Thursday, November 13, 2008

McIntosh MC-250 update


I decided to give my McIntosh MC-250 a much needed update - here is the input board:

Here are the parts (circled in red) that I am going to be updating: the main input board power power supply capacitors will be increased with 1000uF Philips units. The input capacitors are replaced with Ero Metallized Polypropolenes and the output capacitors should be replaced with bipolar electrolytics.


Once the two bolts on top have been removed you can see the bottom of the PCB board. I applied my soldering iron and removed the old parts. If you do this yourself, be sure to work carefully since these vintage PCB boards are fragile. Also be sure not to bend the attached wires too much as these can also break. It certainly would help to have a 3rd hand - one hand to hold the board still, the other hand to pull on the leads of the old component and another to handle the solder iron.


Here you can see the new capacitors are mounted. The Ero .47uF capacitors were tight fit and needed to be raised off the board a bit in order not to interfere with nearby components.


So how does it sound after the changes? It definitely makes the MC-250 sound 'less vintage' with a more modern representation. The original capacitors are over 30 years old and must have drifted in value since then. There appears to be more detail too - but I'm doing comparisons by memory so you can take this observation with a grain of salt. Some people may prefer the vintage sound - so keep this in mind if you are thinking of upgrading any old amplifier. Of course old electrolytics should be replaced anyways as a safety measure.

Next time I'll bypass the main reservoir capacitors and replace the other aging electrolytics mounted on the PCB boards.


For schematics and part values the McIntosh MC-250 service manual is available here.

2 comments:

bulldane06 said...

Hello,

I also have a MC250, and am wondering if the input PCB cap upgrade has robbed any of the smoothness, or simply increased the detail?
I don't have any test equipment to take measurements with, so I'm wondering if my amp would benefit from new caps. I haven't pulled the bottom off yet to know if it's been serviced. However, it sounds simply wonderful, and after a couple minutes of "warming," I have to stick my ear practically into the tweeter to hear any hiss. From the various posts I've seen about the 250, seems the majority of owners haven't had to replace anything yet, owing to its simplicity and durability.
As for the power supply section, namely the 9300uf filter caps, I assume they're still good if I'm not hearing any 60Hz hum? So, even though I like to tinker, I'm torn whether I should even mess with anything.

Regards,
Steve

dividebytube said...

I too feared 'losing the sound' when updating the capacitors on the input board - but as the caps broke in I haven't really noticed a major change to the character of the amplifier. It still is smooth, but has more detail. I wish I could A/B the difference between then and now, but I think I'm preferring the new sound (at least with my cheaper second system).

For safety reasons I would recommend upgrading the electrolytics - though you can keep the 9300uF units if they are still working. From the reading I've done they are apparently well made and should last a long time.