OK, so you are saying with the 2068 fitted that the voltages are now correct... very odd but it seems to prove the IC's are faulty.
The chips should be readily available all that will depend on your locality. You can fit other chips in order to get it all working.
4558's, NE5532's, 4560's even TL072's will all work in order to prove everything else is OK.
Look at the circuit... with the 2068 now fitted in place of a 4556 you could link either pins 5 and 7 or pins 3 and 1 of the original 2068 location (which is now empty) and you should hear music from whichever channel the 2068.
The chips should be readily available all that will depend on your locality. You can fit other chips in order to get it all working.
4558's, NE5532's, 4560's even TL072's will all work in order to prove everything else is OK.
Look at the circuit... with the 2068 now fitted in place of a 4556 you could link either pins 5 and 7 or pins 3 and 1 of the original 2068 location (which is now empty) and you should hear music from whichever channel the 2068.
As Mooly said 4556s are easily available (and cheap), but I do have a few pairs of spare 4556s lying around that I'd be happy to send you should you need new ones. Just PM me, and we can work out the details!
Yeah, it plays. Nice 🙂
I'll try to find alternatives in local stores, though I will need to ship the 4556's - i couldn't find any around.
So do you think that's what happened? Faulty opamps?
Opamps are pretty tough overall, so much so that its difficult to kill one unless you are very determined... so I don't know what has happened here tbh.
Could they be fakes? i.e. not even a dual opamp...
The only thing that bothers me is you mentioning the crackling when you moved things because whatever the problem is, it should be immune to physical inputs like that. I think all you can do is fit known good parts and see how it all plays out.
Opamps with DAC/AMP came from JDS so hardly believable it is fake. It also could be that there is malfunction somewhere else on the board that causes to break the opamps, idk.
Well, I'll give a try with the chips you mentioned before trying with 4556. Will report back.
Thanks Mooly much for all your help
You're welcome... and good luck 🙂
(and as to opamp indestructibility, the only things that will realistically kill an opamp are incorrect supply polarity and/or feeding supply voltage into any of the other pins when the main supply rails are missing. Even then you have to be very very determined to kill it off by ensuring lots of current is available and also that it has somewhere to go through the other pins... and once its supplies are present its all pretty much protected anyway)
(and as to opamp indestructibility, the only things that will realistically kill an opamp are incorrect supply polarity and/or feeding supply voltage into any of the other pins when the main supply rails are missing. Even then you have to be very very determined to kill it off by ensuring lots of current is available and also that it has somewhere to go through the other pins... and once its supplies are present its all pretty much protected anyway)
Tried with NE5532 and it works fine. Will PM CHiroshi if I can purchase his 4556's opamps 🙂
Thanks again !
Try to install you original chips one more time.
maybe it is something mechanical with socket or chip legs
maybe it is something mechanical with socket or chip legs
Tried it again - no sound. I did it quite a few times during the testing before with same results.
Thanks anyways.
Odd, indeed. I'll send him my 4556s, hope he doesn't fry them! [emoji854][emoji16]Excellentif a bit of a strange one.
Try moving/bending whatever you mentioned at the start and see if you can provoke any weird behavior.
The only scenario I can think of is one of the two rails disappearing and the opamps then placing either a - or + 12 volts across the headphones which would draw a fair bit of current... actual value depending on the DC resistance of the 'phones and how a 4556 behaves under a missing rail condition. Would that be enough to zap them though, and both in the same way... I still have big doubts on that.
The only scenario I can think of is one of the two rails disappearing and the opamps then placing either a - or + 12 volts across the headphones which would draw a fair bit of current... actual value depending on the DC resistance of the 'phones and how a 4556 behaves under a missing rail condition. Would that be enough to zap them though, and both in the same way... I still have big doubts on that.
Isn't the amp protected against one of the rails disappearing, by the comparator circuit? I thought it should shut off the amp should i.e. one of the battery come loose. Shouldn't it do the same trick, even when AC powered, shoud one of the rails fail for whatever reason?
Possibly, although I was thinking of something like a break in the print that might remove one of the rails to the 4556. Impossible to second guess really.
Missing supply will not damage 4556 (at least in my case), I killed couple of ad8397 that way but 4556 was more robust.
I'd be surprised tbh if a missing supply could cause damage but couldn't really think of anything else.
Fake parts is probably the number one suspicion.
Fake parts is probably the number one suspicion.
Did you used these opamps in voltage-gain stage or as output buffers?
I wonder if anyone here tested OPA1656 in output buffer, paralleled, of course. That should do 150mA, but not sure about it's long term stability, and short-circuit protection.
Thanks!