Mechanical noise from F-1X transformer (delamination rattle).

[dfung60]

Remo -  
 
I have a couple of thoughts and things to try here as well.  
 
1) Try plugging the preamp in somewhere else and see if you're getting the same noise.  Try someplace really different - take it to your office, etc.
 
2) If you pull the transformer from the PCB and connect it to the mains with no load, see if you still hear vibration.  You can probably do this with your original transformer since both were showing the problem.  You mentioned that you work on copiers and are comfortable doing this level of test - obviously it's lethal if you don't know what you're doing!.  
 
3) Make sure that the transformer is firmly affixed to the PCB with silicone/RTV or hot glue.
 
4) See if there's a lot number of the transformers.  It seems very unlikely that your transformer will be from the same production lot, but that might be an issue as well.
 
A physical vibration problem like this in the transformer is sort of the opposite of a microphonic pickup.  The windings or armature structure are physically able to move and are doing so at the line frequency (plus you're having the resonance problem from the case that you already identified).  
 
This shouldn't happen under normal circumstances, but I think the chances are much higher if your preamp happens to be in a magnetic or electrical field which is enhancing the intereference.  It's also possible that there's something producing noise on the AC supply that is triggering this problem.  
 
Moving the preamp out of your studio will get you away from any fields that you are not aware of.  Powering the transformer outside the circuit will also show whether the problem is because of the line power or if it's actually a function of that particular transformer.
 
I would be on the lookout for any powerful magnetic fields in the vicinity of the preamp including other power supplies, speakers, monitors, or motors.  You should also look for any devices that might introduce noise into the powerline - motors, dimmers, etc.  A steel case will shield normal ambient electronic noise, but won't stop really strong magnetic or electrical fields.  
 
If proximity fields are the problem then it may be very difficult to address short of moving your equipment location to someplace that doesn't have interference.  Holding everything firmly to the PCB may reduce the vibration to an acceptable level.  
 
Good luck,
David Fung

[peter_jonas]

Hi Guy,
 
Yes, I can hear the buzz, I have not fixed it yet, but I am still testing, and there is hope.  
 
Details below:
 
I have now received your power supply PCB with the replacement transformer installed as well as the original transformer.
 
As interesting as it is unlikely, both transformers appear to come from the same production batch (dated 9850).
 
My other observations:
 
The PCB powered up on its own is very quiet, cannot tell it apart from the PCB I have in my unit.
 
The original transformer on its own is also very quiet.
 
All voltages check out fine on the supply.
 
I could not fault your soldering of the transformer, but I desoldered it all the same and resoldered while it was firmly clamped to the board.
 
Jumpers are all set correctly, all other solder joints and tracks appear to be fine. I cannot find electrical fault. I have to say the original transformer appeared also OK.
 
So I installed your supply in my F-1X, and while the unit was open it was fine. I could hear it from close up, but it was OK. However, when I put the lid on I could hear some reasonably loud buzz. Certainly louder than my unit with its own supply, but perhaps not as loud as I expected from your recordings.
 
I then experimented and tried a few things. David (in his above post) has had some worthwhile suggestions, and I have checked all those. I don't think the buzz is externally generated or induced. It also does not seem to matter where the unit is plugged in.
 
Some time ago, trying to get rid of an extremely stubborn hum coming through my speakers, in a last ditch desperate effort I fabricated an L shaped shield made out of mild steel plate, and fixed it to the side of the power supply PCB right next to the transformer. (see photo below).
 
It did not eliminate the hum at the time, but I have had it in the preamp ever since. So, tonight one of the things I tried was to see if that shield had an effect on the buzz.
 
Well, believe it or not it did! When I installed the shield, replaced the lid and tightened the screws the unit was not any louder than mine. I could still hear it from about half a meter (20 inches) away, but I thought it was OK.
 
I do not know if its effect was a result of magnetic shielding or accoustic dampening.
 
Unfortunately, this afternoon I left my SPL meter at work, so I cannot quote you dB figures to compare, but I think the buzz was no louder than mine. It is your power supply PCB in my F-1X on the photo.
 

 
Well then. As far as electrical functionality and mechanical integrity is concerned I cannot fault the transformers. However, as they both appear to come from the same production batch I cannot entirely eliminate the possibility that they are the source of the buzz.
 
One thing I have not done is to desloder my transformer from my PCB and install it in your PCB, then try it in my unit. I am going to do that in order to help either confirm or eliminate the transformer's guilt.
 
However, I have run out of time tonight and probably won't be able to do too much until Sunday night. My apologies for the delay, but I'll keep you posted.
 
Cheers,
 
Peter Jonas

[adriaan]

Uh, isn't is more likely that the L shaped shield is actually resonating, causing the mechanical buzz?
 
You might have mentioned earlier that this was a modded F1-X ...

[keith_h]

Adriann,
I do not believe the Guy's F1-X is modded. He sent his power supply to Peter for testing. Peter does have a modded F1-X but appears to be able to reproduce Guy's problem.  
 
Keith

[adriaan]

Keith,
 
Thanks for clearing this up - sorry if I've been adding to the confusion. (Me?)

[peter_jonas]

Hi Guy,
 
I have finally had a chance to swap the transformers on the PCPs and do some testing.
 
The conclusion is that my transformer in your PCB produces less hum, then your transformer in your PCB.
 
My transformer was made in week 18 of 1999 (9918) and therefore it is slightly newer than yours, which is a 9850. The age is propbably insignificant here, rather, coming from a different batch is what accounts for the slightly different performance.  
 
When I have my shield in there the difference is negligable, but with a standard setup the difference is audible and measurable.
 
In the end I decided the leave my transformer in your PCB, return the Power Supply board to you to test it in your chassis, and see if it makes any difference.
 
If it is better than what it was with your transformer, I am happy for you to keep it.
 
The unit still sings a little, and you may or may not find it acceptable. I have certainly never found it a problem. It still does not bother me, but now that I am aware of it, I can hear it. Here is what I have been able to come up with to make it DEAD quiet:
 
1) Place a sizeable and thick newspaper on the table or whatever you have the preamp resting on. (I used the Sydney Morning Herald, but I am sure the Melbourne Age, New York Times, L.A. Daily or the blessed Frankfurter Allgemeine Zeitung will all be just as good for this purpose.) Now turn the preamp upside down so that the lid rests on the newspaper. I could not hear a thing.
 
2) If for whatever reason you don't like your amp being upside down, find a nice, heavy, soft cover book, and place it on top of the chassis lid. I used a handy leftover from the dynosaur ages the Reference Manual for Visual dBase V. It's about 2 inches (50 mm) thick, and it worked very effectively, but I am sure you could find something equally worthy.
 
Seriously, the lid seems to act as an acoustic amplifier, and dampening is vibration will all but eliminate the buzz. However, I do hope that with this different transformer installed, there will be no need for such drastic measures.
 
Enjoy your F-1X.
 
Cheers,
 
Peter Jonas
 
 
PS. I am also returning your old transformer. It is electrically perfect, although it seems to generate the same amount of buzz as the new one Alembic sent you. However, in my opinion, it could not be called as defective.

[dfung60]

Great sleuthing Peter.  It's sounds like this is an inherent issue with the transformers which becomes audible because of case vibration.  If so, then it might be worth diassembling the case pieces and adding some vibration damping material between the various parts.  Ideally, you'd use something like Sorbothane/polyurethane vibration damping sheet.  You put a very thin piece of it in there (maybe 1/10) and it's compressed when you assemble the case back up.  Just a narrow strip at the joint is all that's required.  
 
If you can't find this fairly dense stuff (this is something you're more likely to find at an electronics supply house than a hardware store), then I suspect any kind of compressible weatherstripping type material will work, as long as it's not so think that you can't close the case.
 
You could also shoot a bead of silicone sealant along the edges, although you'd have to replace it if you pulled the top in the future.
 
I seen these sorts of problems with things like computer cases in the past, where the vibrating thing isn't that annoying on it's own, but happens to stir up a resonance in the case which is loud.
 
Good luck,
 
David Fung

[bassdr]

I would suggest trying some of the dampening material used in car audio installations. It's used in the doors and other places to quiet things down. You can order some on line from Parts Express in Dayton, Ohio. (www.partsexpress.com). They have alot of pro, home and car audio stuff. Also have good prices on Eminence speakers. Michael

[remo]

thanks for all your work on this everyone..  I will look into this dampening material and running a bead of something around the top of the chassis although the F-1X lid already sits flush when the cap screws are in.  I will see how Peter's transformer goes first... I will post any updates...   thanks again guys!

[dfung60]

Remo -  
 
Alembic uses a really high quality metal case on everything thing they build, so your flush lid should continue to be flush after you add some damping material.  Even though it's a precise case, there's still going to be some play between pieces, so putting the deadening material is basically putting a little resistance between the pieces so the entire edges is under compression when you screw the case shut.  So, you want something sort of soft and compressible (as opposed to firm).  You won't want to make it impossible to close the case down fully though.
 
I have a little sheet of 1/4 hemispherical black rubber feet, the kind you buy at a hardware or electronics store to put on the bottom of a vase to keep it from scratching your dining room table.  The feet are molded in a sheet and die cut.  The feet are bigger than what you'd want to use here, but the backing sheet material is the right material, pretty thin, and cheap.  You might see if you can find something like this.  You don't want to spend $40 on an audiophile dampening sheet!
 
One other thing I forgot the first time.  You probably want to put a drop of blue Locktite (low-strength liquid threadlocker) on all the case screws when you put things back together.  What this does is chemically lock the screws in place, but in such a way that simple hand screwdriver force will remove the screws in the future.  With the additional tension on the case, it may increase the chances of a case screw vibrating loose.  Whatever you do, *DON'T* use high strength threadlocker (red Locktite) which will make a permanent seal that you can't break loose.  They've fixed it now, but for many years in the US, blue Locktite came in a red tube, which probably caused endless confusion and frustration to weekend auto mechanics.  When you have an application for blue Locktite you don't even want the thought of red passing through your brain for fear that you grab the wrong tube (I don't know if they put red Locktite in blue tubes just to bait the unwary).
 
David Fung

[remo]

thanks David.  Are you suggesting I should stick the audiophile acoustic dampening material on the entire underside of the cover?  So it forms a roof over the entire contense of the unit?

[bob]

I shouldn't speak for David, but I think he is suggesting you not use the fancy/expensive stuff to coat the entire inside top of the case.
 
It seems to me there are two likely sources of case resonance, and ways of dealing with them. The most likely, I think, is that you get little vibrations along the edges, where the top meets the sides -  particularly along the back top edge. This might be dealt with fairly simply, with a few small pieces of some material.
 
Another possibility is that the entire top of the case is resonating. Here again, you might deal with this by filling the gap along the top back edge. Alternatively, a piece of the audiophile damping material attached to the inside of the top would also probably add enough mass to inhibit the resonance.
 
I would suggest a simple experiment. First, try using your thumb or one finger, to press down firmly on the top back edge, in the center. If that's enough to make the difference, then just insert some thin, slightly squishy, material in the gap (even a small stick-on piece of felt pad might work).
 
If not, try gently resting the palm of your hand on the top of the unit - not enough to really press down, but enough to dampen it slightly. If this is more effective, then applying a dampening sheet to the inside might be the better approach.
 
Basically, you just need to figure out where it is vibrating, and do whatever is simplest to stop it. My guess is that the top back edge is most likely the culprit, but it might be somewhere else.
-Bob

[dfung60]

Remo -  
 
No, dampening the entire top of the cover isn't necessary.  It's just as Bob followed up - you want to make sure that all the parts of the case fit together tightly along the entire area of contact.  So just a few little pieces of material along the mating faces will do the trick.
 
In Peter's earlier test of your unit, he found that he could quiet the noise by putting some weight on top of the unit.  This indicates that your noise is probably due to looseness around the mating surfaces which then resonates through the metal of the case.  If you can suppress the vibration between the parts of the case, then the sound will hopefully go away.
 
If you try Bob's test and find that heavily dampening the top supresses the noise, then your best chance of getting rid of the problem will be to see if you can find a spot inside the case where you have clear access from the top sheet metal to the bottom.  Drill a hole in one side (I guess the bottom would be better) and screw a small wood dowel in there so it stands up and touches the top.  You want to adjust the length of the dowel until it puts a little upward pressure on the top when the top is screwed down.  Again, this makes the case act as one piece and will shift the resonant frequency.  The closer you can get to the middle of the case, the better, but it's not that critical.
 
David Fung

[David Houck]

I'm thinking a nice Coco Bolo wood dowel wood work.  Or a Spalted Maple wood dowel with Walnut laminates.

[bob]

Wood would work :-)
 
Actually, myrtle might be an interesting choice. Believe it or not, I happen to have little blocks of this stuff under my hi fi components...