Magnum MP-250 Pre Amplifier
This discussion was created from comments split from: The "Royds Do Loud" Club.
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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?
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.
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.
Sorry, Col!
It provides a little insight into what these 'lectronics do.
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....
Until then, from memory, the socket closest to the back panel was empty - does that tell you anything Col?
The new capacitors, in place. Also, the phono stage.
Col, should the other 8 caps at the front be changed too?
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.
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.
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.
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.
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.
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.
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!!
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!
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!
OK - a resistor was soldered between the transistor and the other resistor. Resistance is futile.
'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?
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!