Yamaha PM1000 16 channel recap. PS Help

[darnell]

Hey all,

I've used the search, and while there is a lot of info, I still am seeming a bit uneasy about buying parts. I am going to start recapping my Yamaha PM1000 16ch, starting with the power supply. Looks like there are 4x 470uF/50v, 7x 220uF/80v, 3x 1000uF/16v, and one large cap can @ 1000uF/80v. My question is, how much can I increase these caps, what will be the advantage, and which caps will specifically need increasing. I understand (i think) that by increasing you smooth out the ripple and will get better constant dc filtering. Just now sure how much is too much.

I also am wondering about the master section in regards to recapping. Same questions with electrolytics there too.

Here's a link to the schematic download.

http://www.yamaha.co.jp/manual/english/result.php

Any help would be great.

Thanks,
Daryl

[The Scum]

My first thoughts:

The PM1000 power supply is stone-age mediocrity.

Swap it for a PowerOne 48V linear supply, tweaked down to 44V with the trimmer or by swapping feedback resistors.

I can't give you a good guideline on increasing those caps...you can try to do it empirically - bump them up until it starts blowing fuses when you turn it on. The hangup with increasing the cap values is that they need to be charged when you first turn things on, and for a moment, they draw a lot of current. The bigger the caps, the longer that moment lasts.

Do you have a hum problem now? If not, then more filtering isn't really called for.

You might track down a copy of Horowitz and Hill, and read their thoughts on caps in power supply design. The end takeaway - you need to know know much current you're dealing with.

[darnell]

Is this the power one I would be looking for....

http://search.digikey.com/scripts/DkSea ... 79-2315-ND

or this one....

http://search.digikey.com/scripts/DkSea ... 79-2335-ND

Not sure how I would swap that out. Maybe better keeping the ps that goes with it, unless I can figure out how to integrate it.

d.

[The Scum]

If you keep a careful eye on Ebay, those supplies sometimes show up as surplus for peanuts.

Again, without knowing how much current the thing draws, it's hard to make a good recommendation. The .5A might be too small, and the 3A might be overkill...they also have a 1A in between.

[Milkmansound]

I bet there is a little bit of magic in that old power supply - I would keep the cap values the same and just replace them. They are probably a bit shot just because they are old. The performance of new electrolytic caps slays the old ones - I would try and cram Sprague Atom's in there if they will fit.

Remember to "form" the new caps with low voltage or a light bulb in series with the AC line.

Increasing the caps usually leads to a more consistent output from the power supply - the caps store more with a higher value. But they also draw more on power up. Depending on how much you are slamming the board, you may get decreased power with low value caps, and more power on reserve with high power. I wouldn't worry about it though.

I love those old "stone age" linear power supplies! They are so easy to work on compared to their modern switching brethren. I'd say save some cash and recap with similar values.

[The Scum]

The PM1000 supply is stone age.

It's about 6 generations of design know-how removed from a modern switcher...and predating the pleatu of linear supplies, as well.

It's a Zener voltage reference and a couple of pass transistors, heavily filtered all around. I'd posit a guess that the Zeners are noisy...not exactly a good foundation for a high-spec supply.

A modest 78xx or LM317 + pass transistor combo would probably be far superior from noise & regulation standpoints, though they make take some jakery to get +44V out of them. And that's about what Power One use in their supplies - no surface mount, no switching voodoo, no audiophile BS, and good reliability - that's why they get recommended fairly often.

[Milkmansound]

good points.

I think my head has been in the tube amp world for too long! Sometimes a somewhat crappy power supply gives it some extra mojo in that case.

I bet you could run that whole console on 48V right?

[The Scum]

48V might not be so direct - I seem to recall that the transistor used in it is rated to 45V max Vceo.

But if you're already upgrading, what's swapping one more part?

Though dialing the trimpot on a 48V Power One will get you 44V, as well.

[digitaldrummer]

Though dialing the trimpot on a 48V Power One will get you 44V, as well.

that's what I was thinking too, but then you'll have phantom power running at +44V too - may be a problem or may not be...

I doubt the power supply is the weakest point on the PM1000. Just replacing the power supply caps (with the same value) would probably be the simplest place to start and certainly can't hurt. they are 30+ years old...

[The Scum]

that's what I was thinking too, but then you'll have phantom power running at +44V too - may be a problem or may not be...

Not so.

The PM1000 supply has both 44V and 48V rails. The 44V is on pin 15 of the strips, to feed those 45V max transistors. The 48V is on pin 17, and is only for phantom. You can probably use 44V for both, and never notice the difference - phantom is usually a good approximation (+/- 10%), and not a rock solid reference-grade 48.000V.

To fully replace the supplies in a PM1000, you need to do the 44V and 48V, but also the 13V bulb rail and the 12V headphone amp rail.

And a clue for sizing replacement supplies: the 44V and 48V rails each have 2A fuses on them (in 24 and 32 channel boards, there are actually 2 sets of rails, divided between the strips.). 2A for phantom is pretty overkill in my book. You could also use the fuse holder to drop an ammeter on the rail, to measure the actual draw.

[JohnSuitcase]

I have 4 channels of PM1000 racked up, with the Power One supply, trimmed back to 44v. Works great, very quiet. 44v is more than enough for any phantom power application I've come across. Many recorders only provide 18v.

Mounting the power supply in an external case was key to eliminating some noise issues, not sure how that'd apply to a console. I imagine having the supply external, and a reasonable distance from all those transformer and inductor eq's is a good idea!

[digitaldrummer]

that's what I was thinking too, but then you'll have phantom power running at +44V too - may be a problem or may not be...

Not so.

yeah, you're right I forgot about the bulbs and all - but I thought you were telling him to replace the whole supply with one 48V supply and obviously that won't work, which is why I said that replacing the caps was the easiest place to start. If noise is still an issue, then you work from there...

Mike

[CZ101]

Speaking of bulbs, would anybody happen to know what type of bulbs the PM-1000 VU meters take?

[JdJ]

Hope y'all don't mind me hopping in on this conversation, but I am in a similar boat with our PM2K...

To fully replace the supplies in a PM1000, you need to do the 44V and 48V, but also the 13V bulb rail and the 12V headphone amp rail.

Seems to be similar in our PM2K (except the audio amp rails are +25VDC/-25VDC, and the values for the other accessory rails are different). My plan (if we determine the PSU is a major shortcoming which I think it is) is to split the supply so the illumination & headphone amp are handled by the stock unit, while the audio amp rails are handled by something with some more available current. Otherwise it looks like a complete supply system is going to be a lot of $$. I figure if I get a couple of good quality supplies for the audio rails, I can then build them into a complete system once funds are there. I can't think of why this route is a bad idea. Can you?

And a clue for sizing replacement supplies: the 44V and 48V rails each have 2A fuses on them (in 24 and 32 channel boards, there are actually 2 sets of rails, divided between the strips.). 2A for phantom is pretty overkill in my book. You could also use the fuse holder to drop an ammeter on the rail, to measure the actual draw.

So after measuring the current draw in this scenario (we have a 24channel PM2K with 2 sets of 2A fuses for the rails as you said) how much do you think I should scale it up to have all the necessary current and then some? 10%? 50%?

Here's the schematic if anyone's interested.

Many thanks!

Josh

[The Scum]

Speaking of bulbs, would anybody happen to know what type of bulbs the PM-1000 VU meters take?

Never been inside them myself, so I'm not sure. It's on my laundry list, but hasn't been tackled yet.

I'd pull one out, then check with an auto parts store, and Chicago Miniature (chml.com).

When I couldn't find anything that was a sure fit, I'd roll my own replacement with discrete LEDs.