This power amp makes a strange noise!
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Friday May 3, 2024
David Mellor
David Mellor is CEO and Course Director of Audio Masterclass. David has designed courses in audio education and training since 1986 and is the publisher and principal writer of Adventures In Audio.
Sure its not the meter movement making the sound?
If not, clean the valve contacts.
@postoronny: Дроссели выходных фильтров.
@AudioMasterclass replies to @postoronny: Google translation: 'Output filter chokes'.
@rudy_g51g2: I just bought this amp and I cannot get rid of ground hum. This thing works for Bluetooth but as soon as I go to aux, the hum starts. Could it be the amp or preamp? Anyway to test?
@CatFoodDraino: I call this "singing transistors". When unloaded and driven hard, the transistor is screaming. Not good for the ic's :)❤
@Douglas_Blake_579: Add a 0.1uf capacitor across the meter movement at the rear connections... if it clears up you got off easy.
@callumbrowns: Nice content man, Can you do a video on what sound's better, a 7 inch record or a 12 inch
@AudioMasterclass replies to @callumbrowns: I might.
@berndtlindstrom830: About this i mean https://youtube.com/watch?v=xE_BnfVMFi0&si=MgHmxo1rVjLUiXTM
@AudioMasterclass replies to @berndtlindstrom830: While a quick scan of your link shows it to be a decent video, I have to wonder what it has to do with my squeaky power amp.
@berndtlindstrom830 replies to @berndtlindstrom830: @AudioMasterclass Subscribe and never miss a post from you. I apologize for being clumsy.(too many whiskeys). Keep up your interesting videos.
@deanrantala: In general, many class D amps should not be run without a speaker load connected. While i am not an EE, i have done many projects utilizing various Class D chips and the source of that sound is (as previously mentioned), the internal inductor coil. When a class D amp is outputting signal while unloaded, the voltages sent out by those integrated chips evidently spikes higher than usual and can even damage the internal components or even the chip itself. The speaker (when connected) is actually part of the RC filter network needed by the chip to damp the output. Without the speaker connected, excessive voltages can be developed within the choke and ultimately get fed back into the chip. This is all dependent on the chip and implementation of coarse. Some class D amps are fine without load, others may not be. When dealing with these china mini amps, i would suggest you not attempt any high volume operation without speakers connected just as a precaution.
@humblestever24: .
"Hyde Park Corner"
What is that long lost theme
With the sound of a long lost band.
Bobbies two by two
In the green and pleasant land.
@michaeldeloatch7461: I wonder if it's the VU meter.
@SteveD-m6z: The class D amplifier chip requires an output LC filter. The LC filter introduces a phase shift that can influence the stability of the circuit. The load impedance acts to damp the Q of the LC filter and increases stability by diminishing the phase shift. Normally the circuit design would include a Zobel Network that provides a load at high frequencies to help circumvent this problem.
@paulstubbs7678: Are you sure it's not coming from the meter movement?
Yes you have to be a bit brutal to make a meter movement sing like that, but it can.
@fogbullit1000: Filter coils can sing and transformers can do the same 😃
@AudioMasterclass replies to @fogbullit1000: Yes it's clever how it can turn my music into actual singing.
@Roosville1: A long-long time ago I would use a old electric bar fire as a load for high power amplifier test, you could clearly hear Dark Side of the Moon from the electric bar fire, I guess the reflector helped with the audio.
@AudioMasterclass replies to @Roosville1: One of the many crazy ways to be an audiophile.
@spacemissing: Yeah... Energy has to go somewhere.
Amplifiers with output transformers will "sing", too, sometimes.
@analoghardwaretops3976: Your. amp really does like the song & wants to dance to it's beat ..The meter does put up a nice dance show...and is not shy of HYDING in the Corner..😅😅
@DID70Sworkedoutforyou replies to @analoghardwaretops3976: in older decks thatrecord still with perfect sound, once i noticed i could record to plus 3 or 0 but in a certain position the needles seem to dance more and the recordings started to have more dynamic sound
@andymouse: I would say as it's off load perhaps thats inductors rattling along with the tune or some other coil like structures digging the beat....cheers!
@jimdavis5230: Hi David, I understand you have a degree in audio and technical stuff. I don't have a degree just an HND in electronic engineering. Far lower than your degree. Now I have designed and built my own pre and power amplifiers that sound superb. Therefore why don't you do the same rather than waste time with these cheap modules? I have never heard any power amplifier that sounds better than my own designs.
@AudioMasterclass replies to @jimdavis5230: I have a Tonmeister degree with a couple of electronics modules, and quite a lot of professional practical experience in electronic design and construction. But I've been there and done that to my satisfaction so I'll leave high-end amp building to others.
@adotopp1865: Well if you mess about this is what you get
@Roddy451: Oh... Huh?.. eh... hmm... Riiiiiiiiiiight... Well, the song is great. No comment on the amplifier.
@moe5809: Shocking. Don't worry the Aiyima T9 Pro Ultra plus will be out soon. It will be twice as good.
@麻辣燙-u1v: Powering off preamp makes a popping sound, is it bad for the speaker? My preamp is 7.5W class A. If I turn the volume all the way down, it will minimize the popping sound. If I wait for 5 minutes to let the class D amp go into standby mode, no popping sound at all. Please advise, thanks!
@Douglas_Blake_579 replies to @麻辣燙-u1v: Simple solution ... turn the amp off first... turn the pre-amp on first.
No it's not harmful... just very annoying.
@AudioMasterclass replies to @麻辣燙-u1v: Professionally, power amp goes on last, goes off first. If it makes any noise on switch-on, get rid of it.
@麻辣燙-u1v replies to @麻辣燙-u1v: Thanks a bunch!
@麻辣燙-u1v replies to @麻辣燙-u1v: @Douglas_Blake_579Thank!
@marxman00: By plugging in the valves you have passed the test ....you now have a low level interocitor...use it wisely !
@AudioMasterclass replies to @marxman00: This Island Earth I believe.
@rienpost: The cymbals that come in at 1:45 in Hyde Park Corner. Absolutely brilliant. (And thanks for making it available on Bandcamp! Bought it.)
@earthoid: Just another example of tubes adding distortion to the sound.
@idtubenod: 🤣🤣🤣
@jimbohnenkamp5082: Hyde Park Corner...not the worst thing I've ever heard.
@AudioMasterclass replies to @jimbohnenkamp5082: Come on, it would be an honour to be worst.
@robertgwatts1858: Sounds like you were actually broadcasting on short wave. The unloaded cables acting like antennas to the amps switching frequency.
Not enough RF power for me to tune into you in Spain, unfortunately. 😂
@joewlodynski3521: David, do you have an option on the T9 to bypass the tubes and go direct solid state. I have a T10 which is a pre amp/DAC and I can bypass the tubes. Your site is GREAT. Joe Wlodynski Wesley Chapel, Florida USA
@AudioMasterclass replies to @joewlodynski3521: Being of a sneaky disposition I did try it with the tubes out. It works, but quieter. It would seem therefore that the tubes are in parallel with the signal path.
@ac81017: Just listened to Hyde Park Corner 3 times. Love it. Where can I get a copy of the lyrics. Yes, I'm a bloody northerner.
@AudioMasterclass replies to @ac81017: Another bloody Northerner says Bandcamp. There's a handy explanation of what they mean also.
@Audiodreamer192-24: Hyde park corner…😂😂😂
@frankd.b.9233: 1 question why do you use USB if you have other options, I always try to avoid USB, why ... USB 2 crap
@middleearthltd: Thankfully we have the chat to get this explained
Shout out to the chat
@Douglas_Blake_579: Sounds like output coil noise ... this can often happen with Class D amplifiers when no speakers are connected. The speaker impedance is actually part of the output low-pass filter and with no speakers connected that filter becomes inadequately damped causing back EMF in the coils that can, in some cases, damage the amplifier chip.
Hook up to a dummy load, see if the noise is still present. If it is, get another amplifier.
@AudioMasterclass replies to @Douglas_Blake_579: Your answer is floating to the top of my belief system at present. I do have a dummy load handy and I'll give it a go. I'll wait a few days for more speculation from my commenters.
@Douglas_Blake_579 replies to @Douglas_Blake_579: @AudioMasterclass
FWIW ... I've been running a lot of these little mini-amps through my test bench lately and some did surprisingly well... others not so much. The one common theme in the bad ones is noisy coils. It's a saturation effect and the source of the sound is actual vibration of the wires in the coil.
Some coil noise is acceptable as the amplifier approaches clipping and largely results from an increase in harmonic content. But when you start hearing it at lower powers you know the coil is underrated, saturating early and likely to overheat and fail.
@ac81017: It's cheap non-audiophile crap that's the problem.
Will check out your new release. 👍
@matthewhilty4209: That is probably coming from the coils vibrating. Hot glue them and see if that helps.
@gjnbouwmeester5860: Hahahahahaha, Man cave... Green screen u mean
@AudioMasterclass replies to @gjnbouwmeester5860: I’ll be replacing it with a holodeck later this year.
@nazzario_music: The tubes are not the source of that sound. It the coils on the amp's output. It is very common with class D amps. Almost all of them have output LC filter and if they are made cheaply, you will hear music coming out of it.
@AudioMasterclass replies to @nazzario_music: Thank you for calling my track music. The mic is by the tube, by the way, because that’s where the sound seemed to be coming out, from the hole.
@johnsutton6797 replies to @nazzario_music: Depends, if the amp outputs are connected to a load.
Also, inductors have no internal magnetic field to act as a voice coil.
@paullongtailpair3812 replies to @nazzario_music: You hit the nail on the head !
@paullongtailpair3812 replies to @nazzario_music: @johnsutton6797 The magnetic field in the ferrite cores is generated by the coils.
@Douglas_Blake_579 replies to @nazzario_music: @johnsutton6797
The sound comes from the wire windings of the coil vibrating. Cheap inductors!
@johnsutton6797: 😅Hi David
I'll bet the noise is coming from the meter movement, acting like a speaker.
Enjoy your channel.
Jack
@Douglas_Blake_579 replies to @johnsutton6797: Most likely output coils but this is also a valid possibility.
@jeremymorrison3494: Bandcamp 2 ? Never watched the first movie. Was it any good? 😉
@AudioMasterclass replies to @jeremymorrison3494: It was fabulous.
@jppj1231: Good to hear you man