Transformer Hum?! STOP IT!

Rarkov · 2003-01-06 8:39 am

Hi,
A while ago I completed my "Optimos" amps. The PSU in them are:

500VA
Single BR
4x6800uF (2 per rail)
+-68.1V

If you want any more details about the setup, just ask...

The problem is that the amps hum...Not through the speakers, but if I'm sat next to them, they make an irregular pulsing humming noise.

I haven't got snubbing caps on the BR or HF caps after the large ones, but I didn't thing they would cause these problems. It is a torodial xformer. The only other thing is that I don't have the Earth wired in...All grounds are wired to a HQG point...

Thanks in advance for any help!

Gaz

peranders · 2003-01-06 8:52 am

If you get uneven and unregular hum from the transformer itself you probely have DC on the mains. Maybe you shuold get a DC trap?

Two anti parallel diodes 5 A plus a capacitors 2200-10000 µF across them. Put this gadget in series with one of the primary wires.

If people uses hairdryers with halfwave rectification DC is created OUT from the hairdryer. (is it dryer or drier BTW)

Rarkov · 2003-01-06 9:04 am

Hi,
Thanks for your reply Peranders...

I think your first spelling was right, but don't quote me on it!

English never was my strong point! :xeye:

I have never heard of a DC trap, is that basically a cap inline with the mains? I was thinking I should do this anyway...

If it is just a cap, what type should I use?
1uF 450V?

Thanks,
Gaz

peranders · 2003-01-06 10:09 am

Rarkov said:
If it is just a cap, what type should I use?
1uF 450V?

No! A couple of thousands of µF and low voltage (is enough) but you must protect the caps with diodes. The diodes must withstand the inrush currents of the transformer.

AND!!! In SERIES with one of the primary wires.

Cobra2 · 2003-01-06 10:41 am

DC - block / filter

Something like this? (Pic).

Arne K

rwagter · 2003-01-06 11:21 am

Arne,

Isnt there a small mistake in your picture. It says that C1 and C2 must be AC rated but IMHO that must be C2 and C3

Ralph

Rarkov · 2003-01-06 11:28 am

Wow!
I don't have that much room in my Monoblocks' Chassis!
The other thing is that I am (maybe wrongly) skeptical about feeding a 35V (assuming >16V anyway) capactior with 240V from the UK mains...

Am I missing somthing? Thanks,

Also, can I simplify that as much as possible to take up as little room as possible?

Gaz

Freddie · 2003-01-06 11:49 am

I have built built the circuit posted above. It works good, no hum from the transformer anymore.

/Freddie

mrfeedback · 2003-01-06 12:16 pm

"I have built built the circuit posted above. It works good, no hum from the transformer anymore."

Hi Freddie, any change in sonics of the system ?. (apart from no transformer buzz)

Eric.

1/137 · 2003-01-06 12:34 pm

Different Hum Problem

I have two large monobloc tube amps...the power supply transformer on one of them is emitting a 60 Hz hum..real annoying at low levels..any suggestions. I don't think it's dc on the mains because..as I said...only one amp does it.

thanx
rt

Freddie · 2003-01-06 2:04 pm

Hi Freddie, any change in sonics of the system ?. (apart from no transformer buzz)

Well, I really can't tell the difference cause I haven't tested my "new" amplifier without the the circuit. I built and installed it at the same time as my new amp cause I've had problems with toroids buzzing in my other amplifiers before.

/Freddie

mrfeedback · 2003-01-06 2:30 pm

"The problem is that the amps hum...Not through the speakers, but if I'm sat next to them, they make an irregular pulsing humming noise."

Because they haven't learnt the words yet.

Eric.

bossman2 · 2003-01-06 2:33 pm

Hi all.Cobra2 what do the anti parallel diodes do ? .The hum with the transformer is it transfered to the chassis maybe insulating the transformer with rubber pads etc might cut the noise.

Michael

Jeff R · 2003-01-06 2:39 pm

rwagter said:
Arne,

Isnt there a small mistake in your picture. It says that C1 and C2 must be AC rated but IMHO that must be C2 and C3

Ralph

C2 and C3 see the full AC voltage but due to their impedance the current though them will be very small. I think these could be a standard film or ceramic capacitor.

I don't totally understand C1 and C2. With anti-paralled diodes, there should never be more than about a volt across either capacitor. I presume the high capacitance value is to smooth out the discontinuities in the didoe's conduction and provide a low impedance path during the diode off time. Seems to me a lower voltage capacitor could be used, but for safety's sake, 16 volt and with a ripple current of an ampere or so (depending upon actual AC current), would not be a bad idea.

Would not using Schottky didoes help?

Rarkov · 2003-01-06 2:40 pm

Hi,
Yes, the buzz does seem to be transferring to the chassis. It is isolated using the rubber mat provided. This mat is the diameter of the xformer and about 1mm thick (from recolection)

Could it be transferred through the bolt holding it in place?

Thanks,
Gaz

dhaen · 2003-01-06 2:43 pm

Would not using Schottky didoes help?

No.
We want reasonable voltage drop to accomodate the DC.
The caps pass the AC.

saurus · 2003-01-06 3:40 pm

Me too

I also have a buzz from my Plitron 400VA toroidal, but my hum is very regular and even. It isn't always present, but it doesn't seem to correspond to turn-on, or warm-up, or anything else I can recognize. Seems to fade in and fade out over hours. Do you think this is also a DC-in-the-mains problem? I have a 100 R/100 nF across the mains before the transformer. I can live with it, if it isn't damaging the transformer (?). Thanks for the help!

- Phil

Rarkov · 2003-01-06 4:00 pm

Sounds like mine, except the humming on mine pulses. It is these pulses that are irregular. They can also last anywhere from 3 to 5 seconds from min humming - max humming - min humming. This could happen twice in a row, or it could go 30 secs before another. It sounds "powerful" and dangerous...That's the only way I can descibe it...When it "winds up" (from min-max humming) it feels like it is going to keep going until it blows up - yet the chassis is safe (at least I don't die if I touch it!

) and the sound dissappears.

I hope I haven't confuse people more! If I have, just go on my original post...or ask and I'll try to explain it again...
Gaz

Philo · 2003-01-06 4:16 pm

The sound dies when you touch the chassis? Could be that your xformer just happen to hit a resonance in the chassis which varies in tone as temps and AC mains change. I know you rubber mounted the xformer. Try hard mounting it, then dampen the chassis and add some blue tack or lead tape (golf shops have it) to the stack of the xformer. Just use temporary stuff, until you isolate the problem.

mlloyd1 · 2003-01-06 4:24 pm

I submitted the picture initially.
The big electrolytics need to be able to handle the ripple current. Those are the C1 and C4 caps. The note at the top of the figure is an error. The note for C2 and C3 is correct.

Thanks,
mlloyd1

PS - in the original discussion, a few people tried this and said it successfully solved the problem for them.

rwagter said:
Arne,

Isnt there a small mistake in your picture. It says that C1 and C2 must be AC rated but IMHO that must be C2 and C3

Ralph

Transformer Hum?! STOP IT!

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