Pro Audio PA Amps - Bargains to Be Had?

those 2 fans are different powers too...

 

I noticed.

 

Well I just spoke to MC2 - seems the fan furthest from the vent is faster than the one closest to it and this is by design as it causes turbulence which is good for cooling.

They wouldn't like to comment how some lowered speed (ie quieter) fans for PCs would work, they haven't tried it and neither has anyone he knows of. He did say that in a domestic environment he doubted the fitted fans would ever get off their lowest speed unless you pushed it and that they recommend replacement of the fans after 4 years or so if its been used heavily professionally (which this one almost certainly has) - conclusion, these fans are probably noisier than they should be and past sell by date (the filth will have contributed) and possibly running faster than they need due to the state of the heatsinks.

New fans - £8 a pop. Or try some of the acoustifan dustproofs (which do three speeds) - I had a nosey in our local Maplins just down the street and they have these on special for £9.99 at the moment.

He also gave me the heat sink temperatures at which the fans come on (50c), speed up (55c and then 60c), step down the headroom first stage (85c) and shutdown (92c). He couldn't remember when the second step down was but somewhere between 85 and 92. Combined with a probe thermometer, could be very useful if I did want to try experimenting with slower fans.

I now have some nice shiny heatsinks and clean fans - this gunk is disgusting, but it has all come off.

 

Uncle,
This is interesting stuff, let us know how you get on.
Cooky

 

First the good news is I went and got the last 4 of the acoustifans - on the basis if they didn;t work I could fit em in the helicopter of a PC I've got here.

To my astonishment it all worked (and its nice and clean now) and is very near silent - these realy are good fans - also keeps it cool enough.

The bad news , I went back to tidy some bits - tighten things up etc. There was a crack and a pop shortly after switch on and now its got a fault light upon one channel - not sure what but I've jiggered something. No other harm done though. I think I'll just send it to MC2 for a service.

 

That's a bummer. Cold comfort but MC2 are reasonable with their costs-it's the 2 lots of shipping that hurts.
Cooky

 

Give it a good kick and see of that fixes it (that's what the pro's would do)..

Seriously, is there something that's obviously blown in there.

It's times like these you need a technician who owes you a favour as I bet they'd be onto the problem within 5mins.

 

No nothing obvious and the fuses are all intact, nothing brown or burnt looking. I was more worried about any possible damage to thespeakers, but they seem fine.

I'll talk to em tomorrow and get it, or maybe just the power supply and the output sections - might save a bit on shipping if I'm not sending a bloody great transformer and case as well.

I know some technicians, but none that owe me a favour at the moment Probably easiest to use MC2. I imagine they won't charge too much.

 

Just searched for "MC2" on eBay and found nothing but auctions for Mariah Carey's new album.

 

Give 'em a bell
http://stores.ebay.co.uk/GDS-SOUND-AND-LIGHT

 

You need to keep a look out for loose bits of metal in the case when doing this sort of thing. If you take a screw out for example, a little bit of swarf can come out if it was never removed before. Also make sure none of the under-board is shorting on the case. If you did any soldering, make sure none fell off the iron over some tracks.

I've lost a few bits of kit this way in the past. Usually with DIY stuff whee you mess about all the time changing things. Repairable a lot of the time thank god.

 

Who knows, could be, it could just be something failed. No soldering or anything like that.

Everything is repairable ... it more a question of how much you want to pay to get something repaired

 

I officially nominate myself for this month's idiot.

When is a fuse not a fuse? ... and what was that little nut doing there?

She lives, she breathes ... but thankfully not too hard. :MILD:

 

So Uncle, can your nephews here come in for a listen?

 

"It's alive, it's alive!"

 

Dev, whenever you like

Cooky, I think its a stayer. These fans are far more acceptable. The sound I'm getting from the speakers is marvelous. I found out the damn thing won't fit in the meter cupboard, so the only remaining obstacle to domestic harmony is the looks of it (and I must admit visually its starting to get on my wick too - horses for courses and all that) - however I have a cunning plan involving a man who can ... black anodising aluminium and a handy way with a hacksaw in this case ... literally.

 

LOL, well you're right they aren't 'lookers'-the very reason I've just bought a mc650-(much prettier than the T's)to match the MC1250 and am about to sell a T1000.I'd just hide the damn thing behind the sofa!
So glad 1. you're chuffed with the sound and 2. you quietened the fans-makes me think..........
Cooky

 

Well there's still a bit of work to do on that front I feel. Its silent on the lowest fan setting but you can just about hear it at the middle setting ... or more to the point Auntie Ants can (she's the one with bat ears in this house, far better hearing than mine), and she often as not listens to music sat at the dining table, which is a lot closer to the amp and further from the speakers than the official listening position.

There are a couple of things I can try I think. Taking it apart has if nothing else given me a much better understanding of how it works in terms of cooling.

 

Okay, more progress. Yesterday I ordered 4 of these:

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here

They are Zalman Fan Mate 2s - basically a little pot that you fit inline with a fan and it allows you to gradually drop the voltage to reduce its speed. They can be had from about £3 each.

The idea here is to reduce fan speed enough that the fans become inaudible at full blast as dictated by the onboard controller, but hopefully not so much that they can't do their job. I think its a given that the fans at reduced speed wouldn't stop it redlining if we were asking it to drive a PA at full welly, but at home the headroom indicators suggest that even at considerable volume the amp is barely getting into a jog, so at a lower speed (and thank you Tenson for prompting this line of thought with your comment about quiet fans achieving it by spinning at reduced speed) they might just be fast enough and remain quiet. I checked it with the guys at MC2 and they thought it might be worth investigating and gave me some useful information re operating temperatures.

They arrived today and as I was working at home this afternoon, I had a chance to play with these things.

I fitted one to each fan and mounted them on an old permostat box. The leads are long enough to be able to route through the case and out of a conveniently placed hole where there was a blanking plate for fitting a remote option. I shall name it the "Stealth Box"

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I set the amp so that it gives me a red light at the first headroom reduction point rather than shutdown as my probe thermometer isn't suitable for running with the lid down and I needed some way of knowing when it was getting a bit too warm without actually going as far as shutdown. I have a suitable twin sensor thermometer coming tomorrow which will help fine tune it - a Revoltec Thermoeye, again a PC cooling type product, about £12. Twin sensors will be useful as it means I can monitor each channel separately, battery driven and good up to 120c.

I ran the amp for a while with the fans disconnected so that it was up to the sort of temperature that would have the fans running full speed, plugged the fans in and dropped the lid, I set the fan speeds to minimum and adjusted up until with my ear next the intake hole I could just hear them, inner fans first then outers, and then adjusted them down until they were inaudible.

I then put Bob Marley and the Wailer's Exodus on at a volume just past what I would normally consider my max volume and waited for the red light (no neighbours today). It did eventually, but took a while. Slight tweak of the fans and off again ... a result, silent fans, and the ability to take some welly and still stay cool enough for my purposes.

Auntie can't hear the fans ... and if she can't hear them they can't be heard, and its not redlining even at volumes I would barely consider ordinarily, let alone the low volumes where it was a problem before. I'm pleased. Long term, one of these might be better run off an independent 12v supply:

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Now that you know what speed you need the fans, you can measure the voltage after the Zalman little control devices. From that you can work out a simple resistor value to achieve the same.

So you can do away with all the extra stuff and just put some resistors in line with the fans.