The gate voltage depends on the absolute supply voltage and so plus 8.4 volts suggests you are running on batteries. There is no problem there.
Follow my guide here (post#3775) and see where that gets you.
The Objective2 (O2) Headphone Amp DIY Project
Follow my guide here (post#3775) and see where that gets you.
The Objective2 (O2) Headphone Amp DIY Project
Hi everyone, and thank you for the amoun of information in this thread 
.
I have built a O2 amp from the diy kit purchased at JDS Labs, and I am facing a few problems. First one being that I didn't pay attention that the power supply needed to be AC and not DC (seriously, who uses AC anymore ? ), so I have to run it on batteries.
Now I have tried the troubleshooting as described on NwAvGuy's blog and have seen that the voltage on the pins at U4 where in the range of 8V instead of the 11,8 indicated in the testing section.
Anyway, I put the op-amps in and tried the amp (connected to my computer's soundcard) and without the gain the vocals seem to be very "distant". With gain activated it actually doesn't sound bad, but maybe a tiny bit mushy, the sound doesn't seem to be very detailed. I have checked the board extensively a few times, there doesn't seem to be any unwanted solder bridge, the componants seem fine.
Any idea of where that problem could come from ? Thanks a lot.
[Edit : I've checked again with every op-amp connected, I get a positive (!) reading of 14,9V on pin 4 and 15,5V on pin8 of U4. That seems really weird
.I have built a O2 amp from the diy kit purchased at JDS Labs, and I am facing a few problems. First one being that I didn't pay attention that the power supply needed to be AC and not DC (seriously, who uses AC anymore ?
), so I have to run it on batteries.Now I have tried the troubleshooting as described on NwAvGuy's blog and have seen that the voltage on the pins at U4 where in the range of 8V instead of the 11,8 indicated in the testing section.
Anyway, I put the op-amps in and tried the amp (connected to my computer's soundcard) and without the gain the vocals seem to be very "distant". With gain activated it actually doesn't sound bad, but maybe a tiny bit mushy, the sound doesn't seem to be very detailed. I have checked the board extensively a few times, there doesn't seem to be any unwanted solder bridge, the componants seem fine.
Any idea of where that problem could come from ? Thanks a lot
.[Edit : I've checked again with every op-amp connected, I get a positive (!) reading of 14,9V on pin 4 and 15,5V on pin8 of U4. That seems really weird
Last edited:
Taking the negative side of BT2 as ground, I get ~ +8V at every 4 & 8 pins of the op amps when the amp is not turned on. When it is, I get the following readings :
- U1 : +0.27 on 4, +16.26 on 8
- U2 : +0.27 on 4, +16.22 on 8
- U3 : +0.27 on 4, +16.20 on 8
- U4 : +15.53 on 4, +16.18 on 8
Post edited, sorry.
- U1 : +0.27 on 4, +16.26 on 8
- U2 : +0.27 on 4, +16.22 on 8
- U3 : +0.27 on 4, +16.20 on 8
- U4 : +15.53 on 4, +16.18 on 8
Post edited, sorry.
Last edited:
Put your black meter lead on the common junction of C2/3/4 and 5. That is ground.
Now measure from there to your batteries. You should read + 9 and -9 on the appropriate terminals, and you should also measure zero volts on the remaining 'common' connection between the batteries.
This problem sounds like broken print somewhere. Have the circuit in front of you and then the measurement points will make sense.
Now measure from there to your batteries. You should read + 9 and -9 on the appropriate terminals, and you should also measure zero volts on the remaining 'common' connection between the batteries.
This problem sounds like broken print somewhere. Have the circuit in front of you and then the measurement points will make sense.
I don't get what you mean by "common junction between..." so I took the negative side of one of the condensers (C3 in this case, but same reading with the others), and I got -7.5V on all 4-pins and +8.3V on all 8-pins. I get -7.73 at the negative terminals of the batteries and +8.58 at the positive one. And 0 in the middle ones.
Like this. Black lead to the point shown here, and you should then have +9 on the two red arrow points and -9 on the two blue arrow points.
There should also be zero volts on the ground arrowed at C8 and C9. Measure the voltage to this point by still keeping the black lead on its original location.
There should also be zero volts on the ground arrowed at C8 and C9. Measure the voltage to this point by still keeping the black lead on its original location.
Attachments
OK It sounds like you are getting there.
There is a full faultfinding guide in post #3775 should you run into any problems:
The Objective2 (O2) Headphone Amp DIY Project
It sounds like you are getting there.There is a full faultfinding guide in post #3775 should you run into any problems:
The Objective2 (O2) Headphone Amp DIY Project
I had problem that my few years old O2 right channel was almost no hearadble sound level this morning.
I found out that second 4556ad was broken because if i swap those 4556ad the broken channel was left. I swap again and right.
I use Mooly great quide to measure voltages before i found problem voltages were okay and i measure resistors those were okey too.
So i order pair of 4556AD 8.75€ from ebay.
But i have one question, if i change that 2068d op amp to NJR MUSES 8920 (i love this opamp sound) do i get that little warmer sound out of O2 or does this headamp filter it out ?
I want that Muses 8920 in the chain so what i can buy to do so if op amp swap does not do that ?
I found out that second 4556ad was broken because if i swap those 4556ad the broken channel was left. I swap again and right.
I use Mooly great quide to measure voltages before i found problem voltages were okay and i measure resistors those were okey too.
So i order pair of 4556AD 8.75€ from ebay.
But i have one question, if i change that 2068d op amp to NJR MUSES 8920 (i love this opamp sound) do i get that little warmer sound out of O2 or does this headamp filter it out ?
I want that Muses 8920 in the chain so what i can buy to do so if op amp swap does not do that ?
Exact same problem here, AGAIN.I had problem that my few years old O2 right channel was almost no hearadble sound level this morning.
I found out that second 4556ad was broken because if i swap those 4556ad the broken channel was left. I swap again and right.
I use Mooly great quide to measure voltages before i found problem voltages were okay and i measure resistors those were okey too.
So i order pair of 4556AD 8.75€ from ebay.
But i have one question, if i change that 2068d op amp to NJR MUSES 8920 (i love this opamp sound) do i get that little warmer sound out of O2 or does this headamp filter it out ?
I want that Muses 8920 in the chain so what i can buy to do so if op amp swap does not do that ?
This is the second time this has happened to me, I barely managed to set up the O2 at my workplace before it blew. Luckily I still have some extra op-amps from my previous repair operation, Head'n'Hifi was kind enough to mail the amps super-cheap.
Did the measurements and repairs. U3 had gone bad and was outputting high voltages to pins 1 and 7, the exact same issue I had last time (not sure if it was U3 or U4 last time).
Is this a common issue with the 4556 or is it possible that there is something wrong somewhere else within my O2? All the other multimeter measurements seemed to be fine except for the U3. Been using Hifiman HE-400 and DT-770 80ohm headphones with it.
Opamps are incredibly reliable as a rule. My first thought would be that the act of removing the opamp and replacing it is perhaps masking some physical issue with the board or IC sockets.
Only if the opamp can be quickly used in a test circuit and verified bad would I start asking questions about what might be going on.
Only if the opamp can be quickly used in a test circuit and verified bad would I start asking questions about what might be going on.
Sigh... back to the tinkering table.
I perceive a small but very noticeable channel imbalance which seems to be present in all volume and gain settings (right channel is louder). It could be an issue with the cheap 3.5mm--->2xRCA cable, luckily I have DAC-X6 to do some listening tests. Also need to check if the gain switch (S2) is in contact with the R21 which seems to be the most typical cause for this problem.
Also another thing I noticed: during both power down and power up there is a very noticeable "thump" noise on the left channel, the very same channel that has already died twice. Coincidence?
I perceive a small but very noticeable channel imbalance which seems to be present in all volume and gain settings (right channel is louder). It could be an issue with the cheap 3.5mm--->2xRCA cable, luckily I have DAC-X6 to do some listening tests. Also need to check if the gain switch (S2) is in contact with the R21 which seems to be the most typical cause for this problem.
Also another thing I noticed: during both power down and power up there is a very noticeable "thump" noise on the left channel, the very same channel that has already died twice. Coincidence?
Gain differences should be easy to determine with a scope and test tone. The gain of the opamps is determined 100% by the feedback components and so its unlikely there will be problems there.
You could apply an input to just one channel and link that to the other channel to get true mono from a single input. That would show if there was a real imbalance or not.
Switch on/off thumps are a design failing as the 02 has no output muting during power on/off. I would have thought both channels would behave the same though.
You could apply an input to just one channel and link that to the other channel to get true mono from a single input. That would show if there was a real imbalance or not.
Switch on/off thumps are a design failing as the 02 has no output muting during power on/off. I would have thought both channels would behave the same though.