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A DC Blocker to help stop transformer HUM

DonH56

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Toroidal transformers are more sensitive to saturation caused by DC (or just too much current) than conventional EI transformers. One of the trades for a more constrained EM field around them (so you can cram circuits closer without them picking up noise).
 

Count Arthur

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One of the trades for a more constrained EM field around them (so you can cram circuits closer without them picking up noise).

Aren't they also more compact for a given output power than EI and R core transformers?

I got a DC blocker from Van Alstine - they call it a "HumDinger" - was $140 and instantly did the trick - no more hum.

I essentially built a copy of this: https://www.atlhifi.com/shop/fully-assembled-devices/high-power-dc-blocker-trap-filter-assembled-device/, which is perhaps a bit cheaky of me, but I quite like tinkering, so I wanted to build it myself. Given the cost of the parts and the time it took me to build it, I actually think the price ATL Audio is charging is very reasonable.

I already had a mains filter, with EMC/EMI filters, using this type of circuit, so I placed the DC blocker in the case ahead of the filter circuits:

CMF-Felix.png
 

Geert

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The above mention DC has a small problem I can well I can see two, but one is more important, the 1.4 approx voltage drop across the bridge will cause noise on the mains at zero to 1.4VAC
But do you expect that noise to be audible? Does a linear power supply even draw current around the mains zero?
 

pjug

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I bought the Emotiva DC blocker hoping it might silence transformer hum but it didn't help, so dirty power does not seem to be my problem. I can't hear it except when I am within a foot or two of the amp but still it annoys me.
 

Count Arthur

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Wouldn't the big caps in a linear PSU "fill in the gaps"?

The reason I opted to go for the "big" version using the 50A bridge rectifier, was so I could place it before the mains filter board, which has 6 outlets. Regardless, the DC blocker seems to be doing it's job, no more transformer hum, and with no detriment to the sound that I can discern.

I couldn't view what you linked to earlier, I get a message: "You do not have permission to access this thread. "

 
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Colin James Wonfor

Colin James Wonfor

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Wouldn't the big caps in a linear PSU "fill in the gaps"?

The reason I opted to go for the "big" version using the 50A bridge rectifier, was so I could place it before the mains filter board, which has 6 outlets. Regardless, the DC blocker seems to be doing it's job, no more transformer hum, and with no detriment to the sound that I can discern.

I couldn't view what you linked to earlier, I get a message: "You do not have permission to access this thread. "

It is not the gaps it the non conduction a backing EMF come from the transformer when current is switched of fast, it is the noise it put down the mains to other equipment that concerns me. OH you have to sign on to the SECA site.
 

maty

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DC Scraper kit for the GT-102 (NODC) - $24.95
https://www.akitika.com/akitikastore.html#GT-102A

DC_Scraper_AssembledC.jpg


[ You can install the DC scraper kit to quiet the buzz. It works by removing the DC component of the input power, leaving just the AC that all transformers love. So, even if your neighbors (or you yourself) have a heat pump or air-conditioner that draws nasty asymmetric currents when it runs, you can Scrape away all the DC, and keep your transformer quiet... ]

[PDF] https://www.akitika.com/documents/DCScraperAssemblyManualRev1p02.pdf


YouTube DC Scraper Kit for the GT-102 Nullifies the Effect of Asymmetric Power

 

eliash

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What is the max forward voltage I see anti-reversal diodes but no over voltage protection on caps.
Under peak in rush this could be high and on s/c loads it will be high.
Also I would like to see a temp rating of 105C not 85C, also what is the max ripple current?

Having just check his website I am even more concerned.

I think 85°C caps are ok, since the circuit is not mounted inside an amp and self heating will be rather low at that low diodes flow voltage. The max allowable inrush current is dependent from the diodes max peak current. In my T+A amp they are even smaller in size and it has 650W max output power via a big toroidal transformer. To me the board looks OK...
 

DonH56

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And the question I always ask about this type of AC power product:
"does it have the required "UL" stamp?

Yes -- I am a little surprised. From their website:

High-performance glass passivated semiconductor. High-case dielectric strength of 1500VRMS. UL listed. Flame resistant IEC socket/connecter/chassis (Fireproof polymers UL94-V0).
 

DonH56

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Yah, it's pretty clearly a marketing and not engineering description...
 

voodooless

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The hum wasn't loud enough to be heard over music, it was fairly faint.

Could be that you were so used to the hum that your brain just filtered it out. Once the the hum is missing you’ll start noticing it. It does the same with your heart beat. But the absence of that will be noticeable in other ways :confused:

On topic: any cheap AliExpress implementations out there?
 

Count Arthur

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Could be that you were so used to the hum that your brain just filtered it out. Once the the hum is missing you’ll start noticing it. It does the same with your heart beat. But the absence of that will be noticeable in other ways :confused:

On topic: any cheap AliExpress implementations out there?

I don't think I got used to the hum, but it was more noticeable at certain times; presumably the DC offset varied according to what else was in use nearby.


iFi released two new products to tackle DC offset and HUM:

http://ifi-audio.com/products/dc-blocker/

That's rather pricey; given how small it is, there can't be much in it: https://www.amazon.co.uk/dp/B08XWHJRZ1

I built a some DC traps using ATL Audio PCBs: https://www.atlhifi.com/shop/bare-p...ker-filter-for-toroidal-transformers-toroids/

It cost me around £90.00 to build two, including the PCBs, the cables, boxes and all the components.


DC-Blocker.jpg
 

deafenears

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It cost me around £90.00 to build two, including the PCBs, the cables, boxes and all the components.
What's the formula for pricing something for sale? Cost of materials plus labor, then multiply that by three or four as a base?
 

eliash

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What's the formula for pricing something for sale? Cost of materials plus labor, then multiply that by three or four as a base?

Pure marketing price, from my perspective. But it addresses pain points not properly covered by many equipment manufacturers, otherwise such stuff would be obsolete. Btw. for that price you can demand a proper homologation!

...and since there is serious and valuable testing going in this forum (Amir!) it would be reasonable to include some statements in these tests, whether equiment brings a forced ground (e.g. via the IEC con.) with it, or shares the same ground for analog and digital ports as a warning. Measured by itself such equipment may look bright, but hooking it up to other equipment with the same design philosophy ruins the customer experience completely...hum loops, digital crosstalk to analog, RFI interference, etc...
 
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Count Arthur

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What's the formula for pricing something for sale? Cost of materials plus labor, then multiply that by three or four as a base?

I studied industrial design and for most products, kettles, vacuum cleaners, refrigerators, etc. we would typically work on retail price being 5 x the cost of manufacture. So if you want to sell a kettle for £20, you have to be able to make it for £4.

However, with audio gear and some other products, clothing, shoes, cars, fashion items and things where a great deal of money is spent on marketing and building a brand, it's more a case selling for as much as you can get away with.

In the past few decades I think we've seen this trend increase and even fairly utilitarian items, like vacuum cleaners and refrigerators, are heavily marketed and branded and the price of "top spec" models has increased significantly over that of the base models, despite not being significantly more expensive to make.

Car manufacturers make far more profit on luxury cars than they do on the base models and other sectors have followed the example. A fancy refrigerator with a water chiller and temperature indicator on the front might only cost 5 or 10% more to make than a standard one, but will retail for 50 or 100% more.

I became quite dissilusioned with industrial design, I think there are very few products that are genuinely better than their previous incarnations. For the most part, it's just a styling excercise or inclusion of an ever increasing array of superfluos features, like refrigerators that connect to the internet and have a screen to remind me to buy milk, or a mobile phone with a camera sensor with 2 more megapixels than last years model.

Anyway, enough of my off-topic rant. :)
 
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