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HELP with cmoy board design

post #1 of 22
4/28/09 at 4:29pm
Thread Starter 
Since i can't find a radioshack proto board i've decided to design my own layout of the cmoy design based on the protoboard one.I just need someone to do a check for me and tell me if my design will work so that i can start work.

Here is the diagram from which my design is based of




And here is my design(on a sheet of paper with somewhat real dimensions to what the board itself will be)


NOTE:red dots are cap holes,green dots are resistor holes and blue are Signal In/Out and battery +/-

2ND NOTE:the resistor R5 has been removed and on the left side of the schematic on the place of R5 there is a blue line.What i wanted to show with that is that i'm going to use a jumper to go over the line connecting the V+ of the IC socket to the battery
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post #2 of 22
4/28/09 at 6:34pm
Looks correct.
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post #3 of 22
4/29/09 at 10:35am
Thread Starter 
good i hope you're right .I've already started to build the board and bought all the elements except the C2 caps which i cannot seem to find.I've went to several electronics shops and everyone said they didn't have any 0.1uF or 100nF caps at all
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post #4 of 22
4/29/09 at 11:05am
Quote:
Originally Posted by DragooNArT2 View Post
good i hope you're right .I've already started to build the board and bought all the elements except the C2 caps which i cannot seem to find.I've went to several electronics shops and everyone said they didn't have any 0.1uF or 100nF caps at all
If you're going to use a JFET input opamp or a modern bipolar input opamp like LM4562 or AD8599, you probably don't need those C2 input caps. Most sources like iPod's, CDP's etc already have output caps. I've never heard of a source with large DC-offset.

The only good those caps do is giving the amp a cool and professional look. I think input resistors will do more good preventing oscillation.
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post #5 of 22
4/29/09 at 11:06am
You can use up to 1uf or so for these; higher is better. C2 in conjunction with the 100k resistors (R2 in your case) to form a high pass filter, whose corner frequency (cutoff or -3dB) is determined by the formula 1/(2 * Pi * R * C) where C is in farads. So, using 100k R2s and 0.1u C2, you have 1/(2 * 3.14159 * 100000 * 0.0000001) or 15.9 Hz. As you can see, increasing C2 value lowers the cutoff frequency, giving somewhat better bass response. I would look for 0.47uf as these can be found in a suitable size.

Or what Nelson said... the best cap is no cap
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post #6 of 22
4/29/09 at 11:09am
0.1uF is actually a little low. Higher values will actually give you better low frequency response, so you could substitute a 0.22, 0.47, or 1.0uF cap if you can find any of those.
It might be a good idea to try an online retailer, such as Mouser or Digikey. They're cheaper and they usually carry pretty much everything.
Also, dial-up modems usually have ~0.047-1.0uF film capacitors which I have used as coupling caps in a CMoy or two. They're a little big, but they work.
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post #7 of 22
4/29/09 at 3:23pm
Thread Starter 
ok so i'll be bypassing the C2 caps since my audio card (Auzentech X-plosion) already has DC Decoupling caps on it's opamps,by the way is there a differance between diodes? cuz if there isn't i'll probably get a bigger(5mm) superbright one.
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post #8 of 22
4/29/09 at 3:27pm
Thread Starter 
ah and another thing i forgot to ask about,On the POT which leg is which?Mine has two rows of three legs,someone said to me that the middle is for connection to the board and the other two don't matter(not that they won't be connected to gnd and 3.5mm jack)


BTW: I have in my possession currently LT1364,LME49720,OPA2134,LT074,NE5532
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post #9 of 22
4/29/09 at 5:11pm
Quote:
Originally Posted by DragooNArT2 View Post
ah and another thing i forgot to ask about,On the POT which leg is which?Mine has two rows of three legs,someone said to me that the middle is for connection to the board and the other two don't matter(not that they won't be connected to gnd and 3.5mm jack)


BTW: I have in my possession currently LT1364,LME49720,OPA2134,LT074,NE5532
The first part is correct (center pins are the outputs). You need to pay attention to the other two if you want the pot to turn clockwise to increase volume. Looking at the pot from the front, with the pins down, the left pins go to ground; the right pins go to the input jacks.
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post #10 of 22
4/29/09 at 7:01pm
Quote:
Originally Posted by DragooNArT2 View Post
ok so i'll be bypassing the C2 caps since my audio card (Auzentech X-plosion) already has DC Decoupling caps on it's opamps,by the way is there a differance between diodes? cuz if there isn't i'll probably get a bigger(5mm) superbright one.
Check the forward voltage and maximum current. Most normal LEDs are rated for ~2V forward voltage drop and 20 mA of current. If the ratings are slightly different on the LED you want to use, no big deal, it's just a matter of changing the current-limiting resistor.

R = (V_source - V_LED) / I_LED

Example (2V, 20mA LED):
R = (12V - 2V) / 0.02A = 500Ω
(500Ω isn't a standard value, so a 560Ω would probably be used instead)

Remember that a shiny new 9V battery is much more than 9V. This is also a minimum value, for maximum brightness. If you want longer battery life, you can use a larger resistor.

You also need to make sure that the resistor is rated for the load. It must be greater than the following value:
(V_source - V_LED)² / R = Power (Watts)

Example (2V, 20mA LED & 560Ω resistor):
(12V - 2V)² / 560Ω = 0.179W
In this case 1/8W is too low, so a 560Ω 1/4W resistor is required. However, if we increase the resistance from 560Ω to 820Ω:
(12V - 2V)² / 820Ω = 0.122W
Which means a 820Ω 1/8W resistor could also be used, if you don't mind the LED being slightly less bright.
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post #11 of 22
4/30/09 at 3:47pm
Thread Starter 
Hi,again.I've almost finished the build.I've even test ran the amp but it didn't quite turn out the way i expected.One channel was very quiet and the other was at moderate volume,while the phones used directly trough my phone are far louder.What i mean is that the amp actualy quietens the sound instead of increasing it.
also someone told me that the gnd for the headphone out should be the battery's - lead instead of the virtual ground.What i'm concerned about however is that one of the channels doesn't actually work and i'm actually not quite sure which leg is which on the 3.5mm jacks.Here are some pics of what has been going on today







Can someone tell me which lead is what on the 3.5mm jack on the last pic please ?
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post #12 of 22
4/30/09 at 5:46pm
Quote:
Originally Posted by DragooNArT2 View Post
<snip>
also someone told me that the gnd for the headphone out should be the battery's - lead instead of the virtual ground.
Wrong. Input and output grounds go to the virtual ground. The battery minus is really your V- and the battery plus is V+. Virtual ground is ideally half way between these two.
<more snip>

Quote:
Originally Posted by DragooNArT2 View Post
You forgot to reverse your board pattern, so when you flipped the board over to build it, it is wrong. For example, V- should be going to pin 4 of the opamp. In your build it is going to pin 5. No real way to fix it other than to remove all components and put them on the copper side. Good luck soldering some of them. Sorry.

Quote:
Originally Posted by DragooNArT2 View Post
Can someone tell me which lead is what on the 3.5mm jack on the last pic please ?
The terminal by the nut is ground. You should be able to visually see which one of the other two contacts the tip of a plug: that will be the L channel.
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post #13 of 22
4/30/09 at 6:44pm
Thread Starter 
lol the only thing that could be wrong is the IC socket and CAP's resistors doesn't matter
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post #14 of 22
4/30/09 at 8:56pm
Thread Starter 
FIXED IT !!! Turned the IC Socket on the copper side,then checked all my chanel connections and found out that the jumper(C2 cap) was not actually soldered

P.S:I noticed that there is this popping at 1/2 intervals when there is no signal,however as soon as i start something even if it is turned down the popping dissapears
2nd PS:I can't turn the volume more than half way it's distorting,could it be because i'm using only one 9v battery?also my R3 value is 2k
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post #15 of 22
5/3/09 at 11:16am
Thread Starter 
I've got one last question.Is it possible to connect the 6th and seventh leg of the IC socket togeter instead of using a jumper(R5) to jump over the BAT+ path
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