Hello!
I am looking to change caps (especially the elcos) in my MFB 544 amps. The ones I think about are the large amp output elcos (change to audio grade?) and the PSU double cap.
Any other dried out elcos worth changing? Any other components that are better nowadays - especially capacitors...
If you have found suitable replacements, can I have component number, producer etc.? Would help a lot not to reinvent the wheel again...
Thank you for any help!!!
Thomas
Hi!
The large caps are normally not so bad, but some people change the one in series with the woofer.
What is worth to change are the small elcos in the signal path, and if you change the output elco, you should change the big one on the low stage as well.
There is a servicedoc with partnumbers and links tot the parts from the e-store on http://webwinkel.mfbfreaks.nl/
Just click on the 544 box, then you will see a page with links to the service docs and the partnumbers, with great thanks to Herman 😉
I tend to use 105C elco's. Of course there exist expensive special elco's for audio, but i doubt if you hear that.
Oh yes change C581. that one causes switching off too fast whe the MFB's get old.
THe big PSU cap is 2x 2350, I guess it's OK to use a 4700uF?
I think that the PSU CAP is still okay. If not, you see it is leaking, but these large ones normally are pretty good. Believe me that it are the small ones that give most times problems when aged.
Hi,
If the cpacitors are connected paralel then yes you can use a 4700µF instead but if they are in series then no, better use the 2200µF types then.
Good luck. 😉
Besides changing elco's the exchange of output transistors will improve the sound as well.
particularly changing the midd/high output transistors will improve the sound.
( the old ones have suffered a lot of heat due to high current )
The 544's power-supply has an error in it's wirering (probably the same in other types) : On the PCB, the amplifier and the rectifier-bridge are situated, not the filter-cap. The filter-cap is connected using two (thin) long wires to the PCB, placing the filter-cap out of the line the current follows.
The effect of this construction is an artificial high impedance of the power-supply (adding many tenth of milli-ohms to the Cap's ESR), limiting current deliveryspeed from the Cap.
Since changing the location of the Cap with regard to the PCB is impractical due to the limited housingspace, the wirering should be changed in such a manner that the cap is inbetween the rectifierbridge and the amp. The result will be a more powerfull and defined bass.
I solved the problem, using 4 2,5mm2 multi-strand wires connected to the Cap and cutting the copper tracks on the PCB close to the original fitting point of the wires. The 2,5 mm2 wires are a bit of a pain in the neck fitting into the housing, but it can be done.
Shure, changing the (4700uF/65V) Cap into 10.000uF (use the 80V types!) will also increase bass-performance, but sorting out the wirering should come first.
Modern Caps are usually Computer-grade types, using them makes sorting-out the wirering problem a priority.
