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Musical Fidelity A1:
Brief details of related Musical Fidelity products...
You'll note that there's only info here about Musical Fidelity's earlier products. If anyone is able to offer information on their later products, I'd be fascinated to hear from you. I'm keen to see what configurations they are using today, especially knowing how well-reviewed their products currently are.
Thanks to Marc Huske for supplying the following pictures of a "David" and a "David II". As far as I can establish, this was a tuned version of the A1, sold to the German market. The pictures here show the original version of the A1 circuitry.
From the front, there is a "David" logo in place of the "A1" designation. Inside, things look normal at a glance, but you can just see two large black polypropylene capacitors hanging off the right-hand end of the PCB which appear to be connected in parallel with the main smoothing capacitors. Also, there are bigger loudspeaker binding posts and an IEC mains inlet instead of the captive two-core lead - the case of this unit is connected to mains earth. This mains transformer looks like it might have 4 primary wires, meaning that it could probably be converted to 120VAC operation - most examples I have seen, including my own, have just 2 primary connections, meaning a new mains transformer would be required for 120V operation.
The quad op-amps in both the phono preamp and the main line preamp are in sockets, but apparently they are still the standard TL084's.
These pictures show a mark 2 David:
Looking at the PCB, it says David II on the silkscreen, between the input sockets and the power supply. From a recent examination of a MK3 A1, it's clear that the PCB is MF's latest version.
Note how the primary lead-outs of the mains transformer and the rest of the mains wiring have been double-insulated using what looks like heat-shrink tubing. I can't see if there are four primary wires, so I don't know if this model could be re-wired for 120VAC operation. The large polypropylene capacitors have been accommodated on the PCB, and the power supply has an extra pair of smoothing capacitors and 0.47 ohm dropper resistors - the output of the first smoothing capacitor is split two ways, so that each supply has its own capacitor - almost dual-mono, perhaps...
The line preamp has moved slightly, and has an extra 4 transistors to implement a rather crude power-on mute. Here, Marc has upgraded the TL084 to an OPA4134. The 1uF input capacitors on the power amplifier have been changed for polyester units (like I did when I replaced my preamp). The phono preamp is slightly different - they've dropped the complicated regulation arrangement that the original version had, and there is a pair of TO92 voltage regulators supplying the dual op-amp instead.
Many thanks to Marcus Ackel for these pictures of his Final Edition. As you can see, this is the B200 circuit, with an outboard power supply that gives higher supply rails and a higher output - 40 watts per channel.
The first image shows the general view with the cover removed - click these images for a larger view. The "Final Edition" sticker can be clearly seen on the PCB. The connection from the outboard PSU appears to be a 3-pin XLR - raw AC from the external transformer is switched by the power switch, meaning that the transformer is continuously powered when it is plugged into the mains supply.
Looking at the enlarged version of the picture showing the underside of the PCB, you can clearly read "B200 MK2 ISS 4" towards the bottom-right of the image.
These two picture show the output stage, with the LM318 op-amp and BUZ900/BUZ905 output MOS-FETs. The smoothing capacitors are 6800uF each, and a bridge rectifier is used instead of the 4 discrete diodes of earlier models. They retained the Alps "Blue Velvet" volume potentiometer...
Thanks to Justin Goh for submitting this picture of a Final Edition with a striking silver/chrome finish:
And according to the accompanying certificate, here are the differences between the standard model and the Final Edition:
Some of these are clearly of dubious merit! But, as only 200 of these were ever made, they are quite collectable, and raise good money on places like eBay...
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, so by my reckoning, there's 1.75 amps of standing current per channel, resulting in around 160W of heat dissipation. If you follow the reasoning the designer gives on the technical page, the standing current is half that, but that's still 80 watts or so. Either way, not really enough to earn the Class A badge. 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, and failures are all too common. All other comments about the A1 apply to this model, so check for noisy controls and dried up electrolytic capacitors...
Something that amuses me - reviews often say that the phono stage was much-improved compared to the A1, but it's exactly the same!
This is a monoblock amplifier built into an A1 case, released in 1985. It's just an A1 with a bigger power supply - the PCB is the same, just the components relating to the pre-amp aren't fitted. Both power amp sections are fitted, and the outputs are wired in parallel. Apparently they are even more unreliable than the A1!
These all use Musical Fidelity's op-amp plus MOS-FETs power stage. This includes the P140 (70Wpc), P170 (85Wpc), P180 (80Wpc), P270 (135Wpc), P370 (185Wpc) and the B200 - no-doubt there are others too.
The design was gradually refined over the years, but follows the basic topology explained on the Technical Page.
This is a picture of the insides of a P180 - you can see the multiple output MOS-FETs all on their individual heat sinks. Some how, they don't seem big enough for an 80W amplifier but at least there will be a saving in thermal resistance because the devices won't need to in electrically insulated from the heatsink. The outboard PSU appears to have an XLR connection to the umbilical lead that connects to the main amplifier.
I don't recall where this image came from, so if you recognise it, please let me know and according to your wishes I'll either credit you, or remove the image.
Comments? Questions? Please, let me know...
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