Please buy any 3mm LED preferably red, yellow rated at 1.5V , bend it as per case and all set
That's not true, see what NwAvGuy writes on the subject:
"POWER LED: You might think this doesn’t need a mention but there are some special requriements. First, the normal forward current for most LEDs is 20 mA. That’s as much power as the entire rest of the amplifier needs! So a 20 mA LED would cut the battery life in half. The O2 uses a “HE” high efficiency red LED that is sufficiently visible with only about 0.5 mA. Second, it’s powered symmetrically from the rails (18 – 24 V) on purpose even if that seems less efficient. Otherwise one battery will drain slightly faster than the other. That gets you nothing except mismatched batteries. Finally, the LED’s forward voltage is a critical element of the power management circuit. You can’t change to a different color (especially white or blue) without making other changes as that will require more current and the different forward voltage means the power management circuit has to be altered."
I think Mooly had a post about how adapt the required component to other leds
Thanks CHiroshi, does that still apply if I'm not using batteries, just the wall wart?
Yes.
I am in no way am EE, but my diy:er understanding of it is that
1. The LED had to be red since it is used as the voltage reference for the power management circuit. Other color LEDs have a different forward voltage which will cause the power management not to function as intended
2. The LED used is very high efficiency. As NwAvGuy writes, other regular LEDs draw by themselves more current than the rest of the amp when sitting at idle
Thanks for that input, I should say that I'm not interested in the light emitting element of it, any diode would do me as long as it worked with the circuit.
Just read the part called Checking the voltage comparator and switched output rails. in post #3775. It tells you what to do.
Hi Mooly,
Been away so I didn't get a chance to test the amp.
With only the 3.5mm input connected and a stereo source connected, shorting the C11/C12 does indeed turn off the channel.
I am still getting the channel problem, any more suggestions?
Thanks,
Myles
Been away so I didn't get a chance to test the amp.
With only the 3.5mm input connected and a stereo source connected, shorting the C11/C12 does indeed turn off the channel.
I am still getting the channel problem, any more suggestions?
Thanks,
Myles
The most effective way to test this would be with an oscilloscope and to look at the signal as it passes through the amp.
Its an odd fault because it seems to be non symmetrical, right channel gives output from the left but left does not give output from the right.
The only way that makes sense is to factor in different impedances... the right channel must be feeding its audio from a low impedance point in the right channel and into high impedance point in the left. In reverse that wouldn't work, the question is where is the problem.
You could try using a meter on its AC volt range and applying L and R test tones to the amp. The 02 will handle a 2vrms input level (higher the better using just a meter) and so a 0db MP3 test tone should be suitable. That would allow comparative checks and let you measure the signal at the various points in the amp. That might be the best way to get a handle on what is happening.
Use a lowish frequency tone of say 400Hz as any meter should be happy with that.
Its an odd fault because it seems to be non symmetrical, right channel gives output from the left but left does not give output from the right.
The only way that makes sense is to factor in different impedances... the right channel must be feeding its audio from a low impedance point in the right channel and into high impedance point in the left. In reverse that wouldn't work, the question is where is the problem.
You could try using a meter on its AC volt range and applying L and R test tones to the amp. The 02 will handle a 2vrms input level (higher the better using just a meter) and so a 0db MP3 test tone should be suitable. That would allow comparative checks and let you measure the signal at the various points in the amp. That might be the best way to get a handle on what is happening.
Use a lowish frequency tone of say 400Hz as any meter should be happy with that.
I will try the test tomorrow and see what I find, with the meter I would check the VAC on the J2 pins underneath right?
I should also mention If I didn't make it clear with my earlier post; shorting C11/C12 turns off the corresponding channel.
I should also mention If I didn't make it clear with my earlier post; shorting C11/C12 turns off the corresponding channel.
Yes, begin at the input and work along. Check at pins 3 and 5 of the first opamp and then at the opamp outputs. The L and R should show no interaction. Then check at the volume control, the wiper of the volume control and so on all the way to the output.
I'd like to make a custom modification to my O2 ( and maybe odac if I go that route). I currently have my computer hooked up to my O2 through the line out and A2+ speakers hooked up to the computer via USB, taking advantage of the onboard DAC in the speakers.
I also have the speakers connected to my turntable, and this is where I feel the need to begin modding. I'd like to listen to the turntable on headphones or speakers.
I'm thinking of
1) buying an odac
2) putting the O2/odac combo in a B3-080 or comparable case
3) adding an RCA-in on the back for the turntable which would initially connect to a 3pdt switch. The line level output from the odac would also go into this switch
4) connect the output from this switch to the O2
5) audio out from the O2 goes to another 3pdt switch so I can select the device to play; headphones from a jack on the front or speakers from a set of RCA-outs on the rear
Would this work? Introduce noise? Am I overlooking a more elegant solution?
I also have the speakers connected to my turntable, and this is where I feel the need to begin modding. I'd like to listen to the turntable on headphones or speakers.
I'm thinking of
1) buying an odac
2) putting the O2/odac combo in a B3-080 or comparable case
3) adding an RCA-in on the back for the turntable which would initially connect to a 3pdt switch. The line level output from the odac would also go into this switch
4) connect the output from this switch to the O2
5) audio out from the O2 goes to another 3pdt switch so I can select the device to play; headphones from a jack on the front or speakers from a set of RCA-outs on the rear
Would this work? Introduce noise? Am I overlooking a more elegant solution?
I did some testing, first I played used 500Hz Left then Right test tone. All the results came out symmetrical. Then I tested with a mono 440Hz; U3 and U4 gave no ACV. I checked if audio was coming through and it was. Now I am more confused 🙁
I'm not sure how you have this connected up but you need a stereo test track (tones) and not just to swap leads around.
Your test track should be say 30 seconds of left channel followed by 30 seconds of right channel followed by 30 seconds of L+R (mono).
You may be doing that already 🙂
No ACV ? Do you mean no measurable audio ?
Do you want an MP3 test track to use ?
Your test track should be say 30 seconds of left channel followed by 30 seconds of right channel followed by 30 seconds of L+R (mono).
You may be doing that already 🙂
No ACV ? Do you mean no measurable audio ?
Do you want an MP3 test track to use ?
I would like an MP3 test track thanks.
I played test tones via my phone connected to the 3.5mm input jack, I then tested the volts (P1, VR, U1/U3/U4/U2 and P2) in AC with my meter. When I tried playing a mono test tone I wasn't getting any volt readings from the U3/U4.
Forgive me I am a noob when it comes to this.
I played test tones via my phone connected to the 3.5mm input jack, I then tested the volts (P1, VR, U1/U3/U4/U2 and P2) in AC with my meter. When I tried playing a mono test tone I wasn't getting any volt readings from the U3/U4.
Forgive me I am a noob when it comes to this.
Yes, follow the signal through. You should see no L and R mixing anywhere in the signal path.
Just ran the test; couldn't find anything incorrect, can't see any L/R mixing not even at the P2 output. Testing with AC Volts on a basic multimeter probably doesn't help (0.1 AC Volts being the smallest measurement).
I wonder if connecting the headphones is creating a grounding loop.
N.B. Listening with the headphones - left is fine, right is mixed and mono is mostly right.
:S
I wonder if connecting the headphones is creating a grounding loop.
N.B. Listening with the headphones - left is fine, right is mixed and mono is mostly right.
:S