B&K Ex442 amp question

[rompstar]

I have the classic B&K Ex442 amp (not the Sonata), I love this thing, sounds very good and smooth / I never owned a tube amp, so I can't compare, but people say it sounds tube like / I just replaced the original Caps (that made a big sound difference) in quality, richness, sound stage, it wasn't small - ya the Caps were old, still working but old.. then because I upgraded the caps from 17,000uf to 22,000uf per cap each / I also upgraded the old rectifier bridges, better, newer with higher voltage rating...

So that brings me to the last thing.....

the transformer hums / it goes in and out, will hum for a while and then stop and not hum, I havn't measured it or anything to see if the pattern is random or exactly the same..

Now here is the Question, should I spend $120 on a DC voltage blocker device (maybe this is it), or just spend $100 on a new transformer ?

also - if new transformer, which do you recommend ? / I don't mind spending the money to restore this to it former glory, because I got the amp with a bunch of other stuff for only $75

I mean, did this hum when they were new ? none of my other amps hum, just this one, thanks!

I also own the 125.2 and the 125.2 S2 with a matching Pre-Amp on the S2 / these are also great amps, no hum there...

 

[onanysunday]

I have increased power filter capacitance more than 5,000uF without changing anything else in the power stage w/o issue. I wonder what would happen if you put the old rectifier bridges back in if it would stop humming? It should stop the hum since increasing power filter capacitance by itself has never caused a new hum to start (or any other issue) when there wasn't one before (for me at least). I don't think it would blow up, so it's worth a try.

 

[rompstar]

it hummed with the old (capacitors) then new capacitors (old bridges), and now with the new bridges it hums too.. so thinking the transformer needs to be replaced ?

 

[onanysunday]

Oh, well that's something else entirely then. I'm sorry to hear that. I was hoping the issue had been brought on by the work you did which would make it easier to backtrack to an earlier state where it was silent. Hopefully someone else will chime in with a solution. One thing to check is make sure the transformer is properly tightened down and that you aren't hearing a mechanical vibration because it's mounted loosely or has worked itself somewhat loose. See if you can put your hand over it and squeeze it or push it down with your hand if you can make the hum temporarily go away. Good luck.

 

[rompstar]

Oh, well that's something else entirely then. I'm sorry to hear that. I was hoping the issue had been brought on by the work you did which would make it easier to backtrack to an earlier state where it was silent. Hopefully someone else will chime in with a solution. One thing to check is make sure the transformer is properly tightened down and that you aren't hearing a mechanical vibration because it's mounted loosely or has worked itself somewhat loose. See if you can put your hand over it and squeeze it or push it down with your hand if you can make the hum temporarily go away. Good luck.

When I first opened it up to upgrade the capacitors / it was all loose, the bolt that was holding it down was stripper around the metal washer at both the bottom and top, because it would rotate overtime and it wasn't holding it down for sure / I replaced the bolt with a new set and tightened it down much better than before, I think it is super secure / but I can try the push down when it is open next time... but this is why at this time I am thinking a new transformer.. ??

maybe it need more rubber washers ?

trying to hear from someone else who had the same problem ?

yes, the amp hummed before I ever opened it up to upgrade the capacitor or bridges, exactly the same it hums now...

 

[onanysunday]

If you can determine that applying external pressure quiets it down tells you one thing (and you may be able to fix that), but if that makes no difference you are definitely looking at new parts. The transformer windings can de-laminate themselves from within and generate a hum that will never go away if that is the case. If you're lucky, you may be able to tighten it externally somehow. I would say the new rectifier bridge may have caused it, but we know that isn't the case since it hummed before -so it's nothing "you did".

 

[rompstar]

If you can determine that applying external pressure quiets it down tells you one thing (and you may be able to fix that), but if that makes no difference you are definitely looking at new parts. The transformer windings can de-laminate themselves from within and generate a hum that will never go away if that is the case. If you're lucky, you may be able to tighten it externally somehow.

I will try this next time, so let's pretend it is not helping by pushing it down or extra rubber seals, which transformer is recommended, as close to drop in replacement as possible... ?

 

[onanysunday]

Honestly, if you have to replace it I'd look at getting one from an identical parts unit or maybe you can find a manufacturing part number off the original transformer itself (or its service manual) to point you in the right direction. I personally wouldn't "substitute" anything and expect it to work as good as the original, but maybe someone else with more experience with that may chime in.

 

[rompstar]

was thinking this as replacement (once I confirm) pressing does nothing. .. I mean ratings are ratings, voltages are voltages, as long as it is the right transformer, it shouldn't make any difference to the original part... especially if you have to remove it, the amp sound much better now than it did before Capacitor and bridge upgrade (can't much tell if anything the bridge) is effecting the sound, but it has a better protection now with high in-current rush vs. the original, I can't tell anything from that, but capacitors, big Upgrade for the better...

AN-5450 - 500VA 50V x2 + 12V + 18V Servo Motor Power Transformer | eBay

They are specially designed to work on all standard 115V or 230V at 50Hz or 60Hz. The dielectric test is more than 3500V in between primary and secondary coils.

www.ebay.com

 

[rompstar]

Honestly, if you have to replace it I'd look at getting one from an identical parts unit or maybe you can find a manufacturing part number off the original transformer itself (or its service manual) to point you in the right direction. I personally wouldn't "substitute" anything and expect it to work as good as the original, but maybe someone else with more experience with that may chime in.

I figured it out, its fixed... when I was replacing the main stripped bolt and nut / somehow I put the bottom rubber gasket on the outside of the amp, lol / maybe I was drinking a beer that time, I put it inside the amp on top of the metal bottom bracket and the hum went away, its been now a few days and I don't hear anymore.. finger crossed, I also put an extra rubber seal at the top too and extra tightened the nut...

 

[coonmanx]

I figured it out, its fixed... when I was replacing the main stripped bolt and nut / somehow I put the bottom rubber gasket on the outside of the amp, lol / maybe I was drinking a beer that time, I put it inside the amp on top of the metal bottom bracket and the hum went away, its been now a few days and I don't hear anymore.. finger crossed, I also put an extra rubber seal at the top too and extra tightened the nut...

Sometimes it's the simple things...

 

[rompstar]

also, finished designing the PCB Board to replace the power board / trying to create something much better... asking for some feedback from the KiCad Group, have some question about the overall process and then I will submit to have the Prototypes made.. the Amp is Quiet and I love it...