First build: CMOY2

[UglyJoe 0]

This will be my first build, and I have a couple of questions. First of all, my headphones are Grado SR125s; I have read that the CMOY2 is similar in design to the A47 and should therefore pair well with the Grados. If anyone has built this amp and used it for Grado headphones please comment on the amp as well as the proper gain setting for these headphones. Here is the part list I was planning on buying:

 

Part Supplier Part# Qty Price Total

 

10 R Resistor Newark 58K3794 2 $0.109 $0.218

10 kR Resistor Newark 58K3797 8 $0.109 $0.872

LED resistor Newark 58K4959 1 $0.094 $0.094

 

OPA2227PA Newark 80K6017 2 $3.96 $7.92

LM6171 Newark 41K6219 1 $2.83 $2.83

DIP-8 Sockets Newark 14F2700 3 $2.46 $7.38

 

uF Capacitor Newark 18C4895 5 $0.342 $1.71

1000 uF Cap Newark 01H8711 2 $0.345 $0.69

 

3.5mm phono jac Newark 96F9608 2 $2.27 $4.54

 

9V strap Newark 16N942 1 $0.393 $0.393

 

POT Tangent RK097 1 $3.25 $3.25

 

Volume Knob Newark 92N4099 1 $3.07 $3.07

 

If any of these seem unreasonable or the wrong part please let me know. Also I am assuming that the PCB is still available (I have tried contacting jasonhanjk, but so far have been unsuccessful). If anyone has a CMOY2 PCB for sale let me know. The last question I have is how difficult (or possible) would this design be to mod so that it runs off two 9V batteries or can be plugged into an AC source?

 

Thanks in advance for any help I can get, you guys rock!

Edited January 1, 2007 by UglyJoe

[1bit 0]

hi joe, welcome to sgheadphones!

and happy new year too, btw

 

i've built my cmoy2 about a year ago and i'm quite happy with it. currently i'm using it at home with either alessandro ms1 (32 ohm) or sennheiser hd590 (120 ohm). i've set the gain to 6x by changing the feedback resistors to 50k ohm. in this way, i can use both headphones. for the alessandro i raise up the volume knob to around 40% and for the senn around 80%.

 

looking through your part list, it seems alright. it's just that you seem to forget to put the led and the enclosure/casing in the list. and also don't forget the switch, you'll need this.

 

btw, i opened the newark website and it looks like the (well i'm not too sure about this) the resistors are ordered not per pieces but in tape/reel. i'm not sure how many piece of resisters per reel of tape, but you could end up with more resistors than you need. not that it's a bad thing anyway lol. you can try matching up the resistors that way. and keeping spares is always a good idea anyway. but anyway, i'm not sure about this, please check with newark.

 

you could probably get a pair of higher capacitance caps for the coupling capacitors (C1& C2). i managed to fit in two 3.3 uF polyester caps replacing the 1uF ones. you need to be sure about the size first though, so need to open up the datasheet sigh ...

and if you have more money to spend or a bigger enclosure you can try finding exotic caps both for the coupling and the electrolytic caps. a low esr electrolytic cap should be better i think.

 

i'm not sure about the availability of the pcb. you need to check it with jasonhanjk.

 

you can use two or more 9v batteries in parallel. this won't be a problem. to use two batteries in series, you'd need to change the electrolytic caps to ones with higher voltage rating (currently they are 6.3V). i think the max you can use is 2 batteries in series as it is limited by the absolute max supply voltage that the opamps can take. please check the data sheets.

 

electrically, i think it's gonna be ok if you wanna use a wall wart (adapter) to power the amp. just use something with around 9V output and be careful with the polarity when you do that. it's just that some say the sound quality will be affected in some way.

 

another option is to build your own power supply. it roughly consist of a fuse, a step down transformer, diodes in bridge configuration (rectifier) and a regulator.

 

hope this helps

[UglyJoe 0]

1bit

 

Thanks for the help.

 

Quick question for you; about how long of a battery life do you get with a single 9V battery? Thats the only reason I am thinking about changing anything, if the battery life is reasonable then I will leave it as is. Since I am just using Grados only for this amp do you suggest I change the gain at all? I will probably just grab an LED here; I am unsure as of yet what kind of enclosure I want to use, going to build the amp then decide based on size issues. Also that POT has a built in switch.

 

Thanks

Edited January 2, 2007 by UglyJoe

[1bit 0]

hmm i can't say for sure about battery life. never really test it proper.

i'd say it's between 5 to 10 hours or probably longer.

 

well the gain setting is up to you, when i first made it i used the standard part list (gain 2x) to drive my cheapo koss 100 ohm headphones and i felt unsatisfied. that's why i increase the gain. that time i haven't got my alesandro yet and therefore never had the chance to try the 2x gain on a lower impedance phones.

 

cmoy2 can fit inside an altoids tin, but it's a pain to make the holes for the pot and jacks.

[williamneo 0]

hmm i can't say for sure about battery life. never really test it proper.

i'd say it's between 5 to 10 hours or probably longer.

 

well the gain setting is up to you, when i first made it i used the standard part list (gain 2x) to drive my cheapo koss 100 ohm headphones and i felt unsatisfied. that's why i increase the gain. that time i haven't got my alesandro yet and therefore never had the chance to try the 2x gain on a lower impedance phones.

 

cmoy2 can fit inside an altoids tin, but it's a pain to make the holes for the pot and jacks.

 

I use single hole paper puncher which can purchase at book store, The size of the hole fit nicely to input, output, toggle on/off switch, Power led and pot. If you want to see how it look like i have the pic at my blog the tools section.

 

regards

william

http://williamneo.blogspot.com