Musical Fidelity P150 owners take note!

[event horizon]

Something just reminded me that i ought to post this in case anyone else owns this stereo power amplifier.

I can't remember what made me take the top of of 1 of my P150s but i was in for a bit of a shock I bought a pair of them to driver a pair of 2 way active speakers & i probably thought i'd just check them out internally.

Anyway, i noticed that more than one of the main PSU capacitors looked like there was a rather lot of pressure build up inside. The end of the capacitors was literally bulging (snap in electrolytic). So i looked at the voltage rating, 63V & all should be ok on a 75W per channel amp. That was until i checked the rail voltages which were +/- 69V DC idling Talk about a sagging supply under load, the transformer is kind of undersized..

So, if you own one of these MF amp make sure you change the main PSU storage capacitors for something like 80V versions. I was lucky & happened to have 8 x 80V capacitors with the same capacitance, if i remember right it was 6800UF. I doubt you'll be able to stick anything bigger in as the amps are already quite slimline. You'll need 4 caps per amplifier.

You have been warned

[AMV8]

Hi
You are not alone in finding power supply capacitors in Musical Fidelity equipment with a lower voltage rating than the rail voltages.
I own a few of the larger MF amplifiers. In an A370 and 2 number P270's I found elna power supply capacitors with a lower voltage rating than the rail voltage. I do not know for sure thst they are original capacitors; but they do seem to be and they are the same size and model of capacitor.
I mentioned this in an earlier thread. One reply I got from another member of diyaudio was to say that no major manufacturer would ever do that - I think suggesting that I should not have mentioned it!
Well - you just have to decide for yourself what you want to believe. But, it is interesting to hear that you found the same.
Don

[nattawa]

I believe sometimes when the bean counters figured the de-rating is being overated and their e-caps of choice won't blow up operating over-voltage that way for a few years, or even some of them do blow up, as long as there would be no liability issues, they'd go ahead and put a a lower voltage rating cap in the production amp. My Parasound HCA-1000 has about 69VDC rail voltage at idle too, and the stock main caps are 63V rated and all had the bulged top. All other smaller e-caps on the rails are 63V as well. I re-capped the amp with 80V and 100V rating caps. The 63V/6800uF caps removed are light in weight and, when shaked, feel like something solid yet sticky rattle inside.

[event horizon]

Hi Don, well lets just say that i had two of these amps with vastly different serial numbers (which is true) They both had the same voltage of cap, type of cap etc fitted to both of them.

Now what is the chance that someone or should i say two different people seeing as i happened to buy 2 amps (which weren't together previously) should happen to have the same type & voltage rating of capacitor fitted?

Pretty slim i reckon.. Think about it, same voltage, same manufacturer & the same value... Nah, they were the original capacitors

I didn't understand why the hell they'd do it, though i guess the surge voltage on 63V caps will be a little higher, but we aren't talking surge here. If idling the things are consistantly 4V DC higher than there ratings


Bests, Mark.

E2A:- Hi nattawa, thanks for your post fella! I'll be taking a look inside my Parasound HCA1206 & checking it out without a doubt. Just in case you understand

& thank you for possibly saving me some grief

[jez]

A common problem on MF amplifiers......
The sag under load on these (and the P140 and B200 which have the same transformer) is horrendous!
I used to work for MF and could tell you tales that would make your hair fall out with shock

[raymondo]

yeah i wrote MF about 12 years ago complaining about the caps in my e300 - they were running at 53V and rated at 50V.
got a pathetic response about them being rated to 10% above . a common problem across the product range years ago. i guess the 63V versions at the time were too big to fit in the case.

i like the sound of MF stuff, but the engineering is terrible a lot of the time.
or certainly was.

[event horizon]

Originally Posted by jez

A common problem on MF amplifiers......
The sag under load on these (and the P140 and B200 which have the same transformer) is horrendous!
I used to work for MF and could tell you tales that would make your hair fall out with shock

Yes, i should imagine the poor transformer has a rather hard time of it. It looks to be about 125VA to my eyes, though it might be a tad more..

What i saw when i opened up the amp & saw the caps & measured the rail voltage was enough to give me goosebumps

Originally Posted by raymondo

yeah i wrote MF about 12 years ago complaining about the caps in my e300 - they were running at 53V and rated at 50V.
got a pathetic response about them being rated to 10% above . a common problem across the product range years ago. i guess the 63V versions at the time were too big to fit in the case.

i like the sound of MF stuff, but the engineering is terrible a lot of the time.
or certainly was.

That's a pathetic excuse. They are talking about surge voltage, not something continuous

Likewise, the P150 sounds quite nice considering. I doubt i'll buy any MF stuff ever again knowing what i now know

[jez]

"Yes, i should imagine the poor transformer has a rather hard time of it. It looks to be about 125VA to my eyes, though it might be a tad more..

What i saw when i opened up the amp & saw the caps & measured the rail voltage was enough to give me goosebumps"

Oh that's nothing!! just the tip of the iceberg!!!!

Try 11W wirewounds across the PSU in pre amps just to make the case get warm so they could claim it was "Class A" to the technically naive......
Try so called valve amps in which only the heater was wired up....
Try B200 integrated amps being sold as A1 amps (same casework just different silk screening) when they had temporarily run out of A1's to fulfill an order....

I could go on but I think you will have got the picture by now!

[Jen-B]

Sometimes (not necessarily MF) it goes like this...

Management (in UK) specifies the design
Design is proven on correctly hand-built prototype
Approved Design is then put out to tender for manufacturing
Manufacturing contract awarded to very cheap overseas (normally Asian) factory
Very cheap factory decides to save themselves some costs, and substitutes lower specificiation / quality components
Management (in UK) do not bother to quality check the production from overseas because they are too greedy to get profit from quick sales
Amplifier goes bang

: (

[jez]

MF's boards were indeed built overseas, in Taiwan to be precise, and then fitted into the casework in the factory in Wembley.
This does not however explain the deliberate measures which I outlined earlier