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Musical Fidelity B1 question
Musical Fidelity B1 question
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Old 25th January 2013, 09:37 AM   #1
tedv is offline tedv
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Default Musical Fidelity B1 question

Sometime ago I killed my almost 20yr old Musical Fidelity B1 trying to replace the volume pot meter - but, this week, I found another on a local online market place, so I'm the happy owner again of a B1.

For the last years my amp was a Cambridge Audio Azur 340 (not SE).

After plugging in the B1, it sounded good (tested it at the seller as well) but for some reason it was not entirely what I remembered it to be. I know it is hard to tell sound difference from memory so maybe it is just my imagination and hopes set too high, but I thought I would do some small checks.

First thing I noticed is that two of the eight 2N3055 are a lot hotter then the other ones. You can touch them, but not for long. The cooling ribs are fine. All the 2N3055's are still original.

Looking at the schematics, and from my old electronics knowledge I would figure it is weird for only two to get hot. Four would make more sense? Only reason I got think of is that there is some DC offset somewhere? See the picture for the ones that are hotter.
All resistors and capacitors feel cool and none look bulged or anything.

I do have a reasonably good multi meter, and a Denon test CD which I play (uncompressed - WAV) from my rock-boxed Sansa Fuze v2. I checked the AC voltage on the speaker outputs with a 1Khz wave with the volume at about 10 o clock and it was 0.5V on the left and 0.425V on the right (also after switching left & right speakers) That amounted to 1db in difference and which could be corrected with a 1% balance adjustment in my Sansa Fuze. Audible it is barely noticable. My Cambridge Audio was better balanced however. (0.5v vs 0.49v)

The question is, is it normal (2 of 8 transistors getting hotter), or are there any more checks that I can do?

I do have the schematics but my analogue electronical skills have always been much less then my digital ones. I don't have a wave generator or oscilloscope. The test CD and the multimeter is my only equipment.

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Old 25th January 2013, 09:48 AM   #2
Zen Mod is online now Zen Mod  Serbia
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Musical Fidelity B1 question
check DC voltages across all 0R47 emiter resistors , then we'll know more
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Old 25th January 2013, 10:41 AM   #3
tedv is offline tedv
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Join Date: Jan 2013
on the left side

R63 0.05
R64 0.015
R65 0.013
R66 0.015

on the right side

R63 0.04
R64 0.02
R65 0.038
R66 0.020

Edit: I thought something was wrong with my left speaker - woofer didn't do anything anymore after playing a loud song and seeing it distort. A week ago the kids knocked my left speaker to the ground, this probably loosened the bolt connection a bit (Monitor Audio BX2) - playing a loud sond allowed it to resonate in the cabinet and probably cause a faulty cable connection or so?. Fastened and retightened everything and works fine again.

Last edited by tedv; 25th January 2013 at 11:05 AM. Reason: thought something was wrong but it was a loose cable
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