The 38v is correct to have across the capacitors, but it's not correct to have it on the 24v rails
A transistor had failed, could be the source of the issue
A transistor had failed, could be the source of the issue
Slow down the markings on the board are not correct remember that MF used the same board for the A1 with 24Vdc rails and 20W of power and for the A100 with 50W power with raised power supply (+/-38Vdc)
What voltage were the original power caps ?
What voltage were the original power caps ?
If they used the same physical board and didn't make a second run, how come the board says A100 in two places, did they scratch off the A1 markings on the old board then silkscreen on A100
Or did they use the same board but had a new silkscreen and they forgot that it was 38v instead of the A1's 24v haha
When you ask for the voltage, are you asking for the rating or the output voltage?
Thanks for all your help and engagement so far, everyone on here
Or did they use the same board but had a new silkscreen and they forgot that it was 38v instead of the A1's 24v haha
When you ask for the voltage, are you asking for the rating or the output voltage?
Thanks for all your help and engagement so far, everyone on here
Voltage rating of the capacitors on the power supply that you replaced
The version with 24Vdc rails had 25V capacitors
About the A100 marking on the board and the rails voltage I have seen worse mistakes.
The version with 24Vdc rails had 25V capacitors
About the A100 marking on the board and the rails voltage I have seen worse mistakes.
I don't actually remember, when the amplifier arrived I saw that they were bulging so I removed them, when I placed the order for the amp I also ordered replacement caps that were 63v as recommended to me
All I have are photos of how it looked when I opened the amp as I threw the old caps in the bin as they were dud! Unfortunately in the photos you can't actually see any specs haha
All I have are photos of how it looked when I opened the amp as I threw the old caps in the bin as they were dud! Unfortunately in the photos you can't actually see any specs haha
So basically you saw the 24V mark on the board and assumed that the rail was 24Vdc so all the questions from post 1 where just an assumption based on that same marking.
If you have followed the link posted on the first page (and read it) you would have find out what I just told you.
Oh well you live and learn....
If you have followed the link posted on the first page (and read it) you would have find out what I just told you.
Oh well you live and learn....
Well I think if the board says 24v and is also marked with "A100" you're going to assume it's the correct board with the correct silkscreen and that you should be seeing 24v out of the board
I wouldn't had expected Musical Fidelity to **** up that bad personally
The link on the first page is to a write up by Mark about the A1, no mention of the A100 apart from saying that there's a bigger transformer giving it higher supply rails, to me that just looks like it's saying it's capable of delivering more current and not that it's higher voltage
Especially seeing as in my mind it's 24v powered as it says 24v
I wouldn't had expected Musical Fidelity to **** up that bad personally
The link on the first page is to a write up by Mark about the A1, no mention of the A100 apart from saying that there's a bigger transformer giving it higher supply rails, to me that just looks like it's saying it's capable of delivering more current and not that it's higher voltage
Especially seeing as in my mind it's 24v powered as it says 24v
It seems quite clear that Mark Hennessey's "the bigger transformer gave it higher supply rails" refers to voltage. I guess if you hadn't been soaking up electronics lingo for half a lifetime that it could be just as easy to interpret the statement as referring to a specific bias current derived from the rail supplies but that would make it an ad hoc term with no currency. Such are the perils of inexperience but you live and learn, right?
It could mean a host of things really; even the voltages relative to another rail supply, as in class G and H amplifiers but a reference to higher current rails is seldom if ever used in regard to audio circuits. It always refers to a fixed quantity like the supply voltage. Current varies with the signal and bias settings of the various loads on the supply so the current supply can't be termed a rail, by definition.
As far as MF's record of manufacturing practice is or rather was concerned, you should refer to Jez Arkless, a member here (jez) and at other forums, who was also the service manager for MF in the early days. He could and did tell us quite a few of the doubtful manufacturing practices that ended in his resignation.
IOW, don't get all starry-eyed about MF's past practices and quality. In this country, it took a while but we found that the products were cute but over-expensive, bodged, used under-rated caps, cheapest possible semis and were very unreliable in our warmer climate. They were soon in for service (what service??) or scrapping.
It could mean a host of things really; even the voltages relative to another rail supply, as in class G and H amplifiers but a reference to higher current rails is seldom if ever used in regard to audio circuits. It always refers to a fixed quantity like the supply voltage. Current varies with the signal and bias settings of the various loads on the supply so the current supply can't be termed a rail, by definition.
As far as MF's record of manufacturing practice is or rather was concerned, you should refer to Jez Arkless, a member here (jez) and at other forums, who was also the service manager for MF in the early days. He could and did tell us quite a few of the doubtful manufacturing practices that ended in his resignation.
IOW, don't get all starry-eyed about MF's past practices and quality. In this country, it took a while but we found that the products were cute but over-expensive, bodged, used under-rated caps, cheapest possible semis and were very unreliable in our warmer climate. They were soon in for service (what service??) or scrapping.
From mark Hennessy site
"The A100
Released in 1986, the A100 is a beefed up A1 in a slightly taller case producing 50 watts per channel. To achieve this, there's a bigger transformer giving higher supply rails. Musical Fidelity claim that it operates in class A 99% of the time, but I suspect that this refers to the time spent outside of class A operation in typical use with music rather than test tones; in other words, we almost certainly can't infer anything about the standing current from that statement!
There are two fans which become noisy with age, and when the bearings get tired, they slow down and innevitably the reduced airflow leads to reliability problems. Also, they suck dirt and dust through the case...
The output transistors seem to be the same 2N3055/MJ2955 combination as used in the A1. I'm surprised at this frankly, but it certainly explains why failures are all too common - it's definitely worth upgrading to MJ15003/4 pairs. All other comments about the A1 apply to this model, so check for noisy controls and dried up electrolytic capacitors..."
"The A100
Released in 1986, the A100 is a beefed up A1 in a slightly taller case producing 50 watts per channel. To achieve this, there's a bigger transformer giving higher supply rails. Musical Fidelity claim that it operates in class A 99% of the time, but I suspect that this refers to the time spent outside of class A operation in typical use with music rather than test tones; in other words, we almost certainly can't infer anything about the standing current from that statement!
There are two fans which become noisy with age, and when the bearings get tired, they slow down and innevitably the reduced airflow leads to reliability problems. Also, they suck dirt and dust through the case...
The output transistors seem to be the same 2N3055/MJ2955 combination as used in the A1. I'm surprised at this frankly, but it certainly explains why failures are all too common - it's definitely worth upgrading to MJ15003/4 pairs. All other comments about the A1 apply to this model, so check for noisy controls and dried up electrolytic capacitors..."
No need to bitch about the bleeding obvious - Is it not just the same board being used without fully revising the silk screen as a record of all the changes?. That could well be the case where the other models and variations based on A1 were produced and probably only in short runs. As a manufacturer, you would definitely need to identify each model's board assembly to prevent production, storage and servicing mistakes. That means the model identification number would need to be permanently marked on it but not necessarily showing all changes - that would take a lot of documentation and time. The necessary details would all be covered by notes distributed to the service agencies and may never appear anywhere else.
To expect better from MF is one thing but to deny the inconsistencies in what you have in front of you is pointless. Just get on with the task in hand and let the navel-gazers ponder them.
To expect better from MF is one thing but to deny the inconsistencies in what you have in front of you is pointless. Just get on with the task in hand and let the navel-gazers ponder them.
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The board isn't actually identical to the A100, the A1 and A100 use different boards, at least that I can see from Google
Which means the A100 board was made from scratch, and after they printed the board they'd had needed to add a silkscreen to match the new layout
So if they made a new board, and they also had to silkscreen that board, it means that the +24v and -24v silk screened onto the board was an error by them, must had forgotten that this board was now 38v and not 24v like the PCB they worked on previously for the A1
I'm also not bitching about anything, I couldn't care less that they got it wrong it just hinders me a little as I'm a first time amplifier fixer/tinkerer
I am unsure if your comment is light hearted or not so forgive me if I am reading it in more of a "finger pointing towards me" manor
Which means the A100 board was made from scratch, and after they printed the board they'd had needed to add a silkscreen to match the new layout
So if they made a new board, and they also had to silkscreen that board, it means that the +24v and -24v silk screened onto the board was an error by them, must had forgotten that this board was now 38v and not 24v like the PCB they worked on previously for the A1
I'm also not bitching about anything, I couldn't care less that they got it wrong it just hinders me a little as I'm a first time amplifier fixer/tinkerer
I am unsure if your comment is light hearted or not so forgive me if I am reading it in more of a "finger pointing towards me" manor
Hi, from the picture provided by your 47#, you can be 100% sure that this is an A100, and its transformer voltage is AC (25-0-25). I have repaired this model many times, which is certain.
I haven't done much in terms of fixing the amplifier, I've been working on replicating the PCB in software so I can get some custom matte black ones printed
A couple burned resistors have separated a few pads so I thought I'd just make a new board
Musical Fidelity A100 PCB replica project
A couple burned resistors have separated a few pads so I thought I'd just make a new board
Musical Fidelity A100 PCB replica project