Electrocompaniet Help

[Andypairo]

Hello,
I'm trying to fix a Electrocompaniet amp.
Not sure about the model, it should be AW65, even if the only schematic I have found ( thanks ManUtd) doesn't match perfectly.

The amp is of a friend and was heavily modified (but looking at the inside it seems built from scratch, even if with original electrocompaniet boards...) on the assumption that the PCB was the same for the 65 and the 100 model by the same guy who sold it to him.
So I'm not that sure about the exact model, the PCB silkscreen has some writings "Electrocompaniet 120R-5" on one board and "120L-5" on the other (the boards seem mirrored but the guy mounted them the same way so one has the trimmers pointiing down!!)

Unfortunately this guy probably didn't know Ohm's law that well, so when I opened it I found 40V main capacitors working at 45V,
just one pair of output devices (with no emitter resistors) a inrush protection board that didn't protect anything, a home-made anti-bump board and a 10k resistor in series with the inputs (to reduce sensitivity?) along with small film caps....

I'd like to remove it but the amp seems to have a balanced input (the input pads have "POS", "GND" and "NEG" writings...) so I have to give it a better look.

Does anyone have schematics/service manuals/inside photos of Electrocompaniet AW65 - AW100 so I can identify it correctly and make it work as it should?

Any hint/help really appreciated

Cheers

Andrea

[Andypairo]

While waiting for some help (c'mon boys, don't be shy! ) I made further investigation on the amp: the 10K resistor I mentioned before was from the cinch input to gnd, then the amp is cap coupled (with a 0.1 uF film capacitor from input to the "in pos" pad of the PCB and another from GND to the "neg in"... ehy wasn't the input unbalanced ??!!)... I think I'll remove this network since the amp has a servo DC..

Probing the output with a sinewave at the input I noticed that the distance between the main reservoir caps and the amp pcb made it oscillate on the positive peaks (the + rail has the longest wires). Placing a bypass cap near the pcb shifted the problem to the negative part at higher power levels, so I think that one more cap for the negative rail can't be avoided

Still wonder how could someone do that to such a beautiful amp...

Cheers

Andrea

[Jan Dupont]

Andrea,
It seems like that the best thing to do is to rip out all the "modified" circuits, and use some of the better parts and the enclosure to make a new diy amp

[Andypairo]

I was tempted to do so... I even have 2 suitable boards ready to be populated , but this would be another amp... and the owner might not agree...

If I can identify the exact model (I'm not sure it is a AW65 as the "serial" number would state...) I can probably restore it properly...otherwise I'll make as few mods as I can to make it work without the current flaws.

Cheers

Andrea

[Jan Dupont]

Ok Andrea
It was just a suggestion

[Andypairo]

Of course this doesn't mean they won't be populated .. just not in that enclosure (even if it is really wonderful)..


Cheers

Andrea

[Jan Dupont]

I never thought so, however restoring a "bad modified" amp without any schematics etc. seems quite like waste of time

[Andypairo]

I partially agree with you, fortunately this so-called "expert" (who is the same who did a real mess with the tubes of a Luxman CL-32 preamp) didn't make other (visible) mods to the amp board, so I think it is possible to restore it quite well (with the oscilloscope on hand... you never know ) even without schematics.

Of course having them would be far better but...

BTW I noticed that the output devices don't have any resistor on the emitters (and no provision is made for this purpose on the PCB).... this seems really weird to me....

Cheers

Andrea

[Jan Dupont]

You say there are just one pair of output transistors per channel...
Try check to see if the resistors are put on the rail supply to the output transistors...........

[Andypairo]

I checked again and... there are no power resistors !

It's probably the first design I see that doesn't use 'em...

Cheers

Andrea