I have changed my preamp input opamps op627 to NJR Muses03 bought from official channel in Japan.
I since started having problem with transistors blowing in my amp.
Could or does any instability or oscillation in the opamps in the preamp cause dc time to time getting into the amps input. dC coupled preamp.
I have measured no dc at the preamps outputs. No capacitors at the output.
Could this happen unexpectedly on rare occasions?
These opamps are widely interchanged by diyer.
I since started having problem with transistors blowing in my amp.
Could or does any instability or oscillation in the opamps in the preamp cause dc time to time getting into the amps input. dC coupled preamp.
I have measured no dc at the preamps outputs. No capacitors at the output.
Could this happen unexpectedly on rare occasions?
These opamps are widely interchanged by diyer.
Last edited:
Then you can try by process of elimination.
At the preamp output, add a large coupling capacitor,
and also an RC low pass filter for ultrasonic noise.
For example, add a series 10uF bipolar, a series 1k resistor,
and a shunt 6nF capacitor.
This should protect your power amp reasonably well, and
now you can test to see if there are any further problems.
Do you have a 100MHz (or better) scope?
Agreed, but if you are replacing an opa627 and you have to add an electrolytic to the new opamp output, I call that a downgrade not an upgrade
I have been using it fine for weeks at a time, but it happen 3 times that transistors in the amp blew.
This happened after swapping opamps.
I have checked preamp does not output any dc.
Trying to eleminate the preamp causing issues.
That is why my question on instabilty causing problems at the amp.
This happened after swapping opamps.
I have checked preamp does not output any dc.
Trying to eleminate the preamp causing issues.
That is why my question on instabilty causing problems at the amp.
Its just that I dont get that replacing opamps just for the sake of it, the design is more important than the opamp, plus we are talking opa627 not a 741, Replacing a 50 dollar opamp with a more expensive 70 dollar opamp does not ensure better performance.
Try using the power amp with a different preamp (or none at all),
to see if it seems to be ok without the preamp.
Certainly if you feed the power amp a large ultrasonic signal,
it could possibly overheat and fail, unless it has an input low pass filter.
Is the replacement op amp unity gain stable?
Neither are decoupling requirements. Seems a bit suspect to me
Decoupling, or lack of could do exactly this. I would swap them back
Brian
No clue Op Amp rolling.
No schematic, no measurements, no audible difference, just imagination and confirmation bias.
Or to say it better, there is a difference, now transistors blow.
And to boot you are replacing original transistors with what can be presumed as fakes, and no certain supplier carrying the good ones.
We might call this Audio Darwinism.
Thanks guys!
I too now can only suspect that the opamps are probably oscillating.
I guess i have been reading too much on opamp swapping here and the headfi forums where many are just swapping them.
I presumed all was fine and probably need a scope
beforeundertaking such in future.
My best bet will swap back the opamps. Even if i test on a scope, not sure if it will show unless its doing it right off the bat and not have a solution as the opamp socket is already well decoupled and no other soution then.
Might be just easiest to revert back to the unity gain stable 627's.
I too now can only suspect that the opamps are probably oscillating.
I guess i have been reading too much on opamp swapping here and the headfi forums where many are just swapping them.
I presumed all was fine and probably need a scope
beforeundertaking such in future.
My best bet will swap back the opamps. Even if i test on a scope, not sure if it will show unless its doing it right off the bat and not have a solution as the opamp socket is already well decoupled and no other soution then.
Might be just easiest to revert back to the unity gain stable 627's.
Last edited:
I have got transistors from official source and also from the Taobao web real cheap.
Did some research and didnt use the chinese vendors.
I have had a hammer to them and cracked 2 of the new transistors to compare withbth blown originals as well as referencing to the thread here years back and photos of fake transistors. I was going to throw these questionably cheap new ones away.
Surprisingly, the Taobao ones where exactly the same internally as the originals. So i have a number of these spare transistors now.
Just as a side track, many obsolete chips are bought up by China or sent there somehow. I have managed to source some obsolete parts that can not be easily found anywhere else.
Amazingly, not all china sellers are fake and got them cheap too!
Did some research and didnt use the chinese vendors.
I have had a hammer to them and cracked 2 of the new transistors to compare withbth blown originals as well as referencing to the thread here years back and photos of fake transistors. I was going to throw these questionably cheap new ones away.
Surprisingly, the Taobao ones where exactly the same internally as the originals. So i have a number of these spare transistors now.
Just as a side track, many obsolete chips are bought up by China or sent there somehow. I have managed to source some obsolete parts that can not be easily found anywhere else.
Amazingly, not all china sellers are fake and got them cheap too!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.