Make sure that the orientation of the band on D2 and D6 matches up with the symbol on the PC board. Also try re-heating the solder joints on those even if they look OK.
With the AC adaptor and headphones unplugged, batteries in and the O2 power switch on, what voltage do you measure from ground (shell of the gain switch) to the battery terminal closest to the edge of the board and to the terminal farthest from the edge of the board?
I do know that a click and thump is expected on turn off and on (as per documentation), and while it is not startlingly loud, it is a solid click and thump. Voltage measurements are close to expected (if a tad low throughout, especially U2-p7 at 8.5v). Hopefully it is nothing to worry about. Voltage at output is under 4mv, with ac, no batteries, and no input. Measuring voltage at on and off, the most extreme value I have seen was -7 volts at turn off which quickly comes below a volt and decreases to < 10mv within a minute.
All good? Would you risk $1000 headphones without further testing?
All good? Would you risk $1000 headphones without further testing?
The calculation is quite simple:
The NJM2068 cannot swing to more than about 1.2..1.5 V of either rail (datasheet says 1.5 V), so the maximum allowable gain stage output amplitude is approximately
Vmax,p-p = (V+ - V-) - 3 V
with V+ and V- being your supply voltages.
For sine output this means
Vmax,rms = Vmax,p-p / 2.83
The maximum allowable gain is
Gv,max = Vmax,rms / Vsource,rms ,
with Vsource,rms being maximum source RMS output (2.16 V in this case). (Note that for digital sources like CD players, very "hotly" mastered material may produce peaks up to 1.5..2 dB above nominal 0 dBFS amplitude, so 10..30% of extra headroom can't hurt.)
With a gain of 3.2, you'd normally be fine during mains operation (+/- 12 V) but would run into clipping when running on batteries (+/- 8.4 V .. +/- 9.45 V typ). I'd recommend a low gain of 2. High gain would depend on whatever you have in terms of portable devices; 6x is fine for a Clip+ or similar (you won't get more than 0.80 Vrms out of that whatever happens), "Euro-capped" players may require more than the maximum 8x (18 dB).
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Thanks agdr and sofaspud! I had soldered D6 in backwards. DC output levels while running from batteries are below 6mV.
I did notice whilst performing the low voltage shutdown tests that output DC spiked to around 1.5V, but then quickly settled down around 164 mV. Is this within acceptable limits?
I did notice whilst performing the low voltage shutdown tests that output DC spiked to around 1.5V, but then quickly settled down around 164 mV. Is this within acceptable limits?
Seems quite high (the figure quoted in another thread was 50 mV max). Such a peak would be about 40 dB above my normal listening levels.
Are people plagued by dead regulators lately or what? (Shouldn't appear when running on batteries then, however, so I don't know what's up here.)
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Whoa! No, that doesn't sound right, if that -7.0V is on the output jack going to the headphones. I would expect maybe 100mV at most, dropping down to 3mV is a few milliseconds. I have to run right now, but best to hold off plugging in the phones until me or someone else here can help you with that.
The -7V was the most extreme I saw on P2, from square to farthest, when holding black probe to black and red to farthest of P2 -- turning off with headphones UNplugged. After a few seconds it falls below 200mv and within a minute of holding probes is below 10mv.
With headphones plugged in it is an entirely different story. The highest I saw was -170mv and dropping to 0 within a second of turning off. The turn on max was less than -100mv and dropping to 3.4mv within a second.
With headphones plugged in it is an entirely different story. The highest I saw was -170mv and dropping to 0 within a second of turning off. The turn on max was less than -100mv and dropping to 3.4mv within a second.
I better make sure I'm understanding your test correctly. Is it the case that with the amp on and the headphones unplugged the voltages you measure on P2 are around 3mV, but then after the power switch is turned off you got that -7V, which then dropped down to zero? On my first read I was taking that -7V to be on P2 with the amp turned on.
The voltage you would want to measure is the voltages on P2 with the amp having been on for several seconds and the headphones unplugged. Should be somewhere around 3 - 8mV. If you are getting that on both channels then your O2 is passing the output DC bias check. RocketScientist has the 8mV figure in his instructions. I've been lucky and seen around 3mV on mine. That comes down to differences in op amp batches.
-7Vdc on the headphone jack continuously with the amp on could be enough to damage headphones if applied for several seconds.
Try reheating the solder joints on both ends of R12 and R13 regardless of the voltage measurements. Couldn't hurt.
Here is another test to try. Ideally the power supply rails after the mosfets should drop at about the same rate and in the same way. With the headphones unplugged take a look at the voltage from ground to pin 4 of U3 and compare what it does with the voltage between ground and pin 8 of U3 when the power switch is turned off. Then make the same comparison when the power switch is turned on. The polarities will be opposite, but the rate at which the voltage rise or drop on the two pins should be about the same. You shouldn't see something like the voltage on pin 4 coming up almost instantly but the voltage on pin 8 taking 5 seconds, etc.
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I would agree with sgrossklass, that 1.5V sounds on the high side. I don't have any ideas there at the moment though.
Just curious - what part numbers do you have in for Q1 and Q2? There were several options listed in the BOM.
Yes the -7v was a surge for a moment. On turning off, with probe on P2 and headphones unplugged, the DMM has -5v (or -6.5 or 2.1) immediately on turn off and is below 200mv within a couple seconds. On turn on, P2 comes to 3.4mv within a second and holds steady, never to rise above 4mv until the surge at turn off.
U3, pins 4 and 8 on turn on nearly immediately rise to -11.7 and 11.7. At turn off, both drop below 1v within a few seconds. (Same observation from U4, pins 4 and 8).
U3, pins 4 and 8 on turn on nearly immediately rise to -11.7 and 11.7. At turn off, both drop below 1v within a few seconds. (Same observation from U4, pins 4 and 8).
You are probably OK then. That steady-state output offset voltage of 3.4mV (I'm assuming you get something similar on both output channels) is OK. One second is about as quickly as a person is going to be able to measure something moving on a DMM. Sounds like the post-mosfet rail voltages on P4 and P8 of U3 are tracking well in time also, at least at one or two second granularity.
As for the voltage spike after the switch flips off, with load (headphones) you measured a couple of hundred millivolts which then dropped quickly. I seem to recall reading a reply from RocketScientist in one of the comments on his site where he indicated something in the 100mV was normal for turn off, but that one would really take RocketScientist or someone else here who knows more about it than me to give a good answer. So unfortunately I'll have to punt on that one and admit I'm out of my depth there.
The default, Fairchild FQU11P06TU (Q1) and FQPF10N20C (Q2), from the December BOM.
Good deal! Those are the 30V max gate units, which is more than enough even if the regulators are at the full +/-0.6Vdc-or-so tolerance limit on output voltage. If one had been a 25Vdc gate mosfet I was going to suggest trying a 30V unit, but you are already there.
Hey guys. I just finish building an O2 with the B3 case and got the RCA jack installed and I have grounded the negetative to the case as per the schematic but I'm getting an hollow sound and when I touch the RCA connectors I can hear static.
Did I connected wrong? Am I supposed to ground to the case?
Thanks!
Did I connected wrong? Am I supposed to ground to the case?
Thanks!
Yes I did but maybe not enough. So please confirm that I connected it right. I solder two wires from the middle hole of J1 ( input jack ) and connected each to the ground tab of the RCA jack. I left the plastic isolating ring in the outside but from the inside I scratches the anodize of the case and put the ground ring and put the other pastic isolating ring on top and finish with the two nuts.
Hey Everyone,
I must say this thing sounds amazing after just finishing mine up this afternoon.
I do have a question though as during normal listening levels U2 seems to heat up quite alot. I can still put my finger on it but its very hot to the point that if i was to keep my finger on it i would get burnt.
Would this have anything to do with the gain setting as I am running AKG K271 MKII's
Cheers guys and thanks a whole heap for this brilliant amp
Archie
I must say this thing sounds amazing after just finishing mine up this afternoon.
I do have a question though as during normal listening levels U2 seems to heat up quite alot. I can still put my finger on it but its very hot to the point that if i was to keep my finger on it i would get burnt.
Would this have anything to do with the gain setting as I am running AKG K271 MKII's
Cheers guys and thanks a whole heap for this brilliant amp
Archie
J1 is the DC power jack. That is why you have hum if you connected to the ground there,. There are some really big current spikes moving back and forth between the power jack and the filter capacitors.
The ground ring of the RCA connectors goes to the center (middle of jack, towards the front of the board) pin of J2, the input jack that you connect to your music source. And you should only use one wire, not two, or you risk a ground loop. Just run one wire from that pin on J2 to the ground ring on either RCA jack. The other RCA jack is touching the case with its ground ring, and you just grounded the case with your other RCA jack ground ring and your sanding, like MrSlim said.
If you just made a typo and really are connecting to J2 instead of J1 then the two wires, rather than one, may be the cause of the hum. Also try to route that single ground wire away from the area around the DC jack and 4 filter capacitors C2 - C5 to avoid hum pickup.
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Disregard gents,
I have had a good look over the testing pages and started with a replacement U2 still no change, swapped out the FET still no change.
270 ohm resistors look very similiar to 270k resisters hehe. Placed in the correct resistors and its all good.
Sounds awesome for the small period of time I have been listening.
Thanks a heap