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Old 26th September 2021, 02:40 PM   #141
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by xrk971 View Post
All good suggestions, guys. My next step was to bring trafo outside chassis. I’m quite sure that works as that simulates the flat splayed out arrangement earlier before I buttoned things up.
If you move the trafo only, you'll have long AC wires from the trafo to the amp/SLB, which might emit some 60 Hz noise into the audio circuits, and you'd still see the 60 noise. In order to avoid the possible pickup of any 60 Hz noise I'd say it's better to move all the AC stuff away from the audio circuits for debugging.

Quote:
Originally Posted by xrk971 View Post
SMPS does not have a massive winding that emits large scale magnetic flux leakage.

In addition to switching probably in 400kHz range that is inaudible...
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Originally Posted by JPS64 View Post
with SMPS you put the problems in the inaudible MHz range
This is all true, but... many SMPS units have variable switching frequencies in order to optimize the efficiency depending on the load. A variation of the switching frequency may show up as a modulation in the audible range. Also, even with a constant switching frequency, modulation of the switching frequency with the audio signal may cause unwanted audible effects. I compared a 50 Hz toroidal transformer with an SMPS in my Aleph-J amp. While the SMPS worked fine, the transformer PSU was better to my ears.
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Old 26th September 2021, 02:41 PM   #142
wtnh is offline wtnh  United States
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Have you tried powering the modules from your bench supply? That would tell you something. Also, wondering if the toroid leakage field is getting induced into the choke (they are very close)? Mumetal might help there.
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Old 26th September 2021, 02:53 PM   #143
xrk971 is offline xrk971  United States
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I think it’s the proximity of toroidal and inductor. And I did think of mumetal but that only can do so much when the two are this close together. I actually put my very last piece of mumetal in between the trafo and the SLB (that’s all I had enough for). It dropped the noise a tiny bit. But a small piece placed between the trafo and inductor actually made things worse. Like it diverted the field and concentrated it.

I think the ideal solution would be a separate chassis for the PSU altogether. Sort of like what TA did on the VFET.

DIY Sony VFET Builders thread

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Old 26th September 2021, 06:13 PM   #144
wtnh is offline wtnh  United States
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Ooof - that would be a shame. Would you try to match that beautiful chassis with an external box from the same shop? Very pricey. But you are correct I think - it would be the ideal solution.
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Old 26th September 2021, 06:20 PM   #145
xrk971 is offline xrk971  United States
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My hopes are pinned on the SMPS at this point. It just might be that this style of chassis cannot have signal path inductors or transformers that pick up EMI so easily.

I may have to get a third chassis but not sure I can get a matching unit.
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Old 26th September 2021, 07:11 PM   #146
TungstenAudio is offline TungstenAudio  United States
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Meper just wrote about an external SMPS that he built for his VFET amp in the builders thread. Looks worth investigating.
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Old 26th September 2021, 07:23 PM   #147
xrk971 is offline xrk971  United States
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Thanks for that. I’ll be using a Micro-Audio SMPS and those have a topology that doesn’t care about lots of bulk capacitance at the output. Sami actually provides a free PCB to add up to 4 snap in 22,000uF caps if one wants. Not sure it is needed, but my experience with Micro-Audio is that they are very quiet. I measured the background noise floor from one of my other amps using a Micro-Audio SMPS and there was no 60Hz bump even and the floor was at -130dB on the FFT. I think drawing 6.1A continuously will raise the noise floor. But the main thing is to reduce the 60Hz EMI given off.
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Old 26th September 2021, 08:00 PM   #148
TungstenAudio is offline TungstenAudio  United States
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The Micro Audio products also look very promising. I haven’t seen many reviews or listening impressions, so waiting to hear more.
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Old 26th September 2021, 08:13 PM   #149
daanve is offline daanve  Netherlands
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With good layout and proper power supply these amps should be quiet.
The aforementioned Grandinote Shinai amplifier has two independent mono amplifiers in one chassis and it was perfectly quiet; toroidal power supply transformer almost next to toroidal output choke; working with the same 3A quiescent current.
The EI choke is more vulnerable for strayfields.
Please note that rectifying voltage with these currents is quite a task for rectifiers and capacitors; check datasheets for capacitors being able to cope with these continuous currents, not all of them can.
A choke in the power supply would do well but takes money, room and weight.
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Old 26th September 2021, 08:45 PM   #150
xrk971 is offline xrk971  United States
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Looks like a steel tray holding the trafo’s above the amp might have some shielding to it. On the SLB PSU, I am using LT4320 active bridges with low RDson MOSFETs so very little heat dissipated on rectifier. The CRC needs to be looked at as it was designed for 5A continuous and had high ripple current rated caps to withstand the punishment. I measured the temp of the first cap at 51C. Still well below rated temp but everything inside the chassis is going to be about 50C given that’s how hot the heatsinks are running.

Edit, that photo shows the amp on its side. There are two banks of toroidal inductors and power trafos. Note that they are mounted with as much space in between them as possible.
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