Mod ideas for McIntosh MC252

[kurtbauer]

I've taken the plunge and opened up my MC252. It's a 250Wpc SS amp that uses Toshiba 2SC2500 power transistors. I am looking to improve the dimensionality of the sound -- it's a little flat. I'm looking for suggestions on changes that may make the most impact.

So far I've made two modifications:

1. Changed out input coupling caps from Rubicon electrolytics to Black Gate Standard electrolytics
2. Bypassed 27,000µF/100V PS caps with 47µF/160V Black Gate VKs
   [/list=1] I'm thinking these changes will make a difference (and improvement, hopefully!). I'm considering some other mods as follows but don't know what will make an appreciable impact.
   
   1. There are unbypassed Rubicon YXE 10µF/100V electrolytics decoupling caps on the rails of the amp boards. I'm thinking of replacing them with Black Gates and bypassing them. Polyester, polypropylene, polystyrene? I don't have loads of room so size is a consideration.
   2. There are two other small-value caps on the rails. One is a 100pF/100V NPO ceramic between the gate and the collector of a driver transistor on each rail -- I believe this is to inhibit HF oscillations. The other is a 0.47µF/100V metalized polyester film (WIMA RN) that appears to be solely for decoupling. I'm thinking I shouldn't fool around with the ceramic but would doing something with the MPF make any difference.
   3. There is global feedback with a 0.0047µF/5V MFE WIMA cap in it. Worth some action?
   4. There is also a "current limiter" feedback look applied to the driver input of each rail. The gate of each current limiter transistor is coupled to ground with a 47µF/35V Rubicon electrolytic. This doesn't seem like a high-impact area but I really don't know.
   5. The bridge rectifier might also be an upgrade opportunity but since I don't know how to characterize what I've got already, any change would be a bigger guess than the others.
      [/list=1]
      I think that's it. Any thoughts or suggestions would be most appreciated.
      
      KB

 

[destroyer X]

Schematic?.... picture?.... this use to motivate folks

regards,

Carlos

 

[kurtbauer]

Sorry, no schematic

Destroyer, I totally agree that the schematic would make things much more interesting.

Unfortunately, I'm not comfortable posting it.

I was hoping for some general guidance but understand that it may be to difficult.

Cheers.

KB

 

[clm811]

Non-polar caps for signal coupling

So far I've made two modifications...Changed out input coupling caps from Rubicon electrolytics to Black Gate Standard electrolytics

May I recommend that you'll get better sound quality if you use Non-Polar caps for signal coupling. The resulting distortion of polar caps in this position will outweigh the gains in cap upgrade.

There are unbypassed Rubicon YXE 10µF/100V electrolytics decoupling caps on the rails of the amp boards. I'm thinking of replacing them with Black Gates and bypassing them. Polyester, polypropylene, polystyrene? I don't have loads of room so size is a consideration.

There is some disagreement on bypassing Black Gates.

Martin Colloms wrote that "existing selected quality 0.1uF polypropylene de-couplers on the power amp supply lines had to be removed from the circuit as they were found to audibly degrade the performance advantage even of a 47uF 25V standard polarized BG used with no other supplemental high frequency decoupling"

Personally, if I have to bypass, I use 0.1/50v BG NX-H. If higher voltage is required, try 0.01uf/600v film/foil polystyrene caps(if you can find them).

-Chas