Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Interesting observations poweramps 556, 557, 558, 559

Looking through the schematics, it's interesting to see that the 558 is basically an improved 557.
Whereas the 559 and 556 seem to have more in common.
I'd hazard a guess that the same idea (or designer) developed the 557 and 558, and another the 556 and 559.

Interestingly (annoyingly) all use 16v rated capacitors for 15v voltage rails.
I guess this is why we're now seeing a lot of these products now needing service. Although after around 25 years we shouldn't complain too much!

That’s interesting re: the design similarities between certain models.

what sounds better? or did they target specific types of speakers. the 557 can do 4ohm the 556 should not? always wondered how the Meridian amps stacked up ~ these older 500 series, G56/57, or 857.

I had similar question re the 556. The back of the unit says ‘minimum 8 ohm speakers’. Does that mean they won’t work properly / could be damaged by low efficiency 4 ohm speakers? I was hoping one of these power amps might give some oomph to some highly inefficient small bookshelf speakers I have

Looking at the User Manual in Duncan’s Meridian Info it mentions 4 ohm to 15 ohm so I guess that answers my question…..

The only review of the 556 I can find seems to suggest the 556 might be on the bright side though? Other Meridian stuff I’ve had (tuner and CD player) have been on the lush / smooth side which I like

The 559 sounds almost identical to the 588, have done back to back testing, the only difference is in the treble, the 558 is very slightly flatter, but most wouldn't notice in a blind test.
Oddly the 558 is louder than the higher spec'd 559.

The 558s though go up in smoke after a while, there is a design fault somewhere, perhaps the lower rated capacitors as you mention, think some resistors have gone in mine, sadly no-one really wants to fix them as they sound very nice, but are hard to dissemble.
I also have a 555 but doesn't sound remotely the same as the 558 or 559, haven't tried a 556 or 557, they're perhaps more reliable than the 558, but then most 5 channel amps seem to lose channels after a while.
Keep an eye on yours, keep it well ventilated.

I'm going to sell a 558 pretty soon which needs repair, still works on 2 channels, but lost 3, perhaps someone would like to take it on as a project ?

yes, I think all that amp packed into 1 box is what lends them to only last 20-25 years
I'm actually in the process of renovating my 558, it developed an intermittent crackle.
also i have another 558 that i picked up sickly, this will be the next after mine, i'm getting used to working on them .
if you do want to sell yours on as a project let me know,
there are not many people willing to take these on, they are hard to work on, and the cost of the parts is high, e.g. the main large smoothing capacitors there are 10 of.

I like the 557 and 558, i've not had the chance to try a 556.
it should be capable of 4ohm speakers with no issue though, i suspect a typo somewhere!

The problem is that the Meridian "datasheets" are not accurate. I cannot recall the thread where this is addressed directly but my go-to example is one of the 6k's datasheets says each speaker only has 2 bass drivers.

I have 2 of them also, had them a while, time to let one go to new home for some TLC.
The old Meridian repair shop didn't seem too interested when inquired about a repair, unless for loads of money.
PM me, China might be a bit too far to send it