If so please e-mail me at:
forquermt@billings.k12.mt.us
I am trying to trouble shoot my "new" Musical Fidelity A100
Thanks for the help,
Tal
forquermt@billings.k12.mt.us
I am trying to trouble shoot my "new" Musical Fidelity A100
Thanks for the help,
Tal
Tal,
I have one, but don't have a scanner....
I will try to scan it somewhere else and send it to you.
The schematic is the same as the A1, only difference is the powersupply and output transistors.
In the one I repaired the 10uF and the 47uF electrolytics in the poweramp where mounted with wrong polarity. I don't remember if the indication on the pcb was wrong or not, just check it out with a dvm.
In the mean time I could help you if you tell me what your problem is.
Dick.
I have one, but don't have a scanner....
I will try to scan it somewhere else and send it to you.
The schematic is the same as the A1, only difference is the powersupply and output transistors.
In the one I repaired the 10uF and the 47uF electrolytics in the poweramp where mounted with wrong polarity. I don't remember if the indication on the pcb was wrong or not, just check it out with a dvm.
In the mean time I could help you if you tell me what your problem is.
Dick.
OK, I'll scan my schematic and post it later. Please replace ALL caps as these are dangerous amps in terms of exploding caps. This is no joke. A100's run far too hot for the components to survive. My experience is that when you only change semiconductors you'll probably have to open the unit a week later for a defective cap.Replace them with 105 degree types !!!
Clean the heatsinks thoroughly when you're sure that the unit runs fine and apply a small amount of heat transferrring paste. Even better are the compounds that are used for cpu's like Arctic Silver or the like.
Clean the heatsinks thoroughly when you're sure that the unit runs fine and apply a small amount of heat transferrring paste. Even better are the compounds that are used for cpu's like Arctic Silver or the like.
I have had some concern as one of the fans has started to get a little noisy at times.. Do you know where I could get replacements in the states?
I replaced ALL electrolytic caps with the 105deg C .
There were a few resistors that were out of tolerance I replaced as well.
Problem is, when I had it dis-assembled I noticed that the selector board had been damaged (cracked) and repaired with buss wire and soldering.
The amp now works but still has these issues.
If I was to keep the MF A100 pre I should probably change out the Volume pot as well.
I would like to remove the Mf A100 pre entirely from the circuit and just use the A100 as a straight amp, controlled by my Nak CA-5 control amplifier.
At least this is what I was thinking....
but then I assume I would still need a pot for matching amps up?
The fans are something I have had ZERO luck locating and the same goes for the selector board that had been cracked and repaired.
Thanks for your time and help.
Tal
I replaced ALL electrolytic caps with the 105deg C .
There were a few resistors that were out of tolerance I replaced as well.
Problem is, when I had it dis-assembled I noticed that the selector board had been damaged (cracked) and repaired with buss wire and soldering.
The amp now works but still has these issues.
If I was to keep the MF A100 pre I should probably change out the Volume pot as well.
I would like to remove the Mf A100 pre entirely from the circuit and just use the A100 as a straight amp, controlled by my Nak CA-5 control amplifier.
At least this is what I was thinking....
but then I assume I would still need a pot for matching amps up?
The fans are something I have had ZERO luck locating and the same goes for the selector board that had been cracked and repaired.
Thanks for your time and help.
Tal
Tal,
I don't know what kind of fan you need, but the best place I've found for fans is Jameco (www.jameco.com). They have 189 different fans listed at their website. They even have the usually hard to find 5VDC fans. And their prices are low too.
Good Luck.
Mike L.
I don't know what kind of fan you need, but the best place I've found for fans is Jameco (www.jameco.com). They have 189 different fans listed at their website. They even have the usually hard to find 5VDC fans. And their prices are low too.
Good Luck.
Mike L.
I dont know what types of fan you need either. However if they are just like ordinary fans like the brushless DC used in computers then they are quite easy to sort out. Usually for me the sign of a dieing fan is significantly more noise produced. This is because the bearing that holds the fan has run dry. Simply find access to the bearing (most of the time its beneath a rubber plug located in the centre of the fan) and fire in a bit of WD40 or some other lubricant. This has got dead fans working time and time again for me in the past, it may work here too.
WD40
Hi 5th element,
WD40 should only be used to unlock rusty bolts!
I applied ballbearing grease to the fan in my GAS Ampzilla amplifier and this made the fan more quiet. Papst has some nice quiet fans that response to higher temparature with a sensing element. AD and Maxim bring no IC's to control ordinary fans.
5th element said:
Hi 5th element,
WD40 should only be used to unlock rusty bolts!
I applied ballbearing grease to the fan in my GAS Ampzilla amplifier and this made the fan more quiet. Papst has some nice quiet fans that response to higher temparature with a sensing element. AD and Maxim bring no IC's to control ordinary fans.
A bit on fans...ususally it's either 90mm 80mm or 120mm...comes in 110VAC...220VAC...or the "standard" 12VDC version...might have 5V ones...their special...look at the original fan for it's specs...and if it says nothing on it's airflow rate...buy the biggest airflow one that you can find...if you find the fan too noisy...you can try reducing it's speed with a diode strung together with the fan...or a little regulator...the LM317 with a pot to control the fan speed comes into mind...or if you got the space...build a temp. monitor and fan speed controller...hehehe 
Hello ,
Thanks for the advice.
The fan I will need to be replacing is a Papst the model I am not sure but I have not been able to find anything even reasonably similar, this fan has no cage around it. the motor bolts onto a crossbrace in the center of the space alloted it. Everything I've found has its own housing. Further the two fans are linked to each other via a capacitor??
I even went to papst's websight but had no luck finding one there.
Same at jameco.
Thanks for your efforts guys.
Warmest regards,
Tal
Thanks for the advice.
The fan I will need to be replacing is a Papst the model I am not sure but I have not been able to find anything even reasonably similar, this fan has no cage around it. the motor bolts onto a crossbrace in the center of the space alloted it. Everything I've found has its own housing. Further the two fans are linked to each other via a capacitor??
I even went to papst's websight but had no luck finding one there.
Same at jameco.
Thanks for your efforts guys.
Warmest regards,
Tal
schematics of A100 (better stil MA50/100)
Mr Middelkoop, maybe you can make a short description of the changes or differences with respect t to the circuit of the A1. That circuit is published on the site of Geoff Moss, his class-A JLH site. A few lines of text could suffices to make it clear. I think:
- other AC rails of the power supply
- larger caps in power supply
- other idle current
- some explanation how the power resistors are parallelled.
By the way: does anybody know the circuit of the MA50 or MA100? The use exactly the same pcb and chassis as resp the A1 and A100 but are used as monoblocks.
If nobody replies to the topic I better post a separte thread on this.
Mr Middelkoop, maybe you can make a short description of the changes or differences with respect t to the circuit of the A1. That circuit is published on the site of Geoff Moss, his class-A JLH site. A few lines of text could suffices to make it clear. I think:
- other AC rails of the power supply
- larger caps in power supply
- other idle current
- some explanation how the power resistors are parallelled.
By the way: does anybody know the circuit of the MA50 or MA100? The use exactly the same pcb and chassis as resp the A1 and A100 but are used as monoblocks.
If nobody replies to the topic I better post a separte thread on this.
schematics A1/A100
The c ircuit diagram of the A1 can be found at the class-A site of Geoff Moss. The circuit of the A100 is the same as the A1 except:
- 32V rails instead of 25V rails.
- idle current at 1,25 A in stead of 650 mA (the collector resistors become .22 instead of .47, and the 1M8 resistors become 2M7).
Probably the MA50 is the circuit of the A100 but in the housing of the A1 (and thus built as a mono-unit with better power supply). Hope that someone can confirm the latter (I wonder if the MA50 has one or two parallel pairs of power transistors).
Rudy
I built the A100 schematics in mono-form a few weeks back with 300VA power supply and the sound is on par with the JLH and Hiraga that I also have in the house. Each of these amplifier has its own strengths. I can supply of photo of the built circuit on this forum if people like to see.
The c ircuit diagram of the A1 can be found at the class-A site of Geoff Moss. The circuit of the A100 is the same as the A1 except:
- 32V rails instead of 25V rails.
- idle current at 1,25 A in stead of 650 mA (the collector resistors become .22 instead of .47, and the 1M8 resistors become 2M7).
Probably the MA50 is the circuit of the A100 but in the housing of the A1 (and thus built as a mono-unit with better power supply). Hope that someone can confirm the latter (I wonder if the MA50 has one or two parallel pairs of power transistors).
Rudy
I built the A100 schematics in mono-form a few weeks back with 300VA power supply and the sound is on par with the JLH and Hiraga that I also have in the house. Each of these amplifier has its own strengths. I can supply of photo of the built circuit on this forum if people like to see.
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