Need help with noise on headphone amp! (op-amp issue?) - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 06:28:24 am
content: 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.

author: Whales
author_rank: Super Contributor
timestamp: September 12, 2019, 06:32:22 am
content: 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.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 06:46:17 am
content: Quote from: Whales on September 12, 2019, 06:32:22 amHello, 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!

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: September 12, 2019, 07:04:55 am
content: 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.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 07:06:39 am
content: Quote from: EEEnthusiast on September 12, 2019, 07:04:55 amHello 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.

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: September 12, 2019, 07:10:27 am
content: Quote from: Mp3 on September 12, 2019, 07:06:39 amThen the headphone impedance is too low for the OPAMP. Try using a 300 Ohm impedance headphone or add a driving stage after the OPAMP.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 07:21:32 am
content: Quote from: EEEnthusiast on September 12, 2019, 07:10:27 amIt got hot very fast with a different op amp (original is JRC 4558, also tried NE5532)I'm not sure how to tell if the op-amp is oscillating. Should i add a resistor somewhere? The amp circuit it is based on is made for 32 ohms headphones, but i'm not sure about this clone I have.

author: Whales
author_rank: Super Contributor
timestamp: September 12, 2019, 07:32:11 am
content: > I used a power supply i knew was good quality, and was able to measure a constant 12.12V, so that seems fine.1. Was this measurement taken whilst your amplifier is being powered and having problems, or in some other circumstance?2. Is your power supply 0 & 12V, or -12 and +12V?I would still recommend you try another PSU. It's a quick way to rule out several problems. There are some hidden issues here regarding shorted GNDs from different sources, so it's also worth trying to feed audio input to your amplifier from something isolated (eg a laptop not plugged into its charger, a phone or music player not plugged into its charger).> It got hot very fast with a different op amp (original is JRC 4558, also tried NE5532)Make sure both opamps have the same pinout. There are two common pinouts for 8 pin opamps.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 07:41:19 am
content: Quote from: Whales on September 12, 2019, 07:32:11 amFirst off, thank you again. I will verify the op amps had the same pinout.I don't actually know how to test if my power supply is 0V & 12V or 12V & -12V, thus i would not be surprised if that's the problem. I did some more research after you mentioned this and I think my power supply probably only does 0v & +12V - not -12v & +12. I will find a proper AC supply (not DC) and try again!

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 08:09:58 am
content: Ok, so i found an AC-AC adapter, plugged it in, and instantly blew up the OP-AMPLuckily I had a spare JRC 4558, so i put it in and get the same behavior as before. About 15-30 seconds clear audio, then slowly gets more distorted. Seems like the signal gets progressively more cut off as time goes on...While the distortion happens, i measure the DC voltage at power input with audio playing.+12V & Ground - 0.8-0.9v-12V & Ground - -11.9V constantJRC 4558 not getting warm to the touch at all. but still might be oscillation.

author: magic
author_rank: Super Contributor
timestamp: September 12, 2019, 08:11:24 am
content: If it's an NJM4558 from China then it's not an NJM4558, although probably a very similar Chinese chipBut I think I see an NJM4556 on your fist picture and it looks like it might be genuine. NJM4556 is beefy enough to drive most headphones, that's why Grado used it. NE5532 might work too if output current isn't too high, but it is more prone to oscillation (which would result in overheating, among other problems).Using too weak of an opamp will not make it overheat. Quite the contrary, a too powerful one may overheat if it is driving too much power into the load. Heat is (12V-output voltage)·(output current).Now grounding: this circuit is clearly made for a bipolar PSU and the midpoint of the PSU must be grounded. This means a PSU with three connections: ground, + and -.If you simply apply voltage between ground and + or ground and -, it will not work.If you simply apply voltage between + and -, the two electrolytic capacitors form a divider which splits the voltage in half and provides a ground for the circuit. But it only works for a while, because current consumption from each rail isn't 100% equal. So what happens is that the midpoint between the capacitors (ground) charges up or down until it reaches one of the rails.Do an experiment: connect power and measure voltage from ground to + or from ground to -. You will see that one raises and the other falls.Solutions:- use a proper bipolar PSU- use a "rail splitter" like TLE2426 to generate ground- add a resistive divider (like 1kΩ/1kΩ) between the rails and connect its midpoint to ground

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 08:19:32 am
content: Quote from: magic on September 12, 2019, 08:11:24 amAha..... you rock!! I think you have solved the problem.Unfortunately the instructions that came with it were only in Chinese so that is probably why I had to come here for helpI'm going to look for a bipolar PSU online, i thinkIf i have a strong enough resistor around, i will try doing what you say!Thank you so much!

author: magic
author_rank: Super Contributor
timestamp: September 12, 2019, 08:24:55 am
content: 12V applied to 1kΩ is 144mW. And that's the absolutely pessimistic limit, because normally there will be about ±6V and hence 36mW per resistor. Just about any THT resistor will do.CMoy amplifiers use 4k7/4k7 and that seems to be enough for them, but lower is better.editBipolar PSUs have their own problems. When one rail gets damaged or disconnected, the opamp may end up applying voltage very close or equal to the opposite rail to the load. You can try it using your unipolar PSU now. The exact behavior will also depend on the type of opamp used.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 08:34:07 am
content: Quote from: magic on September 12, 2019, 08:24:55 amThank you again! I found this and it seems to be what i want.https://www.amazon.com/DROK-Converter-Non-isolated-Regulator-Transformer/dp/B0752TRXDC/ref=sr_1_1?keywords=negative+voltage+12v+amplifier&qid=1568277742&sr=8-1In the meantime, i would like to learn how to implement the resistive divider, but i don't think i properly understand it. In fact, i am almost certain it is wrong. I would like to wait for advice before going further. as you can probably see, i have a hard time implementing EE theory in real life

author: Whales
author_rank: Super Contributor
timestamp: September 12, 2019, 09:17:30 am
content: Quote from: Mp3 on September 12, 2019, 08:09:58 amYeah, you don't want ACQuoteYep, that's a 12VDC power supply, not a +/-12V (bipolar) supply.This will still work fine, IF you are using an isolated power supply OR the amplifier is designed for use with arbitrary ground-level devices. Isolated power supplies tend to be the old-fashioned heavy (transformer) wall-worts, not the newer lightweight ones (switchmode power supplies). I've blown up amplifiers before making this mistake - more than just the voltage matters.I presume you are feeding audio into your amplifier from a grounded device (eg a computer)? Try a non-grounded (battery powered) sound source like a phone or laptop (not plugged into the charger) instead, see if that fixes some of the issues.Edit: magic has spotted the triple-input and has realised there is no spare op-amp to make a virtual ground if this is a stereo amp. WoopsFollow magic's advice.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 09:22:27 am
content: Hey, thanks again. I did try playing directly off a phone, and didn't notice any changes, so i am like 99% sure all my problems are because of the incorrect power supply. I bought the bipolar converter board I linked above, and the reviews say it's what people needed for their amps so i am hopeful it will solve the problem.For now, i'm not sure i can do much else unless I can figure out how that voltage divider schematic works

author: Whales
author_rank: Super Contributor
timestamp: September 12, 2019, 09:24:13 am
content: Quote from: Mp3 on September 12, 2019, 08:34:07 amIncorrect wiring. For this to work you:(1) Need to wire PSU12V to amplifier+, PSUGND to amplifier-, and use the resistors to make the amplifier's ground.(2) Need to use an isolated power supply. The one you show and link above is not isolated. This will lead to all sorts of *bang* problems when connecting your amplifier to other equipment.Ie you either need a proper bipolar (3-wire) power supply or an isolated 2-wire power supply.

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 09:25:26 am
content: Quote from: Whales on September 12, 2019, 09:24:13 amNoted! I will await delivery of my bipolar converter, and then see if everything works as it shouldThank you all again very much!

author: Whales
author_rank: Super Contributor
timestamp: September 12, 2019, 09:26:50 am
content: Ninja edited with more details, apologies.

author: blackdog
author_rank: Frequent Contributor
timestamp: September 12, 2019, 09:27:15 am
content: Hi,You need a symetrical powersupply for this device!!!Buy or create a +12 and a -12V power supply don't mess with SMPS power supplies, that always interferes with audio.Don't throw away time and money by tampering with power splitters.Kind regarts,Bram

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 09:46:59 am
content: Quote from: Whales on September 12, 2019, 09:26:50 amNot a problem! I know i've been refreshing this page like madQuote from: blackdog on September 12, 2019, 09:27:15 amThank you Bram!!for clarification: when you say power splitters, you mean with resistors? or also you mean this is bad too?https://www.amazon.com/gp/product/B0752CK8DK/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1I am looking around online for bipolar power supply, i won't use a switching supply! it's hard to find one, though. This looks like it might be good:https://www.ebay.com/itm/Car-Audio-Isolated-Power-Supply-Module-Buck-Converter-DC-12-6-24V-To-12V-Output/332134726757?hash=item4d54c5bc65:g:eJkAAOSwDrBc3c6Q

author: DimitriP
author_rank: Super Contributor
timestamp: September 12, 2019, 10:11:31 am
content: QuoteWhen you have three power connections to make and only two leads from a power supply, you STOP!In the meantime why not use two lousy 9V batteries to see if the thing works before this thread gets any longer ?

author: themadhippy
author_rank: Super Contributor
timestamp: September 12, 2019, 10:11:59 am
content: for testing 2 9v batteries should get you going,infact the original circuit diagram shows the chip supply as +9v and -9v

author: Mp3
author_rank: Frequent Contributor
timestamp: September 12, 2019, 10:56:17 am
content: I tested with two 9v's and all is good. My amp sounds great now. Thank you, thank you both.I will await delivery of my isolated bipolar power supply and think this thread has served its purpose and for that I am very grateful

author: magic
author_rank: Super Contributor
timestamp: September 12, 2019, 05:19:54 pm
content: This schematic shows how to make a passive rail splitter from unipolar 18V. Few things are simpler than that.https://diyaudioprojects.com/Chip/CMoy-Grado-RA1-Headphone-Amp/

author: tooki
author_rank: Super Contributor
timestamp: September 13, 2019, 11:52:39 am
content: The NJR4556 works on as low as ±2V. So with your 9V supply, you can easily split it into ±4.5V and the opamp will be happy.Look at the power supply section (bottom left) of this:https://www.paia.com/prodimages/hdasch.pdfSee how the ground there comes out the middle? Then the top rail is your +4.5V, the bottom is the -4.5V. Use those where your schematic calls for +9V/-9V.It says 12V, but 9V will be fine for your opamp.P.S. Please replace the embedded imgur images with images attached here. They're already broken.