Hi!
Just completed my o2 today. Not sure it wasn't mentioned here yet - my searching skills might be too weak )
a little advice for beginners like me - be extremely careful if you decide to use super-glue to fix the cap on the power/gain switch. One of them in my kit was lousy so I made an epic decision to glue the cap to the switch. The glue was not fresh and it took like a minute or so to get dry, instead of a few seconds, and it was enough for the glue to sneak into the power switch and glue it forever in an "on" state. Good for me, I don't need the gain switch for now, so I desoldered working gain switch, replaced it with a bridge and soldered it in place of the spoiled power switch. It was a big deal for me to desolder those switches, because earlier me, thinking "what ever can go wrong with switches?!" soldered all the pins, even the shell of the switches. In short, think before you do, or you'll pay twice
Just completed my o2 today. Not sure it wasn't mentioned here yet - my searching skills might be too weak )
a little advice for beginners like me - be extremely careful if you decide to use super-glue to fix the cap on the power/gain switch. One of them in my kit was lousy so I made an epic decision to glue the cap to the switch. The glue was not fresh and it took like a minute or so to get dry, instead of a few seconds, and it was enough for the glue to sneak into the power switch and glue it forever in an "on" state. Good for me, I don't need the gain switch for now, so I desoldered working gain switch, replaced it with a bridge and soldered it in place of the spoiled power switch. It was a big deal for me to desolder those switches, because earlier me, thinking "what ever can go wrong with switches?!" soldered all the pins, even the shell of the switches. In short, think before you do, or you'll pay twice
So I pretty much installed everything started measuring and following troubleshooting steps. Measured D1,D5 fine, but when i measured U4 with U2 socketed
pin4 = 2V, pin8 = 0.26V (doesn't look right ) so i then measured U2 socket pins.
pin/Vol
1 9.37
2 3.16
3 3.70
4 2
5 3.7
6 9.36
7 8.43
8 11.88
i'm not really electronic savvy. Where should i look?
pin4 = 2V, pin8 = 0.26V (doesn't look right ) so i then measured U2 socket pins.
pin/Vol
1 9.37
2 3.16
3 3.70
4 2
5 3.7
6 9.36
7 8.43
8 11.88
i'm not really electronic savvy. Where should i look?
so i ordered new switches and connected it by a wire. Got right voltages on 4,8 pins, tested U2 by shortening R9 then went on audio circuit.Pins 1,7 with U1 socketed have 0 volts on them. I guess 2,3 5,6 are music imputs and P1 is for ODAC? So i started to do some measurements with some music imput (without U1 in) to see what input it's
getting.
pin 4,8 = -+12V
pin 1,2,6,7 = 0V
pin 3 = 1mV
pin 5 = 1.7mV
My guess is that pin 3,5 are from music input and U1 should amplify them on 1,7? but it doesn't? i dont really know could you please help me out.
getting.
pin 4,8 = -+12V
pin 1,2,6,7 = 0V
pin 3 = 1mV
pin 5 = 1.7mV
My guess is that pin 3,5 are from music input and U1 should amplify them on 1,7? but it doesn't? i dont really know could you please help me out.
Have you followed the fault finding guide I posted a link to in post #1 ?
This was the guide,
http://www.diyaudio.com/forums/head...eadphone-amp-diy-project-189.html#post3806667
Fit all the IC's.
Pin 4 of all the opamps should have minus 12 volts approximately, and pin 8 of all the opamps should have plus 12 volts.
Pin 1 of all opamps should be zero volts to within a few millivolts.
Pin 7 of all opamps should be similar.
This was the guide,
http://www.diyaudio.com/forums/head...eadphone-amp-diy-project-189.html#post3806667
Fit all the IC's.
Pin 4 of all the opamps should have minus 12 volts approximately, and pin 8 of all the opamps should have plus 12 volts.
Pin 1 of all opamps should be zero volts to within a few millivolts.
Pin 7 of all opamps should be similar.
Its hard to say what's going from the description. Make sure that pins 1 and 7 of the opamp feeding the volume control has zero volts DC on it.
If you remove U1 and then link pin 5 to pin 7 and pin 1 to pin 3, then that first stage is bypassed and the input signal will be applied to the volume control directly.
If you remove U1 and then link pin 5 to pin 7 and pin 1 to pin 3, then that first stage is bypassed and the input signal will be applied to the volume control directly.
BTW, to what extent should these voltages be equal? mine reads like -11.85 and 11.92, but since it sounds perfectly fine I didn't raise the question here. But it still bothers me a little since I'm a newbie to electronics - shouldn't such a difference distort the signal? like, author made a lot of efforts building power control circut to prevent unequally drained batteries to cause dc in the output, but then I see this difference in supply rails voltages. Won't this affect the signal? Sorry for a dumb question, if it seems dumb to you
Unless you have good reason to suspect the pot then I'd be looking elsewhere tbh. The voltages are probably OK, but sound a little on the high side in absolute terms. Any offset is opamp specific and the 2068 isn't one I've used. You still hear the noise with the opamp U1 removed so there can't be a problem there at the moment.
BTW, to what extent should these voltages be equal? mine reads like -11.85 and 11.92, but since it sounds perfectly fine I didn't raise the question here. But it still bothers me a little since I'm a newbie to electronics - shouldn't such a difference distort the signal? like, author made a lot of efforts building power control circut to prevent unequally drained batteries to cause dc in the output, but then I see this difference in supply rails voltages. Won't this affect the signal? Sorry for a dumb question, if it seems dumb to you
Its a good question
The voltages will be within the tolerance of the 78/79 regulators used. I'd have to look at a data sheet for them but up to -/+0.5 volts either way wouldn't be abnormal.
Unequal rails have no impact on the performance apart from causing assymetric clipping. If one rail were +6 and the other -20 for example, then it would all work correctly up to -/+6 volts output, beyond that the top of the waveform would clip at +6 volts but the lower half would be good to -20 volts. So its not a problem.
And some DC offset at the output, right? so they may be unequal up to the extent where DC level at the output is lower than the acceptable level. Thanx for the explanation!
And some DC offset at the output, right? so they may be unequal up to the extent where DC level at the output is lower than the acceptable level. Thanx for the explanation!
Unbalanced rails don't affect DC offset at all. The opamp will maintain its zero volts output all the way down to a supply voltage where the opamp stops working. Try it
(try and remember how an opamp works and how the output voltage is determined, either steady state DC or an AC signal. The output looks to maintain the difference in voltage between the inputs as zero)
Unbalanced rails don't affect DC offset at all. The opamp will maintain its zero volts output all the way down to a supply voltage where the opamp stops working. Try it
Thanks for an explanation, once again. I think I have a cheep opamp to experiment with, I'll try that on a weekends. however, it seems I misunderstood the whole purpose of the power management circuit, thus, I'll have to re-run some of the tests on my o2. Should've pay more attention when reading nwavguy's blog...