Like any faultfinding we start at the beginning...
Remove both batteries and with the AC adapter connected measure the voltage from ground to C4 and C3. In other words the voltage across each cap.
If you have 16 volts DC or more across each of the above caps then measure the voltages across C6 and C7. There should be 12 volts across each.
If it fails those two first tests then remove D1 and D5 and repeat the above tests.
Post your results here
Ok, so i found that C3 reached 16 volts while c4 had 0, and for c7 it was 12 volts while c6 was 0. I didnt remove D1 and D5 yet (ill do it tomorrow) but i found that d5 produces voltage while d1 produces nothing.
Those results tell us that the negative rail is OK (that's everything from C3 through to C7)
If you really have zero volts on C4 then you need to do a couple of checks.
1. With the amp OFF measure on ohms range with your meter across C4 and then across C6. Is there a short ? or very low reading.
2. Check the diode D3. As it stands now it must be either open circuit or there is print that is open circuit. If it were short then it would stop the negative rail from developing.
So up to there is either a problem with or around D3 or a short somewhere has caused D3 to fail open circuit.
r14 / r20
Hi guys,
Just built my o2. As i did the initial testing, r14 /r20 are reading 8kR
Everything else is within the specs.
Voltage checks are also ok.
Any idea why r14 / r20 are so far from what it is suppose to be?
I built a o2 with odac.
after putting together everything anyway, i turned it on and it works.
sounds pretty good.
Any thoughts appreciated.
marc
Hi guys,
Just built my o2. As i did the initial testing, r14 /r20 are reading 8kR
Everything else is within the specs.
Voltage checks are also ok.
Any idea why r14 / r20 are so far from what it is suppose to be?
I built a o2 with odac.
after putting together everything anyway, i turned it on and it works.
sounds pretty good.
Any thoughts appreciated.
marc
Sorry I can't help you but I just checked mine and strangely, those 2 also read 8k (amp seems to work fine though)?
I tested all resistors before fitting so I don't 'think' it's build error?
I'm sure one of the clever people on here will have an answer for it.
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Ok so first im using a manual dmm. When i measured c4, the 200 and 2000 ohm option produced nothing, when turned to 20k, it produced a number between 13.32 and 19.75, but once it hits 19.75, it blinks off to the normal screen that sais 1, which im guessing means no resistance. For c6 it worked on the 200 ohm option, to which i recieved about 111 ohms, the 2000 ohm option gave me 1151 ohms and 20k gave me 10. 05. Im not really sure what that means as i have little experience with dmms.
D3 didnt work. the screen did not change from 1 (no resistance?) but it did flash random numbers when i took the dmm pins off. not sure if that means anything to you.
I know im a noob but thanks for putting up with me. And just to make sure, these measurements are without U2 installed right?
it is suppose to be a 10k out of circuit.
in circuit, according to this
o2%2520resistances%2520no%2520power%255B3%255D.png (image)
it is suppose to be 100-300
but i get about 8k.
it works though. just wondering why it isnt to spec
ok so i replaced the led with the one listed and the amp works with the led on but voltage readings say -11.6v and -9.9v. anyone have a chart of what the correct voltages across the board are? here's some of my readings
An externally hosted image should be here but it was not working when we last tested it.
also i have white noise when the amp is turned to the highest position.
Your link isn't working. What voltage readings are those? Is one of them D5?
Some small amount of background noise/hiss with the O2 in a high gain position and using sensitive headphones or IEMs is normal for this amp. But it should be right at the edge of being heard, not loud at all.
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Its no problem. At this stage having U2 fitted or not doesn't matter.There is something basic going wrong here and it could well be D3 that is open circuit. Look at the circuit diagram. The left hand end of diodes D3 and D4 are joined together. Measure with your meter on ohms that they really are connected. If they are then put your meter on AC VOLTS and with the amp ON measure the AC voltage from ground to the left hand ends (as shown on the circuit) of D3 and D4. Both should be the same voltage and probably showing around 12 volts AC.
If that is OK then change the meter to DC volts and measure from ground to the right hand end of D3. Is there any voltage present ? That tests is really just a double check that there is no break in continuity anywhere.
Also D3 and D4 should read similar on your meter if you put it on the DIODE check range. You should read around 600 to 700 with the red lead of the meter on the anode (the left of D3) and the black on the cathode. Pull the AC adapter from the board to test those.
You can't reliably measure any high value resistors in circuit. Its one of the most basic "rules" of faultfinding. There are many reasons why it doesn't work such as slight residual voltage (from caps) upsetting the DVM reading. Reading in circuit also reads "across" other components connected to the same points. The DVM on ohms range puts out a small voltage across the leads and that voltage can turn on various semiconductor junctions internally in the IC's etc which again give totally misleading results.
I'm just amazed that the diagram even suggests measuring components in circuit.... I'll say no more
There is something basic going wrong here and it could well be D3 that is open circuit. Look at the circuit diagram. The left hand end of diodes D3 and D4 are joined together. Measure with your meter on ohms that they really are connected. If they are then put your meter on AC VOLTS and with the amp ON measure the AC voltage from ground to the left hand ends (as shown on the circuit) of D3 and D4. Both should be the same voltage and probably showing around 12 volts AC.
If that is OK then change the meter to DC volts and measure from ground to the right hand end of D3. Is there any voltage present ? That tests is really just a double check that there is no break in continuity anywhere.
Also D3 and D4 should read similar on your meter if you put it on the DIODE check range. You should read around 600 to 700 with the red lead of the meter on the anode (the left of D3) and the black on the cathode. Pull the AC adapter from the board to test those.
MISSION SUCCESS!!!!!!
I found the problem and it was just as simple as you said it would be. It turns out that one of the power plug's contacts did not fit very well into the solder point and was rubbing against the side of the contact causing the entire piece to sit slightly elevated, which must have created a poor connection. Because when i was doing the tests you wanted me to do, i plugged in the cable and it just popped out of place. I must have not noticed it when putting it together cause i was so excited to finish, silly me
Thanks for everything, i can now contently listen to my DIY amp.Sorry about that, hopefully this or http://imgur.com/GsWwYYs link works. I am getting negative voltage readings on both sides of the led (led is luminaid). the amp works fine but is it supposed to stop working if the led is removed? also there is no white noise when the input plug is removed which leads me to believe its my computer and iphone injecting hiss into the amp, right? and thanks to everyone for the help, your time is greatly appreciated.
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The LED is referenced to the negative rail so your readings are correct. If you remove the LED then the voltage on pins 3 and 5 of U2 will rise toward the positive rail. This means the output of pin 1 should go high and pin 7 low thus turning off the amp. Is that not happening ?
I would highly recommend (WARNING: Very exhaustive-patience required) to read this before you attempt any "opamp rollover"
NwAvGuy: Op Amp Measurements
NwAvGuy: Op Amps: Myths & Facts
NwAvGuy: O2 Design Process