Help with my first CMOY. No sound in right channel.
Nov 18, 2008 at 7:50 PM Thread Starter Post #1 of 19

mark1

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Hey guys. I decided to build my first CMOY recently after reading up about it for a while on Tangent's site. I followed his tutorial exactly and bought pretty much exactly the same parts/board etc. I plan on getting some Beyerdynamic DT770's to use on it.

I have never soldered anything together like this before but i'm quite pleased with how the soldering turned out. I tried to use as little solder as possible and tried to prevent solder bridges by using a stanley knife to cut a little groove between all solder points that were'nt meant to be connected.

Now my problem is that the right channel isn't working at all, not even any noise or anything. The first time i tested it the left channel worked but was popping/noisey. After cleaning the pcb and making sure there were no solder bridges it now sounds perfect. But the right channel still shows no signs of life.

For the voltage readings, there is a slight difference between v+ and v- of about 0.1v. I can't be more specific than that as i'm using an analog multimeter. Using two 9v batteries, v- (left) reads about 8.1v and v+ (right) about 8.0v.

Will this have a significant impact on what's going wrong? I'm hoping it's just bad wiring with the cables and not anything too tedious.

I'll try and get some pictures up of the front and back of the board a bit later.

Cheers for looking.

note: it is not yet mounted in an enclosure if that makes a difference.
 
Nov 18, 2008 at 9:52 PM Post #2 of 19

mark1

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ok here's the two pictures, sorry for the quality.

amp1vh2.jpg


amp2sm1.jpg

The side with the yellow cable is the one that isn't working.

Also, i know the colours of the cables is confusing. I accidentally got the colours mixed up and cba to change it
tongue.gif
 
Nov 18, 2008 at 10:22 PM Post #3 of 19

Pars

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The first thing I would check is to make sure that the "M" jumpers are actually connecting all 3 pads together, as this is the connection completing the feedback loop. If need be, pull the opamp and ohm out pins 6-7 on the socket; should show about 10K (R4 + R5, if IIRC).
 
Nov 18, 2008 at 10:31 PM Post #4 of 19

Uncle Bob

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If the left channel works then it's most likely a wiring problem or a dry joint somewhere. Some that soldering work looks a little poor.

I suggest that if you have a solder sucker, clean up the problem side of the board and rework the joints.
 
Nov 18, 2008 at 10:59 PM Post #5 of 19

mark1

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Cheers for the help.

Pars, when you say 'ohm it out', which points do i actually have to measure from? Pins 6-7 or from pin 6-gnd and pin 7-gnd? Sorry, complete electronics noob here!

Uncle Bob, i thought it might be something to do with my shoddy soldering skills
biggrin.gif
. I was planning on resoldering the right side if i couldn't find the problem soon anyway. Once i get the time this weekend i will try and get that done. I'll do as good as i can with my rubbish £5 fleabay soldering iron.

Could it also be from bad connections on the panel components for the right channel that's causing problems?
 
Nov 19, 2008 at 12:15 AM Post #8 of 19

shortkidsrus

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It looks like the yellow output wire is attached to the wrong pad. It looks like it is bridged with a bunch of solder, but you might want to move it one pad up (toward the power source) so it is on one of the pads shorted by the M-jumper.

Edit: You can use your multimeter to check continuity.
 
Nov 19, 2008 at 12:38 AM Post #9 of 19

Pars

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Quote:

Originally Posted by mark1 /img/forum/go_quote.gif
Cheers for the help.

Pars, when you say 'ohm it out', which points do i actually have to measure from? Pins 6-7 or from pin 6-gnd and pin 7-gnd? Sorry, complete electronics noob here!

Uncle Bob, i thought it might be something to do with my shoddy soldering skills
biggrin.gif
. I was planning on resoldering the right side if i couldn't find the problem soon anyway. Once i get the time this weekend i will try and get that done. I'll do as good as i can with my rubbish £5 fleabay soldering iron.

Could it also be from bad connections on the panel components for the right channel that's causing problems?



I meant check the resistance between pins 6 and 7, as this will show the feedback loop. You should see around 10k ohms if you used stock resistor values. If you see an open circuit, its probably your M jumper. And the output (yellow) wire on top should also be connected to the M jumper.
 
Nov 19, 2008 at 9:14 AM Post #10 of 19

mark1

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Quote:

Originally Posted by shortkidsrus /img/forum/go_quote.gif
It looks like the yellow output wire is attached to the wrong pad. It looks like it is bridged with a bunch of solder, but you might want to move it one pad up (toward the power source) so it is on one of the pads shorted by the M-jumper.

Edit: You can use your multimeter to check continuity.



The original output cable was too short. When i went to remove it i found it difficult to get out and decided to just cut it at the pcb and solder the new cable one pad down, connected by a solder bridge. However, i'll re-do this today to put it back in it's correct position and eliminate that as a possibility.

Quote:

Originally Posted by Pars /img/forum/go_quote.gif
I meant check the resistance between pins 6 and 7, as this will show the feedback loop. You should see around 10k ohms if you used stock resistor values. If you see an open circuit, its probably your M jumper. And the output (yellow) wire on top should also be connected to the M jumper.


When i try this i get no reading on my multimeter. It also happens on the left side as well so it might just be that the multimeter isn't working right. I'm nearly 18 and it's older than me! I'll pick up a new multi when i get the chance.

I'm considering just rebuilding it from scratch. Maybe i can do a better job of it now that i have some flux and a bit more experience with the iron.

Also, slightly off topic, but how would i go about adding a second, unamped, output? I want to use the amp with my pc, having the amped output for the Beyer's and the unamped output for my speakers. Is it just a case of connecting the L and R channels of the input jack to another output jack? Or will this not work...
 
Nov 19, 2008 at 11:50 AM Post #11 of 19

Uncle Bob

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Quote:

Originally Posted by mark1 /img/forum/go_quote.gif
Also, slightly off topic, but how would i go about adding a second, unamped, output? I want to use the amp with my pc, having the amped output for the Beyer's and the unamped output for my speakers. Is it just a case of connecting the L and R channels of the input jack to another output jack? Or will this not work...


Yep, you just need to wire a pair of output jacks onto your input jacks to allow the signal to pass through to another device.
 
Nov 19, 2008 at 11:54 AM Post #12 of 19

Uncle Bob

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Quote:

Originally Posted by mark1 /img/forum/go_quote.gif
When i try this i get no reading on my multimeter. It also happens on the left side as well so it might just be that the multimeter isn't working right. I'm nearly 18 and it's older than me! I'll pick up a new multi when i get the chance.


It could just be that the meter is set to the wrong resistance scale. Try changing the dial setting on the meter until you get a reading on the left channel, then check the right channel.
 
Nov 19, 2008 at 7:29 PM Post #13 of 19

deltaydeltax

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The right channel has (very very very very very very very very very very very) ^10e^100 good reason for now working. It's not connected.

I've not seen the schematic for this "cmoy" amp, don't even know what it is really. Is it just one of those simple amps built into a mint tin (which look pretty darn snappy if you ask me).

Errrr, in any case, it is just a dual OP Amp, I'm guessing you'll be pulling the outputs from pins one and seven. Pins four and eight are the power pins. Pins two and six are the inverting inputs, while pins three and five are the non-inverting. (from memory, please forgive me if I said something dumb).

SOOOOOOOOOOOOO how to fix it. Well, solder another jumper from pin seven to the yellow wire. Then, BAM! AUDIO! WOOOOO!

unless that is...you're trying to build the worlds shortest transmission wireless headphones...
 
Nov 19, 2008 at 7:32 PM Post #14 of 19

deltaydeltax

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Quote:

Originally Posted by deltaydeltax /img/forum/go_quote.gif
The right channel has (very very very very very very very very very very very) ^10e^100 good reason for now working. It's not connected.

I've not seen the schematic for this "cmoy" amp, don't even know what it is really. Is it just one of those simple amps built into a mint tin (which look pretty darn snappy if you ask me).

Errrr, in any case, it is just a dual OP Amp, I'm guessing you'll be pulling the outputs from pins one and seven. Pins four and eight are the power pins. Pins two and six are the inverting inputs, while pins three and five are the non-inverting. (from memory, please forgive me if I said something dumb).

SOOOOOOOOOOOOO how to fix it. Well, solder another jumper from pin seven to the yellow wire. Then, BAM! AUDIO! WOOOOO!

unless that is...you're trying to build the worlds shortest transmission wireless headphones...



What a dumbass! <---me that is...I just realized it is connected on the bottom! wow...

I also second the flux with soldering idea. Flux is some amazing stuff!
 
Nov 19, 2008 at 8:21 PM Post #15 of 19

mark1

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Hey guys, nobody's a dumbass. It was connected on the bottom because it was hard to get it underneath the blue cap. I fixed this just now anyway. Relocated it to the top where it should be. T'was i that were the dumbass.

Anyhoo, i got it working!!!! So pleased right now.

To fix it i did a few things. I cleaned up some of the solder joints as people on here suggested. I then resoldered the right channel wires. Changed the M jumper, making sure the middle bend was long enough to connect all pads. I resoldered the right channel opamp power wire. When i tested it the right channel was noisey. I cleaned it again, dried it and BAM it worked.

Thanks so much for all your help. I now don't feel that i've just wasted all my money. I love building things yourself, so much satisfaction when you're done.

Now i need to sort out mounting it in the enclosure (luckily i don't need help there
tongue.gif
) and it will be perfect.

Cheers once again guys
mark1
 

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