Magnum MP-250 Pre Amplifier

edited June 2013 in Amplifiers
This discussion was created from comments split from: The "Royds Do Loud" Club.

Comments

  • No mate, I don't remember anything about replacement drivers - that doesn't mean I haven't forgotten though!

    My rig goes considerably louder now it has an active pre, and some very wonderful things are happening in the mid-range, imaging, and percussion. Nowhere near 100dB loud though!!!

    I wouldn't want more volume TBH, the dynamic swings can be a bit shocking as it is. More scale, maybe.
    What active pre are you using?
  • edited June 2013
    It's a 25 year old Magnum MP250. It came as a set with a MF250 power amp, which my friend now loves. He is now thinking about selling his other 'last amp he'll ever need'.

    I have some reservations about the MP250, I'll post something definitive in a week or two. It loses out to the lightspeed in several areas, but where it is better it is so good! Col has advised me to replace the power supply capacitors, which I'm going to bravely attempt. I wonder if it'll be an all-rounder then?

    image
  • So, this is the inside. Brain_Dead has advised me replace the 4700uf capacitors, which we hope will cure the issues with the Magnum.

    image

    I am going to do the 4x 50v, and maybe the 8x 25v caps, although I'm not sure they're necessary. Perhaps Col will clarify?

    This is what he said about the capacitors:

    "It is a least 25yrs old (or 210,000 hrs) and electrolytic normally last
    between 5000 - 15000 hrs. So if we say preamp has seen 10% of life, 21,000 hrs. To close, so change them when you can for Low ESR 105C type."

    Overall, I like the sound this makes. It really adds some presence to the low powered SECA amp, some punch even at low volume. I'm not sure it goes much louder than with a passive pre, but it is certainly more dynamic. If I listen at an average of 85dB I am on the verge of the SECA clipping. (It is perfectly loud enough, but a bit more wouldn't hurt, just to get some more scale.)

    The tone is really lovely, there is a richness that really connects to the music somehow, like you're right on the front row, eye to eye with musicians rather than half way back in the concert hall. The imaging too is startlingly good, really really wide and three-dimensional.

    The issues we are trying to cure with the capacitor change are bass related, a certain slowness, and a bloated, ill-defined character. It sticks out like a sore thumb compared with the quality of everything else. Hopefully I'll be able to get thie done within a week, and report back.
  • Ooh! You had me going there. I thought we were talking ice creams, then a detective with a dodgy 'tache...  :O


    Sounds interesting, nonetheless.

    We await nooz...
  • New Vishay capacities are in there now, just the four big ones. Initial impressions are of a much cleaner lower mid and bass.

    I still think the LDR has it licked in terms of treble sparkle and outright transparency, but the soundstage definately collapses a bit, and the LDR just can't get to the textural detail in the midrange (particularly guitar strings) that the Magnum can.

    We'll see if things change as its left in the system a few days.
  • Very interesting. Things are never clear cut, are they?
  • I just found this, it was caught in my span filter; Colin sent it 5 days ago and I didn't even know it.

    Sorry, Col!

    It provides a little insight into what these 'lectronics do.

    image

    No further listening took place tonight as we were watching 'telly, an after that some recorded Star Trek Voyager. Oh yes, we're living the high life here in East Sussex....
  • edited June 2013
    Now for a shilling can we all sing the Spam song?
  • I just found this, it was caught in my span filter; Colin sent it 5 days ago and I didn't even know it.

    Sorry, Col!

    It provides a little insight into what these 'lectronics do.

    image

    No further listening took place tonight as we were watching 'telly, an after that some recorded Star Trek Voyager. Oh yes, we're living the high life here in East Sussex....
    How very like Col to hid a tasty snack inside for the inquisitive punter.
  • The Cheese and Onion crisps are mine hands of Ben.
    Alan take the MC shield of and re-photograph so we can see which MC stage it is please.
  • Without taking apart first the HiFi, then the Magnum again, I can't photograph it just yet. Next time I get it out of the system I will take a picture.

    Until then, from memory, the socket closest to the back panel was empty - does that tell you anything Col?
  • edited June 2013
    image

    The new capacitors, in place. Also, the phono stage.

    Col, should the other 8 caps at the front be changed too?
  • Alan if you can afford to yes. This MC stage is the second style after  I left Magnum Tony did not want to pay for the use of the Patent, so he designed a cheaper and my opinion a crap MC stage to replace it.
    The first version had re-chargeable batteries.
    The A Class  o/p stage can be improved also this type did not like loads below 1K.

    So now you change the caps how does it sound?

  • I'll write more as time permits mate, but I am liking this more and more. Those caps will have to be changed next... I think there's more mileage in this then, given how good it is now and what you have said about O/S mods.

    LDR is for sale now - not because it's bad (far, far from it) - but because in this game of swings and roundabouts I prefer this new set of compromises.
  • ...and how was the doughnut...?
  • I made some written
    notes yesterday, for the first time - I was starting to get confused
    about the differences between the Lightspeed and the Magnum. Writing
    down my impressions when listening is a new level of nerdiness for
    me, but it yielded some results which surprised me!

    The parts I knew I
    liked liked about the Magnum was it's ability to winkle out amazing
    detail on strings, be they violins & cellos, or guitars. As my
    primary interest is songwriter music, guitars (particularly
    unamplified) are very important to me. It also allowed exceptional
    control over bass, both at extremely low and high volume.

    The Lightspeed has a
    hard-to-live-without quality, which I suppose is what is referred to
    as 'transparency'. It's as if it's just not there, and when I swapped
    it back into the system it gave a sense of a refreshing gust of fresh
    air – it felt good every time. I can't help thinking of it as a
    reference standard of 'transparency'. (Please forgive me for using
    HiFi speak – I know what I mean, but I have no idea if we think of
    the same things when words such as 'transparency' are used.) It
    seemed more subtle than the Magnum, maybe more finesse in the way it
    portrayed detail – perhaps even more detailed overall?

    Both amps had qualities
    I want to keep, but I never knew which way to jump when it came to
    making a choice. Partly, this is because of the difficulties of
    making a direct comparison, due to the monumental faff of swapping
    pre-amps and associated cabling, and partly because there is no way
    to even approach volume level matching (what with one being active,
    the other passive). So, this is why I wrote notes of my thoughts
    during an hour or two of listening, then I swapped the Magnum for the
    (pre-warmed) Lightspeed, and wrote notes again. Both times, I just
    went for a comfortable volume on the higher side of average.

    I listened to the
    Magnum for a while noting several previous criticisms I held
    previously didn't seem quite so, er, critical! These included a
    'warmth' to the whole experience, something I've observed many hifi
    enthusiasts striving for. I never wanted warmth, I'm a detail freak
    (having played music myself, I want those 'warts 'n all). The
    'warmth' is quite nice to have, but thankfully has toned right down
    in the week since I changed the capacitors.

    Related to the 'warmth'
    was, I felt, a 'softness' to the bass, it seems somehow a little
    lower in the mix than with the Lightspeed. This isn't a dealbreaker,
    because somehow it still presents the detail in the bass as clearly –
    in fact, probably more clearly – than the lightspeed.

    I played several tracks
    that are 'flavour of the month' at chez Brown – mostly summery
    songs, and others were selected because of less-than-perfect
    production, which makes them tricky for the hifi. They included the
    first 2 tracks from Ane Brun's Live in Stockholm album (The Puzzle,
    and Singing one of your songs), several from Ben Taylor's 'Another
    run around the Sun', a bit of James Blake, Massive Attack, Ray
    Lamontagne ('Empty'), The xx, and some choral music, also some live
    Big Band (Matt Catingub).

    I noted the bass, in
    particular the separation between kick drums and bass notes even when
    it got busy. I found each note and stroke was perfectly distinct,
    though not isolated – just as it is when you're there. I was no
    longer sure the bass was soft at all, and the feeling that the bass
    was somehow 'slow' was now gone – I guess the new capacitors have
    seen to that. Something else I noted was ride cymbals ringing on, and
    being distinct even over the rest of the music. In fact, all the
    cymbals had a very nice quality to them, the overtones and shimmer
    was just as as I remember them from playing myself.

    I put the Lightspeed
    in, and played the same tracks. The first thing I noticed was an
    obviously less 3-dimensional stereo image. This is fine, but it was a
    shame when I had been quite enjoying that aspect. I also noted a
    slight stridency in the treble – the cymbals in particular weren't
    doing what they had been. The bass was fine and good, not so warm,
    but it struggled a little with 'flabbiness' (if you know what I
    mean?) - The Magnum had provided a great deal of control, and
    texture, yet the Lightspeed felt like it was allowing bass noted to
    'shout' a little, even to overshoot on occasion, which only served to
    obscure the texture I had heard an hour or so before.

    The real strengths of
    the Magnum weren’t challenged at all by the Lightspeed, but I knew
    they wouldn't be. I was interested in seeing if the Lightspeed could
    almost match the Magnum at least, and I felt it didn't. The
    transparency was still appealing, but the way it managed to sound
    'loud' all the time wasn't. It was like a thin layer of distortion
    over everything above the midrange (I think this is called 'grain'),
    and a lack of shape and form on the bass.

    I have had the
    Lightspeed for a while now, and I know it's above reproach. My own
    thoughts are that the SECA I'm using benefits from active
    pre-amplification, although it doesn't need extra gain – neither
    pre manages to be louder before clipping sets in (the SECA is only 10
    watts).

    The re-capping of the
    Magnum has changed it from being a flawed, if interesting amp to a
    still flawed but very convincing contender. It has lost the
    disagreeable coloration and warmth, which I'm pleased about, and I
    expect further improvements as I apply more suggestions from Colin,
    who designed both the Magnum and my SECA.

  • Ok then - results from replacing the capacitors  a quote from above
    Replacement caps - "Alan June 14 QuoteFlag
    Moderator
    New Vishay capacities are in there now, just the four big ones. Initial impressions are of a muchcleaner lower mid and bass.

    I still think the LDR has it licked in terms of treble sparkle and outright transparency, but the soundstage definately collapses a bit, and the LDR just can't get to the textural detail in the midrange (particularly guitar strings) that the Magnum can. 

    We'll see if things change as its left in the system a few days.
    Initial impressions are - not light and day then?

    I bought a Hafler DH200 as a spare for mine (have had it for 34 years I built it) - the one i bought had hardly been used and the difference between the two amps? ... well i thought the older one sounded better at first than the new one  ... then asked my wife and daughter to ask which sounded better ... after half an hour of switching back and forth the answer came ... i can here a slight hum with one when the music isn't playing (the windings on my original are getting old and the transformer hums slightly).

    So I have to ask ... if it sounds ok to your ears then is replacing the caps a value for money upgrage or maintenance  item?

    Oh one more thing - someone said above about powered preamp vs passive - to my ears i have yet to hear a passive pre beat a class act powered pre-amp.  Now that could be that most amplifiers like an input of a volt or more and the low output of the passive ones drain the life out of stuff?

    I don't know the answers but perhaps I am lucky in that i listen to the music not the equipment.  I chose my system on careful listening and I was lucky enough to work in the trade for a time so got to hear lots and compare lots.  The end result is one of synergy ... and of course the medium used. All CD players sound different but none of them sound "right" when compared to a good analogue recording replayed on Vinyl through a good turntable arm cartridge combination.

    Most people who bought Kef104/2 or Kef 105s never heard them perform at their best because they mated them to amplifiers that did not give of their best into a load that dips below 4ohms.   Similarly Gale 401s - somehow they never sounded as good on a valve amp as they did on a transistor one - and again they needed an amp that could deliver at less than 4ohms.








  • I guess that is what makes this a fabulous hobby - we have those who spend a fortune on cables when the money spent on a better arm and cartridge would have yielded ten times the improvement (the analogy that springs to mind is the 20 year old clapped out VW Golf with brand new shiny alloys that are worth more than the whole car and do little to help it's performance).

    I always look at how much music does someone possess before I question them about their hifi - all to often have i seen someone with 100 albums or CDs with a massive expensive system and then you have to wonder what matters most - the music or the equipment.

    Anyways enough of my ranting - I am just going to settle back and listen to an old Larry Adler record through my ancient Systemdek IV, with mission arm and Decca cartridge, an old Audio Research SP9 pre, my hafler DH200 amp through a pair of Art Impressions (fed by 500 and something strand OHC copper speaker cables) and will have a big smile on my face.
  • Initial impressions are - not light and day then?
    ...

    So I have to ask ... if it sounds ok to your ears then is replacing the caps a value for money upgrage or maintenance  item?

    Oh one more thing - someone said above about powered preamp vs passive - to my ears i have yet to hear a passive pre beat a class act powered pre-amp.  Now that could be that most amplifiers like an input of a volt or more and the low output of the passive ones drain the life out of stuff?




    Hi Uzzy, Thanks for chiming in!

    In answer to your first question - I'd have to answer - both. I'm not being perverse, but the Magnum is definitely improved with the addition of the new electrolytic capacitors. Note, I'm not in any way saying the new caps are better than what was originally in there, simply that the original electrolytics were well past their best, and bringing the MP250 back to it's original spec has shown what it is capable of, and has been hugely rewarding.

    It has turned it from a very interesting but fatally flawed bargain (IMO) into a thoroughly decent pre amplifier in it's own right, and one that has tremendous synergy with my power amplifier.

    Cost of MP250 - £100. Cost of the 12 large capacitors I replaced - £42. I'd call that value for money in absolute, if not relative terms!  :)

    As to it's comparison with the recently departed Lightspeed, well that was a very interesting passive attenuator (based on LDRs rather than pots or stepped attenuators). I think this approach has a lot going for it, and I'd like to return to these in the future. It is so transparent, that the main criteria for keeping the Magnum was to remove as much of it's 'character', or sonic signature, as possible. Losing (what I heard as) the warmth, and wooly bass by virtue of the new parts has helped enormously, although it's still imposing itself on the music in ways the Lightspeed never did. However, I'm comfortable with the compromises I've made.

    @Brain_Dead has a few tricks up his sleeve WRT LDR attenuators, once he releases these into the wild I wouldn't be surprised if the issues I took with the LDR passives were resolved, as extra gain doesn't seem to be the issue here. I suspect it's more to do with Col's ongoing battle with his pet hate, phase distortion, although I am almost entirely guessing here.

  • image

    With the extra capacitors installed. Also, with some decent wire I had knocking about I have rewired the outputs, the CD inputs (all I ever use), and since this was taken also the ground to the output board, and the output from the volume pot.
  • Well, I am looking forward to Col's suggestions wrt improving the SECA (Single Ended Class A) output stage, which, he tells me, is the same as his original 7w SECA amplifier. I have to say, that having had a few weeks to settle down this Magnum is now very neutral - the warmth & cuddliness is gone, and there isn't a hint of the diffuse character that bothered me previously. It has improved in just the ways I had hoped it would, but to a greater degree.

    It is just superb when it comes to imaging, I never did hear instruments placed so well L to R, and also Front - to Back from a HiFi. I don't mean they are separated as individuals (I've heard that done, and it's not natural), there is an approriate degree of 'wash' between everything, until something starts a solo, in which case it hangs in relief all by itself down front. Quite lovely, and something all my passives failed to do so well as this.

    There is also a wonderful texture to all stringed instruments - guitars are awesome. The amount of 'What was that?' experiences I've had over the last few weeks has been ridiculous, the start of Fleetwood Mac 'The Chain' was the funniest example ( I was with a friend, and we restarted the server amongst other things trying to explain this new - and hitherto unheard - anomaly)!

    Bass is now so well controlled, after going through the now familiar 'where has the bass gone' phase that seems to follow modifications. it has shape, and attack - the 'slam' is amazing, and manages to be so even during busy passages. I like the way kick drums have this thumping great dynamic impact, yet have a shape and texture to them - all of this is preserved rather simply a powerful 'thud' and remains perfect even with a busy bass line superimposed over the top. The bass, be it acoustic or guitar has an airy, uncongested air with it, almost as if I now have full-range speakers and there is 'room' for everything to happen. I get the distinct impression the system, and room, could take much stronger (and even lower) bass.

    One of the weirder things - issues which I had pegged as room acoustic problems seem to be minimized almost to the point of being gone. I remember avoiding a few albums altogether when I used the big NVA and passive as it boomed and shouted (only a very few albums, mind), but now I can enjoy them to the full. Even new, loudly compressed stuff sounds really very palatable, much more so than before. I can only wonder at where all this control has come from, and laugh that it is produced by 10 watts into 83dB speakers!!

    Col says that the more complex 'Listen' pre is better on all counts, and does lower bass to boot - but for a stonking pre-amp, a slice of SECA magic, zero phase shift or distortion, and a weighty lump of an amp for about a hundred notes, I think the MP250 must be hard to beat. Even with mods, the total cost has been £160, and some very simple fun with a soldering iron. I absolutely recommend this old Magnum to anyone.
  • Bake-off against the Listen?
  • Sounds good!

    I have to visit Jim(-bob) in maybe 3 weeks (it'll be mid-week, during the day) - you want to come with it? I'd like to compare them to his Croft. Otherwise I'll have to swing by your place sometime.

    Your 'Listen' will win of course, but not in terms of bang-for-buck. However, I hope there will be no bangs!! ;)
  • Been reading this thread and would be interested to know if my 20w seca could be upgraded in anyway as Alan mentioned upgrades to his seca.
    atb Chris
  • Chris,

    Which SECA have you?

    Col
  • Hello Colin,
    mine was bought from quickie after he had serviced it, was just interested to know if it could be improved in anyway.It is already a splendid amp.
    atb Chris
  • Chris see PM
  • edited September 2013
    I went to see 'Our Col' last week, it was good to catch up again. I bought the Magnum along with me - Col had a modification to the output stage in mind.

    If you look at the picture above which Col labelled up, you'll note the voltage regulators and the SECA (Single Ended Output Stage). These transistors all got bigger heatsinks, as Col noted "they'll be handling much more current now". Then, Col put a resistor between one leg of the (SECA output) transistors and a leg of a nearby capacitor. It was more fiddly than anything, that was basically it.

    All that remained was to re-solder some of my sloppy work from a previous mod (and correct my switching L & R around on the CD input! :\"> ), and put it on the signal generator & 'scope. We looked at some impressively square waves, with Col patiently explaining to be about rise time, and it's relation to phase and bandwidth, and the now extraordinary damping factor the Magnum would have. After putting the lid back on, Col mentioned that as well as a general improvement, the Magnum should now go deeper in the bass.

    To start with, I found the sound a little thin, even lacking in bass - but my only listening was on the first night I got home, before proper warm-up. And general TV use at low volume for a few days.

    Having had a decent play since, I agree with Col about the general improvement. The system sounds great, much improved in every 'hifi' sense but in reality it's just more realistic. The way the system drives the whole room has improved, it actually seems to set off room's acoustic character less than before - a really 'clean' sound, even when playing loud. Much louder than before, it seems - without my noticing!

    The bass is indeed deeper, although I have few tracks that show this off. It is better controlled, starting and stopping much faster, which seems to give the music room to 'breathe'. I have never heard so much of what each instrument is doing, how they interplay with each other, yet the 'whole' sound is fully integrated, not in the least 'picked apart'.

    This Magnum MP250 was built by Col's fair hand when I was 6 years old, it now sounds better than it ever has. It really is an extraordinary thing. Thanks Col!


  • "If you look at the picture above which Col labelled up, you'll note the voltage regulators and the SECA (Single Ended Output Stage). These transistors all got bigger heatsinks, as Col noted "they'll be handling much more current now". Then, Col put a resistor between one leg of the (SECA output) transistors and a leg of a nearby capacitor. It was more fiddly than anything, that was basically it. - See more at: http://www.audiochews.com/discussion/1093/magnum-mp-250-pre-amplifier#Item_28

    It was a resistor Alan.
  • edited September 2013
    dem blue things? OK, my bad!  :\">

    OK - a resistor was soldered between the transistor and the other resistor. Resistance is futile.
  • Exterminate ! Exterminate !   \m/
  • You still got that whisk stuck to your fore-head, Col?
  • Yep that will teach me to cook NVA amps.  >:)
  • edited January 2016
    This thread, is back from the dead!!

    'Maggie' has been to meet her maker, for nothing more than sentimental reasons as I visited Col last week. It works fine, save for a fault which I caused myself when I re-wired from the PCB to the RCA sockets (I swapped R & L, OK? Anyone could have done that...)

    My embarrassment was short lived though, as Col had a closer look at how the volume pot and switches were wired up. Wrongly, as it happens.

    My particular Magnum, like many out there, was built after Colin's involvement with the company ended (I'm being tactful and diplomatic here). It's basic design is Colin's, but certain components and other bits & pieces were cheapened by the TV repairman who ran the company afterwards (but less so here). In the case of my amp (literally, inside the case of my amplifier), was a convoluted way of wiring the front panel controls, which Colin surmised was to stop people understanding the circuit and copying it. It's possible he was being generous when he said that.

    Looking closer, he found a short due to dodgy wiring (obviously a minor one as it's been there since about 1982!), so he ripped the lot out and rewired the signal path with some nice silver wiring.

    End result?

    image

    Quite an impressive boost all around, notably the upper mid-range presence and texture and a sweeter top end altogether. It started a little hot, almost fatiguing for a few days (I was worried, 'Maggie' always had a warm sound before) but has settle down now. In fact the bass is definitely faster, tighter with more slam. In fact, the improvements are across the board, making it sound like a much more modern piece of kit. The imaging is deeper, closer to me in the listening position.

    Funny, isn't it? It had a fault all this time and nobody noticed, not the previous owner who developed his own equipment and ran the Magnum in a huge Apogee ribbon setup, and certainly not me. ..As a post, obviously! ;)) So you should obviously ignore everything I just wrote.
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