Power amp transformer hum [Archive] - The Art of Sound Forum

alcarmichael

03-07-2018, 10:22

Any advice on what to do to help prevent transformer hum? I believe the first thing to try would be a DC blocker type thing but have done a bit of research and these can possibly have a bit of a negative effect on power amps. Anything else I can try?

The amp in question is an Avondale ZAP 250 and when listening to music at anything other than very quiet the hum isn’t an issue, on the rare occasion though that I listen at quiet volumes for a bit of background music it’s annoying!

Mr. C

03-07-2018, 10:36

Is the noise actual transformer hum or an electrical noise through the speakers?

Barry

03-07-2018, 10:44

Without a source connected, is the hum electrical (i.e can be heard when listening close to the speaker), or is it mechanical (i.e. can be heard when listening close to the amplifier)?

Is the transformer in the ampifier a toroid?

alcarmichael

03-07-2018, 11:13

Contact Avondale Audio. I'm sure they'll be very helpful.
Sometimes just tightening a screw somewhere can be enough to reduce any vibration and quieten things down considerably.

I keep meaning to do this! It’s the obvious starting point!

Is the noise actual transformer hum or an electrical noise through the speakers?

Actual transformer hum.

Without a source connected, is the hum electrical (i.e can be heard when listening close to the speaker), or is it mechanical (i.e. can be heard when listening close to the amplifier)?

Is the transformer in the ampifier a toroid?

The amp hums with absolutely nothing connected to it, it does so when connected to different mains sockets.

I assume it’s a toroid, I’m not certain though, I don’t even know what other types there are!?

bumpy

03-07-2018, 11:17

Barry

03-07-2018, 11:21

Toroidal transformers are prone to mechanical 'hum' if there is some DC present on the mains (> 100mV). But other transformer designs can vibrate mechanically at the mains frequency (and hence 'hum) if the laminations are not tighened up.

I would suggest you contact Avondale and seek their opinion and advice.

STD305M

03-07-2018, 12:24

2fastgt4

03-07-2018, 12:41

I'm using a dc blocker for my amp. And it works very well. For your use I will advise to try one out.
The reputation is various because of various reasons. Some are also quite expensive. Actually you can get them very cheap on eBay, and they do the work.
Actually my experience is that if you first have the hum and remove it with dc blocker, your amp will make a better sounding stage. Better dynamics and headroom ( maybe of most part because the noise flour is lower). Either way it is a plus for audio listening.

Here is a link for what I'm using

https://m.ebay.com/itm/DC-trap-blocker-filter-for-toroidal-transformers-assembled-in-case/131654666919

Tommy

alcarmichael

03-07-2018, 12:50

I have sent Avondale an email seeking their advice, should I not make any progress off the back of their reply I’ll have to try a DC blocker such as this.

Bigman80

03-07-2018, 14:04

A DC blocker is unlikely to eradicate the problem. I use one and they still buzz, although it does reduce it *very little*

I have transformers which have Mechanical buzz, which is what you have.

The ONLY way to entirely rectify it, is to replace the TFs with audiophile quality ones. Airlink and Toriody (I like Toriody) have audiophile quality TFs but drop them an email and specify that's what they are for.

I've used multiple cheaper Chinese alternatives and ended up throwing them out due to the noise they make

They buzz because the laminations arent glued together 100%. Whilst this has no bearing on functionality, it does make them noisy.

This one is in my valve phonostage, after chucking the noisy Chinese bought one. Worth every penny. https://uploads.tapatalk-cdn.com/20180703/456053b1653121240fe965571a9a0219.jpghttps://uploads.tapatalk-cdn.com/20180703/1ac1ef6bccd74c082c1a440e5ebafc76.jpg

2fastgt4

03-07-2018, 14:41

You could be right about this.
But maybe your dc blocker was not removing enough dc volts?
Some only removes 0.5 volts. Others removes up to several volts.
If you have dc 2 volts and use a dc blocker that removes 1 volt you will notice a difference. But the hum only gets lower .
This is possible to measure and build a blocker that is strong enough.
I'm not shore about hove much the one I linked to removes. But I think I did read somewhere it is in the range of somewhere between 2 and 4 volts.
It's easy to calculate if you have the skills, I don't.

In my case in an acoustic treated (quiet)room I could hear the hum from 4 meters. Of course the noise was depending on howe mutch dc it was at the moment. But worst case cenario 4 meters.
With the dc blocker it's always quiet. Or the truth, if I put my ear dawn on the top of amplifier and the room is totally quiet I might sometimes hear it. But that is good enough.
A DC blocker is unlikely to eradicate the problem. I use one and they still buzz, although it does reduce it *very little*

I have transformers which have Mechanical buzz, which is what you have.

The ONLY way to entirely rectify it, is to replace the TFs with audiophile quality ones. Airlink and Toriody (I like Toriody) have audiophile quality TFs but drop them an email and specify that's what they are for.

I've used multiple cheaper Chinese alternatives and ended up throwing them out due to the noise they make

They buzz because the laminations arent glued together 100%. Whilst this has no bearing on functionality, it does make them noisy.

This one is in my valve phonostage, after chucking the noisy Chinese bought one. Worth every penny. https://uploads.tapatalk-cdn.com/20180703/456053b1653121240fe965571a9a0219.jpghttps://uploads.tapatalk-cdn.com/20180703/1ac1ef6bccd74c082c1a440e5ebafc76.jpg

Tommy

2fastgt4

03-07-2018, 14:47

Forgot to tell that my amplifier is fully balanced and have 4 toroidal trafos. 4 times 500va.
And I suspected first bad quality trafos since they are 20 years old. And in that case the dc blocker as mentioned above will not help.
But all 4 is quiet now.

Tommy

NRG

03-07-2018, 14:54

^^^ Exactly. Also Torodial transformers don’t have ‘laminations’ as such, the core generally being wound from a single continuous strip of nickel iron or moulded to shape from a ferrite material.

anthonyTD

03-07-2018, 15:16

:)
Just to add to the below comment from Andrew, try to establish if the noise gets worse at paticular times of day/night, and if the frequency changes slightly.

Bear in mind that the problem might not be the transformer itself anyway. I've known steel enclosures to rattle due to induction from the transformer. The cure is to move the transformer within the enclosure (if that's even possible) or to tighten or loosen fixing bolts or somehow damp the movement of the enclosure.

Bigman80

03-07-2018, 15:32

I think you're over-stating the problem a bit, there. E-I transformers can rattle/buzz very badly, but the problem isn't that hard to cure and you don't need "audiophile" transformers. The bolts that hold the laminations together can be be tightened (or even loosened in some cases) which can have a beneficial effect. Also, potting the transformer in varnish should eliminate rattles and buzzes. That's something which can be done at home with ordinary oil-based varnish.
However, toroids are constructed differently so the same methods as used for E-I transformers don't apply.

Bear in mind that the problem might not be the transformer itself anyway. I've known steel enclosures to rattle due to induction from the transformer. The cure is to move the transformer within the enclosure (if that's even possible) or to tighten or loosen fixing bolts or somehow damp the movement of the enclosure.I don't think I am, I bought a Airlink TF for my BMU, it buzzed like a bee in an echo chamber. I sent it back after trying to bolt it tighter, adding rubber washers under it, doubling the isolation etc and in the end, the only way to rid myself of the buzzing was to specify it had to be silent. I've been in this situation on 3/4 occasions and this solution is the best remedy.

TFs dipped in varnish have remained noisy IME

Bigman80

03-07-2018, 15:34

Cheers Tommy, the design of the PCB is one I bought online. There may be capped for more blockage.

How can I test what it's blocking?
You could be right about this.
But maybe your dc blocker was not removing enough dc volts?
Some only removes 0.5 volts. Others removes up to several volts.
If you have dc 2 volts and use a dc blocker that removes 1 volt you will notice a difference. But the hum only gets lower .
This is possible to measure and build a blocker that is strong enough.
I'm not shore about hove much the one I linked to removes. But I think I did read somewhere it is in the range of somewhere between 2 and 4 volts.
It's easy to calculate if you have the skills, I don't.

In my case in an acoustic treated (quiet)room I could hear the hum from 4 meters. Of course the noise was depending on howe mutch dc it was at the moment. But worst case cenario 4 meters.
With the dc blocker it's always quiet. Or the truth, if I put my ear dawn on the top of amplifier and the room is totally quiet I might sometimes hear it. But that is good enough.

Tommy

alcarmichael

03-07-2018, 16:24

With regard to a poor quality transformer being the potential cause, surely a company as highly regarded as Avondale would use good quality transformers?

Sherwood

03-07-2018, 16:29

If the hum is mechanical and if you feel,comfortable, this is what I would do.

Put the amp on till it hums then remove the top to see if this in itself has had an effect. Then bare down on various parts of the chassis and transformer with a wooden stick. You may well find that tightening down or a new rubber washer will sort things out.

Good luck

Unless you have a fully paid up funeral plan I would not start poking around a powered up valve amp with a wooden stick or anything else for that matter! For your education I am attaching a picture of a rat that tried to chew one of my "live" hifi power cables in Malawi!

23788

Pay careful attention to the emission trail to the right of the photo!

Geoff:deceased:

Mr. C

03-07-2018, 16:34

I would suggest finding the null point of the transformer first that's always a good place to start, every TX has one you, you just have to find it.

Jazid

03-07-2018, 16:35

Not necessarily poor quality, these things can develop with time in EI cores at least. Another problem is manufacturers using 'tightly spec'd' transformers which work harder and more efficiently but are more prone to hum. I've had this with MF kit, annoying it is too.

Sent from my BLA-L09 using Tapatalk

2fastgt4

03-07-2018, 16:36

Hi there. There are ways to measure the electricity in the wall socket for how much dc you have. Then there is a formula to calculate how you need too build the dc blocker. I did read a lot about the problem in Norwegian forums. But as mentioned before, this is way over my head.
So for people that just buy a accidentally dc blocker it might be to small and not remove enough dc.

But you are also right about the audiphile trafos. But maybe people here reacts to word as "audiophile" or "high end" trafoes [emoji3].

The truth is that it is difficult to make perfect trafoes. But when the quality is good the trafo will not "hum"
So if you change to quality trafos, the hum will be gone.
Of course the dc is still in your electricity net. So some high end people still believe that the best is to have dc blocker even if it is quiet.
Cheers Tommy, the design of the PCB is one I bought online. There may be capped for more blockage.

How can I test what it's blocking?

Tommy

blackmetalboon

03-07-2018, 17:43

As AnthonyTD said, if the buzzing was caused by DC offset, I would expect the buzzing to vary during the day.

2fastgt4

03-07-2018, 18:02

As AnthonyTD said, if the buzzing was caused by DC offset, I would expect the buzzing to vary during the day.Yes, this is correct.

Tommy

Barry

03-07-2018, 18:27

If the transformer noise is due to DC offset on the mains, the 'hum' will be at 50Hz. If due to loose laminations, the 'hum' will be at 100Hz.

alcarmichael

04-07-2018, 09:38

So, these are my transformers:

I have no idea how they rank quality wise...?https://uploads.tapatalk-cdn.com/20180704/a1add6e703768aee0a4e7d1842e5a9f1.jpg

Sent from my iPhone using Tapatalk

Bigman80

04-07-2018, 09:56

I have a Noratel too. Mine is potted. Doesn't hum.

Like I said, in audio application, you really need silence from it.

When I first built the DIY phonostage, I could hear the vibration of the TF through the speakers. It was really bad. It was my experience that having a noisy TF like that definitely affected the sound quality.

Spending the money on the Toriody was worth every penny IMO. Obviously, there are others with other opinions but my mind is set on only buying high quality TFs from now on.
So, these are my transformers:

I have no idea how they rank quality wise...?https://uploads.tapatalk-cdn.com/20180704/a1add6e703768aee0a4e7d1842e5a9f1.jpg

Sent from my iPhone using Tapatalk

anthonyTD

04-07-2018, 10:01

Hi Alex,
Another aspect I have found affects Transformer noise to a lesser, or greater degree, is the over voltage aspect, most European designed transformers are wound for 230v these days...Here in the UK, the voltage can vary between 237v to just under 260v in some areas [yes I have confirmation of this] So, this in itself, will have a very noticeable affect on the transformer in some aplications, not to mention the higher secondary voltages, and their affect on the components, and circuitry design!
A...
So, these are my transformers:

I have no idea how they rank quality wise...?https://uploads.tapatalk-cdn.com/20180704/a1add6e703768aee0a4e7d1842e5a9f1.jpg

Sent from my iPhone using Tapatalk

Bigman80

04-07-2018, 10:21

Interesting. How did mechanical buzz manage to create an electrical signal in the speakers?It was coming through the valves. I put valve dampers on the Telefunkens and it improved. I was able to feel the TF vibrate through the casework with my finger tips when it powered up.

Bigman80

04-07-2018, 10:44

Ah, I see. Yes, phonostage valves are sensitive to mechanical vibration. A better solution than valve dampers is to have the valve bases (or the PCB which they're on) soft coupled to the chassis rather than in hard contact.
Soft coupling the transformers is also a possibility, but they have to be secured well enough to be safe, of course.
If the chassis is steel it's possible that magnetic induction is causing the chassis to vibrate. A spacer between the transformer and the chassis would help with that.The case was Aluminium and it really did vibrate a fair bit.

I didn't know about soft coupling the PCB, how is that done?

alcarmichael

04-07-2018, 11:04

OK, so after a bit of trial and error tightening down the transformers really quite firmly and then loosening them; I’ve made an improvement and reduced the hum. I’ve done so rather crudely with a couple of pieces of speaker wire between the chassis and the transformers, the nuts aren’t really providing any clamping pressure on to the transformers now:
https://uploads.tapatalk-cdn.com/20180704/beb1346f7dedda32eda5a1ea2b14a6bf.jpg

Sent from my iPhone using Tapatalk

Bigman80

04-07-2018, 11:15

Simon_LDT

04-07-2018, 11:32

Apologies for hijacking slightly... What can cause hum to come through the speakers? It's buzzing through both tweeter and woofer also so no idea of the frequency. It's not a ground loop as I do have an amp which doesn't transmit it at all but 3-4 other amps I've tried all do it.

Don't know if it's DC or just dodgy mains. I'm using a dc blocker but it's not doing owt. Thing also is that all my gear with toroids in do have this mains noise but it's very quiet and can only be heard when ear pressed against the case and the room is silent. Even the hum from the speakers is low enough that it can't be heard from about 3ft away so It's not audible at the listening position. It just bugs me that it's there though.

When I stick my head under the stairs cupboard I hear the same noise/hum which makes me think it's dodgy mains... Maybe the 1 amp that doesn't transmit it has something in the circuit blocking it somehow?

alcarmichael

04-07-2018, 11:39

If you can get some silicone/rubber "O" rings, the round ones used for plumbing, you can use those instead of your speaker wire. That will help.

Is that the ideal? I was thinking about getting some sorbothane to take the place of the speaker wire.

Sent from my iPhone using Tapatalk

Bigman80

04-07-2018, 11:52

Is that the ideal? I was thinking about getting some sorbothane to take the place of the speaker wire.

Sent from my iPhone using TapatalkThe ideal is to go for a purpose made audio TF.

Everything else is "bodge" [emoji23][emoji23]

Bigman80

04-07-2018, 12:19

Thanks for that. I'll give that a go!
Use some kind of rubbery stuff to hold the PCB instead of screwing it down tightly. I use large holes in the PCB and fit a grommet. Then I use some rubber sleaving over the screw which passes through the grommet. The screws are rigid but the PCB is loosely fitted to the screws.

There are many ways in which noise can appear through the speakers. It's useful to differentiate between hum and buzz. They're two different sounds and suggest different causes. The transformer could be absolutely perfect but you could still have a hum or buzz through the speakers. One possible cause is incorrect track routing on the PCB which allows spikes of current into the power supply to pollute the audio signal. Unfortunately, there's not much that you as a consumer can do about it - it's a design fault.

Simon_LDT

04-07-2018, 12:30

Just stuck my head under the cupboard with all the incoming mains and sounds like this noise is coming from a particular box (I'm no expert but it doesn't look to be the main incoming, looks like something attached after, maybe it's polluting the mains). I've tried to capture it the best I can with the crap mic on my phone.

https://drive.google.com/file/d/1hh6OoqvHWLRLj84ehKOJnrQ-63hmYiyG/view?usp=drivesdk

Hope the link works ok.

Mr. C

04-07-2018, 12:34

I would also try turning the transformer as well, find that null point and things will improve

alcarmichael

04-07-2018, 13:00

I would also try turning the transformer as well, find that null point and things will improve

Ah, I think I know what you mean now. Rotate them on the stud as if I’m trying to find a balance or equilibrium point?

Would this be a painstaking trial and error job? I’m assuming it’s unwise to handle the transformers while connected to mains power!?

Sent from my iPhone using Tapatalk

2fastgt4

04-07-2018, 13:05

Noratel is a good brand.
However also they can have the hum problem.
Special the older ones.
The newer Noratel is made better. Dc on the electricity net is more normal now then 10 years or even 5 years ago.
Now the Noratel take that in the consideration.
The Norwegian high End brand Musical Innovation made by Roar Malmin have always used the Noratel trafo. They are known to be very quiet.
A lot of people here in Norway did change to Noratel trafos because of the quality.
So, these are my transformers:

I have no idea how they rank quality wise...?https://uploads.tapatalk-cdn.com/20180704/a1add6e703768aee0a4e7d1842e5a9f1.jpg

Sent from my iPhone using Tapatalk

Tommy

bumpy

04-07-2018, 13:47

I think there's a whole load of different stuff getting all mixed-up here. Firstly, a transformer can vibrate and make a noise - but that doesn't mean the cause is necessarily DC on the mains. If it isn't, a DC blocker won't do any good. And anyway, according to this quite comprehensive analysis mains DC, the problem only occurs which toroidal transformers of about 300VA and above:
http://sound.whsites.net/articles/xfmr-dc.htm

EI transformers can be noisy because the laminations rattle. Tightening them and potting them will cure that.

The above is mechanical noise coming straight off the transformer. Electrical noise is something else completely. The magnetic field radiated from the transformer can cause nearby circuits to hum, and rotating the transformer (particularly an EI type) can redirect the magnetic field away from circuit and reduce hum. However, it won't have any impact on mechanical buzzing.

I'm guessing by the term 'electrical noise' you mean the noise that ends up coming from the speaker. I believe there are some simple measuring devices to detect magnetic field.

alcarmichael

04-07-2018, 14:29

OK, I managed to find some sorbothane (or similar) equipment feet. I put a hole in the middle of two, slid them over the studs and fastened the transformers down on top of them. Much, much better! There is now only the faintest level of hum, faint enough to be of no concern. I feel like I have achieved. Thank you to everyone who has chipped in [emoji106]

Sent from my iPhone using Tapatalk

sq225917

04-07-2018, 14:32

1. A loosely wound transformer can vibrate/hum. If this is mechanically coupled into the chassis it will be amplified by the casework. It coupled into valves it can come out of the speakers. Refit the traffo, try soft mounts, pads, tight/loose screw mounting.
2. DC riding on the mains. if it adjusts in sound during the day then this is likely, could be over voltage though. Get a DC blocker, get one rated to handle up to 3 volts. Soljstrom audio do a couple, they work. DC on the trafo can couple into the core and come through as noise from subsequent stages.
3. Overvoltage, can saturate the core, cause physical hum and can come through subsequent stages. Not much you can do here other than measure it and respec new trafo's.
4. Toroids have a gap in the winding where the wires go through, this is usually a quiet spot. If you have 100hz noise coupling into the system try rotating the traffo, if wire length allows, so you can point the quiet bit at the sensitive wires. (Honestly though, fix your ground loops, minimize your loop area and take care of circuit decoupling properly).

Bigman80

04-07-2018, 14:57

This is what I wish I'd had the ability to put into words. Great post.
1. A loosely wound transformer can vibrate/hum. If this is mechanically coupled into the chassis it will be amplified by the casework. It coupled into valves it can come out of the speakers. Refit the traffo, try soft mounts, pads, tight/loose screw mounting.
2. DC riding on the mains. if it adjusts in sound during the day then this is likely, could be over voltage though. Get a DC blocker, get one rated to handle up to 3 volts. Soljstrom audio do a couple, they work. DC on the trafo can couple into the core and come through as noise from subsequent stages.
3. Overvoltage, can saturate the core, cause physical hum and can come through subsequent stages. Not much you can do here other than measure it and respec new trafo's.
4. Toroids have a gap in the winding where the wires go through, this is usually a quiet spot. If you have 100hz noise coupling into the system try rotating the traffo, if wire length allows, so you can point the quiet bit at the sensitive wires. (Honestly though, fix your ground loops, minimize your loop area and take care of circuit decoupling properly).

337alant

04-07-2018, 16:03

I've had a few torroidal transformers from Terry at Canterbury Winding's and they have all been quiet and excellent quality
My mains varies between 240 -250 so I always ask him for 240V primary, Goss band and electrostatic screen
http://www.canterburywindings.co.uk/standard_range.html
Those Torroidy ones look very well made may try some of them on my next amp build

Alan

Simon_LDT

05-07-2018, 15:22

I think you're barking up the wrong tree there. Yes, electricity meters can make a noise, but there's no reason why that should necessarily cause the speakers to buzz. The problem lies elsewhere imo.

Could be, I just find it strange that 1 amp doesn't let it through but the others do. I can only think it has something in the circuit to filter/clean it. Going by my sample is that a buzz or hum? Should it be coming through both tweeter and woofer?

Mr. C

05-07-2018, 16:15

Over the last few years we have come across more TX's actually buzzing through the speakers, rather than a mechanical hum,

Electrically generated noise seems to be the common bugbear currently, usually the TX just needs be swung to find its happy point.
As Simon covered all of the basics for you guys should help you in the future deal with any untoward TX related issues you may come across.

We are fortunate enough to have in house TX facilities, however when we have used outside contractors Air-link have always delivered what was asked, though if you do opt for this route, at the very least have a screen on the primary winding's that taken to ground.

YNWaN

05-07-2018, 19:01

You need one of these:

http://i62.photobucket.com/albums/h90/markemark_2006/DC%20Blocker/D15CE949-41B6-4AE3-9865-B458A4B465DD_zpslv7bprod.jpg (http://s62.photobucket.com/user/markemark_2006/media/DC%20Blocker/D15CE949-41B6-4AE3-9865-B458A4B465DD_zpslv7bprod.jpg.html)

http://i62.photobucket.com/albums/h90/markemark_2006/DC%20Blocker/4ADA3EF3-15D6-4B84-8788-BCFF02BABEFD_zpssjxhf2xt.jpg (http://s62.photobucket.com/user/markemark_2006/media/DC%20Blocker/4ADA3EF3-15D6-4B84-8788-BCFF02BABEFD_zpssjxhf2xt.jpg.html)