mikeks said:
Ahh, Sorry I meant take the lids off and fiddle about with the innards
ANTHONY2181 said:
That is a good deal. I was thinking of maybe eventually selling mine although when modified, I would say, really they are as good as many new amps up to £5000. Recent experience with them suggest to me I might end up keeping them!
I say that figure as a pal works for an upper rung HiFi shop and took his own custom made monoblocks to work where, by staff consensus, they were only beaten by the amp(s) that retailed for >£4000.
My twiddled with 605's were similar sounding to his monoblocks except for the extra octave or more at the top
We compared them on his system, Celestion A1 (or is it A3? ..the big floorstanding ones with 3 bass units each), custom pre amp and possibly the best CD player I've yet encountered, again custom made (both items jammed full with Black Gates as were his amps!). All wires solid silver, inc the CD player, preamp, amp and speakers internals and interconnects and speaker leads. Adequate mains supply. So a fairly revealing system.
Martin Columns, in the HiFi News, I think it was, review stated he felt the 605's (he had four of them) were amongst the top ten amps in the world. When I bought them in 1993 I thought that was to say the least an exaggeration, but now with the benefit of some changes, mainly power supply based, they do sound quite good, and maybe he was correct. I know from 1st hand (not hearsay) that he had modified his own and although he told my pal that the review was about standard ones I can't help feeling that the modified ones coloured, or rather clarified, his view of them.
They do have one major fault, the case is too small to fit a adequate PSU into. And the transistors have been bunched up one end which gets a bit warm.
Also they are pretty wide open at the top but the word is they have unstable tendancies and may melt ones supertweeters!!
I alas lack the technical skills and hardware to properly evaluate and improve, if this is possibly, on the circuit itself. I have 'reverse engineered' it and have a schematic drawn by hand. It's a rather unsusal thing, based around a now extinct Op-Amp, the PMI OP44, almost same as the OP42, but better at higher gains. A DC coupled amplifier with no electrolytic in the feedback path. Or anywhere in the signal path
They then knobled the amp by cutting down the voltage to the mosfets and using a very small main reservoir.
Changing those two areas brings the amp alive. A good mains supply helped too as I replaced the laughable 3 amp, or whatever, leads with some 30 amp or so ones.
I strapped a pair of Nichicon KZ 330@100V and then a pair of Black gate FK 100@100V across the Ansars and sat back in amazement!
I also replaced the Vandenhull stranded copper on the input with some solid silver and even though that was only 9 inches it made a worthwhile improvement.
I changed the output coil to one of the same number of turns but much thicker wire (so I presume slightly lower inductance) (1.25mm diameter instead of 0.89mm I think the original might have been), after all there's maybe 50 inches of the stuff in that coil, and wow, what an improvement! Also at the same time changed the resistor to a slightly lower valve, 6.7R 3Watt power oxide. The original Meridian resitors was 12 Ohms.
Then left them as they were for a few years.
Just changed the output resistor to a Caddock MP821 Kool Tab, 8 Ohms, after having done this on a few other amps with good results. It's made such a big difference I can't quite believe it. Turned the mid/treble up a lot at the expense of male vocal and bass. The female vocal is prety good, but the balance is wrong. I'm going to put the cheap resistor back later and maybe take the nichicons and black gates off, as they can sometimes turn up the treble too and also make the treble confusing sounding. Thought the BG's do usually enhance of transient response and bass depth.
It seems like there is more to come from these 605's. But it may need some circuit value changes and component changes. I was going to start a thread to see if anyone has done that yet as they are a bit hard / harsh in the treble and that maybe their deep rooted character and not improveable. I've heard that the current amount to Mosfets should be fairly high, and it looks like it can't be in this case, the driver and gate resistors may need changing and the resultant heat dissipation problem sorted. The OP44 may transpire to not be the best sounding chip either.
Did a search and, a little surprisingly, this thread was the only find.
I'm new to this board. Do you know if there are some Meridian experts amongst the membership that might already know?
Cheers
I think it is now.
It's actually not very complicated.
Never the less I did on the first attempt, a few years ago, fail to spot a little length of copper track between the DC offset servo diodes until last Friday when I had another look. Then that area became clear to me.
I've checked the rest again.
I would try to get it scanned and, if I could work out how, posted on here.
Maybe I have to save it as a jpg, and attach it.
I have to reboot this PC to get the scanner working. Maybe later.
It's actually not very complicated.
Never the less I did on the first attempt, a few years ago, fail to spot a little length of copper track between the DC offset servo diodes until last Friday when I had another look. Then that area became clear to me.
I've checked the rest again.
I would try to get it scanned and, if I could work out how, posted on here.
Maybe I have to save it as a jpg, and attach it.
I have to reboot this PC to get the scanner working. Maybe later.
The damping factor on the standard 605 is something in the order of single figures, eg, 7.
With the addition of 40,000 low cost micro Farads across the existing Cerafines, it rose to 269. I seem to recall.
And the four 10,000 Nichicon Grade 4 I now have replacing the two 4700micF@80V Cerafines on each 605 are soooo much better than the quite a bit cheaper Elna non audio caps I started with.
Only prob is they won't fit in the case. So I don't have the lids on. Not very child friendly I know, what with the exposed live mains! But it is a talking point when friends call round
The cheap caps still can work well though. Samwah do some 'audio' grade ones that are small enough to fit a bunch of them in there. You need another 40,000 mic really.
I've got 80,000 cheap micro Farads on my single PSU stereo integrated amps.
U gota hav da Joules.
And also parallelling them leads to a lower ESR at low frequencies so you can get better current delivery at 20 Hz, if you're into that sort of frequency.
With the addition of 40,000 low cost micro Farads across the existing Cerafines, it rose to 269. I seem to recall.
And the four 10,000 Nichicon Grade 4 I now have replacing the two 4700micF@80V Cerafines on each 605 are soooo much better than the quite a bit cheaper Elna non audio caps I started with.
Only prob is they won't fit in the case. So I don't have the lids on. Not very child friendly I know, what with the exposed live mains! But it is a talking point when friends call round
The cheap caps still can work well though. Samwah do some 'audio' grade ones that are small enough to fit a bunch of them in there. You need another 40,000 mic really.
I've got 80,000 cheap micro Farads on my single PSU stereo integrated amps.
U gota hav da Joules.
And also parallelling them leads to a lower ESR at low frequencies so you can get better current delivery at 20 Hz, if you're into that sort of frequency.
Hello,
I'm not sure what you're asking.
The output Transistors are Audio MOSFET 2SK and 2SJ types.
Standard power supply as in pretty much all transformer / capacitor designs: 605 has about 400VA transformer, bridge rectifier, main capacitors. The power supply voltage after the bridge rectifier is about ± 60V.
There is a 2nd Bridge giving about ±20VDC to power the Op-Amp via two adjustable (317 / 337) regulators delivering about ±16V to the Op-Amp (OP44).
Meridian used a relay to switch off the mains supply to the transformer if DC is detected at the audio output stage.
thanks
thanks
i am not say clear ,the meridian 605's have four board ,two big two small.the small board is power supply ,i amazed at it is power supply board ,at small board have two Cerafines and 8.5mh inductor and one transistor etc ,now i want to known the type of transistor of the power supply board's
thanks
i am not say clear ,the meridian 605's have four board ,two big two small.the small board is power supply ,i amazed at it is power supply board ,at small board have two Cerafines and 8.5mh inductor and one transistor etc ,now i want to known the type of transistor of the power supply board's
Thanks,
Did consider it when added the caps but 40,000u is not big really and the Bridge is what looks like a 20 to 35 amp type (the square bolt down chassis mount type with the 4 large spade connectors in top). The extra start up current delivery is, of course, limited by the transformer.
Anyway, looks like I made the right call as they've been with the 40,000 instead of 9,400 for nearly 16 years now
Wow, where did that time go!
Did consider it when added the caps but 40,000u is not big really and the Bridge is what looks like a 20 to 35 amp type (the square bolt down chassis mount type with the 4 large spade connectors in top). The extra start up current delivery is, of course, limited by the transformer.
Anyway, looks like I made the right call as they've been with the 40,000 instead of 9,400 for nearly 16 years now
Wow, where did that time go!
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