Transformer Hum

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Just curious as to what transformers they were?

Also I'm really surprised you can charge 400,000uF at 47VDC without a slow charge circuit!
I have 470,000uF in line with a 3A draw with a softstart and there was no way I could start it without blowing 10A fuses! I had to put a slow charge circuit.


Hmm thinking about your test situation, it is possible that those lightbulbs won't simulate a real amplifier load. Light bulbs are purely resistive but an amplifier is not a pure resistive load per say. It will draw 3A if you bias it that way right from start.
I may be wrong on this so if anyone can verify this I'm all ears.

I guess I should have been more clear, I have about 90,000uf a rail.

transformer -> rectifier -> 30,000uf -> 30,000uf -> resistors -> 30,000uf -> amp board.
 
I guess I should have been more clear, I have about 90,000uf a rail.

transformer -> rectifier -> 30,000uf -> 30,000uf -> resistors -> 30,000uf -> amp board.

Actually that was directed to the OP.
If I read it correctly he's using 4 x 100,000uF caps with a rail voltage if about 47vdc. That's a lot of Joules of energy to charge up within the first few cycles. I would imagine the inrush would be in the order of a few hundred amps for the first few cycles that there is no way a fused soft start would clamp .
 
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I had a similar problem with my 1000VA trannies for my poweramps. I used HexFRED diodes and a CRC-filtering (2x23.500uf-0R11-117.500uF). First I used a standard tranny from a well known German company (it was noisy without any load), then from a Polnish specialist (it was dead quite until caps with 4A-load was connected), a British tranny behaved similar, and at least I had success with a custom made tranny from a small Germany company. But its core was much bigger then usual.
Tranny noise is a well know problem, not only for DIY-people, but also for amp-building companies.
For quietest results personally I will never use a big standard tranny any more.....

I have a 1000VA 24+24 transformer on my BA-3 amplifier with 176,000 uF and standard block rectifier bridges. Dead silent. I always use as large a VA as is practicable. Never had a problem with overkill in this department. This is a SUM-R transformer BTW. I have also used several Anteks and they have been silent as well. If power supply and circuit is properly wired, (big if) quality transformers are quiet I find, regardless of VA rating. (within reason)...If properly wired and noisy, usually transformer is poor quality which creates the problem....or something is wrong with wiring or circuit bogging it down.

Russellc
 
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I always oversize my trannies for poweramps with 4-5 times of output power, but if a tranny is noisy without any load this strategy cannot help.
I assume or my experience is that noise increases if you use huge capacitor values because of small current angle for loading them. Then load current peaks can become extremly high causing mechanical rattling from core and windings.
You can check this if you load a tranny first only with a resistor - it may be dead quiet; but if you load it via a rectifier and huge capacitor values you may be negatively surprised.
BTW: I have many years of experience building power amps, but if a simple change from a tranny cures a noise problem it is poofed where the problem was....
 
I am having this problem with my f5 amp. I replaced my 300va Antek transformer with a 600va Antek transformer, thinking there was something wrong with my transformer. I still have a physical hum from the transformer. I have tried some of the things on here but still have a hum. Anything not mentioned in this thread that hasn't been mentioned?
a stereo F5 has a total maximum output of 50W (25+25)
A ClassA amplifier needs a transformer from 6times to 10times it's maximum power.
So your 50W total needs a transformer from 300VA to 500VA . This should operate near cold.
If it is noisy, it is not because it is too small.
You should be looking at finding why it was noisy.
Poor quality, or saturation due to poor design, or saturation due to mains DC, or wired up incorrectly, or amp biased incorrectly.
Replacing it and still being noisy points to similar set of possible causes. It is not because it is too small.
 
I always oversize my trannies for poweramps with 4-5 times of output power, ..........
This is bad guidance.

For ClassAB use a transformer with a VA rating from one times to two times it's maximum total output power. Going to three times brings a small improvement in maximum power due to slightly less supply rail sag when at maximum power.

For ClassA use a transformer with a VA rating from six times to ten times the total maximum output power.
 
Actually that was directed to the OP.
If I read it correctly he's using 4 x 100,000uF caps with a rail voltage if about 47vdc. That's a lot of Joules of energy to charge up within the first few cycles. I would imagine the inrush would be in the order of a few hundred amps for the first few cycles that there is no way a fused soft start would clamp .
Indeed. There is no way a sensibly designed soft start will allow a close rated fuse to charge 0.4F of smoothing capacitance.

A soft start is a primary current limiter to allow the transformer to start without blowing the close rated mains fuse.

A slow charge circuit is to current limit the secondary current charging the smoothing capacitors.

These two current limiting systems operate very differently.
 
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This is bad guidance.

For ClassAB use a transformer with a VA rating from one times to two times it's maximum total output power. Going to three times brings a small improvement in maximum power due to slightly less supply rail sag when at maximum power.

For ClassA use a transformer with a VA rating from six times to ten times the total maximum output power.

..... interestingly that some well-known manufacturers seem to have a similar guidance. Of course they do this only to increase size, weight and costs of their amplifiers.....:D

You should accept that there are not only output power reasons but also sound reasons why oversized trannies are used.
 
Exactly with NAIM Audio I got my first listening experience in the eighties how sound can change with tranny size.

At this time NAIM had external power supplies named "SNAPS" and "HiCap" in their programm. Both were based around a LM317-voltage regulator, the SNAPS had 10mF, while the HiCap had 15mF as smoothing caps.

But biggest difference were their trannies: approx. 160VA in SNAPS, 500VA in HiCap. Both could be used only for their preamps which needed max. 30VA. And though my brain refused I had to accept a listening difference - the HiCap sounded way better.
 

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JZatopa - In my experience, about half of Antek hum. (that may be an exaggreation, but you get the idea.) There's not a lot that can be done, although making some neoprene washers seems to help a bit.

Also in my experience, the shielded Antek (AS-3218, etc...) are usually the ones that don't hum.
 
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