Peavey XR 886, 1997, mixer amp

I'm afraid I found the pic too unclear to be sure what I was looking at.

Is it formed from sheet aluminium ?

Graham

That is about the worst excuse for a 'heatsink' I have seen in my entire life. It's utterly pathetic. In fact it's completely WRONG in just about every way possible.

I have seen another that came close to being that bad but even so at least there were a few more vanes on it (C-Audio btw). The company I was with was considering taking the C-Audio design as a OEM product and re-branding it, but my tests showed a heatsink temp of up to 150C with a 40C ambient on music test signal. This was enough to cause several of the output mosfets to fail open-circuit and I only realised that when later bench testing it and finding asymmetrical clipping.

After declining their offer of the product I later found they'd added more heatsinking but it was a kludge.

Just for good measure, C-Audio also exhausted the searingly hot air right over the PSU electrolytics ! These were well known to need regular replacement which C-Audio justified as they said they were a 'service item'.

My own designs (including one in the local venue) are known for working day in, day out for years on end. I think the one in there is getting on for 10 years old now and is used every night although not every night is a 'loud' band. It has had a 'blow through' or two of the heatsinks and 2 new level pots (only one went crackly but it's best to replace both whilst you're at it, and yes, they're NOT pcb mounted so it's an easy job too. Compare that with a QSC RMX 2450 I also had to do the same to (labour time approx 4:1 ratio).

I never fail to be amazed at the number of amps that illustrate that the designers are completely incompetent when it comes to thermal management.

And don't even get me started on power transformer design !

Graham

Hahahahahahahaa !

What LOONIES. That's STALLING the fan blades. NO wonder putting bigger feet on helps.

How well would a propellor aircraft fly if you put an obstruction in front of the prop ?

Graham

amp

the

flow

contains

either

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etc

the

much

The heatsink is fitted onto the pcb that caries nothing on that area but holds a lot of ceramic W/W seen either side on the pic, usefully, I suppose, in the airflow.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I was rushing around a didn't focus on the right distance. Will have another go closer up , showing the chisel? cuts. Could not find an image of one out there.

Often seen in Sony domestic amps of the 70s/80s TA..., STR...all convection cooled The cutting action must be like those butter or cheese knives/scoops that curl the material into whirls

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

feet on

of

Expressing it like that highlights the flaw admirably.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

A better pic , without yellow ring is now at

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

A better pic is now on

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

That ancient Peavey transformer might be hotter (thermally! not wattagely!) on 50hz than on 60hz, and class AB amps dissipate worst case power at about 1/3rd max power.... its where the load line runs right across the hyperbola on the IV curve... and if the voltage in the club sags when the drink cooler compressor turns on, its a perfect storm of overheat factors.

Voltages in the UK don`t generally sag much if at all

Ron

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Is that in percent or in volts? I've glanced at the power line monitor during the end of a song and seen 105V... should be 120, but with lights and air conditioners and everything else, 115 is more like the nominal. So that 10% low.

Our mains supply is 240 volts

AFAIK the lowest legal voltage the electricity company can supply in the UK is 10% down (from 240) which is 216v, the highest legal voltage is 254v, less that 6% high. Suffice to say you won't normally get those kind of variations at the mains intake at the venue.

I don't know how much voltage drop you might experience due to the clubs wiring before it was deemed unsafe or illegal though.

Gareth.

You beat me to it.

Graham

Whatever you like

Graham

It won't be based on 240V any more because we're officially (on paper) 230V. Maybe 230 +/- 10% but that's just an EU standard - it's NEVER as low as that.

Never seen any worth talking about. Have you ?

Graham

On paper maybe, but in practice its still pretty much 240v.

No, I put that down to good wiring regulations.

(I remember when I was in a function band and we used to play the Forces bases in Germany with dodgy old 220v domestic-at-best wiring. We only had about a 3K system but often had to carefully switch the amps on one at a time to stop the breakers tripping, then all the house lights and all the gears' illumination would dim in time to the kick drum. Frightening really. None of my keyboards ever crashed though.)

So what would be the maximum voltage drop you might expect from a non overloaded mains system?

Gareth.

Crikey. I know where I'd test with a highish power PA rig, the local venue that has some 5kW ? or so of amps but last year I had a separate 32A circuit run in just for the amp rack so I doubt it would be more than a few volts.

Graham

I was just curious, knowing nothing really about wiring regulations.

If the regulations require heavier cable for longer runs to prevent voltage drop, then is there some kind of formula with voltage drop limits? Or can you just run a very long cable (in a large building) capable of carrying the current required and have to live with the voltage drop. Or is any voltage drop just a few volts as you suspect, so the point is mute.

Kind of thing.

Gareth.