The Objective2 (O2) Headphone Amp DIY Project

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#4,541
Mooly said:
Just out of interest, are the other voltages (the other pins) zero ? Even with low supplies like that, the opamps will still function correctly and so you should see zero volts on pins 1 and 7 of U3.

If that is the case then you can try linking the bulb out.
Click to expand...
Yes, the other pins were at 0v. i just removed my precious bulb and the readings are normal (+/- 12v) . Guess the 34V 3W bulb was a bit too much for my 15vac adapter. inserted the last opamp and readings are still normal. Testing with cheap headphones and a mp3 player and... IT WORKS! ;D
Finally its up and running, really Mooly a big thanks to you for the guidance you have given me over the last 5 pages🙂p) of the thread!
So far no hissing, distortions or unbalanced channels. :hphones:
will keep on listening a bit on cheap headphones and then try some better ones.
 
#4,544
Are you following NwAvGuy's check out procedure? I don't think you can get meaningful readings measuring the FETs in that way you describe above.
You should have ~11.7V between C16 & ground and C21 & ground (with proper polarity of course). These readings mean the correct voltages are at the FETs, ready for them to turn on and be distributed to the main circuitry. It sounds like you do have that.
 
#4,545
sofaspud said:
Are you following NwAvGuy's check out procedure? I don't think you can get meaningful readings measuring the FETs in that way you describe above.
You should have ~11.7V between C16 & ground and C21 & ground (with proper polarity of course). These readings mean the correct voltages are at the FETs, ready for them to turn on and be distributed to the main circuitry. It sounds like you do have that.
Click to expand...

Oh my mistake, i should have installed U2 then do the measurement, problem solved.
 
#4,547
Here are a couple more questions:

1) With the ODAC/O2 combo, is there room for RCA outputs on the back of the B2-080 enclosure?

2) As I understand it, the ideal ODAC/O2 combo utilizes the 3.5mm input for the O2 section when connected, and uses the ODAC as a source with the 3.5mm input is disconnected. Is it possible to add RCA outputs from the ODAC to the back of the enclosure, such that the RCA outputs are active when the O2 section is turned off?

Thanks!
 
#4,550
Hiya,

I've had my O2 amp for about a year after putting it together, it worked for a couple of minutes each time I turned it on, then the output signal would slowly degrade and the amp would turn off. I kind of lost interest in it then but I found it in the drawer and I'd like to figure out why it isn't working.

When I turned it on, the red light came on briefly then I heard a click noise and it turned off. C9 had gotten pretty hot and started to bulge at the top so I replaced C9 and C8 with what I had - they were 220uF 25V and I have replaced them with 220uF 35V.

I've checked all the resistors in the troubleshooting guide and have come up with the following significant variances which I'm not sure mean I have an issue:
R5 - measures 55.6k but the troubleshooting guide shows it should be ~100K
R9 - measures 29K instead of 30-40K
R25 - measures 270K instead of 330K

I only have batteries to test the kit with as I can't find the AC adapter I used to have.
Measuring the voltage between + BT1 and - BT2 gives me 17.31VDC.
With only U2 fitted, measuring between - BT1 and pin 4 U4 gives me 2.956VDC which is well away from the -11.4V the troubleshooting guide indicates. Pin 8 U4 measures 8.44VDC.

Any ideas what I've screwed up?

Many thanks,

Andy
 
#4,551
I just found Moolys fault finding guide on post #3775 and checked the output of the regulators.

Striped end of D1 = 8.52VDC
Non-striped end of D5 -8.85VDC

So this is pointing to the regulators at fault or a faulty D1 and D5?

So I should be replacing D1 and D5, and also the MOSFETs in Q1 and Q2?

Many thanks,

Andy
 
#4,552
Without AC power, you can ignore the voltage regulation circuitry. The battery voltage seems fine at 17.3V, I would leave U2 out of the circuit until the other voltage issues are remedied.
I'm only looking at the schematic. Some things to check:
Check the color codes of R5, R9, &R25.
R25 in particular... The schematic shows it to be 2.7M. Easy to have a 270k there by mistake.
 
#4,553
I need a little help please.

I am following the initial testing for my O2 as laid out by NWavguy years ago. So far I am only testing the resistors, and I'm confused by the values I am supposed to get on R14 and R20. All of the other resistors check out (incidentally, they are all supposed to test out at or near their listed resistance values), but R14 and R20 are apparently supposed to measure between 100 and 300 ohms. R14 and R20 are both 10k parts according to the bom.

All the other resistors check out exactly in line with this except these two. Have I done something wrong?
 
#4,555
Completed my build today and amazingly everything tested fine. I found the testing procedure with a DMM a little nerve wracking as I don't really understand the ins and outs of electricity but I proceeded with extreme caution and read everything at least a dozen times! My only previous diy in hifi is a Cmoy. The O2 was much more fun to put together.

Maybe some will find these pics useful as a reference.

An externally hosted image should be here but it was not working when we last tested it.
 
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