DC Blocking / Mains Filtering and all that "stuff" . . .

Hi all,

I've posed similar questions before but not specifically garnering opinion on peoples own experiences and own personal preferences, so I'll give mine too.


I have a good mains supply in my house, it's a new-build (late 2019) and has a nice RCD box and although there are a few structural issues the electrics have been done properly. I'm not far from the local sub station, 200 yards or so (I assume its this one).

My preamp has some transformer hum slightly audible at listening position, as does my phono stage (both tube based with tube rectifiers). I managed to fix a very buzzy transformer on another phono stage by completely isolating it from the chassis, it went from 'swarm of bees' to dead silent, I was very surprised. Unfortunately this is not really possible on either of my other bits of kit so I'm wondering about adding some filtering/DC blocking etc.

Most literature and thinking implies that any filtering should only be applied IF you have a specific problem (as I feel I do slightly) as it does cause some audible degradation to the sound. The SQ is only really improved with filtering in these situations, if the mains is poor to begin with or there are many switching supplies/appliances connected to the same ring, causing issues.



I must agree my experience reflects this completely and as long as conditions are optimal ALL my kit sounds at its best plugged directly into unfiltered sockets/outlets.

I have my main power amplifier plugged directly into the wall outlet, then the rest of my components plugged directly into an unfiltered power strip. The strip does have a row of filtered sockets but the SQ takes a dive and loses dynamics and punch if anything is plugged into them. I'm assuming this is because the component in question cannot quickly draw the current it requires for dynamic demands of the music (more power and maybe pre-amp's rather than DAC's I'd suspect).

Aside from getting a full power conditioner generating a 'perfect' sine wave (or whatever) I'm not really sure what I can do without potentially causing a drop in SQ, not something I wish to do, ever!

I tried a DC blocker once and it did interfere audibly, can't quite remember conditions exactly but I know I didn't care for the result.


Just wondered if anyone has come across a satisfactory solution for similar issues but other than the conditioner and further isolating the noisy transformers from their chassis', I'm struggling to improve things.
To be honest it's a bit nit-picky as the overall sound is superb but on ultra quiet passages I can't help but notice the transformers in the background.

I'm wondering if a dedicated mains block with star grounding and individually wired sockets (rather than in series which they are in the strip at the moment I think) would yield any improvement although I fear it's the small amount of DC on the mains and the design of components and the transformers which are to blame.


All help and advice much appreciated.

Cheers

hi chris
yes i have had 4 isotek syncro dc blockers
they definately have an effect on the product

once used it on a puresound L10 with no hum issues . it really improved the musicality on it

more recently i have used it on an arcam a85 . now the arcam is very good with my sensitive horns . it most certainly tightened up the sound a bit , but some might say it made the sound a bit harder . now that may or may not be a good thing
in my case i have a lovely organic pre amp and valve dac to offset . so its still in situ and seems to be very effective .

occassionally i take it it out to try without [ as always trying to save money !!! ]

its well worth trying one and i am pretty sure it would get rid of your transformer hum

they are about 500 s/h if you can find one . there are plenty on mcru site in new versions but they are a bit pricy

https://www.hifiplus.com/articles/is...yncro-hifi-77/

Thanks Phil, interesting.

I've also seen things like the ISOL-8 MiniSub (2) conditioner which seems to be pretty well liked and reportedly does not rob the dynamics as many do.

I've tried some cheaper 'conditioning' products and remained unimpressed, but this seems to be well designed and thought out. Not a DC blocker as such but sounds like it could help with overall SQ anyway.

Have you seen these?

https://www.ebay.co.uk/itm/184847201...AAAOSwG4xgYt4G

Haven't seen many around but incorporate some filtering and DC blocking into a fairly neat solution. The products vary between different amounts of conditioning and DC blocking, from average to fairly high priced. Can't find any reviews and a lot of talk about:

"The flood of fizz, hash, spikes, snap crackle and pop delivering itself into your sensitive DAC's, Pre-Amps, Amplifiers and Video Displays swamp and confuse everything they are trying to do…… and it gets worse! The DC voltages, normally present in your mains supply, smother and suffocate the transformers in your equipment. Transformers need to "breath" freely and fully, in and out, following the AC mains frequency. The presence of DC leaves them noisily gasping for breath and unable to deliver their full power and punch."

Usually this sort of blurb accompanying an advert sets alarm bells ringing . . . but the products do look well made.

yes puritan audio is getting quite well known . been quite a few of their mains conditioners on s/h market and they sell well . spoken to the guy at bristol show twice now . looks well made

i did have an isol 8 dc blocker not too long ago but still like my syncro

Do you have near neighbours, that share the same phase as you? If so, and the neighbours are sufficiently close, it may be their electrical equipment that is 'dirtying' the mains supply.

Also, do you know what the earthing arrangements are for the incoming mains supply?

Quote:

---

Originally Posted by Barry

Do you have near neighbours, that share the same phase as you? If so, and the neighbours are sufficiently close, it may be their electrical equipment that is 'dirtying' the mains supply.

Also, do you know what the earthing arrangements are for the incoming mains supply?

---

There are neighbours next door (semi-detached), but as all our (and their) electrics are practically brand new (as are theirs, it's a new development of houses) so I wouldn't suspect anything to be having more of a severe effect than a normal circumstance. As for my earthing it's a new RCD box under the stairs not sure about the incoming mains to be honest but I've not noticed the same with other tube equipment so I'm inclined to blame these bits of equipment specifically.

Anyway - UPDATE:

As the chassis of the pre is quite thin and the noise of the transformer 'reverberates' inside, I decided to place a little granite 'coaster' with some soft feet on top, this seems to have dulled/damped the resonance of the buzzing transformer a little. Maybe by 30-50% actually, which is enough to bring it further into the realms of acceptable noise.

Additionally I've plugged the phono stage into a different power strip from another outlet in the room and it too has gotten a lot quieter, for what reason I cannot say. Whatever reason the transformer seems a lot happier connected to this outlet.

This is a win for experimentation, I just thought I'd try a couple of left-field changes/tweaks and it seems to have improved things, just wish I could explain exactly why.

If I was to guess, it seems I've dampened the resonance of the chassis of the preamp (which was amplified by the open space in the chassis). As for the preamp, maybe it's getting an improvement in the stability of the voltage or the longer power cable is helping somehow? Less clear on that one, it is quieter though by some magnitude, along with a lower noise floor through the speakers too.

If I can try some DC blocking without losing money (try before buy or something) I still may investigate that.

Cheers

There seems to be huge confusion amongst audiophiles regarding mains solutions. On one hand you have mains regeneration systems. Turntable power supplies (posh ones anyway) have been doing this for ages but they need a lot less power than an amplifier, for example. Mains regeneration does as it says, it takes the mains, deconstructs it, and then recreates it - hopefully better than it was when it entered. However, whilst it sounds like a great idea there are issues. Specifically, the low impedance of the raw mains it not achieved by (even very large) regenerator. The other problem is that technically competent units are necessarily huge and therefore expensive. Cheaper and smaller units tend, in my experience, make the sound sweeter and smoother but also less dynamic. In fact even vast and hugely expensive units have an element of this too - though peoples sensitivity to this varies enormously.

Separately, there are passive solutions like ‘noise suppression’ and ‘surge protection’. These are really separate issues but surge protection is often just a single component and manufactures love to add it because the cost is minimal and it’s another feature for the marketing department. All the noise suppression and surge protection circuits are of questionable merit as fas as I’m concerned and certainly I have heard such units significantly effect the sound in a negative way.

Then there are DC blockers. This has nothing to do with regeneration and, in theory, DC should not be present on the mains in the first place. However, the reality is that every house my HiFi has lived in has suffered from mains DC issues. Irrespective of appliances in the house the mains fluctuates during the day depending on national usage. The impact of this is that your amp will be quite silent at some times and then humming strongly at other times. Now I don’t mean humming through the speakers, I mean the transformer mechanically makes a noise. How much hum you experience also depends on the type and size of the transformers in your gear. Large toroidal transformers, like the 500VA ones in my power amps, are much more prone to mechanical hum than smaller ones. Now most commercial DC blockers are reasonably small and therefore reasonably inexpensive. However, this also means they are only really effective on lower powered items, like CD players or pre-amps - but then the chance is that such components don’t usually demonstrate this hum problem in the first place. If you put such a small unit on a power amp not only do they not stop the hum but the sound produced is worse - a bit compressed and less detailed (in my direct experience). If you want to reduce DC transformer hum on a power amp you really need a larger DC blocker than those normally sold.

Here’s mine:

https://i.postimg.cc/HncYHcf1/2-AD24...6-A38-F505.jpg

Finally, there are balanced mains transformers (one to one) and star earthed mains - both of these are completely separate issues and quite different to any of the previously discussed solutions. I’m sure you are bored by now (I am rather) so I will leave it at that rather than write an even more long winded essay!

nicely put

Quote:

---

Originally Posted by YNWaN

There seems to be huge confusion amongst audiophiles regarding mains solutions. On one hand you have mains regeneration systems. Turntable power supplies (posh ones anyway) have been doing this for ages but they need a lot less power than an amplifier, for example. Mains regeneration does as it says, it takes the mains, deconstructs it, and then recreates it - hopefully better than it was when it entered. However, whilst it sounds like a great idea there are issues. Specifically, the low impedance of the raw mains it not achieved by (even very large) regenerator. The other problem is that technically competent units are necessarily huge and therefore expensive. Cheaper and smaller units tend, in my experience, make the sound sweeter and smoother but also less dynamic. In fact even vast and hugely expensive units have an element of this too - though peoples sensitivity to this varies enormously.

Separately, there are passive solutions like ‘noise suppression’ and ‘surge protection’. These are really separate issues but surge protection is often just a single component and manufactures love to add it because the cost is minimal and it’s another feature for the marketing department. All the noise suppression and surge protection circuits are of questionable merit as fas as I’m concerned and certainly I have heard such units significantly effect the sound in a negative way.

Then there are DC blockers. This has nothing to do with regeneration and, in theory, DC should not be present on the mains in the first place. However, the reality is that every house my HiFi has lived in has suffered from mains DC issues. Irrespective of appliances in the house the mains fluctuates during the day depending on national usage. The impact of this is that your amp will be quite silent at some times and then humming strongly at other times. Now I don’t mean humming through the speakers, I mean the transformer mechanically makes a noise. How much hum you experience also depends on the type and size of the transformers in your gear. Large toroidal transformers, like the 500VA ones in my power amps, are much more prone to mechanical hum than smaller ones. Now most commercial DC blockers are reasonably small and therefore reasonably inexpensive. However, this also means they are only really effective on lower powered items, like CD players or pre-amps - but then the chance is that such components don’t usually demonstrate this hum problem in the first place. If you put such a small unit on a power amp not only do they not stop the hum but the sound produced is worse - a bit compressed and less detailed (in my direct experience). If you want to reduce DC transformer hum on a power amp you really need a larger DC blocker than those normally sold.

Here’s mine:

https://i.postimg.cc/HncYHcf1/2-AD24...6-A38-F505.jpg

Finally, there are balanced mains transformers (one to one) and star earthed mains - both of these are completely separate issues and quite different to any of the previously discussed solutions. I’m sure you are bored by now (I am rather) so I will leave it at that rather than write an even more long winded essay!

---

Excellent info there,

Thanks for taking the time to do so.

I think I grasped most of those concepts previously but it's really good to have it written out concisely as there.

Nice one.

If you fancy a bit of DIY it's quite straightforward to make a DC blocker. I made one with 2 straight DC blocking outputs and 2 filtered DC blocking using a Sjostrom DC03 and a couple of ATL common mode (EMI/RFI) filters.

https://i.postimg.cc/jjX3bzHn/dc-block-filter.jpg

https://i.postimg.cc/bJwCNsgC/dc-block-filter-rear.jpg

Awesome,

Great work and a super neat solution.

Could well be worth a crack, cheers for that.

How much total build cost may I ask?

Nothing ventured etc.....

Think it was about £200 for the lot including the case.
Sjostrom blank board was from him on a group buy on DIY audio (about £15 I think) and the blank ATL boards were from ATL on ebay (£8 each). Parts all ordered from Mouser and case from Modushop.

I haven’t noticed any negative effects of the filters and might well be my imagination that they improve the sound. I use the filtered outputs for my power supplies (salas l-adapters) and the unfiltered output to my pre and turntable, definitely improves the pre (and stops the buzzing toroidals).
Like most things Hifi, YMMV.

Agree, I had the dc02 and the dc03 is better, zero buzzing now

Hi Chris, I have sent you a PM

@killie99, Hi stuart, well done on your unit. Looks interesting and may have to try assembling one when I get a gap.

I use an Airlink Balanced For Audio Balanced Transformer, I’m sure they will advise. I use one no buzzing, although I used solid state electronics.
Airlink Transformers website https://airlinktransformers.com/

Mike

Quote:

---

Originally Posted by mbic

I use an Airlink Balanced For Audio Balanced Transformer, I’m sure they will advise. I use one no buzzing, although I used solid state electronics.
Airlink Transformers website https://airlinktransformers.com/

Mike

---

Had a couple of Airlink Balanced units in my system over the years.
Its not in the listening room so noise not an issue, but did notice my previous one buzzed a bit when powering my SET 300B power amp.

No such issues now my gears all solid state.

Tried a DC blocker before, made no improvement in the buzzing.

May have been mechanical, rather than electrical...didn't check tontighten down the transformer.

Quote:

---

Originally Posted by Gazjam

Had a couple of Airlink Balanced units in my system over the years.
Its not in the listening room so noise not an issue, but did notice my previous one buzzed a bit when powering my SET 300B power amp.

No such issues now my gears all solid state.

Tried a DC blocker before, made no improvement in the buzzing.

May have been mechanical, rather than electrical...didn't check tontighten down the transformer.

---

I haven't noticed any buzzing around at Colin's when he's been using your old amp, and he's running an Airlink BMU with a DC blocker in the input side.

How's Toppsy getting on with the amp Chris?
Still doing the business fir him?

He's getting along fine with it, Gaz :)

The Mark grant/Tube Distinctions DC blocker is really great. You can find more info on Mark Grants website.

Designed by Anthony and assembled by Mark. It's a fab thing.

Marco uses one in his system.

Sent from my 9001X using Tapatalk

josie . i like them too and use one to good effect
i think its a mains filter though , not a dc blocker . someone correct me if i am wrong

https://www.markgrantcables.co.uk/uk...-power-filter/

Quote:

---

Originally Posted by hifinutt

josie . i like them too and use one to good effect
i think its a mains filter though , not a dc blocker . someone correct me if i am wrong

https://www.markgrantcables.co.uk/uk...-power-filter/

---

You are correct - it’s not a dc blocker but very useful nevertheless.

Ah. Yes... Sorry.

Well, as you both say, it's an excellent bit of kit.

Sent from my 9001X using Tapatalk

Great thread lots of useful info.

Whilst your neighbours may cause some electrical noise that can impact your house and system, most houses have stuff far closer to home. Cheap smps that power our phone , ipad chargers and other cheap consumer electricals can all harm. Dimmable LEDs and variable DC pumps are naughty too. I have many such devices in my home and many on the same ring as my system.

3 years ago we had a very modest system based on a cambridge audio amp, a yamaha CD player and some well regarded mordant short bookshelves. I wanted to get something with better sound quality and bought KEF LS 50 active system, took it home plugged it in and was massively disappointed, sure it was giving me some additional bass but still the music was just as flat, i had a 30 day home trial so back it went.

I then upped my budget considerably thinking I just need to reach further to get good sound, so bought an open box set of proac tablette 10 Se and a Lyngdorf TDAI3400. This did give me a noticeable jump in performance , especially when I the sub.

Since then I’ve put loads of effort into getting clean power and controlling vibrations in the system and now my systems on a totally different level for SQ.

I use a DIY DC blocker power cable that mimics the syncro power cable mentioned above, this feeds an isotek sigmas gen 2.

There are 3 toroidal transformers in my system all small and I had no hum that I could hear but the DC blocker definitely improved the musicality of the system.

If you want to control chassis vibrations there is an excellent product you can get from Japan via ebay called fo.q damping tape.

Ta102 and Ta32 are 1mm thick and 0.3mm thick respectively , they convert vibration to infra red heat and also have antistatic property , I’m convinced its very similar in make up to the NCF technology that furutech use in their plugs and sockets. The thin stuff goes around cables very easily. The thicker stuff very good on chassis especially around power sockets and inlets.

I think you can get issues with power conditioning if you use cheaper filters but if done correctly it can be transformational in a noisy home. The Puritan filters get great reviews and I would be looking to trial one of those if I wasn’t sorted, I think they punch above their price point from reading reviews. They have built in DC offset filtering in their power conditioners.


Sent from my iPad using Tapatalk

Best improvement i got came from adding extra earth bonding strips across the water pipes and cleaning tightening the eathing lead near the meter
. Very obvious drop in background noise and it was easy low cost to do. Never heard much if a difference with filters other than a belkin pf60, i think, that cut the power on an almost daily basis