Hum from a toroidal transformer

[Haflermichi]

The "acceptable level" is up to you. And it seems that it's clearly unacceptable, to you.
Before you go all extra, external device fix hunting I would ask how far you have trouble shot this issue?
Can you lift the unit of the table and have the hum change or reduce in level? Have you tried placing the unit on some kind of foam
or even just a towel just to experiment?
Should cost very little and take mere seconds.

I would also state that it's entirely possible that the mounting bolt is loose. Mistakes happen, especially in high volume production lines where thousands of items are being made around the clock by low wage workers.
Don't rule out simple solutions until you have verified them.

Line DC or not, toroids can hum. When you purchase toroids raw from suppliers, at least reputable ones, they come with a rubber donut for mounting.
That donut is there for a reason.
It could also be that the mounting bolt is TOO TIGHT and is eliminating any noise damping compliance of the donut...
Or maybe there is no donut...

If you have determined not to send it back and are willing to open the chassis AND are comfortable doing so you could investigate the mounting bolt and perhaps
adding more cushioning under the toroid.
Obviously, only do this with the unit unplugged and only if you know what to look for.
If you are not comfortable opening the unit you will indeed be relegated to upstream devices.

 

[JSmith]

It is the Cymax 1ET400A-02 Lite MK3

Did you mean this one, CY-1ET400A-02 LITE MK2?

System Message - Cymax Digital Limited

www.cymaxdigital.com

has a much darker background and greater resolution

What does this mean and how did you ascertain an audible difference when level matched?


JSmith

 

[Old_School_Brad]

It is the Cymax 1ET400A-02 Lite MK3. Overall a mechanically well made device. Great, clear and power sound. Comparing to the 3e audio A5 and 3e audio A7 amplifiers, the Cymax subjectively has a much darker background and greater resolution.
The trigger works very well. The lighting of the mechanical switch can be turned off. All in all, this could already be my target amplifier.
Unfortunately, the damned hum from the transformer causes my satisfaction with the buying of this amplifier to sadly disappear. And frustration has set in for me.
Let's hope it's just a DC problem in the grid.

I wouldn’t buy something without first checking for loose bolts or components inside the cabinet. Mistakes happen, and something could be loose and just need tightening.

I’ve been repairing and servicing amplifiers as a hobby on and off, and I’ve come across many with humming toroidal transformers. Sometimes, the center bolt needs tightening with an extra washer underneath, and other times, it’s the main amplifier board that’s loose and just needs its screws secured.

If something is actually loose and you succeed to fix the vibrations with a DC blocker, wouldn’t you still want to make sure everything inside the amplifier is properly in place?

It costs nothing to check, and afterward, you'll know for sure rather than just guessing.

 

[JSmith]

damned hum from the transformer

Might not be a good quality toroidal... poor core lamination possibly. If the DC blocker or doesn't help, I'd be returning the device.


JSmith

 

[Maciekw]

Did you mean this one, CY-1ET400A-02 LITE MK2?

System Message - Cymax Digital Limited

www.cymaxdigital.com

What does this mean and how did you ascertain an audible difference when level matched?


JSmith

The link you pointed out shows a version of the amplifier with an SMPS power supply.

I bought the version that is not yet on the Cymax website, labeled “mk3”. The mk3 version has an analog power supply with a 750W toroidal transformer.

I decided on this version because it seemed to me that the analog power supply is more reliable in terms of possible failures. And that, unlike SMPS, it will provide more stable power. Some SMPS power supplies provide continuous power at 30% of the declared power.

As for audible differences, I wrote about subjective feelings. Not supported by a more objective assessment.

 

[Maciekw]

The "acceptable level" is up to you. And it seems that it's clearly unacceptable, to you.
Before you go all extra, external device fix hunting I would ask how far you have trouble shot this issue?
Can you lift the unit of the table and have the hum change or reduce in level? Have you tried placing the unit on some kind of foam
or even just a towel just to experiment?
Should cost very little and take mere seconds.

Yes, I have done similar experiments that you write about. Unfortunately, without positive results.

I wouldn’t buy something without first checking for loose bolts or components inside the cabinet. Mistakes happen, and something could be loose and just need tightening.

I’ve been repairing and servicing amplifiers as a hobby on and off, and I’ve come across many with humming toroidal transformers. Sometimes, the center bolt needs tightening with an extra washer underneath, and other times, it’s the main amplifier board that’s loose and just needs its screws secured.

If something is actually loose and you succeed to fix the vibrations with a DC blocker, wouldn’t you still want to make sure everything inside the amplifier is properly in place?

It costs nothing to check, and afterward, you'll know for sure rather than just guessing.

What you wrote makes sense. And I'll do such an inspection of the inside of the amplifier if the DC blocker I ordered doesn't bring improvement.

 

[JSmith]

Some SMPS power supplies provide continuous power at 30% of the declared power.

SMPS units from reputable manufacturers (i.e. not low quality) are generally reliable and capable of delivering their rated power consistently. If an SMPS is only delivering 30% of its declared power continuously, that's not typical for properly functioning or well designed unit.


JSmith

 

[Maciekw]

SMPS units from reputable manufacturers (i.e. not low quality) are generally reliable and capable of delivering their rated power consistently. If an SMPS is only delivering 30% of its declared power continuously, that's not typical for properly functioning or well designed unit.


JSmith

Of course, you are right that everything depends on the quality of SMPS. But even an SMPS from such a venerable manufacturer as Hypex is only able to render the claimed power for 10 seconds. The long-term power output is much lower. For example, 350W instead of 1200W.

 

[JSmith]

350W

It's rated for 350W continuous and that is what it provides. Peak power is the amount of power the power supply can handle for a short period.

Are you planning on needing 1200W continuous?


JSmith

 

[Maciekw]

It's rated for 350W continuous and that is what it provides. Peak power is the amount of power the power supply can handle for a short period.

Are you planning on needing 1200W continuous?


JSmith

I wrote about the SMPS1200A400 power supply. It is marketed as a 1200-watt power supply, not a 300-watt power supply. After all, to find out about these limitations you must read the datasheet carefully, which most buyers are unlikely to do.
Of course, you are right that I have no intention of holding open-air concerts, which would require such huge power.
These are just considerations for thermal endurance, which in the long run may translate into the long-term reliability of the device.
And that's all there is to it. Indeed, I do not deny the advisability of using SMPS power supplies.

 

[JSmith]

These are just considerations for thermal endurance, which in the long run may translate into the long-term reliability of the device.

Fair enough, SMPS' may not last as long... but really depends on multiple factors. That said the other will produce more heat anyway, as not as efficient so more power converted to heat. So one can only hope the amp is designed well in regards to thermal management.


JSmith

 

[popej]

I wrote about the SMPS1200A400 power supply. It is marketed as a 1200-watt power supply, not a 300-watt power supply.

Looks like it is designed for audio. 6dB between peak and average power should be good enough. Probably amplifier modules get similar specification.

 

[JSmith]

Looks like it is designed for audio.

Exactly, which is why the focus is on peak power for transient demand and not continuous (unless one thinks of the stupid FTC "rule" that makes zero sense)... it's not like it's for a server or something, application specific. The 700W toroidal will generate more heat and be unable to match the 1200W peak power of the SMPS.


JSmith

 

[wwenze]

Of course, you are right that everything depends on the quality of SMPS. But even an SMPS from such a venerable manufacturer as Hypex is only able to render the claimed power for 10 seconds. The long-term power output is much lower. For example, 350W instead of 1200W.

Peak output is limited by the output transistor while continuous is limited by upstream power supply (transformer, rectifier, the capacitors --> capacitors also deciding how long is your "peak") and/or heat

I'm not proficient enough to tell the continuous output just from looking at the capacitors (I guess I can compare the 400V caps vs that from a 1200W ATX PSU, and the 1000uF equivalent on the hypex is sufficient), but heat definitely is a limiter if that thing is not given additional cooling. Which begs the question, how much can it provide continuously if sufficiently cooled.

Add: The thing regarding music power supplies and amp is that even if you take like this 1200W and beef it up to do 1200W continuous (say, more cooling), the maximum voltage it provides means it can only still do 1200W at those music peaks and 300W on average so I'd have wasted cost on beefing it up. So I'm not concerned with long term thermal reliability either; 300W @ 90% efficiency = 33W of heat so just bolt that heatplate to the chassis and that's more than enough.

 

[wwenze]

Exactly, which is why the focus is on peak power for transient demand and not continuous (unless one thinks of the stupid FTC "rule" that makes zero sense)... it's not like it's for a server or something, application specific. The 700W toroidal will generate more heat and be unable to match the 1200W peak power of the SMPS.


JSmith

Maybe FTC wants to cover for air raid sirens... Continuous 0dBFS sine wave, check. High power, check.

 

[raif71]

If it hums to the music, then it should be ok but if not, then it's not acceptable

 

[pjug]

it's almost certainly DC in the AC line.

I think this isn't true. It could be DC but also a lot of transformers just have inherent hum because the layered core is not made as well as it should be.

 

[theREALdotnet]

And then the external isolation transformer hums just like the internal one

Ha, that's what happened to me. The isolation transformer was in fact quite a bit louder than the amp's toroid.

I don't have that amp anymore but I kept the isolation transformer to run measurement equipment from (oscilloscopes etc.). Prevents little ground-related mishaps

 

[tmtomh]

I think this isn't true. It could be DC but also a lot of transformers just have inherent hum because the layered core is not made as well as it should be.

This is a point that's been made repeatedly, and it very well might be the case. But in my experience a toroidal does not hum unless there's DC in the AC line. It's absolutely the case that a better-made toroidal might not hum when hooked up to a dirty AC supply while a poorly made one might. But it's also the case that all toroidals are more susceptible to DC-based saturation humming than laminated-sheet EI transformers are.

I'm sure there must be toroidals out there that are so poorly made that they will mechanically hum even with a super-clean AC source. But that hasn't been my experience. In my experience some of them hum based on local conditions, and all of them that hum are helped significantly by a DC blocker. YMMV of course, but if someone is happy with their amp otherwise and they're sure the hum is mechanical (rather than coming through the speakers), and they've tried turning off flourescent lights and old fridges and moving the amp's AC cord to a different circuit and so on, and it still hums, then a DC blocker is the logical next step.

 

[Old_School_Brad]

they're sure the hum is mechanical (rather than coming through the speakers), and they've tried turning off flourescent lights and old fridges and moving the amp's AC cord to a different circuit and so on, and it still hums, then a DC blocker is the logical next step.

By following the steps you outlined, you've effectively ruled out DC as an issue, rather than confirming its presence on the AC mains.