes in Altoids tin (front view)

Holes in Altoids tin (side view)

Bottom of the Altoids tin is covered with insulation.

And my new CMoy has been done.

Finished CMoy amplifier (front view)

Finished CMoy amplifier (side view)

Finished CMoy amplifier (inside view)

Finished CMoy amplifier

I'm very satisfied with my new CMoy. It sounds good and is always close to me ready to play.


Unknown said...

dear sir...
i'm very interested in building one Headphones amps like yours. i am a noobi in electronic world. can i have a list of the parts you use in your amps. my mail is

really appreciate...

Anonymous said...

What were the mechanical dimensions you used to make the PCB fit so well? Did you have a 10.8mm radius on the corners, or did you find a different dimension?

Unknown said...

what capacitors did you use for C2
and Cb (not the values ;)) and where did you get them?
They look funny, like candy or something.

and BTW thanx for the schematic, the developers of cMoyBB aren't that generous.
But take a look at their parts list, because the jacks they use line up with the Alps Pot very nice.

Thanx and a big "thumbs up" for your work.

Unknown said...

Hi Steve,
the "candy" :) capacitors are polyester film capacacitor MPEM see this datasheet I bought them from TME

Josh said...

Dear sir, is your pcb board available for sale? i would really like to make one of those amps myself!

Cheers to DIY

Alexandru IOVANOVICI said...


congrats for the nice design;
will you release the design of the pcb ?
or at least the schematic so we don't have to draw it again ... we are too lazy for that :)

thank you !

BMboomer said...

Hi Miroslav
Thank you for your blog,it has helped me so much to understand the Cmoy improvements like Bass Boost, and a trickle charging circuit.
I have tried a test implementation, by just soldering the components together (minus the charging circuit), you can imagine how messy it looked, but it actually worked.
I tried using 50k trimpots instead of the bass boost resistors, and found that the bass boost gain can be adjusted just as you outlined.
I would love to build some properly assembled amps and wondered if you would sell me a few PCB's.
My email is
Cheers Simon

Ph said...


Could you tell me which PCB designing software do you use?


Miroslav Batěk said...

I use Altium Designer for schematic and PCB design.

Unknown said...

There is no battery is full charging indicator or auto-cutoff charging when full circuit. How long do you charge a 9v 200mAH NIMH Battery ?

Miroslav Batěk said...

@Spit: Yes, you are right there is no charging indicator. It is very simple charging circuit. The charging current is 25mA so I would recommend you 8-9 hours charge time for 200mA battery.

Unknown said...

Thanks. I'll probably mod the circuit to add an LED indicator with auto-cutoff as NiMH batteries are very sensitive to over-charging.

Unknown said...

Hi, nice blog entry. Have some question.
What kind of machine do you use to get that PCB?
Do you have altiums footprint for the mic entry? (I tried doing one but kinda mess it up)

thanks a lot

Miroslav Batěk said...

@Pachones: The PCBs are done by profesional PCB manufacturer. Send me an email if you want the symbols in Altium library.

Aries1470 said...

Hi Miroslav,
Just wanted to say what a great variation and thank you for showing the Bass Boost section too.
I love your symbols :-)

Tidy layout.

You are more than welcome to check out an updated power supply section that I have made.

I normally read the comments in the forum, I guess I should start reading them in blogger too.

jmwreck said...

Hello Miroslav, nice work, thank you for the scheme with the bass section. as mentioned, there is no indicator for charging, is it possible if we can use a different power circuit from another headphone amp?

Juanjo said...

Hello. I have some friends that want to build an amp like you, it´s possible to get the component list and the pcb desing please? Your pcb is great.

Thanks for all.

Alok Bhardwaj said...

Hi everybody can anyone plz send me pcb desing in software ready to burn i dont know how to use pcb drawing application plzzzzzzzzz i want to make it for my project.................................................

Unknown said...

what is the component for V1 n V2? i can describe it from anywhere source that you give.

if you kind, please give me detail component for all of them.

email me at

thank for your kindness

Unknown said...

Thanks for sharing this great article! I feel strongly about it and love learning more on this topic..led circuit board

nalimen::Paijo said...

I just interesting to your design...

about the recharging schema, if what is the voltage input for the charger... 9 Volt or else??
and if i use double 9 volt battery , in series, do i still be able using thing charger schema??or i should adjust with different values of components ?? and what input voltage i should use either??

thanks ...

Unknown said...

hey i want to design this for my project can i get the value of each component please

Unknown said...

hi m8...
I would be interested in building the headphone amplifier like yours. I'm not very experienced in the electronic world, but I have a bromoled to make my pcb built by me and good skills. Can I have a list of the parts that you use in your amplifiers. my mail is, thank you very much

Unknown said...

hello m8

i'm interested in your design. i am also using altium designer for PCB design.

if you don't mind, could you share your footprint design. i am trying to bould this cmoy to with your design

if you want to share the footprint you can send to my mail

thank you very much for your share

tommy29 said...
This comment has been removed by the author.
tommy29 said...

dear sir...
i'm very interested in building one Headphones amps like yours. i am a noobi in electronic world. can i have a list of the parts you use in your amps. my mail is

Unknown said...
This comment has been removed by the author.
Unknown said...

dear sir....
Iam very interested in building one Headphones amps like yours. Iam a noobi in electronic world. Can I have a list of the parts you use in your amps..? my mail is

thanks and a big thumbs up for your work.

Hiếu said...

OPA2132 sound is good, I can repair OPA625, or OPA840, it has sound better

Unknown said...

Hello friend
I just find to your blog and I love doing and I would like amplified
Please could you send me the PCB for printing and the list of components to put to work
Could you explain why the plate in duplex?
my email is
from already thank you very much

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Unknown said...

Can you please email me the complete parts list and pcb layout? Thanks! This is my email: