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jasonhanjk

Guide to fix up a Cmoy 2

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Introduction:

 

A year ago, we start the idea of building a simple to assemble and cost effective portable amp locally.

 

Oh my! It's really been a long time. Just look at this thread, whooping 300 replies, 7000 over views and 20 pages long. rolleyes.gifhttp://www.sgheadphones.net/index.php?showtopic=2400

 

Finally after many trial and error (and money), of course with many help from our passionate forumers. The final product is ready for sales.

 

Get yours now today. Please visit this thread for more info.

http://www.sgheadphones.net/index.php?show...t=0entry49789

post-12-1110093873.jpg

Edited by jasonhanjk

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BOM for Cmoy2

 

10ohm X 2 0.25W

10kohm X 8 0.25W

1.2k/3k ohm X 1 RLED

Pot X 1 RK09L12B0A31, Farnell code 919639.

OPA2134 X 2 Farnell code 791039

LM6171 X 1 Farnell code 638250

1uF cap X 5 Wima polyester cap, Farnell code 149846.

1000uF X 2 Panasonic FC, 6.3V, 10mm Dia and 12.5mm length, Farnell code 9691855.

Stereo Jack X 2 female 1/8 stereo jack

Hammond 1593P X 1 Code 930192 for grey and 930209 for black

9V battery adapter X 1

Switch X 1

 

 

Some technical result

Noise: -105dB A-weighted

18mW THD+N @ 33ohm, AES17 20kHz filter:

63Hz 0.00107%

500Hz 0.00180%

1kHz 0.00181%

5kHz 0.00219%

10kHz 0.00282% <--------- Worst case

15kHz 0.00177%

20kHz 0.00182%

Crosstalk -66dB

Edited by jasonhanjk

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Step 1: Solder resistor R1 to R8.

Resistor are the hardest to solder so you have to start this first. If you never solder before, do some practice first on vero board. Their values are:

R1: 10

R2: 10k

R3: 10k

R4: 10k

R5: 10

R6: 10k

R7: 10k

R8: 10k

 

The max wattage you should use is 1/4w film. Min is 1/8w.

The gain is set at 2. If you want to increase the gain, increase the value for R2 and R6.

The formula is G = 1 + R2 / R3

 

More gain increases the noise.

 

 

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Step 2: Insert the volume pot or bypass it.

The volume pot uses Alps 9mm RK series, RK09L12B0A31. You can get in from Farnell code 919639 at the price of S$7.43. Even at Mouser, 688-RK09L12B0A31 @ USD$2.75.

 

Now, the reason to bypass. When you guys use a portable player or using the PC as a source, there is already a volume pot built in. Thus saves $10.

So short both the number 1 and 2 hole near to C2. See attach picture. Don't short hole 3, that is ground.

post-12-1110095409.jpg

Edited by jasonhanjk

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Step 3: Insert the OPA2134 X 2. S$4.62 from Farnell code 791039.

If you don't like OPA2134, you can choose other dual opamp IC.

Now you have a choice to use socket or not. Just for-your-info, non-socket opamp have better electrical performance than socket one. The problem with direct solder the opamp on the PCB is the user will not have the fun of opamp rolling, pointed out by another DIYer firefox. Thanks.

 

If you are new to soldering, it is highly advisable to use socket. Too much heat on the IC will kill it.

 

Other recommend opamp:

AD8620 (need adaptor)

OP270

 

 

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Step 4: Insert R9 and R10.

These resistor are use to set the virtual ground voltage. It also let the capacitor discharge when the amp is not using. Both of them have the value of 10k.

 

 

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Step 5: Input coupling cap C1 and C2.

I use 2 X 1 uF film polyester cap. This cap is use to block all DC supply in the signal. Overall my output DC offset is always less than 5mV, most of the measurement are 2mV. You can short it if you find that your signal has no DC at all. Normally a good CDP will have near to zero DC.

 

 

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Step 6: Power coupling cap C3, C4 and C5.

I use 3 x 1uF film polyester. You can choose to use 100nF ceramic cap (yellow-brown color one).

 

 

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Step 7:

Insert the electrolitic cap, the one I used is Panasonic FC. 1000uF, 6.3V, 10mm Dia and 12.5mm length.

If you decide to use +-12V supply, change the cap to 16V. Make sure the dimension remains or else you can't fit into the hammond casing.

Ensure you put them in the correct polarity.

 

 

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Step 8:

Insert R11 current limiting resistor for the LED. Omit if you don't intend to have any LED. Try to use 1/2w carbon resistor. There is no polarity indication on the PCB. The top is anode (+) and the bottom is catode (-). The approximate formula is:

 

Iled = 5mA

Vled = 3V

9V = 3V + (R X 5mA)

R = 6V / 5mA

= 1200

 

Note that it is base on 9V supply and you wanted to feed the LED 5mA of current.

I would suggest to set the current lower to 2mA to save power, use a 3kohm resistor.

 

 

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Step 9:

Insert the 2 female 1/8 stereo jack. Attach a male stereo pin picture. As you see the first portion of the pin is for left channel, follow by right and ground.

To test which is which on the female stereo jack, what I do is I wear a lousy earphone. Use a multimeter and select to resistance mode and test the few pins to ground. I will hear pop sound to confirm the channel.

post-12-1110100275.jpg

Edited by jasonhanjk

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Step 10:

Insert LM6171.

Farnell 638250 @ S$6.57.

 

 

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Step 11:

Connect the negative of the 9V to the PCB V-. Connect the Positive of the battery to a small single poll switch then to the PCB V+.

 

 

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Step 12:

The most tedious task, putting into an enclosure. Well, drilling for the enclosure is the hardest part so I left it at the last part. A slight wrong drill and you may have to buy a new enclosure. If you are not sure how to do it, ask other DIYer to do it.

As the front panel is very small, I only manage to squeeze in a volume pot, 2 input output (one ugly thingy sticking out) and a switch. No LED.

Some of you who bypass the volume pot, will have more space.

If you really wanted to mount them all, my suggestion is mount the switch, pot and LED at the front and the input output at the left side of the enclosure.

 

As some of you guys wanted to place it in a tin. You can do so but only the input ground and output ground can be short to the tin only.

 

This enclosure use is Hammond 1593P. Farnell sell this enclosure too. Code 930192 for grey and 930209 for black. Price at S$7.82.

 

Details here: http://www.hammondmfg.com/pdf/1593P.pdf

post-12-1127554911.jpg

Edited by jasonhanjk

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Total cost?

 

 

PCB $11

Film resistor $1.00

2 OPA2134 $9.22

LM6171 $6.57

5 film cap $5.00

2 E cap $1.00

Enclosure $7.82

Pot $7.43

 

Total: $49.04

 

To make it cheaper remove the pot and enclosure. Film cap reduce to 2 (read Step 6). $30.79.

 

 

Ok, have fun DIY. :yeah:

post-12-1125067027.gif

Edited by jasonhanjk

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Step 3: Insert the OPA2134 X 2.

 

If you don't like OPA2134, you can choose other dual opamp IC.

Now you have a choice to use socket or not. Just for-your-info, non-socket opamp have better performance than socket one.

I highly recommend that sockets be used.

Most of the people buying this board and reading this guide will have little or no experience with soldering.

By soldering to the opamp directly, they're very much more likely to damage it through overheating.

Also, using sockets will allow opamp rolling so why take away the fun?

Last but not least, the sonic difference of socket will not be audible on this circuit.

 

In short: Use sockets.

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Noob when it comes to soldering, as well as diy. Agree with Firefox (hey, I'm using you right now) that a socketed one would be better.

Appreciate the work that you have done in getting this out to us and with detailed instructions, no less.

Do keep up the good work.

 

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Ok guys, have fun DIY. I am going to start another thread on building a power transformer. Maybe a few days later.

 

Chiao...

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Sorry, a few newb question.

 

will heat damage resistors and film caps?

 

and

 

I dont understand "So short both the number 1 and 2 hole near to C2. See attach picture. Don't short hole 3, that is ground." How do I short the holes? drip solders into the holes?

 

and

 

I don't need jumper wires underneathe with this PCB?

 

and

 

Is this significantly easier to do than using normal non-PCB?

 

Oh... Thanks! biggrin.gif

Edited by Username

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I am no expert but certainly heating the components for more than 10 -20 secs can damage them. Certainly electrolytic capacitors don't like too much heat, they will pop. I have damaged a few caps that way when I was learning to solder.

 

To short the holes, connect them with jumper wire, either on top or below the pcb, up to you. And this should be a lot easier than using the perf boards.

 

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BTW guys, what is the LM6171 used for? For the VG? Thanks.

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Yup Heady.

 

 

Username.

Add wire between them and solder.

Yes.

Yes.

 

Some of the newbie at head-fi spent relative amount of time fixing up a Cmoy and end up doesn't work. Cmoy2 is to address that issue.

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hihi , got the pcb from tropicalrips today.. did some soldering, but still have to wait to collect the opamps from federal on monday.. so this what i've got right now.

 

user posted image

 

i'm at step 11a , but i don't really know how to continue from here on..

are the holes i shaded the right ones? 2,3 and 6.

 

so i short 2 and 3 under the board, then insert the LM6171 ontop of the board?

 

and whats 0v wire mean? where does the other end of the 0v wire go to? do i connect it to the case?

sorry i'm such a newbie >_> , and thanks in advance smile.gif

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