DC offset and modern gear

[Noddy]

I have an AudioLab 6000A amp. The first went back due to a very loud hum. This one has a slight hum. Apparently it is caused by the toroidal coil oscillating when there is a DC offset on the mains input. Apparently coils vary in how susceptible they are, perhaps a QC issue. So I bit the bullet and ordered the £99 AudioLab DC Block which sits between the mains and amplifier, and removes any DC offset. I could have bought a cheap unit on AliExpress, but I wanted to make sure it was properly designed and safe.

What I wonder is why the components required to remove DC from the mains are not in the amplifier. After all, the DC Block includes a metal case, two input sockets and two cables, as well as the actual internal components. Thus the internal components are a small part of the DC Block product.

The cynic in me reckons that AudioLab are on a win win. They sell their amplifier and make more profit. and then sell a separate product to fix a fault in the first product.

Is this a common issue? Do higher end AudioLab (and other) amplifiers include an internal DC filter?

Lovely amp, but I feel slightly conned.

 

[Al ears]

I have an AudioLab 6000A amp. The first went back due to a very loud hum. This one has a slight hum. Apparently it is caused by the toroidal coil oscillating when there is a DC offset on the mains input. Apparently coils vary in how susceptible they are, perhaps a QC issue. So I bit the bullet and ordered the £99 AudioLab DC Block which sits between the mains and amplifier, and removes any DC offset. I could have bought a cheap unit on AliExpress, but I wanted to make sure it was properly designed and safe.

What I wonder is why the components required to remove DC from the mains are not in the amplifier. After all, the DC Block includes a metal case, two input sockets and two cables, as well as the actual internal components. Thus the internal components are a small part of the DC Block product.

The cynic in me reckons that AudioLab are on a win win. They sell their amplifier and make more profit. and then sell a separate product to fix a fault in the first product.

Is this a common issue? Do higher end AudioLab (and other) amplifiers include an internal DC filter?

Lovely amp, but I feel slightly conned.

I would have to say if you have significant DC on your mains it will affect all amplifiers to some degree, dependant somewhat on their power section type.

 

[DiggyGun]

I had loud humming from two Naim NAP 250 power amps. Started suddenly, but could be heard from the seated position with no music playing.

After establishing that it may be DC Offset as opposed to a ground loop hum, I got two iFI DC Blockers.

These worked very well, virtually eliminating the hum which now could only be heard if you put your ear right next to the amps.

 

[daytona600]

45+ years and 15+ amps and never had any DC hum
Poor design with cheap transformers Chinese Quality Control
Had a UK made 8000A for several years with no Hum back in the 1980s

Recording Studios use Isolation Transformers to cure DC

 

[Noddy]

45+ years and 15+ amps and never had any DC hum
Poor design with cheap transformers Chinese Quality Control
Had a UK made 8000A for several years with no Hum back in the 1980s

Recording Studios use Isolation Transformers to cure DC

There’s so much wrong in the above.

Firstly Chinese quality is often far better than Western QC. I had some Italian made Moka pots, three from different manufacturers fell apart when spot welds failed. Two German ones are well made. The two Chinese ones are far better designed, far better made, and far better finished. The German ones look rough in comparison with welds clearly visible. I have numerous Chinese hand torches, they are beautifully made, CNC machined from aluminium and stainless steel. I had a Chord Mojo, claims to be made in England, it fell apart after a couple of years, £400 down the drain, junk. iPhones and iPads are Chinese made and high quality.

There’s a chap here saying that his mid 1980s made AudioLab 8000A has always had mains hum:

Audiolab 8000a mains hum

My aged hifi has recently been introduced to my new Samsung smart TV and is now producing pleasing sound which is better quality than the smart television itself. There is just one problem, mains hum. My hifi which is comprised of a Marantz CD50, and a Denon TU-260 tuner feeding an Audiolab...

www.avforums.com

DC hum is due to the main supply having a DC offset, mine sometimes has it, sometimes not. It can arise due to appliances in your house, or even in neighbouring buildings. There’s reports of hum from many different brands of amplifier. The AudioLab 6000A does seem to be noted for it. It’s a British designed amp with the company owned by China.

There are comments online that a DC offset is caused by switching power supplies, and these are becoming more common. I am not an electrical engineer, so I cannot comment.

These days if you want UK made, you either get Chinese components assembled in the UK, and falsely labelled as Made in England (or UK) or pay a fortune. My made in England toaster is a beauty, but costs four to eight times as much as most others. And some of the construction is basic e.g. cheap looking plastic handles on the crumb tray which itself is made from roughly finished aluminium plate.

 

[abacus]

There is good and bad manufacturing from all country's, so saying one country is all bad is a nonsense.

Bill

 

[Gray]

What sort of prices are people actually paying for mains DC blockers?

 

[Noddy]

Mine was £99 as I said, there are other single socket units at £149, and multi socket units cost quite a few hundred squids. This post shows how little is in the box:

https://forums.whathifi.com/threads...uy-an-audiolab-dc-blocker.126581/post-1280769

Omitting that from the amplifier is penny pinching IMO. Equipment reviewers presumably have DC blockers in place and won’t have any hum. Thus reviews will not say “Good unit but lack of DC filtering is a negative”.

 

[daytona600]

The cynic in me reckons that AudioLab are on a win win. They sell their amplifier and make more profit. and then sell a separate product to fix a fault in the first product.

 

[Gray]

This post shows how little is in the box:

https://forums.whathifi.com/threads...uy-an-audiolab-dc-blocker.126581/post-1280769

Yes, you're certainly paying more for enclosure and sockets than you are for components 🤨

 

[Jasonovich]

Whatever you say about Chinese electricals/HiFi in the past probably holds true but not anymore, Chinese brands are among the finest, I have Gustard, I have WiiM, I have SMSL, I have FiiO, I have Hifiman, I have Matrix, and not so popular brands, I have Eversolo!
I use Chinese top quality mains conditions and noise filters, do I hear a hum? No not even a gentle fart.

Ps.
It really isn't about one nation as pointed out by @abacus it really is a global market. No nation is immune to poor quality control.

My HiFi setup is pretty reflective of the world economy, I also have British, American, South Korean, Japanese, French, German, Swedish, Danish....Who have I missed? Ah, Austrian!
(possibly all made in Chy-Na.....cough, cough!)

Isn't free market a wonderful thing? 🙂

 

[Shrek]

Ive never had this issue ive been through a lot of Amps mostly Japanese .I still have a old Arcam never liked the sound.