CMOY newb

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Netdewt

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Joined 2010
I'm interested in trying to build a Cmoy. Does this look right for a BOM. Am I missing anything?

2 - 4.75k Vishay metal film
3 - 10k Vishay metal film
2 - 100k Vishay metal film
2 - 1k Vishay metal film
2 - 2k Vishay metal film (for trying if the 1k are too much gain)
1 - OPA2132PA
2 - 220uF Nichicon electrolytic cap
2 - 0.1uF Vishay film cap ORANGE DROP
pot of some kind (ALPS?)
proto board
9V connector
enclosure (thinking a wood one a la Grado)
volume knob
power LED
1/4 phono output jack
RCA input jacks

Could anyone recommend an ALPS pot I could use for this?
RK09D113F25C0A104 ALPS Potentiometers
Would something like that work? There are a bunch of things I don't understand about these. How do i know if it's dual ganged? Is that for 2-channels? How do i know if it has a built in on/off switch? Otherwise I'll just get the recommended one from Radio Shack.

Parts list I'm looking at:
Part Lists and Suggestions

Thanks.
 
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GloBug

GloBug

Banned
Joined 2011
It's been awhile since I built my cMoy, but I think you are well on your way.

I did not bother with a volume control on mine, in fact I don't like to use them unless they are needed.

It sounds slightly better without a volume control, plus I already have the volume control on the iPod etc.

The pot linked above looks like a nice one, but without an/off. You could always add a separate switch.
 
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ddietz

Member
Joined 2011
Basic CMoy is fun and a very rewarding first diy audio project. I bought my alps pot directly from tangent as a thank you for putting so much into the tutorials.

Your missing a resistor for the LED. Input RCA is nice but if you can add a 1/8 or 1/4" also it will be more versetal. Do your self a favor and order enough parts for a few. They addicting at first and you also might screw up. There electrical components cost only pennies so get extras.

You should use 5mm 1uf Wima caps on the inputs, much better sound.
You may also want to add a barrel power jack so you can use a DC wallwart. The device also has more dynamic range with more voltage. The common OPA chips can handle up to +- 18 vdc. It works good with a single 9v but better at higher voltages.
 
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Netdewt

Member
Joined 2010
ddietz said:
Your missing a resistor for the LED.
Click to expand...

I think I put in 3 10k resistors. 2 are used in the amp and 1 is for the LED. I could be wrong...

Input RCA is nice but if you can add a 1/8 or 1/4" also it will be more versetal.
Click to expand...

I was just thinking of using a Y connector in case I need a 1/8 or 1/4" connection. Any DAC I'd buy would have RCA outs anyways.

Do your self a favor and order enough parts for a few. They addicting at first and you also might screw up. There electrical components cost only pennies so get extras.

You should use 5mm 1uf Wima caps on the inputs, much better sound.
Click to expand...

I'll consider that! 1uf or .1uf? The schematic says .1uf. I thought orange drops were supposed to be good stuff?

I can always order more... perhaps. The opamp is $6, and it's a $30 project!

Basic CMoy is fun and a very rewarding first diy audio project.
Click to expand...

I have all the parts to build a Shigaclone, and I want to build a DAC (or partially at least), but I really need to get my feet wet. I've been sitting on that stuff for a year now.
 
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ddietz

Member
Joined 2011
0.1uf input cap gives you a -3dB corner frequency at ~15Hz and the roll-off begins at around 100Hz, however slight. I originally tried the CMOY with a .1uF, later switching to 1uf and noticed an improvement in low-end response and a better sound.

Formula for -3dB corner is 1/(2*3.14159*R*C) where R is 100K to ground and C is the series input capacitor.

You want a good quality polypropolyene or polyester cap for this. I suspect the Orange Drops are perfectly fine for this, but have no experience with them.

Ordering more later is fine, but its easy to bugger something up, no matter how easy this seems. Shipping is expensive. Its easy to mislay or drop a resistor then loose it forever:) Since all passive components of this build, with the exception of the op amp, cost pennies, I suggest ordering more. I promise you will find a use for them later:)

Good luck and keep us updated!
 
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Netdewt

Member
Joined 2010
I got 1uf 5mm polyester Wimas.

If I screw up I'll cry... then I'll just go get parts locally and not worry about getting the best stuff. I just don't want to spend money on stuff I don't need. I try really hard not to be a pack rat. If I need to order more from mouser I'll start another project too. :) I spent $16 + ship.

What's the best way to mount the board in the case? I'm going to make a finger jointed wood box. I just ordered a Dado for my circular saw also, so I can do that.
 
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ddietz

Member
Joined 2011
Mounting can be done lots of ways. My first CMOY I simply used a couple dabs of hot glue to hold the board in place. Later versions used an etched pcb that I mounted the volume pot, in and out plugs, and DC power barrel connector right to. Those hold the pcb in place just fine. You could also use computer motherboard standoffs threaded into the case. Even wood, unless real soft like pine, could be taped for threads, then screw the standoffs in with some epoxy. If you don't want to buy a tap, make your own by filing three tapered grooves into the end of a bolt having the same thread as the standoffs. I've don this a lot (as a professional furniture maker), and it works well. You can also buy small threaded inserts at a decent local hardware store (Ace, TrueValue, Rocky's, etc not HD or Lowe's). Those work great also.


Have fun building!
 
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Netdewt

Member
Joined 2010
I'll post take some tonight which I'm working on the amp section. I hope my work isn't horrendous! The voltage all checked out and I don't see any bridges. I did put some jumpers is slightly the wrong spot and I'm trying to decide whether to work with it or try and get them out (the "S" or "M" jumpers on the sides, I'd angle everything if I leave them).
 
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