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Preamp opamp instability
Preamp opamp instability
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Old 6th June 2019, 03:46 PM   #1
justubes is offline justubes  Singapore
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Default Preamp opamp instability

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.

Last edited by justubes; 6th June 2019 at 03:55 PM.
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Old 6th June 2019, 04:00 PM   #2
rayma is offline rayma  United States
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Quote:
Originally Posted by justubes View Post
does any instability or oscillation in the opamps in the preamp cause
dc time to time getting into the amps input. dC coupled preamp.
Post the circuit of your preamp.
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Old 6th June 2019, 04:02 PM   #3
justubes is offline justubes  Singapore
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Sorry, i dont have the circuit.

It is not a diy preamp.
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Old 6th June 2019, 04:07 PM   #4
sSound is offline sSound
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You shouldnt replace opamps willy nilly, why did you change them in the first place? The opa627 is an excellent opamp.

Last edited by sSound; 6th June 2019 at 04:10 PM.
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Old 6th June 2019, 04:10 PM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by justubes View Post
Sorry, i dont have the circuit.
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?
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Old 6th June 2019, 04:10 PM   #6
justubes is offline justubes  Singapore
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Opamp rolling.

But quest for getting better sonics.

If there is any possibility of problem encountered, i should put them back.
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Old 6th June 2019, 04:12 PM   #7
sSound is offline sSound
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Quote:
Originally Posted by rayma View Post
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.
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
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Old 6th June 2019, 04:12 PM   #8
justubes is offline justubes  Singapore
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I am not sure if the amps have coupling caps at the input already.

Otherwise incould rule out any issues caused by the preamp.
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Old 6th June 2019, 04:13 PM   #9
rayma is offline rayma  United States
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Quote:
Originally Posted by sSound View Post
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
This is for testing purposes.
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Old 6th June 2019, 04:17 PM   #10
justubes is offline justubes  Singapore
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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.
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