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Cmoy power supply question

post #1 of 11
Thread Starter 

Hi,

 

I'm new here and to electronics as a whole so please excuse my probably stupid questions whilst I try and learn a bit. I recently decided to build a cmoy amp and so with my dodgy soldering skills I got going and managed to produce a wonderfully noisy amp with lots of clicking. It was round about this point I decided to rebuild it as my measurements were indicating my power supply had different readings on each side. This was something I checked with a 9v battery up front so I was a little disappointed.

 

Anyway I put together the power supply on a fresh start and my 9v was showing a +4.5 on one side and a -4.5 on the other so I was thrilled. I then plugged in my 24v power supply and again one side is 10.something and the other 13.something (one was negative I can't recall which though). These happen to be the same figures I was getting on my old amp. :-( Is the 24v just making my life difficult?

 

Also on my 2nd amp I added my led with a 10k resistor. This came on with the 9v battery (very softly) but not with the 24v power supply which confused me. The 24v power supply is a 24v 750mA supply. It was my original intention to just this power supply as I don't really need portability. I haven't tried with less resistance yet I suspect this has something to with it but I don't really understand why.

 

Anyway I'd appreciate any help/suggestions/explanations from anyone who understands this better than I do.

 

Thank you kindly.

post #2 of 11
Quote:
Originally Posted by jbv123 View Post
 

managed to produce a wonderfully noisy amp with lots of clicking

 

Clicks usually indicate that it's running into its thermal limits and shutting down. If that's it, the most likely cause is a short somewhere.

 

You acknowledge dodgy soldering, so perhaps watching my soldering tutorial videos will help.

 

(Yes, folks, they're on Vimeo now, so no longer squashed to 320x240. Yay.)

 

If you can't find it on your own, posting high-res pics of both sides of the board will often work, as we can tell you where the problems are.

 

Quote:

my measurements were indicating my power supply had different readings on each side.

 

Within reasonable limits, that's normal for a CMoy.

 

Quote:

my 9v was showing a +4.5 on one side and a -4.5 on the other so I was thrilled.  

 

You did that test before installing the op-amp, right?  Re-do the test with the op-amp installed, and you'll probably find that the voltage has shifted measurably with a 9V battery now.

 

Quote:

Is the 24v just making my life difficult? 

 

More often than not, 24V will make your life easier than 9V.  There are exceptions, but nothing you should be running into at this stage.

 

Quote:
Also on my 2nd amp I added my led with a 10k resistor. This came on with the 9v battery (very softly) but not with the 24v power supply which confused me. The 24v power supply is a 24v 750mA supply. 

 

Either the LED got damaged between the power supply changes, a solder joint broke, or you've hooked the 24V supply up backwards.

 

I don't really believe the latter, since that will usually kill the rail caps, too. Check it to be sure anyway.

 

To test the damage hypothesis, the best tool is a DMM with a diode tester rated for LED testing. (Many diode testers cannot test LEDs properly!)

 

Failing that, use alligator jumpers to hook the 9V supply directly across the LED-and-resistor pair. (Not directly across the LED! That will kill it.)

post #3 of 11
Thread Starter 
Quote:
Originally Posted by tangent View Post
 

 

Clicks usually indicate that it's running into its thermal limits and shutting down. If that's it, the most likely cause is a short somewhere.

 

You acknowledge dodgy soldering, so perhaps watching my soldering tutorial videos will help.

 

(Yes, folks, they're on Vimeo now, so no longer squashed to 320x240. Yay.)

 

If you can't find it on your own, posting high-res pics of both sides of the board will often work, as we can tell you where the problems are.

 

 

Within reasonable limits, that's normal for a CMoy.

 

 

You did that test before installing the op-amp, right?  Re-do the test with the op-amp installed, and you'll probably find that the voltage has shifted measurably with a 9V battery now.

 

 

More often than not, 24V will make your life easier than 9V.  There are exceptions, but nothing you should be running into at this stage.

 

 

Either the LED got damaged between the power supply changes, a solder joint broke, or you've hooked the 24V supply up backwards.

 

I don't really believe the latter, since that will usually kill the rail caps, too. Check it to be sure anyway.

 

To test the damage hypothesis, the best tool is a DMM with a diode tester rated for LED testing. (Many diode testers cannot test LEDs properly!)

 

Failing that, use alligator jumpers to hook the 9V supply directly across the LED-and-resistor pair. (Not directly across the LED! That will kill it.)

 

Tangent, firstly thanks a mil for sharing your knowledge on your site, I've been reading and using it extensively the last few days. I did watch a few clips, I must have missed the soldering one though so I'll definitely watch it as I need all the help I can get it.

 

The click is really just a loud one when switching it on, there was some faint music though so I can't be that far off! You do mention the click on your site so I'll try and do some more basic troubleshooting before I come here (it's probably only a matter of time but I'm understanding more as I go along). I'm really glad to hear the 24v issue isn't really an issue. I'll try and read some of the virtual ground pages, it's a bit over my head at this stage.

 

I will double check the led maybe I'm just doing something stupid, the voltage shouldn't have been switched at any stage I have these clearly marked. Anyway thanks for the info and suggestions, really appreciated.

post #4 of 11
Quote:
 The click is really just a loud one when switching it on

 

In that case, you probably have high DC offset, which you should have tested for with a voltmeter before plugging your headphones in. If the DC offset is low with the headphones out but rises when you plug the headphones in, the amp is probably oscillating, which you can confirm by measuring the amp's current draw.

 

The overheating case typically causes time-varying repeating clicks which may settle on a pattern as the system reaches thermal equilibrium, not just a single click.

 

A CMoy will always have a bit of a pop when turning it on, but not a loud click.


Edited by tangent - 6/2/14 at 1:58pm
post #5 of 11
Thread Starter 

So after watching your soldering tutorial I tried to create a board with hopefully far better soldering. Everything seems to be connected at least.

 

I seem to have a dc offset problem though. This was tested with a 9v input battery and I got a reading of 215mV and 218mV, of course I have no idea why but those figures seem way out.

 

 

 

The amps current draw is 11.39mA (I measured this by placing the multimeter in series from the battery to the board)

 

I haven't noticed anything get hot but I'm all out of ideas for what's wrong and where to start looking.


Edited by jbv123 - 6/7/14 at 6:53am
post #6 of 11
Thread Starter 

Top View

Bottom View

 

Sorry I think these URL's will work.


Edited by jbv123 - 6/7/14 at 6:54am
post #7 of 11

Isn't the -IN on each side of the op-amp connected to virtual ground via those jumpers at the wing edges of the board?

post #8 of 11
Thread Starter 

I think you're right, I can only get stripboard where I am so I was searching for an alternate layout and used this one:

 

http://www.head-fi.org/t/460669/strip-board-cmoy-revisited

 

The winglets are my temp "R5's" in your schematic. Actually looking at the schematic and what I have now I'm very confused, they look quite different.

 

Maybe I need to go back to the drawing board and try and work out a different layout.

post #9 of 11
Thread Starter 

I'm back from the drawing board and I have seen the errors of my ways. 

 

The winglets should in fact be 1k R3's in the schematic. The winglets need to be between  pins 1 and 2 and 6 and 7 in parallel with the 10k R4.

 

 

Apologies for the very scribbly and messy pic from my board but I think I've got it now.

 

Now the real question is have I damaged anything with my stupidty! I'll rectify this issue and see if the amp is now working. Thanks a mil :-)

post #10 of 11
Thread Starter 

After sorting out my issues above and using a lot of crocodile clips to test this all I finally have a working system. Best of all there was no noise, I am very happy. Time to get started on the inputs then. :)

post #11 of 11

Perhaps you would draw up your new stripboard layout and post it publicly somewhere? You're surely not the only one who's had to come up with their own.

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