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The Objective2 (O2) Headphone Amp DIY Project
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Old 9th August 2013, 12:47 AM   #3391
XXTheMatrixXX is offline XXTheMatrixXX
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Unhappy Testing of the O2 failed?

availlyrics: Run all tests as per NwAvGuy guide
So I followed your advice and did all of the "Initial DIY Testing" from the
NwAvGuy: O2 Details article.
And only the following test was failed (other tests up to "Check The Current Consumption" measured correctly):

"Measure Resistances – If you have a DMM, with only U2 in its socket (U1, U3 and U4 sockets should be empty), measure across each of the resistors shown in the diagram to the right (click for larger version). The values marked with a “*” may depend on your DMM. If you get a very different reading, try reversing the leads. If it’s still different, check that resistor carefully. If in doubt, heat one end of the resistor from the top of the board and use a small screw driver to carefully pry that end up from the board so it’s only connected at one end. You can then measure it accurately “out of circuit”. If it measures OK, persuade the lead back into board using needle-nose pliars while you heat the pad and lead.


The wrong resistance measurements are:
R8 is 231Kohm instead of ~245Kohm.
R25 is 287.1Kohm instead of ~330Kohm.
R5 is 117.1Kohm instead of ~100Kohm.
R16 is 1.5Kohm instead of 1.3Kohm.
R22 is 1.5Kohm instead of 1.3Kohm.

Please help...Are the wrongly measured resistors need to be changed?

*I use the VC97+ DMM which is accurate.
**I did follow the instructions EXACTLY.
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Old 9th August 2013, 11:38 AM   #3392
dfy is offline dfy
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You did read that those measurements are supposed to be made with U1, U3 and U4 removed? I know you said you followed the instructions, but that's worth making sure.

Also note how the picture says that the values you mention depend on the DMM and the polarity of the leads. Obviously, wait for agdr to give you a definitive answer to your question, but to me it doesn't seem like those values are anything to worry about.
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Old 9th August 2013, 10:56 PM   #3393
agdr is offline agdr  United States
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The Objective2 (O2) Headphone Amp DIY Project
XXXTheMatrixXXX - I would agree with dfy that those small variances are nothing to worry about. However it sounds like you want your O2 built with standard part values from RocketScientist/NwAvGuy's BOM so that it measures the standard way. That is something you need to work out with whoever sold you the kit.
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Old 10th August 2013, 12:10 AM   #3394
agdr is offline agdr  United States
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XXXTheMatrixXXX - also, regarding your question about turn-on-thump headphone damage, that is something best answered by Shure. Send their tech support an email with the voltage you think the headphones got hit with, how long it was applied, and see what they have to say.
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Old 11th August 2013, 06:27 PM   #3395
availlyrics is offline availlyrics  India
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Originally Posted by XXTheMatrixXX View Post

So I followed your advice....
Variance in Resistance values (when soldered on PCB) may be different as compared to NwAvGuy's guide due to capacitors/ semiconductors or other passives coming in parallel resulting in bit "off the mark" values, no need to worry here. You can verify the resistor values from colour codes.
Imp. point is - Are you still getting ON/OFF transient thumps post repairs?
As for FET's operational reliability - Did you tested your O2 with one battery disconnected & observing for any DC at o/p?(as per NwAvGuy's guide)

Last edited by availlyrics; 11th August 2013 at 06:33 PM.
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Old 12th August 2013, 05:53 AM   #3396
gootee is offline gootee  United States
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I would think that the measurements by NwAvGuy were made in-circuit and should account for any parallel passive components.

If XXTheMatrixXX's meter is forward biasing, or partially forward biasing, some pn junctions in semiconductors, which are in turn enabling the multimeter to "see" additional parallel circuit paths and components, that might explain the first two measurements, which are lower than expected. But the last three are HIGHER than expected, whereas additional parallel anything would always result in a LOWER resistance measurement than expected.

Before re-measuring, I would check to see if the resistors' labeled/marked/color-coded values match the expected/specified values.

When re-measuring, I would first make sure that the meter has fresh batteries. Then I would make sure that it reads near zero Ohms (like 0.5 Ohm or lower) with the probes shorted together, before starting and after finishing. When measuring, leave the probes in place for a long time, i.e. until the measurement stops changing. The voltage that the meter applies in order to measure resistance might be charging a capacitor, somewhere, for example, and your measurement won't be correct until it stops changing. Also, for each measurement, do it a second time with the probes swapped. If it was mentioned in the write-up there must be a reason for it.

Last edited by gootee; 12th August 2013 at 05:56 AM.
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Old 12th August 2013, 08:35 PM   #3397
XXTheMatrixXX is offline XXTheMatrixXX
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THANKS agdr, dfy, availlyrics, gootee and everyone for the explanations.
I"ll redo the "Initial DIY Testing"& "STEP-BY-STEP DC VOLTAGES" (didn't do that one) tests with two different DMM (VC97+ and another one) and FOLLOWING YOUR RECOMMENDATIONS/CORRECTIONS.
(NwAvGuy: O2 Details)
Then I"ll post the FULL detailed results.
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Old 28th August 2013, 02:46 PM   #3398
northernsky is offline northernsky  Italy
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Default O2 amp distortion


I built a couple of months ago an o2 amp kit and bought a Sennheiser Hd600.
I am driving them with a macbook pro, Odac combo.

I now just built a Cmoy portable head-amp and I could compare it to the O2 amp.

I was surprised because I can clearly recognize an audible distortion by the O2 amp, especially audible on music with high power on bass.

The distortion is so clear that I think it is a problem to be addressed to my building or component fault in the O2.

Have you any idea or suggestion?

Thank you

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Old 28th August 2013, 04:10 PM   #3399
Zigis is offline Zigis  Latvia
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Probably too high gain.
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Old 28th August 2013, 04:18 PM   #3400
ericj is offline ericj  United States
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Is anyone currently selling nonmetallic faceplates? I messed up my bamboo panel drilling it out to fit a panel mount power jack when I got tired of the power plug falling out.

.:Sent by pneumatic tubes
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