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First Cmoy Questions

post #1 of 6
12/6/09 at 5:06pm
Thread Starter 
Hello Head-Fi!

I'm in the planning stages of building a cmoy and have a couple of questions regarding the build and modification to best suit my needs.

I will mainly be driving IEM's with the cmoy with my 4g Ipod Nano as a source (using the line out, not the 3.5 headphone jack).

1st Question: Is there any effect of using 1/2W or 1W resistors over the 1/4W resistors or should I stick to what is recommend on the tangentsoft site?

2nd Question: I would like to run my cmoy using a 11.1v Lithium Polymer battery pack.

My passion and also my work is in the hobby industry, I deal with lipo packs on almost a daily basis and also own all the correct safety and balance charging equipment needed.

I understand that I would need to create a voltage cut-off circuit for this to work, and that is no trouble.

What I need to know is are there any modifications I need to make to the cmoy's power supply in order to make the lipo battery source work correctly, or can I stick exactly to tangent's schematics? I am not 100% sure if I need to change the resistors in the virtual ground circuit or not.

I'm sure I will have many more questions as I go on, thanks for any help offered. This site has been heaps of inspiration
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post #2 of 6
12/6/09 at 6:11pm
1: Stick with the smaller resistors (1/8 W - 1/4 W) as the CMoY doesn't consume much current. Larger resistors are of no benefit, other than being physically larger, and more expensive. If you want to get fancy use 1% tolerance metal film resistors, like Vishay Dale RN Series.

2: Depends on the Op-Amp you use, but I recall the limit being fairly high. I built a DC adapter to supply 19 V to mine.
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post #3 of 6
12/7/09 at 1:30am
1) You'll have a difficult time getting 1/2 or 1W resistors to fit the ratshack board without lots of creative lead bending. Larger wattage resistors supposedly have slightly lower noise figures than smaller, but you won't hear any benefit here.

2) The lipo pack will give you ~+/- 5.5Vdc, so no problem. The exisiting virtual ground should be fine, or a TLE2426 for VG would also be fine, or really any VG improvements on Tangents site. Most common audio opamps will go to +/-12Vdc, with many doing +/-15V and higher. Some opamps intentionally made for portable applications will have lower PS ratings.

I would lower the gain to 2 or so if IEMs are your intended application.
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post #4 of 6
12/7/09 at 4:01am
Thread Starter 
Thank you guys for answering my questions

Have started building today, and am having heaps of fun!

I have used 1/2W resistors and as you mentioned Pars, I have done some creative bending/planning to make them fit. So far its looking pretty tidy.

At the moment I am sticking to the standard PS, but will build a second Cmoy soon enough using a TLE2426 for the VG, I was impatient to build so couldn't wait for an order from RS Components.

Will update with pictures and thoughts once completed.

Cheers.
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post #5 of 6
12/8/09 at 7:25am
Quote:
Originally Posted by adamkerrnz View Post
1st Question: Is there any effect of using 1/2W or 1W resistors over the 1/4W resistors or should I stick to what is recommend on the tangentsoft site?
no ill effects to the circuit... can be none/a little/a lot to your wallet though :P

Quote:
Originally Posted by adamkerrnz View Post
2nd Question: I would like to run my cmoy using a 11.1v Lithium Polymer battery pack.
that shouldn't be a problem.


happy building adam, let us know once you're done with the build
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post #6 of 6
12/8/09 at 9:49pm
Thread Starter 
Thank you dhaninugraha

Just need to find myself a 3.5 to 3.5 cable and the amp will hopefully work.

I think for the moment I will stick to a 9v source and draw up a power supply which includes a low voltage cutoff for lipo use.

will include some pictures later on.

cheers.
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