MS275 refresh

zorrobf2 · Post by **zorrobf2** » Fri Dec 21, 2007 6:02 am

Hello,

Who can help me to identify what component have to be replaced on my MS275 Rev E amp, I would replace also OAMP NE5532 with better component (example AD825), which are the best choice ?

thanks

eyesofra · Post by **eyesofra** » Fri Dec 21, 2007 6:34 am

NW5532 is a dual , u would need the AD826 to be compatible or get something like this if u want to use AD825....
http://www.octave-electronics.com/parts.shtml

tried the AD826 before in my Home stereo amp and they really do sound good,compared to the stock OP2604 though the latter is also a good stuff.....
u might need to upgrade the op-amp supply filtering though ,with faster op-amps such as the ADs.....

it seems older PG gears need the power supply caps changed.Our resident gurus , onemoreamp and doc are the best ppl to advice on this...

1moreamp · Post by **1moreamp** » Fri Dec 21, 2007 8:49 am

Welcome aboard the forum !

OPA-2134 is a suitable replacement, although I have been told most folks like the OPA-2604 also.
The OPA-2604 is much older device then the OPA-2134. I have both and have found satisfactory results with both over the years. These are duals, as that is what is used, so singles are not the right part.

On the MS-275 or any MS amp the power consumption is not a issue,< only 3 Op-Amps> but on the more complex ZX/Ti lines where there are integrated crossovers and such the power draw of BB chips becomes a issue, and the cost of devices also makes the switch very expensive. < over 16 chips need to be changed on these more complex models.

Replace all of the 12 volt side caps, and then replace the main rails and lower rails caps with newer and improved caps available today. The SQ gains from this alone are really noticeable mostly due to power supply noise issue that your resolving.

I find that 15 year old caps usually are 1/2 to 2/3rds there original values most of the time. And Doc has a well document series on the 12 volt side caps and their related failures and the board damage that can occur. Doc's the king of fixing this sort of thing, up to and including outright board repair. Just do a search using Capacitors and Doc Fosgate to find his tutorials and pics. He does good work, I am sure you will agree......C

zorrobf2 · Post by **zorrobf2** » Fri Jan 11, 2008 9:43 am

Thanks, I replaced:

all power supply cap
+ three 2,200uF 16V by three 5,600 16V
+ two 4,700uF 35V by two 10,000uF 35V

I think to replace also all other cap with Elna Silmic II, all OP-AMP (from NE5532) with OP275 or OPA2134 or OPA2604 (to find better sound) .

At the end I hope that sound will be better.

1moreamp · Post by **1moreamp** » Fri Jan 11, 2008 9:50 am

Sounds good, you headed in the right direction....C

zorrobf2 · Post by **zorrobf2** » Mon Jan 14, 2008 12:14 pm

Hi Cecil, I replaced all power cap, now I'm ready to rep all three opamp with

OP274
OPA2164
OPA2604

what op APM do you suggest me (I have got all of them) ?

Thanks

1moreamp · Post by **1moreamp** » Mon Jan 14, 2008 12:27 pm

I know OPA-2134P works well, perhaps you might try the OPA-2604. I have heard recently from another forum member that he was very satisfied with the SQ these put in his amp.....The Op device is analogue Devices which has s good name but i have not used them yet....C