Just curious, How did you test them? Under load in present layout?
Can you isolate it by disconnecting mains into all and then powering only one circuit at a time to see if there is a more localized culprit? 'Might also tell you if they are each well behaved but as a group get into mischief.
Thanks
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Thanks for your replies. The input chokes are 28mH 3A Hammond units, 159ZE. I tested one of them by wiring up a choke input filter connected to a 15VAC transformer (+ rectifier of course) and a 12R dummy load, this worked fine without audible vibrations. The transformers were also quiet when I tested one on the bench, but four of them in a row bolted to the chassis seems to have changed that. Perhaps rubber dampers between the transformers and the chassis plate would improve the situation to some degree, unless it's the windings rather than the cores that are noisy.
Next thing to try is to disconnect the chokes and runt the transformers completely unloaded again just to rule the chokes out.
Next thing to try is to disconnect the chokes and runt the transformers completely unloaded again just to rule the chokes out.
I use 10uF paper in oil caps right after the rectifier, in an attempt to save the Schottkys rectifiers from voltage spikes from the chokes. Not much science behind this decision, only my gut feeling telling me it would be a good idea. Perhaps it wasn't?
It can be done, with a bit of effort as the PSU is very non-servicable. In hindsight, I should have put the filament supplies in a separate chassis instead of squeezing everything into the same box in three layers.
It would be interesting to know if the buzzing is caused by all four transformers (the transformers are the prime suspects here but let's not rule the chokes out quite yet) working together or if there is one rotten egg in the basket.
I don't have much technical knowledge but the arrangement of all those transformers and chokes looks a little "industrial" , ie. done with good focus on organized fit and neatness (and successfully at that!) . . . . . . . But I've walked past a lot of humming industrial panels . . . . . . So I wonder if they could be supporting/interacting with each other's fields and as a group getting things moving enough to make the chassis audible.
Though I have only seen a strong mechanical interaction once on a breadboard (and it was easily solved by turning the choke), I don't know much more than that about magnetic field interaction so, I'm more just voicing a question than pointing a finger at anything.
Though I have only seen a strong mechanical interaction once on a breadboard (and it was easily solved by turning the choke), I don't know much more than that about magnetic field interaction so, I'm more just voicing a question than pointing a finger at anything.
Magnetic interference from one iron core to another is one possibility, though I took care in positioning them with the windings "pointing" in different directions to avoid that.
I'll take a closer look once I get home from work. With a little luck there's room for 10mm tall rubber dampers between the transformers and the alu sheet they are bolted onto, but I doubt it. If the buzzing comes from rattling windings rather than vibrating cores there's not much else to do than to replace the transformers with something better. That won't be easily done, I might have to compromise and use four small toroids instead of proper dual-chamber EIs.
Quite annoying, I usually build tube amps from junk/cheap parts just as a hobby, sometimes with very satisfying results. This time I've plowed down 2000+ euros into something I actually intend to use for a long time and everything works like a charm and it sounds really good...except for a few bumblebees trapped inside the PSU.
As a side note, I bought a another couple of small Hammond 230:60-0-60V transformers for the Fet follower supplies and they buzz like crazy at 230VAC, completely useless at their rated voltage. How hard can in be to manufacture products that actually work as intended? I'm sure there is complicated maths behind the design of an mains transformer but a major manufacturer should be able to master that in 2023, am I right?
I'll take a closer look once I get home from work. With a little luck there's room for 10mm tall rubber dampers between the transformers and the alu sheet they are bolted onto, but I doubt it. If the buzzing comes from rattling windings rather than vibrating cores there's not much else to do than to replace the transformers with something better. That won't be easily done, I might have to compromise and use four small toroids instead of proper dual-chamber EIs.
Quite annoying, I usually build tube amps from junk/cheap parts just as a hobby, sometimes with very satisfying results. This time I've plowed down 2000+ euros into something I actually intend to use for a long time and everything works like a charm and it sounds really good...except for a few bumblebees trapped inside the PSU.
As a side note, I bought a another couple of small Hammond 230:60-0-60V transformers for the Fet follower supplies and they buzz like crazy at 230VAC, completely useless at their rated voltage. How hard can in be to manufacture products that actually work as intended? I'm sure there is complicated maths behind the design of an mains transformer but a major manufacturer should be able to master that in 2023, am I right?
Being politically correct I can only tell you that a certain person I know, at a certain time in the past was a distributor for a certain type of power transformer that hummed like an angry massage chair until he dutifully warmed each one and re-impregnated it with some very fancy potting compound. So I'm familiar with the issue to that extent. Yah, you're right !
Where's the 230:60-0-60V made?
Where's the 230:60-0-60V made?
The time for political correctness is long gone, I'm usually a quiet person but buzzing transformers can provoce me into using a vocabulary that would make Eminem blush 
I think these smaller ones are made in China, at least the open-frame chokes are IIRC.
The good news so far is that it looks like there's room for rubber dampers under the transformers. and with some luck I can even get them in place without disassembling the whole PSU.
I think these smaller ones are made in China, at least the open-frame chokes are IIRC.
The good news so far is that it looks like there's room for rubber dampers under the transformers. and with some luck I can even get them in place without disassembling the whole PSU.
I got these transformers months ago, imported via the Netherlands and they weren't very expensive so asking for money back or replacements feels like too much work, but feel free to have a word with them if you like, it would be appreciated!
The noisiest ones that I had to reject immediately are labelled 186D120 (Made in Canada, sorry to say). Can't remember which exact model I'm having problems with in the filament supplies, it's either 185C28 or 185D28.
Finally some luck: After digging through my junk room, I managed to find eight 10mm rubber dampers. It won't be a walk i the park to get them in place but it's worth a try.
Finding better transformers with similar ratings that fits inside this very cramped space would be a real challenge. I'm trying to get used to the idea of removing the input chokes and add some kind of bucking transformer that lowers the input voltage to the filament transformer down to 150V or whatever it would take to get the right DC voltages without the L input filters.
That would be a moral loss, I would really like to have my LCLC-filtered filament supplies, but the mechanical noise in intolerable and there's not much room inside the chassis for any major layout changes.
The noisiest ones that I had to reject immediately are labelled 186D120 (Made in Canada, sorry to say). Can't remember which exact model I'm having problems with in the filament supplies, it's either 185C28 or 185D28.
Finally some luck: After digging through my junk room, I managed to find eight 10mm rubber dampers. It won't be a walk i the park to get them in place but it's worth a try.
Finding better transformers with similar ratings that fits inside this very cramped space would be a real challenge. I'm trying to get used to the idea of removing the input chokes and add some kind of bucking transformer that lowers the input voltage to the filament transformer down to 150V or whatever it would take to get the right DC voltages without the L input filters.
That would be a moral loss, I would really like to have my LCLC-filtered filament supplies, but the mechanical noise in intolerable and there's not much room inside the chassis for any major layout changes.
Before you give up, I'd also try stuff like reversing hookup polarity on alternate chokes or power transformers etc . Goof around with stuff. If the chokes worked originally then there's a way through. If you like the way it sounds now then take your time. Changing circuit will change sound . You know that. Of course, it could get better. 🤪
Yes, I'll try everything I possibly can come up with before I do anything drastic. Parting with the LCLC filters would leave a bad taste in my mouth, I would probably prefer to roll up my sleeves and build new filament supplies in a third chassis.
Operation Rubber Duck is in progress here, 4 out of 8 are in place by now. Quite funny after all: 6'9, 250lbs, goes to the gym three times a week and I'm a bit afraid of lifting the power supply for a 2*6W amp...
Operation Rubber Duck is in progress here, 4 out of 8 are in place by now. Quite funny after all: 6'9, 250lbs, goes to the gym three times a week and I'm a bit afraid of lifting the power supply for a 2*6W amp...
10µF is not effective at 1A - the current waveform is likely to be badly behaved.
220-470µF is good (~10mH choke, 1A DC load). But the rms current in the capacitor is ca. 900mA - too much for any ordinary elko.
Solid polymers of the A750 series are by far the best for this job.
Kemet part nr. A750KS227M1EAAE015 is available at RS and Mouser, and will work very well.
I am not promising that it will fix the buzzing, but it will make the dynamic currents much smoother, so it maybe it will help.
The rubber dampers didn't help at all.
The best idea I can think of right now is to locate four small 24V transformers with 400V primaries, that should result in 13,8V on the outputs but with enough turns to operate quietly.
Edit: Perhaps something like this, or maybe the bigger 63VA version: https://www.tme.eu/se/details/tmm30_a400_24v/transformatorer-med-fixering/breve-tufvassons/
The 30VAs might actually even fit without having to build a separate chassis.
Before I start spending money I have a few tricks left to try. Not very optimistic though, my guess here is that the Hammonds are cheap junk with too few turns in their primary windings to operate quietly at their rated voltage.
The best idea I can think of right now is to locate four small 24V transformers with 400V primaries, that should result in 13,8V on the outputs but with enough turns to operate quietly.
Edit: Perhaps something like this, or maybe the bigger 63VA version: https://www.tme.eu/se/details/tmm30_a400_24v/transformatorer-med-fixering/breve-tufvassons/
The 30VAs might actually even fit without having to build a separate chassis.
Before I start spending money I have a few tricks left to try. Not very optimistic though, my guess here is that the Hammonds are cheap junk with too few turns in their primary windings to operate quietly at their rated voltage.
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As usual, it seems like I've been jumping to conclusions here: Without anything connected to the rectifier outputs, the buzz is nearly gone.
I just unsoldered the wires connecting the rectifiers to the input chokes to insert some resistors when I suddenly remembered to test without any load at all.
This makes me think that it's either the chokes that are buzzing (the one I tested didn't but that's an older 159ZE, the other four are of more recent manufacture. Perhaps it was stupid to assume they would be of equal quality) or that the 10uF caps after the rectifiers are wreaking havoc in the transformers.
Let's put a 1R 5W resistor directly after each rectifier and see what happens.
I just unsoldered the wires connecting the rectifiers to the input chokes to insert some resistors when I suddenly remembered to test without any load at all.
This makes me think that it's either the chokes that are buzzing (the one I tested didn't but that's an older 159ZE, the other four are of more recent manufacture. Perhaps it was stupid to assume they would be of equal quality) or that the 10uF caps after the rectifiers are wreaking havoc in the transformers.
Let's put a 1R 5W resistor directly after each rectifier and see what happens.
Indeed, power supply design in general is the boring part of this hobby.
As the transformers are silent without load, I must assume the noise just as well can come from the input chokes. The layout makes it difficult to hear exactly where the noise comes from.
As mentioned, I tested one of the chokes on the bench with adequate input voltage and current draw but I guess the circumstanses can change when there are five of them in a row, in close proximity and with ferrous metal parts nearby.
I've decided to remove the 10uF input caps, installing them wasn't very well thought out and a quick calculation shows that 28mH and 10uF resonates at 300Hz. I'm no expert but an uncontrolled resonance at a multiple of the mains frequency is probably not a good thing.
To get rid of those caps I'll have to dismantle parts of the power supply, which would be an opportunity to rearrange the wiring so that I can test various filter configurations in situ until I find somethings that works. There are a few options:
* With a little luck, removing the 10uF caps might be enough. Who knows exactly what they contribute to.
* Wire both chokes (28mH + 6mH) in series at the input for maximum ripple capacity, followed by CRC filters.
* Decrease the input voltage, remove one of the chokes and build CLC filters
* Keep the input voltage at 230V, add some caps and resistors and make RCLCLCRC filters... This would probably be the easiest thing to do, but there would be a lot of extra heat to get rid of.
We'll see where this ends, I really don't want to give up on the choke input filters but I'll do it if I have to. I'm hoping to be able to come up with something that works with the existing caps, chokes and transformers. Replacing anything with new parts that doesn't fit in the same screw holes would be a complete nightmare.
As the transformers are silent without load, I must assume the noise just as well can come from the input chokes. The layout makes it difficult to hear exactly where the noise comes from.
As mentioned, I tested one of the chokes on the bench with adequate input voltage and current draw but I guess the circumstanses can change when there are five of them in a row, in close proximity and with ferrous metal parts nearby.
I've decided to remove the 10uF input caps, installing them wasn't very well thought out and a quick calculation shows that 28mH and 10uF resonates at 300Hz. I'm no expert but an uncontrolled resonance at a multiple of the mains frequency is probably not a good thing.
To get rid of those caps I'll have to dismantle parts of the power supply, which would be an opportunity to rearrange the wiring so that I can test various filter configurations in situ until I find somethings that works. There are a few options:
* With a little luck, removing the 10uF caps might be enough. Who knows exactly what they contribute to.
* Wire both chokes (28mH + 6mH) in series at the input for maximum ripple capacity, followed by CRC filters.
* Decrease the input voltage, remove one of the chokes and build CLC filters
* Keep the input voltage at 230V, add some caps and resistors and make RCLCLCRC filters... This would probably be the easiest thing to do, but there would be a lot of extra heat to get rid of.
We'll see where this ends, I really don't want to give up on the choke input filters but I'll do it if I have to. I'm hoping to be able to come up with something that works with the existing caps, chokes and transformers. Replacing anything with new parts that doesn't fit in the same screw holes would be a complete nightmare.
Adding more capacitance after the rectifiers can't be done easily, I must unsolder ~25 wires and remove a part och the chassis first. Stupid design, I know...
Once I'm done rewiring this whole mess I'll be able to test a lot of different configurations, including cLC filters with Kemet eletrolytics per Rods suggestion.
Once I'm done rewiring this whole mess I'll be able to test a lot of different configurations, including cLC filters with Kemet eletrolytics per Rods suggestion.
I'm closing in on some answers here: In order to run som tests, I have partially dismantled the PSU and disconnected the input chokes completely. To isolate the problem, I made a test rig with a 24V transformer, a multi-tapped autoformer (a variac would be much better but I don't have one), a 1000V 8A bridge rectifier, a 4700uF cap and an adjustable dummy load.
The whole idea was to wire up a simple LC-filtered power supply that delivers ~1A DC over a range of different input voltages, just to see how the chokes are behaving placed inside the chassis. Everything else in the PSU is disconnected and unpowered.
The idea to use LCLC filters popped up when I saw an old Hammond 159ZE (28mH 3A) in my junk box and decided to test is as an input choke in a setup very similar to the one I just built. That test went just fine and I ordered four more for the output tubes plus five small 6mH 2A units for the second L's. The old 159ZE is used in an identical filter that produces 6,3Vdc for the input tubes from two 6,3VAC windings.
Here's the (not so) funny part: The old 159ZE (Made in Canada) starts to buzz audibly when the AC voltage in to the rectifier reaches about 18V, while the new one (made in China...) next to it buzzes much more aggressively at less than 14VAC. The dummy load was adjusted to draw roughly the same current in both cases, just over 1A DC. The other three are reasonably quiet at 14VAC, turns out I have a rotten egg in the basket after all.
The whole idea was to wire up a simple LC-filtered power supply that delivers ~1A DC over a range of different input voltages, just to see how the chokes are behaving placed inside the chassis. Everything else in the PSU is disconnected and unpowered.
The idea to use LCLC filters popped up when I saw an old Hammond 159ZE (28mH 3A) in my junk box and decided to test is as an input choke in a setup very similar to the one I just built. That test went just fine and I ordered four more for the output tubes plus five small 6mH 2A units for the second L's. The old 159ZE is used in an identical filter that produces 6,3Vdc for the input tubes from two 6,3VAC windings.
Here's the (not so) funny part: The old 159ZE (Made in Canada) starts to buzz audibly when the AC voltage in to the rectifier reaches about 18V, while the new one (made in China...) next to it buzzes much more aggressively at less than 14VAC. The dummy load was adjusted to draw roughly the same current in both cases, just over 1A DC. The other three are reasonably quiet at 14VAC, turns out I have a rotten egg in the basket after all.
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