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Need help with noise on headphone amp! (op-amp issue?)
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Mp3:
I now know it's not a grounding issue but likely an oscillating op-amp?



Hello all,

I come here begging for your assistance. I have watched several youtube videos and read several discussion threads online about proper grounding of a headphone amplifier, but i am having a really hard time wrapping my mind around it. If anyone can help me solidify what it is I have to do I would be really appreciate it.

Please see my headphone amp below. I am powering it with a 12V DC power supply. I do not have the power ground hooked up at all since i don't know what to do about it. The PCB is mounted on a cork board for now since I don't have any metal chassis to attach it to. The DC power supply does not have a ground wire.

I was thinking about running a ground wire from the power socket to one of the chassis screws, but would that be pointless since it's attached to cork?  I don't want to break anything, so i will await your replies before i attempt anything.

I get about 30 seconds of good clear audio, then it starts degrading and eventually starts go away. At this point i would unplug it. I already checked all my solder work, so i am assuming at this point it needs to have chassis ground.

Thank you all so much.



Not the exact schematic, but the schematic my board is based on (sorry, when i find the paper with the schematic of this amp i will post it) is the grado ra-1.
Whales:
1. If it works for 30 seconds and then garbles: it's not a grounding issue.  Something else is amiss, possibly something overheating.

2. It may already be grounded without you realising.  Can you post a photo of your power supply?

Edit: suggestions include:


* Trying a different power supply or measuring the voltage getting to the board before and during garble-mode.  The power supply may be becoming unstable or collapsing.
* Keeping your finger on the opamp.  If it gets too hot to hold your finger on then it is being overloaded.
Mp3:

--- Quote from: Whales on September 12, 2019, 06:32:22 am ---1. If it works for 30 seconds and then garbles: it's not a grounding issue.  Something else is amiss, possibly something overheating.

2. It may already be grounded without you realising.  Can you post a photo of your power supply?

Edit: suggestions include:


* Trying a different power supply or measuring the voltage getting to the board before and during garble-mode.  The power supply may be becoming unstable or collapsing.
* Keeping your finger on the opamp.  If it gets too hot to hold your finger on then it is being overloaded.


--- End quote ---


Hello, thank you so much for your suggestions. I will keep trying now without adding more ground wires.

I used a power supply i knew was good quality, and was able to measure a constant 12.12V, so that seems fine.

The op-amp is not getting hot to my finger touch, but i will attempt to swap it regardless! (I have some spare op-amps) This time it took about 10 seconds to get to noisy but didn't start cutting out yet (hopefully I didn't speak too soon).

I did notice everything below a certain volume is cutting out. If i turn my media player to about -20dB, the signal goes away entirely until i hit it with a loud signal again.

 However, if i was to add a "chassis ground" to this setup, would this be the correct way to do it? or should this definitely be avoided until i get a metal case? What if i mounted it in a plastic case?



Sorry for all the questions - but very happy to be learning!
EEEnthusiast:
Chassis ground is not required for the amp to work. It is mostly used for safety or to route very high return currents. In this case the OPAMP circuit should work just fine without chassis grounding. Can you post the schematics for us to understand what is going wrong. As suggested earlier, if it works for 30seconds and then blanks out, it is not a grounding issue. Grounding issues show up as 50/60Hz hum, white noise, clicks in the audio etc.

Can you measure the impedance of the headphones that the OPAMP is driving. If it is too low for the OPAMP to drive, then the OPAMP may heat up or act weirdly.
Mp3:

--- Quote from: EEEnthusiast on September 12, 2019, 07:04:55 am ---Chassis ground is not required for the amp to work. It is mostly used for safety or to route very high return currents. In this case the OPAMP circuit should work just fine without chassis grounding. Can you post the schematics for us to understand what is going wrong. As suggested earlier, if it works for 30seconds and then blanks out, it is not a grounding issue. Grounding issues show up as 50/60Hz hum, white noise, clicks in the audio etc.

Can you measure the impedance of the headphones that the OPAMP is driving. If it is too low for the OPAMP to drive, then the OPAMP may heat up or act weirdly.

--- End quote ---

Hello and thank you for your reply!

I just tried another op-amp, and it got hot very very fast. The headphones i tried were 32 and 64 ohms, so i don't think impedance is a problem.

I believe it is a slightly modified version of this.....


Again, many thanks everyone for your help.
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