MA50
Hi David - I have 4 of these amplifiers biamped to a pair of missions. i dont know a lot about them but i think they are a top amplifier. there is a guy named mark hennesy who contributes a lot re these MF amps - he seems to think they are the same as the A100, but the stereo amp is connected to make it a mono amp
how long have you had your MA50's?
Steve
Hi David - I have 4 of these amplifiers biamped to a pair of missions. i dont know a lot about them but i think they are a top amplifier. there is a guy named mark hennesy who contributes a lot re these MF amps - he seems to think they are the same as the A100, but the stereo amp is connected to make it a mono amp
how long have you had your MA50's?
Steve
Hi steve,
I've had them for a good 12 years now. And they were bought second hand. Thay are nice amps but run hot. I would change out the power supply caps but finding the right ones can be a problem as the space is tight. Another mod may be to change the power transformer to a bigger one but again space is tight.
I'm still looking for the schematic as some resistors have turned brown, and I don't know what values they are. So if you have any leads, let me know.
David
I've had them for a good 12 years now. And they were bought second hand. Thay are nice amps but run hot. I would change out the power supply caps but finding the right ones can be a problem as the space is tight. Another mod may be to change the power transformer to a bigger one but again space is tight.
I'm still looking for the schematic as some resistors have turned brown, and I don't know what values they are. So if you have any leads, let me know.
David
Hi David,
I've never examined one personally, but Steve is right according to what I've been told. And, the A100 is pretty much the same as the A1, shown here: http://www.mhennessy.f9.co.uk/mf_a1/
If you haven't already tried, it's worth searching these forums for past threads - a lot of the common problems with A1's and A100's have been discussed before, and apply equally to your MA50's. For example, http://www.diyaudio.com/forums/showthread.php?s=&threadid=31407&highlight=
Finally, your name rings a bell. Have we spoken before about these before? Forgive me, but I get a lot of emails about these amps
Best regards,
Mark
I've never examined one personally, but Steve is right according to what I've been told. And, the A100 is pretty much the same as the A1, shown here: http://www.mhennessy.f9.co.uk/mf_a1/
If you haven't already tried, it's worth searching these forums for past threads - a lot of the common problems with A1's and A100's have been discussed before, and apply equally to your MA50's. For example, http://www.diyaudio.com/forums/showthread.php?s=&threadid=31407&highlight=
Finally, your name rings a bell. Have we spoken before about these before? Forgive me, but I get a lot of emails about these amps
Best regards,
Mark
Hi Mark,
Thanks for the links. Yeah, i must have posted before requesting for an MA50 schematic. I know they all share the same circuit design, but just need to know the exact resistor values as the ones that need replacing have turned brown and the colour codes are gone. Some zener diodes need replacing too and I don't know what to use as a replacement.
BTW, your website is excellent
David
Thanks for the links. Yeah, i must have posted before requesting for an MA50 schematic. I know they all share the same circuit design, but just need to know the exact resistor values as the ones that need replacing have turned brown and the colour codes are gone. Some zener diodes need replacing too and I don't know what to use as a replacement.
BTW, your website is excellent
David
dtkky said:
Thank you
It might be an obvious thing to say, but does the other amp have the same problem? You could check component values there.
Assuming you mean the zeners in the power amp stage, they're 12V. Might be wise to fit bigger replacements - think the originals are only 1/2 watt - go for at least 1.3W BZX85C. Also mount them spaced slightly away from the board to allow for cooling.
Which resistors are affected?
Cheers,
Mark
Thanks for the tip. The other amp works fine but the same resistors are also brown. I'd thought I changed them out before anything happens. I've isolated the problem on my non-working amp to the power trans (shorted). The power supply caps look dodgy but finding the 105 degC caps at the right value ( I don't know if they are original, but they are 6800uF) at that size is difficult.
David
David
MA50 again
lol - hmm - My knowledge of electronics is obviously a lot less than yours - i just plug them in and hope for the best!
they do get very hot though - i direct a fan on them when i am using them in summer, although they are supposed to run at about 70 degrees c according to MF i believe. i bought two of them and a P3A preamp several years ago second hand, and a while later i saw another two advertised [also second hand] so i grabbed them as well - not for any particular reason i suppose other than i liked the sound and i though having two for each channel would give a bit more whack - which it does - they go quite loud. I also bought an MK 12 inch sub as the missions dont have a huge amount of low frequesncy in them - they seem to fall away quickly after about 80hz, so the sub gives it a bit more in the bottom end. i have had only one probelm with a power transistor that blew up, but i got that fixed at Len Wallace Hi Fi in LAne Cove in Sydney - that was a faor while ago now. i want to try and get as much info as i can about them in case they need repair again since they are unusual and might be a bit tricky to get fixed.
Steve
lol - hmm - My knowledge of electronics is obviously a lot less than yours - i just plug them in and hope for the best!
they do get very hot though - i direct a fan on them when i am using them in summer, although they are supposed to run at about 70 degrees c according to MF i believe. i bought two of them and a P3A preamp several years ago second hand, and a while later i saw another two advertised [also second hand] so i grabbed them as well - not for any particular reason i suppose other than i liked the sound and i though having two for each channel would give a bit more whack - which it does - they go quite loud. I also bought an MK 12 inch sub as the missions dont have a huge amount of low frequesncy in them - they seem to fall away quickly after about 80hz, so the sub gives it a bit more in the bottom end. i have had only one probelm with a power transistor that blew up, but i got that fixed at Len Wallace Hi Fi in LAne Cove in Sydney - that was a faor while ago now. i want to try and get as much info as i can about them in case they need repair again since they are unusual and might be a bit tricky to get fixed.
Steve
2 pairs?
Hallo DTTKY,
can you confirm that the MA50's use 2 pairs of output transistors (so 4 pieces per channel)? And can you see from the inside whether both halves of the printed circuit board are stuffed with components or that only one half is used?
The pcb of the MA50 is the same as that from the A1. I wonder which part of the pcb is used.
Rudy
Hallo DTTKY,
can you confirm that the MA50's use 2 pairs of output transistors (so 4 pieces per channel)? And can you see from the inside whether both halves of the printed circuit board are stuffed with components or that only one half is used?
The pcb of the MA50 is the same as that from the A1. I wonder which part of the pcb is used.
Rudy
I Have a pair of MA 50's in my studio,had them 2nd? hand for 10 years, sound fantastic, I live in PHX and I always have a fan on,
blown them up 2x's, once my kid turn the fan different direction, 2nd neighbor kid turn all my faders up, boom.unit 2
unit 1 had a replacement transformer, unit 2 was stock, no info off the original t-formers. I took #'s off unit 1 and had torroid of maryland match. they work great. but I screwed up and pulled the input to amp out of my console, POP!
in the middle of diagnosing it, anyone been through this drill???suggestions where to start?
replaced 15003/15004's , turn on .15003 by rca jack gets hot quick. signal is distorted and low volume.
I'm after transistors bc414c, any cross ref you guys know of??
123ap.
I measured and wrote down values of all transisitors , caps
diode and zeners?? a mystery still to me.I think we should swap values, to ensure future repairs. I have a couple brown ones
blown them up 2x's, once my kid turn the fan different direction, 2nd neighbor kid turn all my faders up, boom.unit 2
unit 1 had a replacement transformer, unit 2 was stock, no info off the original t-formers. I took #'s off unit 1 and had torroid of maryland match. they work great. but I screwed up and pulled the input to amp out of my console, POP!
in the middle of diagnosing it, anyone been through this drill???suggestions where to start?
replaced 15003/15004's , turn on .15003 by rca jack gets hot quick. signal is distorted and low volume.
I'm after transistors bc414c, any cross ref you guys know of??
123ap.
I measured and wrote down values of all transisitors , caps
diode and zeners?? a mystery still to me.I think we should swap values, to ensure future repairs. I have a couple brown ones
Hi to all!
MF A1 and A100 are great amps and despite their problems, schematics and useful hints are widely available on the net – mhennessy site is first choice…
I would like to know more about M50 too. Is it just A1 with serial or parallel output connected transistors or something else?
Pictures will be useful.
About repairing, usual hints for A1/A100 like changing all el-caps do apply, but you first must find all shorted transistors and all open resistors. When you have one good channel or mono amp, just open it and measure. There aren’t too many parts, so you will find faulty components in no time.
I hope for the best, and here a schematic from the net that may help you.
Chicco
MF A1 and A100 are great amps and despite their problems, schematics and useful hints are widely available on the net – mhennessy site is first choice…
I would like to know more about M50 too. Is it just A1 with serial or parallel output connected transistors or something else?
Pictures will be useful.
About repairing, usual hints for A1/A100 like changing all el-caps do apply, but you first must find all shorted transistors and all open resistors. When you have one good channel or mono amp, just open it and measure. There aren’t too many parts, so you will find faulty components in no time.
I hope for the best, and here a schematic from the net that may help you.
Chicco
Attachments
MA 50 getting lost and frustratedconfused:
Help,
some one thow me a line! i'm sinking!
Unit 2 history-worked great for 9 yrs till my neighbor kid blew it up
replaced input transformer, worked fine for 1+months
idiot me ,yanked the unbalanced inputs out while powered up (pop)..distortion.
It turned on,and is very distorted.
So I resoldered.
replaced 15003/15004's
Powered up/// fuse blows quickly, and 15003(Rca side) got hot real quick,others appeared cold. distorted sound.
reread,resoldered
replaced all caps, some with higher voltages
Powered up. fuse blows, don't feel 15003 's heat as above
replaced zener d1-d4,
resodered again.
:
Help,
some one thow me a line! i'm sinking!
Unit 2 history-worked great for 9 yrs till my neighbor kid blew it up
replaced input transformer, worked fine for 1+months
idiot me ,yanked the unbalanced inputs out while powered up (pop)..distortion.
It turned on,and is very distorted.
So I resoldered.
replaced 15003/15004's
Powered up/// fuse blows quickly, and 15003(Rca side) got hot real quick,others appeared cold. distorted sound.
reread,resoldered
replaced all caps, some with higher voltages
Powered up. fuse blows, don't feel 15003 's heat as above
replaced zener d1-d4,
resodered again.
:
Erk. It sounds like you've now got some major problems!
Firstly - do not power this amplifier up without the top on! The top is the heatsink, and you will damage the amplifier quickly by running it with no top.
I will refer to Mark Hennessy's schematic here as it's the most comprehensive one. It says it's for the A1 but the MA50 is just an A1 with no preamp.
http://www.mhennessy1.f9.co.uk/mf_a1/a1_schematic.jpg
D1-D4 are not zener diodes, these are standard rectifier diodes. If you've put zeners in here, you need to replace them with standard recovery rectifier diodes such as 1N5403.
Check the VDR (the resistor with S-shape through it on the schematic, just after the power switch) to see if it's closed circuit. If it is, desolder it. You can get away with not replacing this, it is for protecting the amplifier against power surges.
Check the power supply capacitors for any signs of bulging. At this point I would remove R1 and R2, then power up and check if the fuse stays intact, and that you are getting +24 and -24V on the supply before these two resistors.
If your output transistors blew, I would also replace the driver transistors. These are the BD135 and 136 transistors. Personally I would replace them with BD139/140.
Make sure you have real MJ15003/15004 transistors. Some people are selling counterfeits of these. If they are branded Motorola, or anything other than ON, beware.
Firstly - do not power this amplifier up without the top on! The top is the heatsink, and you will damage the amplifier quickly by running it with no top.
I will refer to Mark Hennessy's schematic here as it's the most comprehensive one. It says it's for the A1 but the MA50 is just an A1 with no preamp.
http://www.mhennessy1.f9.co.uk/mf_a1/a1_schematic.jpg
D1-D4 are not zener diodes, these are standard rectifier diodes. If you've put zeners in here, you need to replace them with standard recovery rectifier diodes such as 1N5403.
Check the VDR (the resistor with S-shape through it on the schematic, just after the power switch) to see if it's closed circuit. If it is, desolder it. You can get away with not replacing this, it is for protecting the amplifier against power surges.
Check the power supply capacitors for any signs of bulging. At this point I would remove R1 and R2, then power up and check if the fuse stays intact, and that you are getting +24 and -24V on the supply before these two resistors.
If your output transistors blew, I would also replace the driver transistors. These are the BD135 and 136 transistors. Personally I would replace them with BD139/140.
Make sure you have real MJ15003/15004 transistors. Some people are selling counterfeits of these. If they are branded Motorola, or anything other than ON, beware.
jaycee said:
Bridged A1 output stages, at least it was on the MA50X.
The board of the MA50 not only has all 4 output devices, but both front ends of the output stages.
MF used four 63 volt/6800uF electrolytic capacitors in the MA50, but rail voltages were the same as the 20 watt A1.
MF did not even bother to change the A1 printing on the boards for the MA50s.
Because the channels were bridged was a reason why the MA50s blew up so many times.
musical fidelity MA 50
thanks for the line..but I'm still underwater
I need to remeasure unit 2
Well, I'm only under the hood because no one in town will touch them,
Q:can you momentarily turn on and off without heatsink without damage?
Q; Are caps with higher voltage ratings okay to use in this beast?
Q:are all diodes in MA 50 rectifier diodes? are they all the same value? schematic is hard to see.
Q: what about these bc414c transistors? should I replace them.
Q: About 1/3 all new parts, should I go all the way and replace all components.
Q; does that thermal switch inside work, or is it needed?
thanks !
thanks for the line..but I'm still underwater
I need to remeasure unit 2
Well, I'm only under the hood because no one in town will touch them,
Q:can you momentarily turn on and off without heatsink without damage?
Q; Are caps with higher voltage ratings okay to use in this beast?
Q:are all diodes in MA 50 rectifier diodes? are they all the same value? schematic is hard to see.
Q: what about these bc414c transistors? should I replace them.
Q: About 1/3 all new parts, should I go all the way and replace all components.
Q; does that thermal switch inside work, or is it needed?
thanks !
