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Old 4th May 2010, 07:40 PM   #11
event horizon is offline event horizon  England
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Or the under rail voltage capacitors either

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
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Old 4th May 2010, 08:06 PM   #12
Uunderhill is offline Uunderhill  Canada
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Thanks for the heads up on early MF Amplifiers.

The A1 integrated amps are well known to be self cooking.

Any comments on the power supplies of the A3.2cr and A308cr series ?
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Old 4th May 2010, 08:14 PM   #13
anatech is offline anatech  Canada
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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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Old 5th May 2010, 08:13 AM   #14
Mooly is offline Mooly  United Kingdom
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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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Old 5th May 2010, 11:07 PM   #15
anatech is offline anatech  Canada
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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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Last edited by anatech; 5th May 2010 at 11:08 PM. Reason: Added comments
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Old 6th May 2010, 02:29 AM   #16
jez is offline jez  United Kingdom
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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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Old 6th May 2010, 04:53 AM   #17
anatech is offline anatech  Canada
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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
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Old 6th May 2010, 06:03 AM   #18
Bonsai is online now Bonsai  Europe
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It would be interesting to see some of the more recent MF circuit diagrams.

Funny thing is, they always get great reviews. How come people keep going back to buy this stuff when its got all the issues discussed above? I guess Anthony Michaelson does a good marketing job . . . .
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Old 6th May 2010, 08:05 AM   #19
gaetan8888 is offline gaetan8888  Canada
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Quote:
Originally Posted by jez View Post
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

Last edited by gaetan8888; 6th May 2010 at 08:22 AM.
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Old 6th May 2010, 08:21 AM   #20
gpapag is online now gpapag  Greece
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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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