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Old 30th January 2009, 09:45 AM   #31
Luke is offline Luke  New Zealand
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MF seems dodgy, do they really sound that good?
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Old 26th February 2012, 08:38 PM   #32
donkeytrousers is offline donkeytrousers  United Kingdom
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Thumbs up MA50 - new electrolytics - wow!

Hi all! I have just completed a replacement programme of all the electrolytic capacitors in my MA50 monoblocs and WOW what amazing amplifiers these things are! I remembered them being praised to the skies in the days when they were available new (mid eighties) in magazines like HiFi Answers. At that time I could not afford such luxuries, but when I found a pair of these on ebay I bought them. I listened and thought I had made a mistake, but then I found Mark Hennessey's site and followed his advice about swapping the electrolytic capacitors as a first step to rejuvenating the amps. I have never done anything like this before, but i managed to work out how to make the changes and executed the soldering with great care (the circuit boards are old and the track has a tendency to come away some times). The results are FANTASTIC! I will post a list of the capacitors I used on Mark's brilliant site in a kind of homage to all he has done to help me. Good luck!
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Old 16th March 2013, 01:13 PM   #33
donkeytrousers is offline donkeytrousers  United Kingdom
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Here, finally is the list of electrolytics I promised shown with approximate prices when I bought them a year ago.

MUSICAL FIDELITY MA50 Monobloc Power Amplifier





































Components





















In my Amp s/no: 761
In my Amp s/no: 739































Capacitors Make Model Deg C V mF
Make Model Deg C V mF
Replace with option Model Deg C V mF Supplier Qty Price






















C1 Rubycon 7822AW 85 63 6800
Rubycon
85 63 6800
F&T F&T 6800uF 105 63 6800 AudioCap 8 7.30 57.68 C2 Rubycon 7822AW 85 63 6800
Rubycon
85 63 6800









C3 Rubycon 7822AW 85 63 6800
Rubycon
85 63 6800









C4 Rubycon 7822AW 85 63 6800
Rubycon
85 63 6800









C6 Rubycon
85 50 1
Rubycon
85 50 1
Multicomp MCRH63V105M5X11 105 63 1 CPC 8 0.15 1.20 C7 Rubycon
85 50 1
Rubycon
85 50 1









C8 Samhwa
85 63 10
Samhwa
85 63 10
NichiCon UPM1J100MDD 105 63 10 Digi-Key 12 0.18 2.16 C9 Samhwa
85 63 10
Samhwa
85 63 10









C10 Samhwa
85 63 10
Samhwa
85 63 10









C13 Samhwa
85 16 47
Samhwa
85 16 47
Sanyo 16SA47M 105 16 47 CPC 8 1.12 8.96 C14 Samhwa
85 16 47
Samhwa
85 16 47
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Old 16th March 2013, 03:21 PM   #34
donkeytrousers is offline donkeytrousers  United Kingdom
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Oops! Sorry! That didn't work. I will try another way.
Attached Files
File Type: pdf MF MA50 components.pdf (9.1 KB, 98 views)
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Old 16th March 2013, 03:29 PM   #35
donkeytrousers is offline donkeytrousers  United Kingdom
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Ah. As that worked, I'll try a photo or two. These are "befores" general layout and heat marks close to the output transistors.
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File Type: jpg Note burn marks near tansistors.jpg (805.1 KB, 255 views)
File Type: jpg Original.jpg (610.2 KB, 249 views)
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Old 16th March 2013, 04:33 PM   #36
Zen Mod is offline Zen Mod  Serbia
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musical fidelity MA50
tnx for sharing
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Old 9th September 2019, 10:14 PM   #37
donkeytrousers is offline donkeytrousers  United Kingdom
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20190822_203329Crop.jpgOkay, so if anyone is stil interested, I have made further discoveries and changes and I also need some help. Firstly, the changes: The areas I mentioned before which look brown and burnt in both amps that I thought was from the output transistors: wrong. The problems causing the brown areas were under-specced resistors and Zener diodes both of which were very much overheating. Resistors 13, 14, 18 and 19 on the right side and 113, 114, 18 and 19 on the left side were all massively overheating as were ZD 1 and 2 on both sides. They were replaced with uprated wattage in each case. Then I found that the resistor used with the mains LED was also shot on each amp. Again, replaced with an uprated wattage silencing the buzz previously heard when the amps were on. I also re-routed and tidied up some scruffy wiring and rubbed down and reprayed the casing (tops and sides) which really made them look good.
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Old 9th September 2019, 10:18 PM   #38
donkeytrousers is offline donkeytrousers  United Kingdom
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Here's the bit I need help with: They sound good. Better than ever before, but one sounds less good than the other. I have searched around until I am going cross-eyed but cannot see what could be causing the problem. It sounds like there's a 6db loss in treble on one amp. Yes, I've tried swapping them and it's definitely one of the amps. Could it be that some other component is no longer working right? Could the transistors in the "hot" areas have been damaged? Until recently they have been very similar one to another but sice all the fettlin' this difference has become really apparent. Any ideas?
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Old 9th September 2019, 11:01 PM   #39
cumbb is offline cumbb
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Quote:
Originally Posted by donkeytrousers View Post
Could it be that some other component is no longer working right? Could the transistors in the "hot" areas have been damaged?
Could be something;-)

The circuit of the MA50 should be same as A1. But balanced.

MUSICAL-FIDELITY A1 AMPLIFIER SCHEMATIC Service Manual download, schematics, eeprom, repair info for electronics experts
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Old 10th September 2019, 01:05 AM   #40
Ian Finch is offline Ian Finch  Australia
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The 2 amplifiers per channel are, according to Mark Hennesy, simply wired in parallel as a single monobloc amp. This will make them very difficult to troubleshoot unless they are separated at output and input. A classic case of "divide and conquer" and a need for matched performance and parts in either amp.
Musical Fidelity A1 › Other models
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