So after 10 otherwise happy years I'm finally sick of the humming from my high power variant of Aleph-Xs and currently looking at potting them myself to dampen the hum. It's not a loud hum/buzz but enough to be annoying in an otherwise quiet room.
I've gotten to this point after a few attempts playing with DC blocking. Originally the amp had 2x 4700uf caps with 2x diodes in antiparallel. I played around with a different variant of DC blocking circuit today this time with significantly larger capacitance and a bridge rectifier ala Bryston's circuit, but nothing changed in the slightest which makes me thing it's not DC. Also it buzzes all hours of the days in all houses I've lived in over the years. One amp has always hummed louder than the other which makes me think it's a construction issue with one transformer in particular.
So to the question:
Does anyone have recommendations as to how to pot these things?
We're talking about 1kVA 240V primary 2x 20V secondaries.
I don't have a vacuum chamber, and I'm looking to keep this experiment cheap, since if I wanted to spend a couple of hundred EUR I'd just buy new transformers.
I've gotten to this point after a few attempts playing with DC blocking. Originally the amp had 2x 4700uf caps with 2x diodes in antiparallel. I played around with a different variant of DC blocking circuit today this time with significantly larger capacitance and a bridge rectifier ala Bryston's circuit, but nothing changed in the slightest which makes me thing it's not DC. Also it buzzes all hours of the days in all houses I've lived in over the years. One amp has always hummed louder than the other which makes me think it's a construction issue with one transformer in particular.
So to the question:
Does anyone have recommendations as to how to pot these things?
We're talking about 1kVA 240V primary 2x 20V secondaries.
I don't have a vacuum chamber, and I'm looking to keep this experiment cheap, since if I wanted to spend a couple of hundred EUR I'd just buy new transformers.
Make a mould of some form and buy some polyurethane resin. Soft ish compound. Mix it and pour into your mold with the trafo in there.
Sorry to makenit sound 'easy'. But if you let the mixed resin stand a while and keep tapping the container its in on the desk it will make the bubbles rise and escape. Then when your pour it in inevitably you will/may get a few bubbles leak out towards the end of the hardening which will leave a few craters but nothing to worry about.
Aliexpress sell trafo 'covers' that you could use assuming they do them big enough. I shall look for the ones I bought.
I used to re form sagging Porsche Boxster gearbox mounts like this.
Sorry to makenit sound 'easy'. But if you let the mixed resin stand a while and keep tapping the container its in on the desk it will make the bubbles rise and escape. Then when your pour it in inevitably you will/may get a few bubbles leak out towards the end of the hardening which will leave a few craters but nothing to worry about.
Aliexpress sell trafo 'covers' that you could use assuming they do them big enough. I shall look for the ones I bought.
I used to re form sagging Porsche Boxster gearbox mounts like this.
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￡4.01 7%OFF | 80*40/90*38/105*60/120*50/130*65/140*74/150*75 toroidal transformer cover
80*40/90*38/105*60/120*50/130*65/140*74/150*75 toroidal transformer cover|Amplifier| - AliExpress
This is the largest but probably not enough for your 1kva.
150x75mm. Or maybe sandwich it between 2 of them if the diameter is enough?!
80*40/90*38/105*60/120*50/130*65/140*74/150*75 toroidal transformer cover|Amplifier| - AliExpress
This is the largest but probably not enough for your 1kva.
150x75mm. Or maybe sandwich it between 2 of them if the diameter is enough?!
Thanks. I'm hoping it is easy, just trying to get some tips around what to use. So I'll look for some Polyurethane resin, that was the first key bit of info I needed.
The transformer seems to be ~170mm and the Ali express ones top out at 150... But my 3D printer bed is larger than that. I may make my own covers out of ABS.
I guess the point here is to encapsulate the toroid but also insulate it from touching anything. In that regard I was looking at doing it in 2 pours, one to build up a base layer, let that harden a bit, put transformer in, and then encapsulate. But I read online that PU won't stick to itself so that may not work well. Do you have any experience or tips around this?
The transformer seems to be ~170mm and the Ali express ones top out at 150... But my 3D printer bed is larger than that. I may make my own covers out of ABS.
I guess the point here is to encapsulate the toroid but also insulate it from touching anything. In that regard I was looking at doing it in 2 pours, one to build up a base layer, let that harden a bit, put transformer in, and then encapsulate. But I read online that PU won't stick to itself so that may not work well. Do you have any experience or tips around this?
Indeed that's a good idea. I was also thinking about pre-forming some standoffs that way it's all the same material in there but there's no big chunky 2-pour.
Thanks for your help. One more question that has me perplexed. Shore hardness. Am I aiming something to solidify the damn thing with a hard resin and prevent movement in the coils, such as with a D70 hardness? I'm guessing if there's internal voids in the windings then the vibrations will persist and the noise may be conducted to outside of the cast.
On the flip side I could go with a slightly more elastic PU resin with an A70 Shore hardness. This wouldn't solidly encapsulate any movement, but it may dampen vibrations and thus not conduct noise outside of the potting.
I can play with potting on other transformers but I only have one shot at trying to suppress the noisy one. Any insights? I won't hold it against you if it doesn't work.
/EDIT: Dear god I just noticed it's been so long since I've posted that I have the wrong country listed and ... an ICQ number!
Thanks for your help. One more question that has me perplexed. Shore hardness. Am I aiming something to solidify the damn thing with a hard resin and prevent movement in the coils, such as with a D70 hardness? I'm guessing if there's internal voids in the windings then the vibrations will persist and the noise may be conducted to outside of the cast.
On the flip side I could go with a slightly more elastic PU resin with an A70 Shore hardness. This wouldn't solidly encapsulate any movement, but it may dampen vibrations and thus not conduct noise outside of the potting.
I can play with potting on other transformers but I only have one shot at trying to suppress the noisy one. Any insights? I won't hold it against you if it doesn't work.
/EDIT: Dear god I just noticed it's been so long since I've posted that I have the wrong country listed and ... an ICQ number!
Garbz....funny I could have sworn you had an NZ flag up there....and then I see your last remark!
I think you need to keep to a soft shore rating. I'm no expert here but I think the frequency of your trafo buzz is less likely to propagate through a soft substrate/insulator. The harder you go....up to say hardness of steel....you may aswell bolt it down hard. Simple analogy I know....but hopefully illustrates my thinking. Soft will absord the vibes.....hopefully.!
I think you need to keep to a soft shore rating. I'm no expert here but I think the frequency of your trafo buzz is less likely to propagate through a soft substrate/insulator. The harder you go....up to say hardness of steel....you may aswell bolt it down hard. Simple analogy I know....but hopefully illustrates my thinking. Soft will absord the vibes.....hopefully.!
Hi Garbz
1. Is the TX rated for 50Hz?
2. The TX core is maybe driven to hard and potting may not reduce the hum/buzz.
3. Do some tests.
4. Remove the secondary load. Does it still hum/buzz?
5. Connect to a Variac and slowly reduce the input voltage. At what voltage is the hum/buzz gone?
6. Raise the input voltage upwards to 264 vac, is the hum/buzz louder?
7. If the hum/buzz is gone @ say 200 vac the TX is POORLY designed. Buy a new TX or place the it in another room.
Good hunting
Duke
1. Is the TX rated for 50Hz?
2. The TX core is maybe driven to hard and potting may not reduce the hum/buzz.
3. Do some tests.
4. Remove the secondary load. Does it still hum/buzz?
5. Connect to a Variac and slowly reduce the input voltage. At what voltage is the hum/buzz gone?
6. Raise the input voltage upwards to 264 vac, is the hum/buzz louder?
7. If the hum/buzz is gone @ say 200 vac the TX is POORLY designed. Buy a new TX or place the it in another room.
Good hunting
Duke
That's easier said than done during COVID lockdown :-/ But really I found enough PU epoxies which don't require vacuums ... allegedly.
It was Australia, but close enough to New Zealand. I moved about 5 years ago. Mind you I now live about 30km from the border of Zeeland, the place that gave NZ it's name, so close enough
That was my thinking too after reading up on transformer buzz. My thinking was that because the transformer is wrapped it's not possible for the epoxy to flow in and fix whatever loose winding is causing the buzz. I'll go for a Shore A85 rating as something which looks the most suitable. I'll let you know how I go. Thanks for the tips ... regardless if it fixes my problem or not
Hey, Yeah these ones were custom wound back when I bought them in Australia. Rated for 50Hz.
The transformer isn't loaded very heavily, it's a 1kVA but I ended up only pulling about 8.5A from the secondaries so it's at about 40% load while idling (though power meter on the house says 50% load). I suspected it was a DC / saturation issue but that's not the case.
I can't remember if it hummed when the secondaries are disconnected, I vaguely remember it may be a yes. I'll do that experiment once more later, but I have tried a few tweaks on the secondaries, bypass caps on the bridges, removing some capacitance from the secondaries. No success.
Unfortunately I don't have a variac but it does take a few seconds for the buzzing to start. I do have two 10ohm 8A thermistors in series with the primaries through so I suspect it wouldn't buzz with lower line voltage. That said it was designed for 240V, but is now running at 230V with no change in buzz.
I honestly suspect it was poorly manufactured rather than poorly designed. I bought two of them. One of them is quiet enough that I can't hear it unless I'm next to it. The other one I can hear across the room.
After ruling out DC saturation I'm now at whits end. I'm going to epoxy the damn thing and if it works great, if it doesn't then I'll open up the purse strings and buy another. Just trying a 50EUR solution before I spend 250EUR.
Use regular synthetic varnish, the kind you would use to brush on wood or furniture.
Put transformer in some kind of plastic container or a can and cover it with varnish.
As bought it's liquid enough to get deep inside.
Leave it overnight.
You may thin varnish a little, say add 10 % of proper solvent, ask the paint shop guy.
If you dare, you can make a cheap disposable vacuum chamber: make a rough plywood/chipboard box with a vacuum cleaner hose sized hole on top, on a corner, not straight of varnish vessel, put potting vessel inside , close cover, and give box a couple vacuum whiffs, only 20 seconds each, let it rest 5 minutes, repeat, enough to draw tiniest bubbles out and let varnish penetrate deep.
Then pull transformer out, tie it by the wires to a broomstick sitting between 2 chairs and let excess varnish drip back into pot.
It will drip for a couple hours and take at least 2 days to dry but in Covid times, that's acceptable.
It will stink for a week.
Actual varnish absorbed is very little, put remaining one back in the can and later use as needed.
Put transformer in some kind of plastic container or a can and cover it with varnish.
As bought it's liquid enough to get deep inside.
Leave it overnight.
You may thin varnish a little, say add 10 % of proper solvent, ask the paint shop guy.
If you dare, you can make a cheap disposable vacuum chamber: make a rough plywood/chipboard box with a vacuum cleaner hose sized hole on top, on a corner, not straight of varnish vessel, put potting vessel inside , close cover, and give box a couple vacuum whiffs, only 20 seconds each, let it rest 5 minutes, repeat, enough to draw tiniest bubbles out and let varnish penetrate deep.
Then pull transformer out, tie it by the wires to a broomstick sitting between 2 chairs and let excess varnish drip back into pot.
It will drip for a couple hours and take at least 2 days to dry but in Covid times, that's acceptable.
It will stink for a week.
Actual varnish absorbed is very little, put remaining one back in the can and later use as needed.
I used to pot tube light chokes by pouring in insulating varnish (used for motor winding), with the chokes in circuit with the lamps lit.
The hum provided the necessary vibration for the varnish to fill the gaps, and being warm from work helped the varnish flow better.
It was fun, the sound would go, and tiny bubbles appeared as the trapped air was displaced by the varnish.
Another way is to take it out of the amplifier, make a crude box with plastic foam, and just submerge it in varnish, but on load, that will do as I said above.
The hum provided the necessary vibration for the varnish to fill the gaps, and being warm from work helped the varnish flow better.
It was fun, the sound would go, and tiny bubbles appeared as the trapped air was displaced by the varnish.
Another way is to take it out of the amplifier, make a crude box with plastic foam, and just submerge it in varnish, but on load, that will do as I said above.
Thanks for the tips everyone. Ended up going the Polyurethane route. Final result is 4dB down from where it was, but sadly still humming and still annoyingly audible.
It only hums under load and I wasn't prepared to play with this toxic goo in the amp itself. But the idea of keeping it on while potting it would have been great, and may have worked with varnish but sadly not with the PU, that didn't penetrate the outter wrapping.
Time to go shopping for a replacement but it was a fun experiment all the same. Pic below. Excuse the horrid wiring (especially the 230V crossing the -18V rail with only single insulation) that will all be fixed.
It only hums under load and I wasn't prepared to play with this toxic goo in the amp itself. But the idea of keeping it on while potting it would have been great, and may have worked with varnish but sadly not with the PU, that didn't penetrate the outter wrapping.
Time to go shopping for a replacement but it was a fun experiment all the same. Pic below. Excuse the horrid wiring (especially the 230V crossing the -18V rail with only single insulation) that will all be fixed.
Attachments
I wish you had posted it earlier.
Scrape off a little PU...after seeing that the housing does not leak, it seems perfect for potting in situ, use varnish, and if needed use box tape at the bottom, with the thing supported, as a leak stopper.
The problems with toroids are basically that the laminations may have burrs from the stamping process, and the wire tension during winding has to be proper, or there may be a gap.
But that is common with transformers made in small work shops, you too have a good and a bad one.
Scrape off a little PU...after seeing that the housing does not leak, it seems perfect for potting in situ, use varnish, and if needed use box tape at the bottom, with the thing supported, as a leak stopper.
The problems with toroids are basically that the laminations may have burrs from the stamping process, and the wire tension during winding has to be proper, or there may be a gap.
But that is common with transformers made in small work shops, you too have a good and a bad one.
Your experience is the same as mine. 30 years ago as an impoverished uni student I got hold of two 500VA transformers. At a good price.
I could not put up with the noise they made and eventually potted them.
They went back into service, but were there only until I could afford to replace them.
They have since sat in my parts bin waiting for a job that can tolerate a noisy transformer. I think the issue is either the core not being secure enough in its manufacture or windings deep inside that simple potting, I.e. without solid vacuum, can not penetrate to.
Next time I will go straight to replacement.
I could not put up with the noise they made and eventually potted them.
They went back into service, but were there only until I could afford to replace them.
They have since sat in my parts bin waiting for a job that can tolerate a noisy transformer. I think the issue is either the core not being secure enough in its manufacture or windings deep inside that simple potting, I.e. without solid vacuum, can not penetrate to.
Next time I will go straight to replacement.
@NareshBrd thanks anyway. I'll keep it in my back pocket for future.
Honestly it's been like this for over 10 years I may just live with it for a little longer. I'm planning on spending big shortly. Got my eyes set on a set of B&W 800D3s and doing a bit of looking around apparently despite the specs there are enough reviews critical of the fact that they rated them 8ohm nominal going down to just shy of 3ohm and sitting at just over 4 for much of the audio band.
Long story short I may need to replace the Aleph X this year anyway. Now time to look at what I want to build next
@googlyone the thing which hurts here is that these were custom ordered from a transformer manufacturer in Sydney and I was just too young and stupid and waaay too slow building to realise the transformer had a problem. If this happened right now I'd return it in an instant.
Honestly it's been like this for over 10 years I may just live with it for a little longer. I'm planning on spending big shortly. Got my eyes set on a set of B&W 800D3s and doing a bit of looking around apparently despite the specs there are enough reviews critical of the fact that they rated them 8ohm nominal going down to just shy of 3ohm and sitting at just over 4 for much of the audio band.
Long story short I may need to replace the Aleph X this year anyway. Now time to look at what I want to build next
@googlyone the thing which hurts here is that these were custom ordered from a transformer manufacturer in Sydney and I was just too young and stupid and waaay too slow building to realise the transformer had a problem. If this happened right now I'd return it in an instant.
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