Author Topic: Mechanical noise from F-1X transformer (delamination rattle). (Read 1042 times)

remo · « **Reply #15 on:** March 22, 2006, 05:02:19 PM »

*update*.. I recieved the transformer from Mica yesterday (I was suprised to see just the transformer as i was expecting the entire power supply PCB). I replaced my transformer with this brand new one. Placed the lid back on and it's still humming!?! Well we can obviously rule out the transformer component now. Is it possible that one of the big caps on this PS board are not great? Is is possible some other component on the PS board is causing the xformer to hum like this?

Australia runs at 240VAC.. I was wondering if I should try running the F-1X at the 220VAC setting to see if it helps or changes the hum. I also own a Demeter preamp and that is running happy at 220VAC (110-220 switchable) (I just had to change the fuse for Australia).

any other ideas?

peter_jonas · « **Reply #16 on:** March 24, 2006, 02:42:07 AM »

Hi Guy,

I am in Sydney and have two of these F-1X preamps. The transformers should be very quite. Please check if your jumper settings are as per the photo. (Both my preamps have factory jumpers settings for 220-240 volt operation.) If not, reset them as shown and check again.

If you have a bit of electrical experience, you may try to see if the transformer buzzes without the rest of the circuitry. The secondary side has both high tension and +/- 17 volt windings and the supply board has two separate supplies, one of which may be overloaded. You could remove the connector that runs to the main PCB and see if the buzzing is still there. If yes, then the problem is on the power supply board, if not, it is either on the main PCB or on the secondary PCB which contains the cross over circuitry. Then you could try to remove the connector from the secondary PCB which also carries +/- 15 volts.

Please be extremely careful with both the mains voltages and high tension lines!!!!

Let us know what you've found.

Regards

Peter Jonas

remo · « **Reply #17 on:** March 24, 2006, 09:31:01 PM »

Hi Peter, thanks for your response. I have set the jumpers for 240VAC as shown on the Alembic setup page:

http://www.alembic.com/support/SVC_F1X_voltage.html

And they do match your settings.

The xfmr is still buzzing with the connector to the main board removed. I put my multimeter (set to 200VAC) on the xfmr outputs and the mainboard connector. I'm not an electronics wizz but here are the results fyi. I'm guessing there is a faulty or leaking component on the PS PCB if you are telling me your 240VAC configed F-1X is silent.

peter_jonas · « **Reply #18 on:** March 24, 2006, 11:33:09 PM »

Hi Guy,

The jumpers do appear to be OK, but some of the voltages seem a bit odd.

Let's start with the brown looking connector in the forground. These are all DC voltages. Let's call the pin on the left Pin 1 and the pin on the right Pin 4. Set your meter to at least 400 volts DC.

Pin 4 is the LETHAL one, that should read about 360 volts to ground unloaded (without the connector attached).

Note that with the brown connector removed the power supply board is no longer connectoed to earth (it becomes floating), so you cannot measure these voltages to the chassis. Pin 2 is ground so that's the common probe for your meter. Do have steady hands, and be careful.

So once more the voltages on the brown connector:

Pin 2 - 4: 360 VDC
Pin 2 - 1: -15 VDC
Pin 2 - 3: 15 VDC

So check these first.

Then the transformer. These are AC voltages, so set your meter to 400 VAC minimum.

There are 6 exposed terminals coming out of the secondary winding of the transformer. Once again let's cal the pin on the left Pin 1 and the pin on the right Pin 6. The others 2, 3, 4 and 5 in ascending order from left to right.

Pins 1,2 and 3 are the low voltage windings. You should get readings as follows:

Pin 1 - 2: 19 VAC
Pin 2 - 3: 19 VAC
Pin 1 - 3: 38 VAC

Pins 4, 5 and 6 are the high tension windings, apply extra care here.

Pin 4 - 5 130 VAC
Pin 4 - 6 130 VAC
Pin 5 - 6 260 VAC

I suspect your high tension line may be overloaded or shorted. So please let me know if you do get irregular readings. Plus / minus 5% is still OK.

Cheers,

Peter Jonas

remo · « **Reply #19 on:** March 25, 2006, 01:15:59 AM »

Hi Peter thanks heaps for helping me out on this one. Here are my readings:

Brown connector:

Pin 2 - 4: 358VDC
Pin 2 - 1: -15 VDC
Pin 2 - 3: 15 VDC

Transformer Pins:

Pin 1 - 2: 20.9 VAC
Pin 2 - 3: 21 VAC
Pin 1 - 3: 41.8 VAC

Pin 4 - 5 149 VAC
Pin 4 - 6 144.2 VAC
Pin 5 - 6 265 VAC

I found I had to try the transformer readings a few times to get these results, sometimes for instance pin 4 -5 would just show 7.9 VAC then if I take the multimeter leads off it and put them back on it would jump back up to 20.9, this was the same for all the pins I checked? I checked them all 3 times in a row each and on about the third check they gave me the readings above which I took to be correct because they were in the vicinity of your readings..

How are we looking on these readings?

?again, thanks heaps for helping me out on this mate!

peter_jonas · « **Reply #20 on:** March 25, 2006, 01:40:56 AM »

What a bummer ...

They all look pretty good (unfortunately).

Let me think about a plan of attack here, I'll be back shortly.

Cheers,

Peter Jonas

remo · « **Reply #21 on:** March 25, 2006, 02:50:39 AM »

if you want any more readings or photos please let me know... thanks again.

peter_jonas · « **Reply #22 on:** March 25, 2006, 03:45:34 AM »

So, if you take the lid off, does it still buzz just as loud?

Now, if you undo the 4 screws that hold the power supply PCB to the chassis, and lift the PCB slightly (do this very carefully), does it still do it?

I would also like to know just how loud this buzz really is?

When I played around with my unit this evening I noticed that after a while I could hear SOME buzz, but I had to turn the sound of the TV completely off (and ask the kids to stop discussing Dawn French tonight on Parkinson), then I could hear it from about a half a meter away.

Then, if I held the back edge of the lid down, pushig it slightly against the rest of the chassis, it nearly completely disappeared. Also, if I take the lid off, it nearly totally quiet.

Let us know what you find.

It is possible that there is nothing wrong electrically with your unit.

Cheers,

Peter Jonas

remo · « **Reply #23 on:** March 25, 2006, 04:50:56 AM »

you're on to something here Peter, when I take the lid off the buzz is without a doubt quieter than when the lid is on (with cap screws tight). I also noticed when I push the lid down onto the chassis the buzz almost all but disappears. I think the buzz from the xfmr is resonating through the chassis and the lid. It is this resonance I can hear. I can hear it with ease at about 3 meters away in a dead quiet room. The freq. of the buzz is different lid on and lid off.

This is my issue as I find this level of buzz unacceptable for tracking in a studio control room.

I recorded both the close up xfmr buzz and the buzz when the lid is on (resonance) for you to compare to your noise.

please find the mp3 files in here:

http://www.nixonaudio.com/buzz

recorded through Rode NT1 -> Amek CIB channel strip directly into logic.

Is it possible the xfmr is magnetically transmitting it's internal buzz to the metal chassis? the xfm and the chassis do not physically contact each other... the PS PCB is only attached to the bottom of the chassis via the 4 lugs.

thoughts?

peter_jonas · « **Reply #24 on:** March 26, 2006, 02:05:54 AM »

Hi Guy,

Nice recordings on some nice gear.

That is some pretty serious buzzing, it should not be like that at all. I don't think it is a magnetic transmission of the buzz, rather the lid just acts as an accoustic amplifier of the buzz generated by the transformer. The lid is actually unsupported and free to resonate along the back edge of the chassis.

I am pretty much stumped here without actually looking at and feeling the power supply PCB.

One option is certainly to ask Alembic for a quote on a new PCB assembly on an exchange basis. The other is to keep experimenting with the unit until to cause of the buzz is identified and eliminated.

The latter may be cheaper, but it may take much longer.

Cheers,

Peter Jonas

adriaan · « **Reply #25 on:** March 26, 2006, 02:37:05 AM »

The lid buzz is a G, so it's a harmonic of 50 Hz, related to your AC. The other one is picking up a nasty buzz from a(nother) transformer at close range.

David Houck · « **Reply #26 on:** March 26, 2006, 06:31:32 AM »

Adriaan;

#1 - So what does this infer? Is it a grounding problem?

#2 - Do you mean a transformer in some other piece of nearby equipment such as a tv?

adriaan · « **Reply #27 on:** March 26, 2006, 07:15:56 AM »

Dave,

#1 is something physical resonating, most probably a part of the tranformer itself. I remember my dad, who is an old hand at electronics, usually blames this type of stuff on the 'tin package' of a transformer (blikpakket in Dutch). If you press down on the whole structure in specific places, the resonance is probably dampened.

#2 - correct. But I guess this is with the lid off, so there isn't much in the way of shielding.
But it might as well be a leaky capacitor or the likes.

remo · « **Reply #28 on:** March 26, 2006, 03:36:56 PM »

hi Peter, I'd be happy to send up my PS PCB for your inspection if you are interested in doing so. Please drop me your postal address at kashmir@bigpond.net.au and I'll get it in the mail to you.

peter_jonas · « **Reply #29 on:** March 26, 2006, 04:27:55 PM »

Hi Guy,

I have sent you an email with my postal address. As mentioned therein, I am happy to have a look, but I cannot promise that I can fix it. I will try anyway.

Cheers,

Peter Jonas