Musical Fidelity P150 owners take note!

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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 :D 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 :eek: 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 ;)
 
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
 
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.
 
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 :D

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 :rolleyes:


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 :D

& thank you for possibly saving me some grief ;)
 
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mf caps

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.
 
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:eek:
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 :eek:
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 :rolleyes:

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

: (
 
Or the under rail voltage capacitors either :rolleyes:

Honestly it really put me right off. Joe average would never know the difference, but i certainly did.

I ask you if you'd like to buy some MF kit & then have to spend hours going through stuff to see if the components are adequately rated. I know i haven't got the time or inclination..

Nothing like a bit of DIY to make sure all is as it should be :D
 
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Hi jez,
I'll back you up on those things. I repaired many here in Canada. But you did forget to make something more clear. The excessive internal case temperatures!

Way back when, I was replacing the capacitors with ones of a suitable rating, and 125 °C (not really good enough). But the most telling situation was how they decided to drive those mosfets. Crank it high and use TO-92 devices as drivers. The driver stage couldn't really deal with the gate charge on the mosfets. Another endearing trait was the wire soldered to the top of the mosfet casing to make the drain connection to the power supply. Outstanding!

At least there were somewhat reliable and easy to figure out when schematics were hard to come by. I had to reverse engineer a few.

-Chris
 
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This thread paints a pretty shocking picture of MF... I'd heard of temperature issues in the past, but some of the things said on here are trully shocking... just the heaters wired up on a valve (you mean to make it look like it's a working valve stage), that's unbelievable.

I found some pictures and see what Chris means about soldering to the transistor directly... here the case of a T03.

Musical Fidelity A1 - Technical
 
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Hi Mooly,
Yes, it's true. I never had a problem servicing these amps. It was clear as to what they needed and also where improvements might be made. Having said that, improving these amplifiers is pretty much a waste of time. There are very basic flaws with the design that really demand a redesign as far as I'm concerned. Owners of these would generally be willing to spend money on these for "upgrades". Upgrade work has pretty been the rage in the Toronto area since the early 80's and show no sign of dissipating. I generally try to avoid doing most of what is popular simply because the normal amplifier needs basic work first. Once that is done, customers find the desire to change things has been much reduced.

The internal heat in these has really got to be experienced to be believed. The effects on the PCB are unmistakable - aided by the other terrible fad around here. Leaving your equipment running all the time. These are just very average parts arranged in a poor design (as far as I'm concerned) in some nifty looking case work. I guess that's all you need to be successful, but don't forget to run everything stinking hot.

The units I have had to replace outputs in were mosfet models. I don't recall bipolar outputs, but I don't go around poking where there isn't a fault or problem.

If you can make the top waterproof (I think it pretty much is with all the grease in there), it will do a splendid job of keeping your coffee nice and ... ah, hot.

-Chris

Edit: Thanks for linking that page Mooly. Now I can see what the next wave of mods is going to be! It would have been so much easier back then if they had the internet on computers. :)
 
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I could tell you even more shocking tales believe me..... I've said enough already to give a good picture though.
We did actually used to heat up pasty's and samosas that we got from the local bakery on the racks of amps that were on soak test so you were closer to the truth than you realised there!
I would often fit a new transformer to an A1 (MA50's were even worse) and after leaving it on soak overnight would come into work to find the mains fuse blown and the transformer toasted.... the plastic cellophane type stuff around the toroid would be melted! These samples we reduced the quiescent current on.
 
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Hi jez,
Understand completely. None of that surprises me at all. I've had friends in the manufacturing sector. They tell of idiotic practices of the same magnitude.

For a real wakeup, my wife used to work at Sonic Frontiers. No way will I reveal what I know of the original management team! Their practices were irresponsible, to put a kind spin on things.

I think the only people that would be surprised by all this are consumers (not connected with the audio industry) and people working at functional manufacturing facilities. My wife is now working in the automotive industry with a company that makes various things required for servicing a car. The company she just left was worse than MF, and the company she is now with have their very own special traits.

Personally, I am astounded that industry functions at all. The avoidable monetary losses are staggering. Management is basically so inept, the proper words just can not be found. It's well beyond belief. After running a small company for years, the resulting viewpoint allows me to see things in a way that anyone who hasn't held a job similar to, or actually running a business, just can not really see. It's sobering, let me tell you.

Jez, no put down or insult intended here at all. Were you acting as an engineer for Musical Fidelity? If so, I imagine you were taking instruction from someone. It does sound as if you are the type of person who would have commented on the short comings, so I was wondering how a situation like this develops. If you can't talk about this without identifying those responsible, or are uncomfortable, don't respond to those questions. From being in a similar position in an entirely different industry (twice actually), I can understand how high the stress can be when the company takes a direction that you strongly disagree with. That much stress can make a person ill.

-Chris
 
I could tell you even more shocking tales believe me..... I've said enough already to give a good picture though.
We did actually used to heat up pasty's and samosas that we got from the local bakery on the racks of amps that were on soak test so you were closer to the truth than you realised there!
I would often fit a new transformer to an A1 (MA50's were even worse) and after leaving it on soak overnight would come into work to find the mains fuse blown and the transformer toasted.... the plastic cellophane type stuff around the toroid would be melted! These samples we reduced the quiescent current on.

Hello

I have experiment same problems with a cheap toroidal transformer in a amp, it was very hot, after few verifications I found out that the core of the transformer was undersize, so the copper wire turn number and ratio was for a much bigger core size, so it do to much maxwell of magnetic flux for the core size and the eddy current was very high, even without any load the core become very hot.

So, in the case that you mention, MF may have used an undersize core for this transformer.

Bye

gaetan
 
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Hi all
The A1 and B200 have found their place in history as a bad example of -heat generated- unreliability plagued amplifiers.

I was quite surprised to see the same problems on a F15 monster.
Heat is trapped inside. Thus, PSU caps dry-out (to the extend of bulging externally and shrinking inside, thus the rattling when you shake the caps), diminish in capacitance and increasing in resistance. Thus x-former and rect. Bridge heat-up (worsening the scenario), DC is no DC anymore, one or more of the PSU series power resistors burn, two or more of the FET output devices fail. (*PS1)

The un-rectified lack of heat management is unforgivable for a manufacturer. Heat build-up is readily measured, consequences of elevated temperatures are well known in electronic components, so there is absolutely no excuse for them selling such equipment, regardless of market price tag. (*PS2)

*PS1. DC voltage on F15 was +/-63V. PSU caps were 65V rated. Although the 2 Volt margin is that small, I don’t think that an 85V cap would do any good. It is solely a high temperature environment issue there IMHO).

PS2. In addition (or due to it?)to high market price, Musical Fidelity was offering an after sales upgrade for F15. They were replacing all the “critical” caps with higher quality parts, they were bypassing all the elcos with polysomething caps, they were demagnetizing the x-former and they were “reorienting” the magnetic fields around the x-former, plus measuring and adjusting the dc residues at the output. All these for ~700UKP. Absurd. I would expect them to address the thermal issue instead of dealing with *@#$!*

Best Regards
George
 

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