McCormack DNA 0.5 Re Cap

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smatiana

Member
2008-06-10 8:22 pm
I bought this amp in 1995 and it's still going strong. I recently noticed that it's sounding less in control of the speakers and the overall sound seems a bit muffled. I understand that the electrolytic capacitors have a limited life and they might already have reached the end of it. I am suspecting that this could be the reason for the decline in its sound quality. So, I have decided to re cap the amplifier. While I am at it, what else should I replace? Do output power transistors also have a limited life? Should I replace those too? Any help or comment in this regard would be highly appreciated.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
I've no experience with the amplifier other than giving one an audition but the principles of recaps for power supplies etc. apply to all amplifiers.

There's quite a few ($$) caps to fit in there and I would first check the preamp and/or program source devices before committing cash to parts. It's also dual mono, meaning 2 independent sets of rectifiers and smoothing caps. which also means you would likely have a different degree of sound loss in each channel if the caps were to blame. At 20 years, I wouldn't expect to hear a marked sound deterioration yet unless it was in daily use and becoming more than warm to touch.

It seems McCormack do or did modifications and offered upgrades. I imagine they know what will impress the most, as it's their product. For some improvement hints, have a look at this old snippet:
Oh No...My Headphone Days Numbered? Speaker Setup Pulling Me Back In
 
Have you done this before ?

That your amp ? (below)

Yes , 21 years ... some electrolytic' s will fail an ESR test , some will still pass.
Quality and total hours determine this.

Output semi's have no "lifetime" ..... they will just fail. Before they do , they will
not degrade. I've repaired Sansui's 40 years old , semi's are still perfect.
The white oxide thermal compound will harden , and will need to be re-applied.

PS - the .5 seems to be (very)well designed .... it might be better to just test
ESR since McCormack seems to have de-rated well.
I like how they split the IPS from the output boards - like my amps with
all separated. They are using 80-V caps with 60V rails - good.

OS
 

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smatiana

Member
2008-06-10 8:22 pm
Thank you guys. That was helpful.

ostripper - I did check ESR on power caps and they do show deterioration. So, they are going. The pic u showed is exactly like my amp. The caps are 4700uf/80V and I am replacing them 5600uf/80V. I also intend to replace the emiter resistors with some newer hi quality metal types. The semis are good as you mentioned. While I am at, I will upgrade the binding posts, since, I don't like the originals. Other than that it should be a fun weekend projects (once I have all the parts from DigiKey.)

Ian Finch - I tried another amp to make sure that the source was ok. And it was! The degradation in sound occurs in .5. If you think it can't be due to the caps, could it be for some other component failure? If so, do you know of any other usual suspects?
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
I said that because it's dual mono and so has dual power supplies, it's likely there would be a difference if the cap. values in either channel power supply were different, actually meaning the total in each was very different. I can't tell from your comments whether that was the case but I assume not. Let's wait until you've finished the refurb. - and do use a bulb limiter when you first power up after a recap. etc.
 
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