Meridian 605 Mono Blocks

[ANTHONY2181]

Hi,
Ive been given a chance to buy a pair of Meridian 605 mono block power amps quite cheap.I was wondering if any of you guys have these amps or have had any experience with them.

They are to drive my Kef 105/3 speakers.

Cheers

Anthony

[mikeks]

Excellent kit....

[mikeks]

..better still, get four 605 monoblocks, and bi amp. your Kefs...

uuuuhhhhh UHHHH....Yes Lord!

[audiofan]

You may look at this one:


http://www.duncanamps.com/tsc/

[audiofan]

Sorry I was in the wrong thread................................

[ANTHONY2181]

I got my 605 mono blocks today.

They sound amazing very powerful on my kefs so detailed

Anthony

[IanAS]

[QUOTE]Originally posted by ANTHONY2181
[B]I got my 605 mono blocks today.

They sound amazing very powerful on my kefs so detailed



Just wait 'til you upgrade them then!

Btw, how much did they cost you?

[mikeks]

Originally posted by IanAS
Just wait 'til you upgrade them then!

To what?

[ANTHONY2181]

Ian,

They cost me £400 the pair mint and boxed.Ive seen them up for £1000 so got a very good deal.

Ive got the upgrade itch again though might go for a Meridian 557 or another pair of 605s so i can bi amp.

Anthony

[IanAS]

Originally posted by mikeks


Upgrade to what?

Ahh, Sorry I meant take the lids off and fiddle about with the innards

Originally posted by ANTHONY2181
Ian,

£400 the pair mint and boxed.Ive seen them up for £1000 so got a very good deal.

Ive got the upgrade itch again though might go for a Meridian 557 or another pair of 605s so i can bi amp.

Anthony

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