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Old 6th May 2010, 10:04 AM   #21
jez is offline jez  United Kingdom
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"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."

No offense taken..... I ran the service department at MF before becoming chief engineer with Alchemist Products (formed from ex MF staff). I was complaining to management on a daily basis about the outlined problems (and I haven't told you about the worst excesses....) and eventually resigned and walked out of the factory there and then.

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Old 6th May 2010, 10:40 AM   #22
ontoaba is offline ontoaba  Indonesia
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The fact can't lie then. Look, the heatsink too, also the resistors leads almost touch it.
They should learn about reliability design, the most expensive to learn (for me), it may cost many thing more than money. That they should take care about.
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Old 6th May 2010, 03:31 PM   #23
jmmartins is offline jmmartins  Portugal
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Originally Posted by jez View Post
"

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.....
You solved a problem I couldn’t understand for years!
I have 2 MF B200 and in fact there are 4 resistors (4 or 5 watt each) that I imagined being bleeding resistors… but it didn’t make sense. Now I understand why they are there!!!
Those resistors are for nothing (I took them off) and they used to get so hot that the pcb is black around them and the nearby regulators for the opamp power supply .
And I was impressed too by the fact that the capacitors are for 63 Volts and the rail was +-68V

But of course I can be wrong and if so, I still would like to understand what are those resistors for.

Thanks for letting us know.

Last edited by jmmartins; 6th May 2010 at 03:41 PM. Reason: Correction
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Old 6th May 2010, 04:33 PM   #24
nattawa is offline nattawa  Canada
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Boy, this thread really opened up my eyes! The only MF piece I've ever had and still having is A324 DAC. I don't see a vacuum tube in it, so wouldn't worry about the wire-to-heater-only thing. There was no evidence of any big resistors for the soul purpose of heating up the unit found either. However, there are two HUGE and HEAVY pieces of inductors, each about the size of one's fist, sitting inside right behind the face plate, giving the unit a balanced, hefty, massive feel, and give one the thought it might worth the price on the tag. Should I begin to worry about these two inductors are just for weight, or for a stable footing on the floor/rack? They could have put in some concrete blocks or some scrap bridge metal in the case work for the very purpose, if it was true, and lowered the price significantly couldn't they? I spent about $500 a few years ago for it, now I'm bother by the thought that half of that money went into the two pieces of weight. Someone please enlighten me.
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Old 6th May 2010, 04:36 PM   #25
infinia is offline infinia  United States
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Quote:
Originally Posted by jmmartins View Post
You solved a problem I couldn’t understand for years!
I have 2 MF B200 and in fact there are 4 resistors (4 or 5 watt each) that I imagined being bleeding resistors… but it didn’t make sense. Now I understand why they are there!!!
Those resistors are for nothing (I took them off) and they used to get so hot that the pcb is black around them and the nearby regulators for the opamp power supply .
And I was impressed too by the fact that the capacitors are for 63 Volts and the rail was +-68V

But of course I can be wrong and if so, I still would like to understand what are those resistors for.

Thanks for letting us know.

It could be that the resistors are pre-loading the transformer keeping the rails regulation within some margin. So removing them might of been making it worse not considering the internal temp rise which is the real killer of caps. A better idea would be designing the output stage with higher idling bias and getting most of this heat out of the case. But that would take some real engineering skills.
Probably a too narrow mains line voltage spec is the real culprit I suppose. If MF specs it at all?
FWIW The price jump of 63V vs 80-100 V bulk caps is huge.
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Old 6th May 2010, 05:31 PM   #26
davidsrsb is offline davidsrsb  Malaysia
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Originally Posted by infinia View Post
FWIW The price jump of 63V vs 80-100 V bulk caps is huge.
Not to mention purchasing lead time.
When I was using contract manufacturers, I was frequently called to discuss component substitution/downgrading

I have 250V mains and a high ambient, which is too good at finding these poor designs
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Old 6th May 2010, 06:23 PM   #27
event horizon is offline event horizon  England
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Quote:
Originally Posted by nattawa View Post
I spent about $500 a few years ago for it, now I'm bother by the thought that half of that money went into the two pieces of weight. Someone please enlighten me.
I wouldn't stress over this if i was you

They actually do make decent choke regulated supplies, they aren't there simply to add mass but to improve the PSU itself


Heck, i really opened a can of worms when i started this thread didn't i
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Old 6th May 2010, 06:36 PM   #28
Mooly is offline Mooly  United Kingdom
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Heck, i really opened a can of worms when i started this thread didn't i
Yep
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Old 6th May 2010, 06:39 PM   #29
event horizon is offline event horizon  England
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lol, i forgot all about the worm emote
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Old 6th May 2010, 07:51 PM   #30
Jen-B is offline Jen-B  United Kingdom
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This sort of fact based discussion of incompetence should be more wide-spread. It might help some potential customers avoid bad companies and products, and might also encourage the manufacturers to take responsibility.

I was just lurking / digging over at head-fi and came across a thread with some details of con-man manufacturing... a very cheap Oppo disc player re-housed and sold as a $3000 Lexicon, and the $1,990 Bel Canto Ref1000 amplifier having the same internals as the $975 D-Sonic Magnum 500M!

Companies like that deserve no customers.
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