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Post by docfoster on Jan 6, 2018 12:00:46 GMT
I find these are a relatively inexpensive way to snuff out transformer hum (there seems to be an ancient curse on the mains supply to my house). But also, and initially unexpectedly for me, myperception is that they improve the sound coming out of the speakers too. I’d be interested to read any experiences others have had with these. (May be it’s just a me-thing...?  ) |
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Post by MartinT on Jan 6, 2018 12:26:35 GMT
I've been using an MCRU DC blocker for a while now, and it did reduce transformer hum and improved the sound of my system. I've taken it out of circuit now as my village was completely re-cabled not so long ago and it doesn't serve any purpose any more as there doesn't seem to be much, if any, DC on my power.
The best thing to do is get a sparky to measure your DC on mains. If it's any more than about 1V, then a DC blocker could yield a nice improvement in SQ and reduced noise floor.
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Post by julesd68 on Jan 6, 2018 12:38:41 GMT
I tried one and didn't notice any difference - Martin's advice looks good for anyone thinking of shelling out for one.
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Post by docfoster on Jan 6, 2018 13:12:24 GMT
Thanks guys.
Your thoughts are broadly in keeping with mine: DC on the mains is unhelpful. If it’s not present in the first place, great; if it is there, get rid.
Also it’s affirming to read that Martin experienced DC changing the sound of his system (as well as effecting transformer hum), as sometimes I suspect that I imagine these things! :-D
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Post by MartinT on Jan 6, 2018 13:27:35 GMT
Many things about mains power affect the sound, but the changes often creep up on you  |
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Post by Deleted on Jan 6, 2018 13:35:59 GMT
I guess this would make a great DIY project for a beginner. Might have a look round for a thread I can learn from. I have no idea about whether there is DC on the mains here. At least they don't use ring mains out here.
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Post by docfoster on Jan 6, 2018 13:49:07 GMT
I guess this would make a great DIY project for a beginner. Might have a look round for a thread I can learn from. I have no idea about whether there is DC on the mains here. At least they don't use ring mains out here. Couldn’t agree more. I’ve made a couple. I use this one for 31 euros: www.lcaudio.com/index.php?page=316 |
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Post by pinkie on Jan 7, 2018 12:55:55 GMT
I'm intrigued that you use DC blockers to cancel mains hum in transformers. (Nothing surprises me any more about what people claim to hear regarding mains supply phenomena)
Your equipment would appear to be powered by a Sovereign BPS. Like any BPS, that is essentially a transformer (albeit centre-tapped). The AC power output from that device, as from any transformer, will have zero DC element (unless you introduce it from somewhere)
A DC blocker could stop the toroidal in James' BPS humming if it does - but I thought he built them chunky. Certainly his own when I was last there was silent as the night.
DC on mains is hard to measure properly. I doubt most sparkies would have ever been asked to do it, although they stand a chance of owning a suitable meter.
DC , if present, does not necessarily cause toroidal hum, core saturation or otherwise. Poorly specified toroidals are more likely the problem. My "hummer" is in the sub-woofer - which hums when none of the others do (Both my Pips, 1 & 2 are powered by a toroidal which NEVER hums). The hum in the sub was due to over-voltage back in the UK. It is quiet here in France where the voltage appears to be a rock steady 235v any time I look.
An engineer friend proved this to me by bringing an isolation transformer and variac to the house. Eliminate DC and take voltage to a level (I think it was 244v, but it was a while ago) and it hummed. Drop the voltage below the threshold and the hum went. The reason DC offset CAN cause transformer hum due to core saturation due to excess voltage is that one leg will be pushed over voltage. (ie assume a transformer which saturates at 244v, if you have a supply with 242v AC and a +5v DC offset, then each cycle will be between -237 and +247 volts)
You will find lots of advice regarding DC blockers curing transformer hum by googling - all from HiFi forums.
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Post by MartinT on Jan 7, 2018 15:08:59 GMT
My old house used to have very high voltage, up to 252V on occasion. This place has a fairly steady 235V and I set the P10 to 235V output, making it work as least hard as possible in generating a clean output. THD in is about 2.7%, THD out is 0.1%.
Hi-Fi forums are likely to be the place for advice on DC blockers as they will care the most about hum, mechanical or otherwise.
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Post by docfoster on Jan 7, 2018 16:29:31 GMT
I'm intrigued that you use DC blockers to cancel mains hum in transformers. (Nothing surprises me any more about what people claim to hear regarding mains supply phenomena) Your equipment would appear to be powered by a Sovereign BPS. Like any BPS, that is essentially a transformer (albeit centre-tapped). The AC power output from that device, as from any transformer, will have zero DC element (unless you introduce it from somewhere) A DC blocker could stop the toroidal in James' BPS humming if it does - but I thought he built them chunky. Certainly his own when I was last there was silent as the night. DC on mains is hard to measure properly. I doubt most sparkies would have ever been asked to do it, although they stand a chance of owning a suitable meter. DC , if present, does not necessarily cause toroidal hum, core saturation or otherwise. Poorly specified toroidals are more likely the problem. My "hummer" is in the sub-woofer - which hums when none of the others do (Both my Pips, 1 & 2 are powered by a toroidal which NEVER hums). The hum in the sub was due to over-voltage back in the UK. It is quiet here in France where the voltage appears to be a rock steady 235v any time I look. An engineer friend proved this to me by bringing an isolation transformer and variac to the house. Eliminate DC and take voltage to a level (I think it was 244v, but it was a while ago) and it hummed. Drop the voltage below the threshold and the hum went. The reason DC offset CAN cause transformer hum due to core saturation due to excess voltage is that one leg will be pushed over voltage. (ie assume a transformer which saturates at 244v, if you have a supply with 242v AC and a +5v DC offset, then each cycle will be between -237 and +247 volts) You will find lots of advice regarding DC blockers curing transformer hum by googling - all from HiFi forums. To clarify: The only DC blocker I use in my hifi system is before James’ BPS (ie in between the wall socket and the BPS). Without it, the BPS hums occasionally; with it, the BPS never hums. My other DC blocker is used on a bass amp / sub which is not a usual part of my system. |
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Post by DaveC on Jan 8, 2018 10:17:32 GMT
DC , if present, does not necessarily cause toroidal hum, core saturation or otherwise. Poorly specified toroidals are more likely the problem. Indeed, there are in my view three causes of transformer hum : 1. Excessive DC on the mains 2. Over voltage 3. Poorly designed transformers To start at the end, a well designed transformer will be immune to DC and to over voltage. However here in Dartmouth we get relentless 250V +/- 3V but less than 1 volt DC. Nearly every transformer sold by RS as their own product hums. Custom made ones for us, do not hum in any circumstances, but they are expensive and bigger. Excessive DC, this depends on the transformer, a well designed one will shrug it off. However in many applications mechanical hum is not an issue so as they say "you will get this" Over voltage. Most transformers are designed for 230V input and in many locations it is 250V+. This is just bad design, and a transformer for the UK should be specified at 240V or be made to work property over the range 230 to 253 volts. However I sold a £9.5K Pass XP-25 phonostage that hummed, Pass had no idea the UK could put out 253V, they firmly believed it was 230V, and they are not the only ones. Poor design. Many transformers run into core saturation, poor design. Many transformers will not tolerate DC, poor design. Many transformers are designed only for 230V, poor design. Many transformers are designed for 60Hz and perform badly at 50Hz, poor design. Many transformers have bad primary to secondary leakage, poor design. Many transformers suffer many or all of the above, extremely poor design. Given time I could think of a few more. There is more to audio design than an application note and a listening test, or worse still just a computer simulation that assumes the components and PCB layout are perfect. So in a nutshell, a properly design transformer suited for the intended application, will not hum in normal use in the UK. Regards Dave |
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Post by MartinT on Jan 8, 2018 10:26:21 GMT
However I sold a £9.5K Pass XP-25 phonostage that hummed, Pass had no idea the UK could put out 253V, they firmly believed it was 230V, and they are not the only ones. My Pass XP-20 preamp can hum a little when directly on the mains. However, when I turn on the regenerator set for pure sinewave and low distortion, the hum reduces to inaudible. Now that I have 235V rather than 252V, it's completely happy. |
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Post by Deleted on Jan 8, 2018 10:29:19 GMT
Blimey I am in agreement with Dave  Well informed post. |
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Post by pinkie on Jan 8, 2018 11:08:10 GMT
My old house used to have very high voltage, up to 252V on occasion. This place has a fairly steady 235V and I set the P10 to 235V output, making it work as least hard as possible in generating a clean output. THD in is about 2.7%, THD out is 0.1%. Hi-Fi forums are likely to be the place for advice on DC blockers as they will care the most about hum, mechanical or otherwise. I realise people on HiFi forums care. And they give advice they honestly believe. But they perpetuate "legend", based on their personal understanding (or lack of it) of the engineering issues, and repeating advice given by others. Sometimes it helps to get an engineer who understands the subject, which is what I was looking for when I googled. There was plenty of authoritative, well meaning advice on HiFi forums, which even I could spot wasn't right. I note your mains has changed, and I am pleased for you that it allows your HiFi to function without a DC blocker. However, cabling has little (no) impact on DC on mains. If your village all agreed to stop using old hairdryers with half-wave rectifiers that might help, but "recabling" isn't obvious. Nor will cabling itself have changed the supply voltage - but if the voltage has indeed dropped, for whatever reason, that is likely to fix the transformer hum. DC's comments were interesting, and consistent with my engineer friends. The problem is that UK mains is within spec at 253v, and, in my opinion, all properly designed equipment for that market, should be able to cope with a supply voltage between 216v and 253v. That is (broadly) an EU standard, although I think the european standard allows the voltage to drop to 207v. French products we buy quite frequently refer to "brown outs" in their literature (with the minor caveat that my french might not be perfect), and appear to be designed to tolerate voltages as low as 200v before causing problems. Of course, it would be nice if the power companies supplied reliable close tolerance 230v - but they don't, and aren't required to, so equipment should be designed accordingly. And I thought you used your DC blocker on the input to the P10, not the output, so the over-voltage (apparently exacerbated by a small DC offset) just made the P10 transformer noisy - since apparently PS audio also fail to supply product suitably designed for UK mains. And I thought that was at your new house, but before they rewired the village. |
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Post by MartinT on Jan 8, 2018 13:11:09 GMT
However, cabling has little (no) impact on DC on mains. If your village all agreed to stop using old hairdryers with half-wave rectifiers that might help, but "recabling" isn't obvious. Nor will cabling itself have changed the supply voltage - but if the voltage has indeed dropped, for whatever reason, that is likely to fix the transformer hum. . . . And I thought you used your DC blocker on the input to the P10, not the output, so the over-voltage (apparently exacerbated by a small DC offset) just made the P10 transformer noisy - since apparently PS audio also fail to supply product suitably designed for UK mains. And I thought that was at your new house, but before they rewired the village. My description of 'cabling' covered pretty much all of the village infrastructure including some transformers (I saw them on low-loaders). DC on my mains has reduced to the point that the DC Blocker makes no audible change. Previously, it did. Your second point confuses me: I've always used the DC Blocker on the input to the P10. My comparison is with and without regeneration affecting other transformers, particularly the power amp and preamp, both of which are quieter on regeneration at the same voltage. I can see the change in waveform from something that looks pretty sawtoothy on occasion to pure sine. The P10's transformer has always been quiet. |
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Post by pinkie on Jan 8, 2018 20:49:10 GMT
Martin
I am confused. Earlier in this thread you stated that the DC blocker "did reduce transformer hum.
More recently on this thread you state the P10 experienced no hum.
You only used the blocker with the P10. The P10 transformer didn't hum
You've lost me
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Post by MartinT on Jan 8, 2018 20:56:13 GMT
The P10's transformer never hummed. However, the power amp and preamp's did (a little). As I remember saying at the time, DC appears to affect the P10's performance through to the components it's powering. This is confirmed by their preferring clean regenerated power over raw mains now.
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Post by The Brookmeister on Jan 8, 2018 20:59:30 GMT
Martin I am confused. Earlier in this thread you stated that the DC blocker "did reduce transformer hum. More recently on this thread you state the P10 experienced no hum. You only used the blocker with the P10. The P10 transformer didn't hum You've lost me Doesn't take much does it dude (lol) DC mostly is caused by things in the house, not effected by having your village re-wired. www.isol-8.co.uk/dc_on_the_mains.html |
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Post by MartinT on Jan 8, 2018 21:04:51 GMT
We've got a farm nearby with some sodding great machinery powered from mains. I can tell exactly when they turn them on and off as my PS Audio Harvesters start going mad, often around 6pm.
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Post by Stratmangler on Jan 8, 2018 21:14:28 GMT
Milking parlour?
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