So I have a cheap DC blocker [ DC Blocker Trap Filter – Assembled in Case – v.3 – ATL Audio Ltd. ] that I purchased for a Preamp that was mechanically noisy. I ended up replacing the noisy (mechanical hum) mains transformer, as it was faulty.
The blocker made no difference whatsoever on the pre amp to cure the hum.
I then tried this on my power amplifier (valve again and EI core) and this also made no difference whatsoever to cure the small hum.
I spoke to the supplier and he agreed this type of device is only really effective for toroidal transformers.
SO - for DC blocking (to cut down mains transformer hum) on an EI transformer any other suggestions, I presume the Elliot design just more of the same?
Can I simply measure DC offset anyway to see if it's really a problem?
Thanks, (I read an earlier post on this and can't seem to answer the question on EI compatibility)
Circuit of mine as attached.
R
The blocker made no difference whatsoever on the pre amp to cure the hum.
I then tried this on my power amplifier (valve again and EI core) and this also made no difference whatsoever to cure the small hum.
I spoke to the supplier and he agreed this type of device is only really effective for toroidal transformers.
SO - for DC blocking (to cut down mains transformer hum) on an EI transformer any other suggestions, I presume the Elliot design just more of the same?
Can I simply measure DC offset anyway to see if it's really a problem?
Thanks, (I read an earlier post on this and can't seem to answer the question on EI compatibility)
Circuit of mine as attached.
R
Attachments
I'm quite new to hifi audio, but what would a dc blocker do?
Edit: I'm following the route down the links now...
Edit: I'm following the route down the links now...
In many locations, the mains network has a 1 to 3V DC component, maybe more.
EI transformers are not so much troubled by it, but toroidals suffer quite badly.
The mechanical hum rises and falls, along with the DC -so you can hear the DC level.
But if you have no toroidals trafos, the DC blocker is not needed.
EI transformers are not so much troubled by it, but toroidals suffer quite badly.
The mechanical hum rises and falls, along with the DC -so you can hear the DC level.
But if you have no toroidals trafos, the DC blocker is not needed.
So how does the mechanical hum in an EI transformer manifest itself, is there another mechanism that creates this beyond an offset of DC?
(probably a dumb question) I can't seem to find much on the web on noisy EI transformers
(probably a dumb question) I can't seem to find much on the web on noisy EI transformers
Mech. hum in EI trafo means a fault, usually. Short-circuited winding-turns would do it. Anything that causes saturation of the core to increase - mechanical damage due to drops; loose laminations etc.
Small EI transformers shouldn't hum. Large ones can and do. Nothing wrong with it. Some places actually use piezoelectric discs to counteract the hum of the casing.
Mechanical hum in any transformer can be caused by running close to saturation. Some are run closer to the edge than others and if the line voltage is high they’ll make a racket. Some generate noise over time if laminations physically loosen up - the closer to saturation it is run the more prone to this it is If it is not overheating, there may be nothing wrong with the transformer itself. Shorted windings will generate a lot of heat, as well as make noise.
Humming transformer is probably not well-constructed. I have both big and small transformers that do not hum at all, or you may need a stethoscope to hear their hum.
can I measure it easily within the DC blocker itself, I know you need to make a device for measuring it on the AC, and it occurred to me that maybe there might be an easy way of measuring with this unit somehow?
Just a thought?
Just a thought?
I built a sjostrom audio DCT03 for my system as all the transformers is all of my amps hummed mechanically. It's simply a bigger version of what you have already.
It solved the noise in my solid state amps, one of which has an EI core, the other have toroidal. It did not make much if any difference to my valve amps which produce 100Hz hum quite loudly from the power transformers. Not sure on the cause in my case, they hummed pretty loudly with no load so I seriously doubt it's saturation. They don't get silly hot, but they do get quite warm after being on for 6+ hours. I'm assuming it's simply a lack of adequate damping between it and the chassis.
It solved the noise in my solid state amps, one of which has an EI core, the other have toroidal. It did not make much if any difference to my valve amps which produce 100Hz hum quite loudly from the power transformers. Not sure on the cause in my case, they hummed pretty loudly with no load so I seriously doubt it's saturation. They don't get silly hot, but they do get quite warm after being on for 6+ hours. I'm assuming it's simply a lack of adequate damping between it and the chassis.
I hope i don't step on anyone s toes, but i once suggested a "DC blocker" on a forum frequented by old electrical engineers, and i got my *** handed to me. And their response was that waveform distortion is due to SMPS with bad power factor is indeed a problem, but that the mains impedance in many places is too low to cause serious issue.
In any case: if you want to make sure there is no DC anywhere: Get a proper insulation transformer(And just move the problem somewhere else), or a saturation transformer. The latter will stabilize the mains automatically, and increases valve filament life.
Just my 2c.
In any case: if you want to make sure there is no DC anywhere: Get a proper insulation transformer(And just move the problem somewhere else), or a saturation transformer. The latter will stabilize the mains automatically, and increases valve filament life.
Just my 2c.
If you ran a tube output trafo at that high a flux density it would sound like crap. If you ran the one in your HT receiver that high it would vibrate itself off the table. Perfectly acceptable for power distribution, with flameouts few and far between. Industrial control and inverter transformers tend to be run at higher flux densities than what they use in consumer audio equipment for the same reasons, with similar results. They are generally well made, but produce more hum than stuff meant for consumer use. Sometimes they can be found surplus for cheap, tempting DIYers to use them for audio projects. Then you’ve got to put up with hum.
Tell Toronto Hydro... I don't know where you live, but if you don't hear power frequency everywhere you go, you might have hearing loss.
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