Transformers, hum & saturation

[Madfloyd]

I know that at least a couple brands of tube amps emit a hum from the transformers (i.e. NOT through the speakers). Perhaps many of them do (I have limited experience with tube amps). Over the course of a few hours mine will get louder. I don't know if this is unusual or not.

My question for the today is: would you expect a change in sonics as this happens?

[kcin]

I assume you are speaking of the power transformers.

To some extent all laminated core power transformers will hum. Some noticeably, others you will have use a stethoscope or chopsticks to ear area to transfer the vibration. At 60 cycles it can be noticeable. If there is dc on the ac line of any sort, if the laminations were not tightened up properly or have worked loose,if the potting or varnishing was not done properly, if you are running a transformer designed for 60cps on another frequency or simply if the transformer requires a isolating pad on the chassis it will hum.

If it begins to hum louder further into your listening session the characteristics of the load to the transformer may be changing over time ( more current through it) or the laminations are responding to the quiescent temperature in sympathy and loosening up.

You need some special equipment to measure dc on the ac line and phase anomalies but... you can check the current draw over time on the amp with some inexpensive digital watt/current inline devices available readily today to get an idea if this is happening- tubes could be changing their characteristics over time in the amp and drawing more current - thus stressing the transformer-- a possibility. You can probably coax your power company to come and assess PF , and the characteristics of your ac for no charge if you pester them enough. Alternatively , you may have something in your home feeding back dc into the line- switching power supplies on TVs or other equipment. etc. Switch your breakers off one by one and see if you can eliminate the hum.

The simplest thing to do is tighten up the laminations or the mounting for the transformer and see if that makes a difference. If your transformer is potted then not much you can do but tighten up the mounting and investigate electrically. You can add isolation grommets or pads if you can reasonably slip them in without taking things apart.

My Aesthetix Io has several transformers in it from Mercury Magnetics- they've isolated all of them on a pad before mount to cut down on hum. On my Wyetech SET 211 you can hear the snap of the core on turn on to the 1500v transformer then it dissipates

It may be quite normal for your amp though-- check with your manufacturer. CAT I assume,would be quite helpful on this quality of amp.

Good luck

[Madfloyd]

I've asked CAT about the hum in the past but got no response. I wasn't overly concerned since I had read about the hum before buying the amps (i.e. it seems to be a well known fact). Why, I have no idea. A friend of mine has Quicksilver amps and the transformers in them also make sound (although I'm sure no where as loud).

I'm not concerned about getting rid of the hum so much as I want to understand why it gets louder and more importantly, can that result in a change of sonics (e.g. more saturation, distortion etc.)

[Dr.Ears]

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[MylesBAstor]

I've asked CAT about the hum in the past but got no response. I wasn't overly concerned since I had read about the hum before buying the amps (i.e. it seems to be a well known fact). Why, I have no idea. A friend of mine has Quicksilver amps and the transformers in them also make sound (although I'm sure no where as loud).

I'm not concerned about getting rid of the hum so much as I want to understand why it gets louder and more importantly, can that result in a change of sonics (e.g. more saturation, distortion etc.)

I think this is a little more of an issue with big tube amps and hence bigger power transformers. I have a little bit of the same with one of my ARTs and the only thing is to do is send it back. Which cj has volunteer to so if I so desire. I assume it just has to do with construction. No I haven't noticed any change in sound quality other than as amp warms up sound gets better especially when it comes to capturing that envelope of sound around an instrument as well as sense of space.

[kcin]

I've asked CAT about the hum in the past but got no response. I wasn't overly concerned since I had read about the hum before buying the amps (i.e. it seems to be a well known fact). Why, I have no idea. A friend of mine has Quicksilver amps and the transformers in them also make sound (although I'm sure no where as loud).

I'm not concerned about getting rid of the hum so much as I want to understand why it gets louder and more importantly, can that result in a change of sonics (e.g. more saturation, distortion etc.)

I've offered some reasons why the hum might be there and why it might get louder.

You need to find the reason for the hum - then you can address it appropriately to see if it makes a difference to you. If it is hum that mechanically couples to the chassis without a relationship to current draw.. then I've have heard this kind of hum affect other tubes in their performance depending on their susceptibility to micro-vibrations. This is a mechanical construction issue or quality of transformer issue. It may be exacerbated by quality of ac you need to assess this to afford the correct solution.


If it is hum caused by increasing current requirements as tubes reach their thermal equilibrium then it can certainly affect sonics. You can measure this as I indicated. Either way you need to determine why- then assess a solution and apply the experiment.

Best of luck

[Rob]

Kcin covered this well, i have little to add other than even toroids will hum, I had an issue eons ago with the ginormous xfmer in a krell MDA-500. it was a beast weighing in at around 90 lbs and potted in a large can, it hummed like a mother within a year of acquiring the amp. I doubt CAT winds their own and most likely acquires their xfmers from a 3rd party, the common CYA response is to blame it on a ground issue or as mentioned, stray dc.

[MylesBAstor]

Kcin covered this well, i have little to add other than even toroids will hum, I had an issue eons ago with the ginormous xfmer in a krell MDA-500. it was a beast weighing in at around 90 lbs and potted in a large can, it hummed like a mother within a year of acquiring the amp. I doubt CAT winds their own and most likely acquires their xfmers from a 3rd party, the common CYA response is to blame it on a ground issue or as mentioned, stray dc.

I think Mark had a transformer hum problem with his KSA 250 IIRC.

[atmasphere]

I think this is a little more of an issue with big tube amps and hence bigger power transformers. I have a little bit of the same with one of my ARTs and the only thing is to do is send it back. Which cj has volunteer to so if I so desire. I assume it just has to do with construction. No I haven't noticed any change in sound quality other than as amp warms up sound gets better especially when it comes to capturing that envelope of sound around an instrument as well as sense of space.

This has nothing to do with the size of the amplifier! It has mostly to do with the transformers in the unit and really, not a whole lot else.

The variables are: core size, percentage of loading, the quality of rectification and the presence of distortion on the AC line.

If the hum consistently shows up over a period of time, loading and the core of the transformer are in play. If the amp is otherwise behaving normally this might indicate a noisy transformer. It likely will not affect the sound.

Power rectifiers can make a transformer become noisy. They do this by providing an uneven load on the winding that is driving them. If one rectifier opens up in a bridge, the transformer can rattle quite a lot and the amp will otherwise seem to be operating OK. Usually this problem will be there as soon as the amp is turned on, but rectifiers can be thermally intermittent, which means this problem can be confused with the first one. The thing is, while subtle, this probably will affect the sound as the amp is getting less energy.

As Deep Thought once said: 'Tricky.'

If distortion is on the line, the two areas of difficulty are the 2nd harmonic and the 5th. DC on the line, caused by a device that only operates on one-half of the line's since wave (such as an aquarium heater or a hair dryer) can cause half of the AC sine wave to have less amplitude. This can be interpreted as a 2nd harmonic if the sine wave has gone through a power transformer. DC blockers can cure this particular issue with no down-side (we build them into all our amps). The 5th harmonic is also tricky- this is caused by a local distribution transformer that is loaded a bit too heavily. a 5th harmonic can also cause rectifiers to radiate noise (not to be confused with 'swept resonance' which is an interaction between the rectifier's capacitance and the inductance of the transformer's windings).

[Socrates]

Ralph, You did not mention the fact of the possibility the mains line frequency 50/60hz maybe causing hum to be accentuated

--the only reason I found this was from NAIM UK

whom have a sometime "Hum" problem in the field with their large seperate PSU's--according to their Techs if the Line frequency can be

"tamed/adjusted" in some way--this should alleviate the aforesaid "hum"

I have witnessed this myself with the acquisition of a Power Regenerator that uses an inbuilt micro processor to curb/correct frequency anomaly

causing Hum to prominence in power products. I can report 100% success with the Units absolutely quiet now.

I fully realise this is only one solution --but in my case --I was driven to distraction with inherent hum in the background--and in this case the

fix above was the cure. YVMV

Soc

[atmasphere]

Socrates, Yes, I didn't. Any good power transformer is designed to be silent on 50Hz. If its silent on 50Hz it will be on 60Hz too.

[david k]

It depends how loud, if you hear it in your sitting position with music off then it's already too loud and unacceptable. The problem for smaller manufacturers is that they can't afford to reject defective transformers the manufacturer sends them so often it's passed on to the consumer but at this price point it's not acceptable, IMO.

david

[atmasphere]

^^ As a small manufacturer myself I can say that this isn't true. A small manufacturer can easily reject defective parts. The trick is to make sure that the spec calls for 'dead silent at full load' in the first place.

[Socrates]

Thank you for the reply Ralph--- this version touted by Naim UK I find rather strange as "hum" deemed to be normal with their specific Toroidal
Power Transformers?

NOTE: Toroidal transformer hum of chassis cannot be eliminated, but can be minimized by using a Naim power cord (the one supplied, or a higher-level Naim power cord), plugged directly into a wall outlet, not to any power conditioning system. Naim has confirmed the "hum" from the toroidal transformer is completely normal.

In my case the the supplied Cords did not remove the Bzz Bzzz Bzz completely --BUT simply lowered the output couple of Hz!.

The Regenerator removed ALL the anomaly.

Soc

[Alrainbow]

On one of my ps audio p5 units it would hum
now and then. Weather it was being used or not. To my ears it was above 60 hertz but that's me guessing. When I emailed them about it. The sited D.C. Offset as well. I sold the house before I got to test it.

[Marcus]

DC blockers can cure this particular issue with no down-side (we build them into all our amps).

My experience with line conditioners (Burmester and PS Audio) that have DC blocking capability is very different. They did block DC alright (transformers stoped humming) but at the expense of dynamics and with some other sonic anomalies. Karan then made a design for a dedicated DC blocking device but it also crushed dynamics and squeezed life from music. When I ordered P.I.Audio UberBuss line filter, the designer told me he's trying to design a DC blocking stage but all designs he tried one way or the other compromised the sound quality.

Since I and a lot of my audio buddies have problems with the DC offset, we all would be very interested in a stand alone DC blocking device that would not compromise sound quality...

[Joe Pittman]

My experience with line conditioners (Burmester and PS Audio) that have DC blocking capability is very different. They did block DC alright (transformers stoped humming) but at the expense of dynamics and with some other sonic anomalies. Karan then made a design for a dedicated DC blocking device but it also crushed dynamics and squeezed life from music. When I ordered P.I.Audio UberBuss line filter, the designer told me he's trying to design a DC blocking stage but all designs he tried one way or the other compromised the sound quality.

Since I and a lot of my audio buddies have problems with the DC offset, we all would be very interested in a stand alone DC blocking device that would not compromise sound quality...

I have extreme transformer hum noise so I am using IsoTek Syncro power cables at the moment. It's not a perfect solution, hum is not totally eliminated and dynamics are slightly reduced. However, they knock down the hum enough to be an acceptable trade-off at the moment. I would would love to find a device which solves the hum problem but does no harm.

Anyone using Syncro's? If so, what is your experience?

[atmasphere]

My experience with line conditioners (Burmester and PS Audio) that have DC blocking capability is very different. They did block DC alright (transformers stoped humming) but at the expense of dynamics and with some other sonic anomalies. Karan then made a design for a dedicated DC blocking device but it also crushed dynamics and squeezed life from music. When I ordered P.I.Audio UberBuss line filter, the designer told me he's trying to design a DC blocking stage but all designs he tried one way or the other compromised the sound quality.

Since I and a lot of my audio buddies have problems with the DC offset, we all would be very interested in a stand alone DC blocking device that would not compromise sound quality...

I genuinely suspect that the DC blocking was not the problem you are describing. There is no significant bandwidth or line voltage issues associated with a DC blocker. OTOH most line conditioners don't come anywhere near what they are purported to do, and with our amps we find that usually they do more harm than good for reasons that have nothing to do with blocking DC! So we usually recommend that line conditioning not be used with our amps.

One of the very few conditioners that really do work were made by Elgar and not for high end audio. I hate to put it this way, but the fact that they are for commercial/industrial means that they actually work The Elgars I've seen correct line voltage and significantly block harmonics, producing an output waveform that has about 0.1% THD regardless of load on the conditioner (some of them can do 28Amps continuous).