| Author | Message | ||
| remo
New Username: remo Post Number: 1 Registered: 3-2006 |
Hi.. my F-1X's transformer has quite a loud electric "humm" to it.. the preamp sounds wonderful and there is no static, hum or noise on the main outputs but when is switch the unit on the actual hum coming from the transformer resonates through the case of the unit and it's really quite loud. At gigs and in rehearsal this is no issue but when I use the preamp in my studio it's quite annoying.. I am in Australia (50Hz 24VAC) and I have correctly switched the internal jumpers to suit 240VAC. I'd like to know if any US F-1X owners have experienced this transformer hum coming from their units or are all other F-1X's dead (I mean DEAD) quiet and there is a problem with my transformer causing it to hum? cheers, Guy | ||
| davehouck
Moderator Username: davehouck Post Number: 3386 Registered: 5-2002 |
Hi Guy, welcome to the board. My F-1X is quiet. Sounds like you have a problem. I'm not an electronics person, so hopefully someone with some knowledge will notice this thread and respond. | ||
| davehouck
Moderator Username: davehouck Post Number: 3387 Registered: 5-2002 |
A couple questions that might be helpful. How long have you had the preamp? Has it always made this hum? Is the preamp in a rack with other components? If it's sitting by itself with no cables attached to the jacks, does it still make the hum when you switch it on? | ||
| remo
New Username: remo Post Number: 2 Registered: 3-2006 |
I have had the preamp for 3 months now.. I purchased it used from a guy in the USA. He said the unit was quiet when he had it. The preamp is racked with a Mackie 1400 power amp.. The preamp hums in or out of the rack. It also hums whe it is sitting by itself with only the IEC power cord attached (and with the unit switched on of course). I'm thinking I might need the new transformer board inside the unit.. I'm a photocopier technician by day so swapping this would be very easy for me. So no-one else has a mechanical hummmm from their transformer... Mine's quite loud as it resonates through the casing of the preamp.. I LOVE the sound of this unit and would really like to get this fixed.. I'd like to hear from some non-110VAC F-1X users in the UK or in Australia if possible to see if this is a 110VAC 60Hz vs. 240VAC 50Hz issue... | ||
| kmh364
Senior Member Username: kmh364 Post Number: 1763 Registered: 9-2003 |
Good on ya, mate! Just my two cents: You might wanna ck and make sure every nut/bolt is tight in the chassis, xfmr and case covers especially. You could also isolate the xfrmr from the chassis with bits of rubber. Just make sure the xfmr is electrically grounded to the chassis if you isolate it. You can run a pigtail (jumper) from the xfmr mounting bolts (at the flange to the nearest chassis bolt. Make sure the connection is free of powdercoat and is clean and tight (use a "star" lockwasher). If possible, "tin" the connections with solder. Keep the grounding jumper a short as possible as well. If none of that works, then I'd try replacing the xfmr next. Cheers, Kevin | ||
| remo
New Username: remo Post Number: 3 Registered: 3-2006 |
thanks Kevin, all your ideas are good and I have checked all nuts and screws are tight. The problem with isolating the xfmr with rubber is there is hardly any clearance above or below the unit. Above maybe 3mm and below it is hard up against the 4 threaded mounting lugs.. so rubber pads are out of thw question as I don't want to make any modifications to how the PCB mounts in the unit. I'm guessing a straight up replacement xfmr PCB would be the best bet.. the part number is 170-049. Is there a possibility I could either return my faulty xfmr PCB to Alembic for a replacement? I will pay shipping both ways. I have previously emailed Alembic about this but I recieved no reply. Can anyone help out? | ||
| davehouck
Moderator Username: davehouck Post Number: 3399 Registered: 5-2002 |
Guy; the folks at Alembic get a lot of email on top of all the other things they have to do, like build instruments, so it does happen that some messages get overlooked. Try them again; or give them a call. | ||
| kmh364
Senior Member Username: kmh364 Post Number: 1766 Registered: 9-2003 |
Guy: No worries, Mate! Looks like you're on the right track. Have a little patience and Mica and Co. will take care of you. Cheers, Kevin BTW, I spent two months in Oz back in '03. I have a bunch of friends in the Melbourne area as well as the gold and sunshine coasts (i.e., Surfer's/Main Beach and Brisbane areas). My biker/bike shop owner Mate from Brisbane is coming over this summer for the Sturgis Rally and to buy bikes (H-D's and custom choppers). Another biker /truck repair shop owner Mate from Melbourne was supposed to join us, but he spent all his vacation/bike money on a '69 SS Chevy Camaro, LOL! | ||
| mica
Moderator Username: mica Post Number: 3120 Registered: 6-2000 |
You can order replacement parts from us, but let's first determine what is the source of the problem you are observing. The laminations are varnished in the transformer, shouldn't really hear anything from the transformer itself. Take the lid off (mind the high voltage!). Can you still hear the noise? With the lid on, if you hold your hand on top of the lid, is the vibration noise reduced enough to be satisfactory? If that's the case, then you could put some rubber-like material between the transformer winding and the lid to damp the vibration like you hand does. | ||
| remo
New Username: remo Post Number: 4 Registered: 3-2006 |
Hi Mica, I have listened to the noise with the lid off the unit and the hum is %100 coming from the transformer. I can slightly reduce the noise by pressing firmly on the lid of the unit I will try some rubber-like material as you suggested tonight and let you know the result. btw what is the estimated cost of a new transformer pcb? I realise there is no direct warranty on mine as it was purchased used but the unit it in fantastic physical condition and looks hardly used (no rack rash, the contacts in the input jacks look hardly marked, all pots are firm and turn "as new" etc..) Would Alembic consider replacing the transformer under an "non user specific good faith warranty" arrangement? I would be happy to pay shipping both ways (I will send you my noisy one for inspection). Otherwise could you please let me know what cost I would be looking at for a new 170-049 transformer PCB assembly? | ||
| mica
Moderator Username: mica Post Number: 3121 Registered: 6-2000 |
We can take you at your word about the testing and the results you've found - we've not heard of a transformer having this problem before in one of our preamps. I can send you the transformer for you to replace yourself under warranty. Click on my username and send an email to me with your mailing address. If you prefer to have us service it, you can send the board to us and we can solder the transformer. | ||
| remo
New Username: remo Post Number: 5 Registered: 3-2006 |
thank you very much Mica, I have just emailed you. | ||
| bassdr
Junior Username: bassdr Post Number: 48 Registered: 10-2004 |
This is another example of why we LOVE the folks at Alembic and the incredible instruments they hand craft! Michael (Flame Koa Essence) | ||
| remo
New Username: remo Post Number: 6 Registered: 3-2006 |
yes.. top shelf service.. thanks again!!! | ||
| byoung
Advanced Member Username: byoung Post Number: 227 Registered: 12-2004 |
Guy, Hey I'm in Melbourne at the moment. Nice town. Brad | ||
| remo
New Username: remo Post Number: 7 Registered: 3-2006 |
*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
Junior Username: peter_jonas Post Number: 40 Registered: 11-2002 |
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
New Username: remo Post Number: 8 Registered: 3-2006 |
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
Junior Username: peter_jonas Post Number: 41 Registered: 11-2002 |
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
New Username: remo Post Number: 9 Registered: 3-2006 |
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
Junior Username: peter_jonas Post Number: 42 Registered: 11-2002 |
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
New Username: remo Post Number: 10 Registered: 3-2006 |
if you want any more readings or photos please let me know... thanks again. | ||
| peter_jonas
Junior Username: peter_jonas Post Number: 43 Registered: 11-2002 |
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
Junior Username: remo Post Number: 11 Registered: 3-2006 |
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
Junior Username: peter_jonas Post Number: 44 Registered: 11-2002 |
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
Senior Member Username: adriaan Post Number: 816 Registered: 6-2002 |
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. | ||
| davehouck
Moderator Username: davehouck Post Number: 3542 Registered: 5-2002 |
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
Senior Member Username: adriaan Post Number: 817 Registered: 6-2002 |
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
Junior Username: remo Post Number: 12 Registered: 3-2006 |
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
Junior Username: peter_jonas Post Number: 45 Registered: 11-2002 |
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 | ||
| dfung60
Intermediate Member Username: dfung60 Post Number: 150 Registered: 5-2002 |
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
Junior Username: peter_jonas Post Number: 48 Registered: 11-2002 |
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
Senior Member Username: adriaan Post Number: 822 Registered: 6-2002 |
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
Advanced Member Username: keith_h Post Number: 374 Registered: 2-2005 |
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
Senior Member Username: adriaan Post Number: 823 Registered: 6-2002 |
Keith, Thanks for clearing this up - sorry if I've been adding to the confusion. (Me?) | ||
| peter_jonas
Junior Username: peter_jonas Post Number: 49 Registered: 11-2002 |
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
Intermediate Member Username: dfung60 Post Number: 153 Registered: 5-2002 |
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
Member Username: bassdr Post Number: 77 Registered: 10-2004 |
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
Junior Username: remo Post Number: 13 Registered: 3-2006 |
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
Intermediate Member Username: dfung60 Post Number: 154 Registered: 5-2002 |
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
Junior Username: remo Post Number: 14 Registered: 3-2006 |
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
Senior Member Username: bob Post Number: 614 Registered: 11-2002 |
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
Intermediate Member Username: dfung60 Post Number: 155 Registered: 5-2002 |
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 | ||
| davehouck
Moderator Username: davehouck Post Number: 3590 Registered: 5-2002 |
I'm thinking a nice Coco Bolo wood dowel wood work. Or a Spalted Maple wood dowel with Walnut laminates. | ||
| bob
Senior Member Username: bob Post Number: 618 Registered: 11-2002 |
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... | ||
| davehouck
Moderator Username: davehouck Post Number: 3598 Registered: 5-2002 |
Hah!!! Yes that wood would have had to have slipped by now wouldn't it! Given the past and present discussions of wood types and their propensity for absorbing and not absorbing different frequencies, there may actually be a preferred wood for this particular application. But that may be taking things a bit too far. | ||
| remo
Junior Username: remo Post Number: 15 Registered: 3-2006 |
a question, does the F-1X FX loop run pre or post the onboard EQ?? | ||
| davehouck
Moderator Username: davehouck Post Number: 4121 Registered: 5-2002 |
In a prior thread, David Fung stated that "in the F-1X, the effects loop is before the tone controls". | ||
| dfung60
Intermediate Member Username: dfung60 Post Number: 191 Registered: 5-2002 |
On the F-1X web page description, the circuit topology is described pretty directly. There's an input buffering stage, then the effects loop, then the EQ, then the full-range out and active crossover. The direct out is switch-selectable to be pre- or post-EQ. | ||
| davehouck
Moderator Username: davehouck Post Number: 4132 Registered: 5-2002 |
David; before posting, I read that page. But I wasn't convinced that I really understood what I was reading. So I quoted you instead! I have found that you have a much higher grasp of things electronic than I ever will. |
