My initial impressions switching from Parasound Halo to an ATI AT524nc

[PENG]

I can hear hum from the ATI AT522NC but only within a foot.
The AT522C had less hum than the ATI AT4002, likely due to the size of the transformers, but could also be unit to unit variance.

From my experience (in my environment) Parasound had less transformer hum than ATI.

- Rich

Thank you for proving my point, that some people are more sensitive to the hum related frequencies, all else being equal such as the so called power quality.

 

[RichB]

Thank you for proving my point, that some people are more sensitive to the hum related frequencies, all else being equal such as the so called power quality.

Actually, I don't think I agree with your point if you think that this is hearing issue.
Anyone with normal hearing could hear transformer hum with my ATI AT6000s. It is just that many just don't care.
It bugged the crap out of me.

Power quality is never equal. Therefore, immunity does matter to some.
My friend had an ATI AT6007 (custom wound transformers) and a Plasma on the same circuit.
When the screen got bright, it was loud enough for "a wife (of significant other) to hear the difference from the kitchen"

There have been many posts from those afflicted with transform hum (perception) that remain uncomforted by number posts of the quietness of their own amps
BTW, I believe Gene had to buy an Emotiva CMX-2 for the Monolith (ATI built) amplifier to get rid of the hum.
CMX-2 Precision Common Mode AC Line Filter With DC Offset Eliminator – Emotiva Audio Corporation

When there is transformer hum is either unit to unit variance, a matter of susceptibility, or both.

I have read that some Bryston amps build in common mode rejection circuitry.
If true, then I suspect much less susceptibility that was engineered into the product.

Amps with very good SMPS implementations do not have these issues. They are not susceptible.

It's like COVID, I didn't get it, do we know why? Is it T-Cell immunity, lack of exposure, the extra vitamin D, or perhaps the 2% of my DNA that 23andMe categorized as unknown. We may not ever know. Perhaps the other 2%ers are also COVID free

- Rich

 

[PENG]

Actually, I don't think I agree with your point if you think that this is hearing issue.
Anyone with normal hearing could hear transformer hum with my ATI AT6000s. It is just that many just don't care.
It bugged the crap out of me.

I only make that point because we have more than 2 members who said their ATI transformers were silent. Power quality does matter and as you said they are not always "equal". However, I don't believe all those 2 or 3 members have power quality so pure that made their transformers silent even with ears on chassis and with the HVAC and/or other things not running to keep the room quiet (yes I did make that point clear to least ADTG).

For me, I have already made it clear multiple times, all transformers hum. Even Noratel claimed their transformers have low noise core, never claim silent. Yet we have people claim "silent". So we can agree to disagree or disagree to agree on that point, but the facts remain, some people cannot hear the hum that you and I can hear. Now I do believe your AHB2's transformer(s) is/are silent because it uses SMPS right? If so, whatever transformers, in those would be too small to make audible noise if they are of high quality ones.

 

[Gmoney]

Any amp that hums is junk! return it! No but really so I had Emotiva amps in the past. Yeah I know, that was before I found out about AH. None of those Emo amps had any hum or any clicking or anything. At full power of course with No source playing volume cranked up all the way absolutely dead quiet. No hissing nothing. Soo umm yeah you got a amp that hums, hiss or anything but Dead silence with the volume cranked up all the way you got a junkie amp send it back. My Carver amp was dead silent.

 

[Gmoney]

just a note, i been reading up on Parasound's 2125v2 and some are reporting issues with one channel dropping out or going Completely dead. So seems Parasound isn't what it use to be. With that line anyways

 

[PENG]

Any amp that hums is junk! return it! No but really so I had Emotiva amps in the past. Yeah I know, that was before I found out about AH. None of those Emo amps had any hum or any clicking or anything. At full power of course with No source playing volume cranked up all the way absolutely dead quiet. No hissing nothing. Soo umm yeah you got a amp that hums, hiss or anything but Dead silence with the volume cranked up all the way you got a junkie amp send it back. My Carver amp was dead silent.

To be fair, my comment about "all transformers hum" is a generalized point. In fact, it would be clearer to day a quiet transformer for audio amplifiers would have audible hum if you get very close to it, such as within a few inches. In that case you can consider it "normal, or typical". If however, you can hear it from a few feet away, or even just 2 to 3 feet, then either the transformer is not a custom wound/made quiet one, or/and it is a line quality issue (such as excessive "dc" offset). Now that's what I know as an EE (I hate to say this but..) with a lot of experience in power, control and electronics. And that's for small transformers only such as those used in audio gear. For large utility transformers, you can hear the hum from far away, even a 100 ft away in many cases.

 

[Gmoney]

To be fair, my comment about "all transformers hum" is a generalized point. In fact, it would be clearer to day a quiet transformer for audio amplifiers would have audible hum if you get very close to it, such as within a few inches. In that case you can consider it "normal, or typical". If however, you can hear it from a few feet away, or even just 2 to 3 feet, then either the transformer is not a custom wound/made quiet one, or/and it is a line quality issue (such as excessive "dc" offset). Now that's what I know as an EE (I hate to say this but..) with a lot of experience in power, control and electronics. And that's for small transformers only such as those used in audio gear. For large utility transformers, you can hear the hum from far away, even a 100 ft away in many cases.

PENG, whey do Transformers hum in the first place? Like the ones on power polls. I was just polking fun at you guy's about power supplys that hum or hiss in amps used for audio. Guess I been lucky I've never had that issue with any amp I have owned that would drive me nuts.

 

[RichB]

I only make that point because we have more than 2 members who said their ATI transformers were silent. Power quality does matter and as you said they are not always "equal". However, I don't believe all those 2 or 3 members have power quality so pure that made their transformers silent even with ears on chassis and with the HVAC and/or other things not running to keep the room quiet (yes I did make that point clear to least ADTG).

For me, I have already made it clear multiple times, all transformers hum. Even Noratel claimed their transformers have low noise core, never claim silent. Yet we have people claim "silent". So we can agree to disagree or disagree to agree on that point, but the facts remain, some people cannot hear the hum that you and I can hear. Now I do believe your AHB2's transformer(s) is/are silent because it uses SMPS right? If so, whatever transformers, in those would be too small to make audible noise if they are of high quality ones.

I believe that some people that claim their transformers are silent may in fact have an environment where transformers are silent.
Some may hear it and not recognize or care about hum.
I don't believe that exceptional hearing accounts for reports of hum.

As I pointed out, I had 3 ATI amps at the same time, 2 AT6002s (standard transformers) and 1 AT6006 (custom wound) transformers. The stock Noratels were louder than the larger custom wound AT6006s. Also, my friends custom wound AT6007 was also quiet when the power was clean.
This provides ample data to understand that ATI knows how to custom wind a transformer to make it quieter but doing so also makes them more susceptible to power issues.

There are products that you can buy that have less susceptibility to the environmental influences that can exacerbate transformer hum.

- Rich

 

[RichB]

PENG, whey do Transformers hum in the first place? Like the ones on power polls. I was just polking fun at you guy's about power supplys that hum or hiss in amps used for audio. Guess I been lucky I've never had that issue with any amp I have owned that would drive me nuts.

I had an amp like liked to sing-along with the case fans, does that count

- Rich

 

[RichB]

Concerning acceptable SINAD, there are many factors and I do not believe that test equipment results are the worst case scenario for distortion and noise.
Negative feedback is less effective on high-frequencies and is adversely affected by load. I've not seen distortion numbers relative to frequency and load.

Stereophile has its simulated speaker load which seems to basically measure the effective output impedance impact on linearity.

HTHFI used to use dual tone 60Hz and 7kHZ (or so) and this tripped up some amplifiers, showing significant increase in distortion products. I like this test better than the full-scale 19+20 kHz signal.

Some amps do well on some tests and worse on others. Personally, I don't think 0.03 THD at full power tells you how an amplifier performs, especially since most amps deliver worse THD+N into low power than at rated power.

AVRs, largely escape scrutiny, possibly because of the value proposition generates low expectations.
An FFT at 1 watt is not the final word but it should be very good to start with.

- Rich

 

[PENG]

PENG, whey do Transformers hum in the first place? Like the ones on power polls. I was just polking fun at you guy's about power supplys that hum or hiss in amps used for audio. Guess I been lucky I've never had that issue with any amp I have owned that would drive me nuts.

Thank you for asking. The answers are actually a very Googleable, you will quickly find many, such as this:

Transformers Are Never Silent (electrical-engineering-portal.com)
PurePower (purepoweraps.com)

Or just imagine this, a transformer has two main parts that would vibrate with an alternating current, at 50 or 60 cycles per second. Namely the core and the windings, the cores are typically made of laminated sheets. Some are wound tighter than others but they will all vibrate because of the applied AC. Anything that vibrates will make noise. Normally this is not really an issue because no one listen to their amp's transformers and they don't listen to music from a few inches away from the amps either.

So those who complained about highly audible hum would likely have some sort of power quality issues that are either there all the time or only when certain devices in the house is running and contaminating the line quality.

DC offset is one most often cited as the culprit for louder than normal hum.

Mains DC and Transformers (sound-au.com)
DC Blocking for Powering Audio (kccscientific.com)

Not all transformer hum the same, some are more immune to power line quality than others. In my house, I can plug all my gear into the same outlet, say one at a time, and some, such as the Denon or Marantz AVRs, my NAD integrated amp and others would not hum audibly from more than an inch away, but the Halo A21, the 4B SST and some of my subwoofers would hum loud enough to bother me from several inches away, in fact two of them are audible from several feet away. So yes, you may be lucky that you have amps that are more immune to poor power quality, or your power line quality happens to be excellent.

 

[PENG]

AVRs, largely escape scrutiny, possibly because of the value proposition generates low expectations.
An FFT at 1 watt is not the final word but it should be very good to start with.

- Rich

For me, ASR's set (the whole set, not just one SINAD test) of test can be better as always, but is good enough for me for decision making, AVRs or not. I absolutely would like to see FFT at 1 watt but since I used my AVR as preamp/processor only so FFT for the pre out is also good enough for me.

 

[PENG]

I believe that some people that claim their transformers are silent may in fact have an environment where transformers are silent.

Do you mean relatively silent, i.e. the room ambient noise vs the transformer noise vs distance? If so, yes I agree, otherwise It is practically no such thing as silent transformers, though it can come close by say potting the whole thing in epoxy. That's not practically done in main stay amps such as ATI's as evidence if the photos you attached. Even truly epoxy encapsulate transformers are not absolutely silent though likely silent enough for me.

Here's one example of such animal, not that the 3, 5 dB lower noise is offered as an option only, so even such potted transformers are not really done for quietness but mainly for other benefits.

Low voltage | Encapsulated (potted) |3R transformer | Eaton

Core features

• Encapsulated transformers are specifically excluded from the scope of U.S. DOE energy efficiency requirements
• Encapsulated transformers are available in aluminum or copper windings
• Standard 115°C temperature rise; 80°C optional. Insulation class 180°C
• Optional low-sound 3dB and 5dB below NEMA ST-20 standard
• Available in 60 and 50 Hz
• Standard NEMA 3R enclosures
• Cores are grounded with a copper lead

Eaton actually made the statement:
"All transformers emit some audible sound due mainly to the vibration generated in their core by alternating flux. NEMA ST-20 defines the maximum average sound levels for transformers."

I would also agree that our sensitivity to certain frequencies will likely not be the issue, but I won't rule it out completely, not in absolute sense either. In some Harman studies, they screened the participants in DBT comparison listening tests and even among those with no (or too little to be a factor by their criteria), they did find differences in their "scores", one being the trained listeners did better. So may be I am trained to pick up lower level of transformer hum that others (just some).

A couple good ones for those interested to read:
(PDF) Quiet Transformers: Design Issues (researchgate.net)
2016-FP-Understanding-Transformer-Noise.pdf (federalpacific.com)

 

[Gmoney]

Thank you for asking. The answers are actually a very Googleable, you will quickly find many, such as this:

Transformers Are Never Silent (electrical-engineering-portal.com)
PurePower (purepoweraps.com)

Or just imagine this, a transformer has two main parts that would vibrate with an alternating current, at 50 or 60 cycles per second. Namely the core and the windings, the cores are typically made of laminated sheets. Some are wound tighter than others but they will all vibrate because of the applied AC. Anything that vibrates will make noise. Normally this is not really an issue because no one listen to their amp's transformers and they don't listen to music from a few inches away from the amps either.

So those who complained about highly audible hum would likely have some sort of power quality issues that are either there all the time or only when certain devices in the house is running and contaminating the line quality.

DC offset is one most often cited as the culprit for louder than normal hum.

Mains DC and Transformers (sound-au.com)
DC Blocking for Powering Audio (kccscientific.com)

Not all transformer hum the same, some are more immune to power line quality than others. In my house, I can plug all my gear into the same outlet, say one at a time, and some, such as the Denon or Marantz AVRs, my NAD integrated amp and others would not hum audibly from more than an inch away, but the Halo A21, the 4B SST and some of my subwoofers would hum loud enough to bother me from several inches away, in fact two of them are audible from several feet away. So yes, you may be lucky that you have amps that are more immune to poor power quality, or your power line quality happens to be excellent.

Thanks @PENG This is way I follow You and a few other ole timers here on AH.

 

[RichB]

Do you mean relatively silent, i.e. the room ambient noise vs the transformer noise vs distance? If so, yes I agree, otherwise It is practically no such thing as silent transformers, though it can come close by say potting the whole thing in epoxy. That's not practically done in main stay amps such as ATI's as evidence if the photos you attached. Even truly epoxy encapsulate transformers are not absolutely silent though likely silent enough for me.

Here's one example of such animal, not that the 3, 5 dB lower noise is offered as an option only, so even such potted transformers are not really done for quietness but mainly for other benefits.

Low voltage | Encapsulated (potted) |3R transformer | Eaton

Core features

• Encapsulated transformers are specifically excluded from the scope of U.S. DOE energy efficiency requirements
• Encapsulated transformers are available in aluminum or copper windings
• Standard 115°C temperature rise; 80°C optional. Insulation class 180°C
• Optional low-sound 3dB and 5dB below NEMA ST-20 standard
• Available in 60 and 50 Hz
• Standard NEMA 3R enclosures
• Cores are grounded with a copper lead

Eaton actually made the statement:
"All transformers emit some audible sound due mainly to the vibration generated in their core by alternating flux. NEMA ST-20 defines the maximum average sound levels for transformers."

I would also agree that our sensitivity to certain frequencies will likely not be the issue, but I won't rule it out completely, not in absolute sense either. In some Harman studies, they screened the participants in DBT comparison listening tests and even among those with no (or too little to be a factor by their criteria), they did find differences in their "scores", one being the trained listeners did better. So may be I am trained to pick up lower level of transformer hum that others (just some).

A couple good ones for those interested to read:
(PDF) Quiet Transformers: Design Issues (researchgate.net)
2016-FP-Understanding-Transformer-Noise.pdf (federalpacific.com)

Parasound Epoxy encased transformer:

- Rich

 

[Irvrobinson]

I can hear hum from the ATI AT522NC but only within a foot.
The AT522C had less hum than the ATI AT4002, likely due to the size of the transformers, but could also be unit to unit variance.

From my experience (in my environment) Parasound had less transformer hum than ATI.

- Rich

Have you thought about calling the power company and having the quality of your mains power assessed?

 

[PENG]

Parasound Epoxy encased transformer:

- Rich

I think it is just the enclosure, but not encasing the core and windings. Even if it is, it may reduce noise by just a few dB. It looks like a metal enclosure, same as Marantz's.

 

[RichB]

Have you thought about calling the power company and having the quality of your mains power assessed?

My fiends custom wound AT6007 buzzed when the Plasma display was turned on.
That would be one of those "Doctor it hurts when I do this" questions.
The eventual solution was to upgrade to an LG OLED.

Here is the look at the power using my friends iPad oscilloscope.

- Rich

 

[Irvrobinson]

My fiends custom wound AT6007 buzzed when the Plasma display was turned on.
That would be one of those "Doctor it hurts when I do this" questions.
The eventual solution was to upgrade to an LG OLED.

View attachment 46146

Here is the look at the power using my friends iPad oscilloscope.

- Rich

I'm not sure what to make of it. Those sine waves are distorted, but I'm not residential power knowledgable. I'd call the power company, tell them you've had issues with noisy transformers, and ask them if they'll do an assessment.

 

[PENG]

Hey Rich, not that you care, but just for information, it looks like Denon actually tried to have a quiet custom wound one for its $8,000, 50 W integrated amp. They claimed:

Google Translate

"The power transformer is the source of power for the amplifier and at the same time the source of unwanted vibration and noise. In PMA-SX1 LIMITED, like the conventional S series, the case of sand-type aluminum casting is filled with special resin to eliminate vibration generated from the power transformer, and the careful magnetic shield suppresses noise in the housing caused by leakage magnetic flux. We are supplying clean power. A transformer with an extra-thick winding that is evenly wound with a margin produces a clear and powerful sound."

It is marketing talks, but at least this one actually makes sense, to an EE anyway. It can be done, (I mean almost) for a price!

Large-capacity power transformer with aluminum sand casting case

I am sure there are other expensive amps that might have something similar.