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:

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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?

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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:

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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!

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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.