PL INT25 is a class A amplifier.
Power supply in class A amplifiers by definition has to deliver a steady voltage continuously.
Using a toroidal power supply transformer in a class A amplifier is asking for trouble when the transformer operates near the treshold of core saturation which in this case seems to be the case.
Actually we witness a serious design flaw here, kudos to Pass Labs....
All tricks like DC blockers, AC regenerators will not help here.
Two options:
1. get rid off the amplifier ASAP by returning it to the seller;
2. ask for a modification by replacing the transformer (there is enough room in the chassis for a bigger transformer), preferably not a toroid.
Power supply in class A amplifiers by definition has to deliver a steady voltage continuously.
Using a toroidal power supply transformer in a class A amplifier is asking for trouble when the transformer operates near the treshold of core saturation which in this case seems to be the case.
Actually we witness a serious design flaw here, kudos to Pass Labs....
All tricks like DC blockers, AC regenerators will not help here.
Two options:
1. get rid off the amplifier ASAP by returning it to the seller;
2. ask for a modification by replacing the transformer (there is enough room in the chassis for a bigger transformer), preferably not a toroid.
daanve, with all due respect, this is just not the case. I've run all my class A amps with Toroids without problems.
I get my transformers custom wound and can set the core flux density to whatever I ask the manufacturer to set it at, consistent with size and weight constraints. Toroids offer very low external mag fields and can be made absolutely mechanically quiet.
@Bonsai,
I agree, but apparently this transformer operates at the treshold of core saturation. In other words too high core flux density.
Toroids can be made quiet but core excitation should not exceed 1 Tesla; otherwise all possible problems lurk around the corner, especially in class A amplifiers where power supply operates continuously at maximum current.
Lower flux density transformers require bigger cores, and too often economics rule.
It really seems that the INT25 transformers runs into saturation and/or winding resonance problems, which is intolerable considering the presumed quality (and price!) of this amplifier.
I agree, but apparently this transformer operates at the treshold of core saturation. In other words too high core flux density.
Toroids can be made quiet but core excitation should not exceed 1 Tesla; otherwise all possible problems lurk around the corner, especially in class A amplifiers where power supply operates continuously at maximum current.
Lower flux density transformers require bigger cores, and too often economics rule.
It really seems that the INT25 transformers runs into saturation and/or winding resonance problems, which is intolerable considering the presumed quality (and price!) of this amplifier.
No it also has an EI transformer that is in the middle left side.
Let’s get the recording of the sound and then we can quickly determine the problem.
[NB The transformer load has no effect on the flux density so whether the load is 0 or 5 A makes no difference.
B = 1/(4.44.f.E.Ae.N) ]
[NB The transformer load has no effect on the flux density so whether the load is 0 or 5 A makes no difference.
B = 1/(4.44.f.E.Ae.N) ]
Yes, flux density is more or less fixed; resonance of windings can interact with load: a transformer can be quiet with alternating load (class A/B) but noisy with constant heavy load (class A).
at this point in the saga we need to see the resolution and hopefully an explanation when the dealer checks the unit out. Not sure why he did not drive it to the dealer months ago for a fix or refund.
I live at the opposite end of the UK. I'm in South England and my dealer is in Scotland. Plus, with my hip injury: I never drove for three months and now only 25 miles maximum to Church.
UPDATE: I've emailed my dealer [Audio Emotion, Scotland] that I would like a refund. It doesn't matter if the amp tests quiet up in Scotland: I bought it to work correctly here at home in England. My dealer should have warned me at the point of sale that Pass Labs suffer from "sensitive" transformers and may require a customer to purchase thousands of pounds of extra equipment to get the amp to work as expected and without a guarantee of success.
This shows current production and if you look closely there are indeed two transformers. This power supply is used in both the XA-25 and INT-25. Something strange is happening here given the number of these in the field and this one being noisy and no other reports of this. I agree it should be very quiet. The Plitron noise paper was written by people that have been at our factory working with us.
You mean it's not normal for my dishwasher to make a humming noise in the Heavy Duty Pots Cycle?
BTW- I live in SoCal... for many years I had an issue with my 120/240 feed to the house. Incandescent bulbs, when set through a dimmer, or when low power ( like 4 watt christmas tree lights) would flash and dim every so often ). A clear sign of reactance in some transformer. My neighbors saw the same thing.
I called the power company and they came here to test... but their tests are DC at 3/4 and full loads... so, they don't detect "noise" on the line caused by a faulty transformer in their vault (all of our local utilities are underground). They came to run their tests several times.
After many years of this... I bought an AC line analyzer and I noted that there were signs of voltage spikes and dips... again, our power company told me they could not do such a test... that it was an issue on my house. Something impossible as my house was fully rewired in 1999.
I hired an electrician and for two days we tested the wiring in the house and the feed coming in... We determined the problem was in the quality of the power coming in, but the power company rejected our results saying they were within spec... so I had to eat the 1000 bucks of troubleshooting we'd done.
When testing, we noticed that the current being delivered to my house was insufficient. When drawing more than 2Kw, the voltage would drop by 10%. This is not much current in a 300A service line... yet the power company, testing only at 230A and 300A loads and seeing a 10% drop -fully within their specs- so nothing wrong. They could not measure voltage swings at very low current draw.
I tried to explain to them that their transformer was not holding voltage with small current draw.... they did not understand... so they did not fix anything.
An since most electric/electronic devices do fine at 110VAC nothing was noted.. except for the aforementioned incandescent and halogen lamps via a dimmer set to a low setting.
So, guess what... after so many years, the Power Company did a maintenance "upgrade" in their vault and put a new transformer... and the problem, including my neighbors', went away. We haven't had any issues now for more than 15 years.
So this could be an issue with the quality of the "mains". Most people won't notice that as most people are not running such amplifiers in their homes and the Power Company is not going to replace their transformer because such failure modes are not considered abnormal for them.
Bottom line? The power company is not set to provide clean power. They provide a nominal setting and so long as they are thing +/- 10% they don't care... and they don't look for spikes or short interval time based behavior.
For the OP, I would suggest something like a PS Audio regenerator.
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I thought that the magnetic field [T] is directly proportional to (class A quiescent) current value AND the number of windings.
Magnetic flux would then be magnetic field [T] times area [m2].
In other words, magnetic flux WOULD depend on the quiescent current..?
It's been a while since I did this in uni... I might be wrong...
Magnetic flux would then be magnetic field [T] times area [m2].
In other words, magnetic flux WOULD depend on the quiescent current..?
It's been a while since I did this in uni... I might be wrong...
There's simply no other way. Mians is dirty. Even if it was clean, it will become dirty if only a few devices with SMPS are connected to the same power outlet to which audio components (without SMPS) are connected.
I had my entertainment system (flat panel TV & OPPO205 + Aleph J, NUC11 with liner power supply and May DAC) connected to the same power outlet. Then, I decided to run a separate power feed for Aleph J, NUC11 liner power supply and May DAC... from a different outlet in the room - one which did not have anything connected to it. The difference was simply unbelievable.
Then I tried to power up NUC11 with various SMPS... that was a disaster.
Re toroid transformers in class A amp (my Aleph J)... I decided to use double the VA rating, compared to what Aleph J constantly burns. So, a 400VA toroid for a 200W Aleph J. My toroid transformer is Toroidy for audio, fully potted and closed with a metal top. It is okay... I can hear a slight buzz... but only if I come very close to my amp and bring my ear very close to the top lid. I think it was completely quiet when I built the amp... can't remember. Anyway... it is a non-issue for me.
I think I read somewhere here on these forums that Nelson used a 300VA transformer for his FW Aleph J... but he specified a larger core... a 400VA core... something like that.
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