No! CMOY Problems...
Feb 19, 2005 at 6:09 PM Thread Starter Post #1 of 14

jerb

Headphoneus Supremus
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no digicam right now should have one tommarrow. i plug in the 9 volt battery and nothing gets hot however when i plug in a source and headphones all i get is very loud clicking noises, no music. when there is no signal i can hear loud static, ad when i unplug the source there is a very loud pop. any idea's?
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Feb 19, 2005 at 8:33 PM Post #2 of 14
To start, never, ever connect or disconnect source or headphones while the amp it powered. Two easy thing to check are. Whats the battery voltage. An old battery will cause problems in a cMoy. Second make sure that the chip is seated completely in the socket. Otherwise Start checking against the schematic, and look at:
http://tangentsoft.net/audio/trouble.html
 
Feb 19, 2005 at 11:53 PM Post #4 of 14
make sure there are no cold joints, i got my cmoy working first go, and i wanted to change the gain. after i got the new resistor in, i had massive loud static, and i found that one of the solder joints came lose.
 
Feb 20, 2005 at 5:21 PM Post #6 of 14
parents just got back so i have a digicam again, i will post lorge pics of the amp.
one problem i think i have is that i am using massive polypropaline(sp?) capacitors. they are huge compared to tangents little blue boxes and i think they might be shorting out.

thank you all for yoour responses
 
Feb 20, 2005 at 6:59 PM Post #7 of 14
no pics
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i cant get the digicam to focus on the solder joints. other than that im scrapping this one
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im gonna desolder everything and try again.

i am using orange 200V caps on it and their not working, their the size of the amp itself and they short everything.

one final note, will any one please explain how to check the dc offset? this way i dont run into the same problem when i rebuild
 
Feb 20, 2005 at 7:53 PM Post #8 of 14
sounds like you are going down the same track as i went down only for me all 4 times if turned out too be the fact i wasn't using the right risistor values,but hey i had anuff parts too build 2 cmoy amps
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Good luck i hope it works for you in the end i know mine dose and i love it,i now go every where with it
 
Feb 20, 2005 at 11:06 PM Post #9 of 14
desoldered everything... i have to make another trip to radioshack, does anyone know of some smaller polypropaline caps (im using 200V ornage drop ones) that will work in the amp? alos how do i check the DC offset?
 
Feb 21, 2005 at 4:10 AM Post #10 of 14
The orange caps should work fine for the input caps (not to be confused with the electrolytics in the power supply, which are 220uf or higher). Even if the orange caps were shorted, the amp would still work.

DC offset: take your DMM set for DC volts, and connect the black lead to the virtual ground (anywhere on the two center rows of the board or a resistor lead going there, etc.). Take the red lead and put it on the R output. Then the left output. This will give you your right and left DC offset. Should be in millivolts (0.00x volts). 0 is great, anything under about 100 millivolts is OK, under 10 is preferred.

Some common newbie mistakes from Tangent's really good tutorial:

1) Electrolytic caps in backwards: when looking at the board as in the view provided in Tangent's board layout, the left electrolytic should have its positive pointing toward the top of the board. The right electrolytic should have its positive pointing down.

2) The "M" jumper: This must connect all 3 sets of double pads. This ties the feedback loop together (R4 and R5, I believe) as well as connecting the output.

3) Double check your resistor values! Use a meter, and pay attention to the K ohms and 0s.

4) R5: make sure you either have a small resistor (47 ohms, less than 100 ohms) or a jumper here.

5) Crappy solder joint, bridging: Look the board over carefully with magnification.

6) Double check the assembly without the opamp in. To do this, hook your meter up with the black lead on virtual ground. Take the red lead, and measuring ohms, check all pins in the opamp socket. The power pins (4 and 8) won't tell you much since you will be charging the electrolytic caps up... it may look like a dead short briefly, then work its way toward infinite resistance. This is normal. The other pins should correspond to the feedback and input resistors. For example, pin 5 is the input for one channel. You should be seeing 100K ohms here. Have the schematic handy, and if the value you are measuring doesn't seem right, fix it. Also check from pin to pin to verify there are no shorts. You will see some resistance between certain pins.

Build the amp itself first and get it working before you put a pot in, etc. Get a pack of jumper clips (with the mini-alligator clips) at Radio Shack, and use these to connect the input and outputs to the amp. I think the bag Ratshack sells has 10 of them which is enough. RS #278-1156 or 278-1157. Don't get any that are 2 short (like 1", you want ones about a foot long). You'll need 3 each for the input and output, and another 2 to connect the battery. Once you get it working this way, you can start wiring the jacks, pot, etc. one at a time, so it makes it easier to troubleshoot.

Have fun!
 
Feb 22, 2005 at 3:43 AM Post #11 of 14
after desoldering (and ruining most of the componants) i have read you post and feel soo dumb!

Quote:

1) Electrolytic caps in backwards: when looking at the board as in the view provided in Tangent's board layout, the left electrolytic should have its positive pointing toward the top of the board. The right electrolytic should have its positive pointing down.


i had both of them facing downward

Quote:

2) The "M" jumper: This must connect all 3 sets of double pads. This ties the feedback loop together (R4 and R5, I believe) as well as connecting the output.


i used a 's' jumper

Quote:

3) Double check your resistor values! Use a meter, and pay attention to the K ohms and 0s.


i realize now that i messed up here aswell

Quote:

4) R5: make sure you either have a small resistor (47 ohms, less than 100 ohms) or a jumper here.


oops didnt put any thing there
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i wish i had read your post befor building
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o well i reordered the parts (with extras this time) and i will be building it again. so much for being cheap
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thanks for the help
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Feb 22, 2005 at 4:12 AM Post #12 of 14
Quote:

Originally Posted by jerb
after desoldering (and ruining most of the componants) i have read you post and feel soo dumb!

i wish i had read your post befor building
eek.gif
o well i reordered the parts (with extras this time) and i will be building it again. so much for being cheap
rolleyes.gif


thanks for the help
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Hey - never mind
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You took your first tentative steps into DIY and you have learned from the experience... And i'm willing to bet you won't make the same mistakes twice
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