Yamaha M-2 Recap - 37 year old PSU filter caps within specs?

[Mr. Yamaha]

Hi guys. So, 2 weeks ago I acquiered a pretty decent Yamaha M-2 power amp. It was very much worth the 1400km travel to France. It was priced more than reasonable and the guy even threw in a 'free' C-4, which is in an OK state.

We all know about the recap theme, some say "do it, after 25 years", other say "don't fix what ain't broken", but that is not what I want to discuss here.

At the moment my M-4 is being recapped, after that my own C-4 and after that I'm planning to bring this M-2 in. The more I'm working on this M-2, the more I realize what a treasure this thing is. Everything is absolutely untouched, unreplaced, etc. I screwed the bottom off and all screws snapped like it was the first time they were loosend. Really amazing, but sorry I'm drooling.

I took the massive 22.000 uF 100V PSU filter caps off to give them a little measuring with my Chinese 'everything tester'. And was a bit suprised by the readings, but maybe I don't understand.

The pretty clean inside:

The caps:

The dimensional measurements (sorry guys, it's metric):

And now the electronical measurements:

At first I thought: "wow, more micro Farad's than original".

But, I'm not sure about the ESR and VLoss, is 9% VLoss and .13 Ohms ESR acceptable?

Should I also replace thes during the recap?

Even Zoë has approved the M-2:

 

[Mr. Yamaha]

Bump for the VLoss and ESR.

 

[gslikker]

Probably the measurement is compromised by the resistance of connectors/wire.

 

[rottalpha]

Probably the measurement is compromised by the resistance of connectors/wire.

Subtract the wire resistance

 

[Mr. Yamaha]

Probably the measurement is compromised by the resistance of connectors/wire.

But I guess, that wouldn't influence the capacitance value or VLoss?

 

[gslikker]

No it doesn't. Although I do not know if there is any validity on the Vloss measurement on big electrolytic caps done by this kind of devices.

 

[Bratwurst7s]

Looks more like 0.9% than 9%. That and 0.13 ohms ESR seem pretty good considering their age.

Cheers,
James

 

[Hyperion]

Very often, the main capacitors are the last thing that needs replacing, and I always leave this task until last if I haven't experienced the sound improvement that I am expecting after a full reconditioning of the rest of the amplifier. But very often, and oddly, people decide this is the first thing they want to change to improve their new acquisition.

The caveat here is if the main capacitors are physically damaged or obviously leaking, or damaged by some other trauma. (blown rectifiers, or (re-)installed incorrectly), then they obviously need changing.

Zoë is wonderful.

 

[Mr. Yamaha]

Very often, the main capacitors are the last thing that needs replacing, and I always leave this task until last if I haven't experienced the sound improvement that I am expecting after a full reconditioning of the rest of the amplifier. But very often, and oddly, people decide this is the first thing they want to change to improve their new acquisition.

The caveat here is if the main capacitors are physically damaged or obviously leaking, or damaged by some other trauma. (blown rectifiers, or (re-)installed incorrectly).

Zoë is wonderful.

Yeah I think you're right. I was told by a guy who works with industrial applied electrolytic caps that they - despite VLoss, ESR and capacity measurements - can dry out on the inside after a long time.

And I was thinking of putting in 2x 33.000 uF

Would that be an improvement to this M-2 or is it unnecessary?

 

[Hyperion]

My initial reaction is that it may be unnecessary, but I would defer to those more experienced with that model of amplifier than myself - as I have zero experience of it.

All the usual caveats apply, power switch/soft start circuit will have extra stress, same for rectifiers, and to an extent the transformer. Will the larger ones fit? - will they be actually equal or better quality than the originals? - just how much difference will it make?..... and so on....

 

[ConradH]

Big caps require a 4-terminal measurement system to get an accurate loss number, but from what you've shown those caps are still healthy. It's not unusual for big PS caps to go for that long and longer with little degradation. Being out of the unit, it would be nice to do a DC leakage check, but one should proceed slowly, as years of running at less than the maximum voltage will have likely "rerated" the cap at the lower operating voltage until it reforms. Those are expensive caps I wouldn't replace until necessary, but you do get into the question of whether two caps of the same value and decent loss, one new and one old, sound any different. A question with little quality data to support any conclusion.

 

[whoaru99]

What do you propose to gain by increasing capacitance, other than inrush current (which has already been a problem, yes)?

 

[Dr. Ear]

That and 0.13 ohms ESR seem pretty good considering their age.

The new ones I got had 0,20 Ohms ESR.

 

[Mr. Yamaha]

What do you propose to gain by increasing capacitance, other than inrush current (which has already been a problem, yes)?

That problem has been solved ;-) I've read that increasing the capacitance will result in a more controlled and punchier bass.

 

[whoaru99]

The Yamaha guys are pretty smart. You think if an easy change like that would make a material difference they wouldn't have done it?

 

[Mr. Yamaha]

The Yamaha guys are pretty smart. You think if an easy change like that would make a material difference they wouldn't have done it?

Maybe in 1979 the Yamaha engineers ware stuck at 22.000 uF due to the physical size of caps in that time to fit in the M-2. Electrolytics have become smaller over the years

 

[whoaru99]

Maybe in 1979 the Yamaha engineers ware stuck at 22.000 uF due to the physical size of caps in that time to fit in the M-2. Electrolytics have become smaller over the years

Or not.

The caps are primarily for filtering, the power is still from the transformer.

The problem with this sort of assessment is you're changing two variables at one time - new caps and larger caps. Which is more responsible for any difference you might perceive?

But, it's a common thing to do so I don't really expect anything different. Just raise the question every now and then to see what people are thinking in terms of why they do certain things.

 

[Hyperion]

Great posts whoaru99, I think it is highly likely the OP would get the best result if he changed the capacitors for top quality exact value and voltage replacements. Always assuming that the originals really are past their prime, which from the readings shown and comments by learned members, it does not appear so, but further readings would confirm.

The main thing to understand is, where do the capacitors get charged from? - ans: the transformer. So if you increase the capacitance, what has to work harder? - ans: the transformer. Usually there is a bit of slack on the rating of the transformer to allow the use of bigger capacitors, which is where the slightly improved bass performance comes from. However, the extra charge on the (bigger) capacitors gets used quickly when the amp is being really 'cranked' - so the transformer not only has to recharge them, (taking longer to do so), but also supply the current to the amplifier.

 

[whoaru99]

Hey Guys, not trying to start any crap here. It's mainly just curiosity why.

Build an external box with 1F capacitance for all I care. I just don't want to hear any whining if an output ever fails shorted and the amp subsequently vaporizes...

 

[Hyperion]

Hey Guys, not trying to start any crap here. It's mainly just curiosity why.

Build an external box with 1F capacitance for all I care. I just don't want to hear any whining if an output ever fails shorted and the amp subsequently vaporizes...

I hope and trust that is understood by the OP, and any readers. And...nor am I trying to stir anything. I just hope that my posts set out the many considerations that need to be taken into account with this kind of replacement / proposed upgrade.