This power amp makes a strange noise!

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Yesterday I reviewed the Aiyima T9 Pro on RU-vid. Today, stupidly, I messed about with it some more. And it made a strange noise. Watch my video to hear it. Warning: Includes shameless self-promotion. Ft. Betty and Debbie.
'Hyde Park Corner' on Spotify - open.spotify.com/album/3rimqS...
'Hyde Park Corner' on Bandcamp - davidmellor.bandcamp.com/trac...
Previous review video - • Does this amp distort?...
The product illustrated was given to me by the manufacturer in return for one review video. This condition was satisfied by my previous video on this product and therefore this video does not contain a paid promotion.
DAVID MELLOR'S MUSIC
David Mellor's music on Bandcamp - davidmellor.bandcamp.com/
David Mellor's music on Spotify - open.spotify.com/artist/6OkaD...
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2 май 2024

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Комментарии : 67

@deanrantala 25 дней назад

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.

@nazarsliunchenko9869 29 дней назад

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 29 дней назад

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 29 дней назад

Depends, if the amp outputs are connected to a load. Also, inductors have no internal magnetic field to act as a voice coil.

@paullongtailpair3812 29 дней назад

You hit the nail on the head !

@paullongtailpair3812 29 дней назад

@@johnsutton6797 The magnetic field in the ferrite cores is generated by the coils.

@Douglas_Blake_579 29 дней назад

@@johnsutton6797 The sound comes from the wire windings of the coil vibrating. Cheap inductors!

@Douglas_Blake_579 29 дней назад

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 29 дней назад

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 29 дней назад

@@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.

@rienpost3145 29 дней назад

The cymbals that come in at 1:45 in Hyde Park Corner. Absolutely brilliant. (And thanks for making it available on Bandcamp! Bought it.)

@user-mu2dp9hg4o 26 дней назад

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.

@humblestever24 25 дней назад

. "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.

@Flarptube 28 дней назад

Well, now that confirms what I think is the second best use for this amplifier: a static display of a living room at IKEA and a fine compliment to the non-functional television. The best is the cause célebrè that gave rise to this entertaining offering on RU-vid.

@spacemissing 28 дней назад

Yeah... Energy has to go somewhere. Amplifiers with output transformers will "sing", too, sometimes.

@moe5809 29 дней назад

Shocking. Don't worry the Aiyima T9 Pro Ultra plus will be out soon. It will be twice as good.

@Roosville1 28 дней назад

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 28 дней назад

One of the many crazy ways to be an audiophile.

@ac81017 29 дней назад

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 29 дней назад

Another bloody Northerner says Bandcamp. There's a handy explanation of what they mean also.

@callumbrowns 22 дня назад

Nice content man, Can you do a video on what sound's better, a 7 inch record or a 12 inch

@AudioMasterclass 21 день назад

I might.

@jppj1231 29 дней назад

Good to hear you man

@andymouse 28 дней назад

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!

@robertgwatts1858 29 дней назад

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. 😂

@Douglas_Blake_579 21 день назад

Add a 0.1uf capacitor across the meter movement at the rear connections... if it clears up you got off easy.

@joewlodynski3521 29 дней назад

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 29 дней назад

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.

@paulstubbs7678 28 дней назад

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.

@user-ol6kh8od3k 29 дней назад

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 29 дней назад

Simple solution ... turn the amp off first... turn the pre-amp on first. No it's not harmful... just very annoying.

@AudioMasterclass 29 дней назад

Professionally, power amp goes on last, goes off first. If it makes any noise on switch-on, get rid of it.

@user-ol6kh8od3k 27 дней назад

Thanks a bunch!

@user-ol6kh8od3k 27 дней назад

@@Douglas_Blake_579Thank!

@jeremymorrison3494 29 дней назад

Bandcamp 2 ? Never watched the first movie. Was it any good? 😉

@AudioMasterclass 29 дней назад

It was fabulous.

@matthewhilty4209 29 дней назад

That is probably coming from the coils vibrating. Hot glue them and see if that helps.

@michaeldeloatch7461 25 дней назад

I wonder if it's the VU meter.

@ac81017 29 дней назад

It's cheap non-audiophile crap that's the problem. Will check out your new release. 👍

@middleearthltd 29 дней назад

Thankfully we have the chat to get this explained Shout out to the chat

@johnsutton6797 29 дней назад

😅Hi David I'll bet the noise is coming from the meter movement, acting like a speaker. Enjoy your channel. Jack

@Douglas_Blake_579 29 дней назад

Most likely output coils but this is also a valid possibility.

@analoghardwaretops3976 28 дней назад

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..😅😅

@RUfromthe40s 26 дней назад

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

@jimdavis5230 29 дней назад

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 28 дней назад

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.