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Old 21st April 2014, 04:12 PM   #1
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Default Headphone amp - POP sound will powering ON and OFF

I am using a Headphone amp with DAC, Topping D2.

There will be a pop sound at the headphone output when powering on or off the unit. The pop sound is more prominent during powering off.

The original amp is using a PS of +15V. I had modified it to +/-15V for the analog circuit and +8V for the digital. The result is good, except I cannot get rid of the POP sound during power ON and OFF.

Diagram A is the output stage schematic. It is similar to that of the miniUSB DAC.

Diagram B: I isolated the output transistors bridge. NO POP.

Diagram C: I isolated the the OPAMP, OP275, the POP remained.

I believed the POP sound is due to the characteristic of the OP275.

I would like know how can I remove the POP sound from OP275.
If I have to change the OPAMP. What other opamp, without the power ON/OFF POP, can I use?
Is there anything I can do to improve the HF of this circuit.

I prefer HF to have more extension and more prominent and sound that is not airy.

I had tried adding a relay for muting the output, and I do not like the results, too much HF roll off.


OP275 Datasheet:
http://www.analog.com/static/importe...eets/OP275.pdf

A: Original Circuit:
Click the image to open in full size.

B: Transistor Bridge:
Click the image to open in full size.

C: OPAMP:
Click the image to open in full size.
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Old 21st April 2014, 09:40 PM   #2
jaycee is offline jaycee  United Kingdom
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Does it happen if you ground the input of the opamp? if no, then the pop is coming from your source.

Circuit B will not function at all. Circuit C means the opamp is directly driving the output, and the transistor stage is completely unused.
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Old 21st April 2014, 10:05 PM   #3
jcx is offline jcx  United States
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not endorsing a particular product but The ε12 Muting / Protect Circuit shows a output relay board just for headphone amps
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Old 21st April 2014, 11:37 PM   #4
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Quote:
Originally Posted by jaycee View Post
Does it happen if you ground the input of the opamp? if no, then the pop is coming from your source.

Circuit B will not function at all. Circuit C means the opamp is directly driving the output, and the transistor stage is completely unused.
Circuit B & C are for debugging.. Just to identify where the pop sound is coming from. The circuit has to be reverted to A to be functional.
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Old 21st April 2014, 11:42 PM   #5
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Quote:
Originally Posted by jcx View Post
not endorsing a particular product but The ε12 Muting / Protect Circuit shows a output relay board just for headphone amps
Yes. Adding a muting relay will mute the pop sound. I had tried, I found I did not like the sound of the relay in series of the output.

I am considering to use other relays.
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Old Yesterday, 06:13 AM   #6
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Don't put the relay in sreies with the output, use it as a shunt to ground, that way it's not in the signal path when the contacts are open.

Mike
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Old Yesterday, 09:12 AM   #7
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Quote:
Originally Posted by Michael Bean View Post
Don't put the relay in sreies with the output, use it as a shunt to ground, that way it's not in the signal path when the contacts are open.

Mike
Yes.. This is good idea..
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Old Yesterday, 09:30 AM   #8
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I do not have the space for timing circuit..
The POP sound is more serious during powering off.

I will use two DPDT relays to short out the two points for muting, so I will not have any short-circuit current issue. I hope.

I will also try other opamps.


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Old Yesterday, 11:49 AM   #9
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I recommend you don't do it that way, it will cause 100% positive feedback (oscillation.) I meant you should shunt the output to ground. Shorting the output shouldn't cause any trouble for the small amount of time it takes for the supply rail to discharge.

Mike

Last edited by Michael Bean; Yesterday at 11:52 AM.
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