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Vintage Musical Fidelity Mosfet amplifier guide

Discussion in 'classic' started by Arkless Electronics, May 25, 2019.

  1. Ali T

    Ali T pfm Member

    Had an A370 for a while, good amp as I recall.
     
  2. kempeu

    kempeu New Member

    My P180 and A100 got switch on thump issue. every time I turn it on, it makes a light thump/pop. Any solution? Will cause damage to my speakers? Thanks.
     
  3. Phill

    Phill New Member

    Hi

    I am new here, recently bought 2 power amps and wanted to bring them back to their glory. Unfortunatley there is almost no info about any of these on internet after hours searching i stumbled up on this conversation.

    The amps are Bose StudioCraft F1

    You can find the old review on google by searching Bose StudioCraft F1 muzines

    Its the same as Musical Fidelity Dr Thomas

    I have managed to find some info about Musical Fidelity Dr Thomas and Musical Fidelity Studio T amps. Studio T amp is bit different but I have no clue what are the differences between them.

    So back to the question.

    In the review i stated above it says it can be bridged. There is nothing indicating that it can be bridged the usual way by using switches or connecting it according to labels.
    I do not want to take risk.

    There might be someone here that know something about the family of these amps (Musical Fidelity P series) stated in the first post and the ways to bridge them.

    Is there a way to connect them? Do you need to modify them in anyway? I would like to use them as mono blocks.

    Any help any info would be greatly appriciated.
     
  4. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    They were never bridged. You could bridge them by feeding them from a balanced pre of course, "hot" to one channel and "cold" to the other and then take the output from between the two red speaker terminals.
    I've not tried it and we never did it at the factory. They may blow up. There is also no good reason to do it IMO as they are powerful anyway and you would just end up with an even more powerful amp which though can only really drive "easy" loads....
    What was done with many of the P/A series amps is to use the channels in parallel. Use a "Y" lead to short both left and right inputs together and then connect the two red speaker terminals together and another wire to connect the two black terminals together. This makes a monoblock with twice the current capability and double the damping factor. Power into 8 Ohms will increase by only a tiny amount (5-10% ish) but ability to drive awkward loads and power into 4 Ohms and less will all be much improved as will general sound quality.
    This was often done with P140/150 and the monster SA570 was an A470 with the channels wired as above. I can't guarantee it will work fine with all models in the range and under all circumstances though.
    It is very important that the channels are well matched.
     
  5. davidsrsb

    davidsrsb pfm Member

    There must be a significant dc and ac output resistance to get away with shorting the outputs together without sharing resistors
     
  6. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    The smaller amps have 0.22R and the big 'uns 0R05 and this is enough. They do need to be very well matched in channel balance etc.
     
  7. cpg

    cpg pfm Member

    I once read that the Musical Fidelity MA50, mono power amp with 50W nominal output, was 2 MF A1 power amps, 25W each side, paralleled together.
    In one of posts above Arkless says he would only expect a 10% rise in power output with 2 channels working in parallel.

    What I have failed to understand correctly?
     
  8. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Higher voltage mains transformer!

    This was probably MF's most cynical and unreliable product.

    10% is fairly optimistic in fact for the power rise and any power rise is simply through reduced resistive losses.

    What the technique does is give double the output current, twice the damping factor and doubles the "ability to drive awkward low impedance loads"

    It should work with Naim power amps BTW but I've not tried it of course and therefore cannot promise it's safe...
     
  9. Phill

    Phill New Member

    Thanks for your answer.

    Will service both of them and make sure they are well matched.
     
  10. 13oots2

    13oots2 New Member

    Just bought my second P180 to run bridged or is it parallel? Very pleased with the results but the temps even at low volume are a bit high, have bodged a couple of 120mm PC fans to be USB powered, have a couple more proper USB fans arriving soon, 2 per amp. Even with one fan per amp the temps are much lower, I have every intention of keeping these amps running for as long as possible. A friend who is a metalhead said my single P180 was frightening, I would think 2 will terrify him.
     
  11. fran

    fran pfm Member

    Are the Elektra series of amps regarded at all?

    I have an Elektra E300 just landed on the bench at the moment, seems to be blowing fuses but I haven't got to look at it properly yet. Nothing seems obviously burnt other than an area of heat around what is probably the driver transistors......
     
  12. simonpyeman

    simonpyeman Member

    A bit off topic for this thread, but do you have any wisdom about the Preamp 2a? I’ve had one for (many!) years sitting happily in front of the Pye/Tannoys, but the right channel now has a crackle on the volume pot. I’ve not managed to find any circuits or proper information about them yet. Are there any known updates/tweaks for these things worth pursuing? I particularly like the MM phone stage for its lively character.
     
  13. torstoi

    torstoi pfm Member

    I happened to have that very problem on a JVC 1010 unit lately & with the help of this forum I completely cured it
    using a can of Deoxit D5.

    See page 41 on this thread:
    https://pinkfishmedia.net/forum/threads/jvc-ax-z1010tn-review-part-ii.190183/page-41

    I opened the amp and sprayed into a hole of the pot from behind whilst covering the surrounding with a substancial amount of kitchen paper squashed into a sausage form to avoid it from dropping too much elsewhere in there.
    Left that paper banana in there in the open amp for a bit to catch up drops still coming from the pot.

    I moved the pot 20 times to max and back each time before I used the amp for like 3 days & after that the crackle was completely gone.

    If that doesn't cure it, I'd have it looked after..my crackle was stereo,
    capacitors on their way out can also make a light crackling noise as far as I know..but I'm no expert.
    Jez is the one to go to.
     

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