Pro Audio PA Amps - Bargains to Be Had?

Congrats

Congratulations Uncle Ants on your new MC750.
I hope you find it works well for you in your system.
I was after it to 'match visually with my 1250 but your good self and another were more determined
Still, smack in the middle of what they tend to go for(£300-£500).
F

 

Well I'll see how she goes If I don't prefer it to the WAD, then it could well be up again soon.

 

Its been a while. It took a while for it to get here and then for various reasons (mostly to do with not having the time to mess with it), I've only just had a chance to play with this thing.

Its good and bad really.

The good is it sounds very good indeed, the most noticable difference being in the bass - much, much better controlled, stop start fast and seems to go considerably lower. After an hour or so, I wouldn't say its noticably worse anywhere else than the Kat88 either - perhaps not quite so 3D. But the overall effect is that they sound bigger, punchier, deeper and louder.

The bad news is the fan noise - far too intrusive. So much so that I can't honestly get a handle on what it sounds like at my more normal listening levels.

This thing has definitely been gigged as a dent to the corner of fascia attests, so I suspected its been used quite hard, so I had a looksee inside. Its filthy with brown dust. The fans have certainly seen better days. Now the interesting thing is that they pretty much look like ordinary PC fans to these eyes and attach to the circuit board with the sort of plugs you get off a PC power supply. Doesn't look like they would be hard to replace.

So it raises the question ... silent PC fans - are they really silent, do they stay silent, which are the best?

If nothing else it has proved to me that these Spendors really do appreciate more welly than my little 36 watter can provide.

 

hoover the thing out as well !

they tend to be quite quiet when new ....but as the bearing wear can get noisier.

must get over for a listen

 

Yeah I know that's the case with yer bog standard ones, but there are more expensive PC fans marketed at the silent PC (music server use etc.) market which are supposedly quieter and stay that way. Just wondered if they really are and if so if there are any fans that are recommended. Maybe I should post it as a separate post and elsewhere - there must be quite a few folk who have put together "silent" PCs for music server use.

I've run it with the lid off and discovered its definitely one of the fans on one side, there are 4 fans and 2 plugs, unplugging one of the plugs leaves just the two fans on one channel running, the fans on one channel are pretty quiet, the fans on the other channel noisy as hell. Don't worry I've only run it briefly fans off just to see if I can tell which fan is the noisy bugger.

 

Try the forum at SPCR. There are many who know a lot about fans, including UK members. Helped me a lot in the past:

http://www.silentpcreview.com/section12.html

 

Thanks, will do, I've isolated to just one of the four fans causing the grief.

 

... and also worked out that for the time being, for some reason, if I put something under it at the front and tip it back a tad, the noisy fan ceases its noise.

I've also discovered that its a bit less sensitive than the WAD, so volume needs to be closer to 11 than 9.30 or so for normal listening ... I've also discovered that you can crank and crank it and it just never seems to harden or show any signs of stress ... so I still haven't realy tried it for normal listening because it keeps whisperig "go on, turn me up big boy ".

It just goes cleanly, louder and louder

 

Hey Uncle,
Maybe you could just rotate the offending fan?
Glad you seem to like what you hear(fan noise exceptedThere's an effortless and bottomless quality to the MC's, as you are discovering-their neutrality becomes very seductive.
Cooky.

 

Possibly, or maybe just replace them with some new ones, it looks like the whole thing has been designed in a modular way with the different modules connected together with push connectors - I'm guessing for easy servicing - from a standard auiophile pov its all wrong . I'll have to remove a good part of the guts to get em out and new ones in, but it doesn't look too hard.

Then I've got to work out where to hide the damn thing. It doesn't pass the Auntie Ants elegant design test that's for sure. Problem is the only place I could really hide it is the meter cupboard, which is next to the speaker position (a good thing I guess), but about 15 feet from the preamp which is passive (so definitely a bad thing and hard to lose because it definitely does pass the Auntie test). Is there such a thing as a little box to take unbalanced outputs and convert to XLRs to drive a long interconnect??

I've spent a good part of the afternoon running through some stuff and quite frankly I'm a bit gobsmacked, the Spendors are a completely different speaker. Luckily the neighbours are out.

 

These Zaward fans are good. http://www.quietpc.com/gb-en-gbp/products/zawardfans

Be careful though, a lot of the quiet fans achieve lower noise by spinning slower, as well as simply being better made. But, if you are not pushing the amp hard, maybe you don't need so much fan assistance? How hot does it get with the fans unplugged?

You can convert unbalanced to balanced either by means of an op-amp or a transformer. Take your pick. You could swap your passive for a TVC based passive which should have balanced out, as all transformers can drive balanced. TVCs that only have single ended outputs will just have one of the transformer output taps connected to ground instead of the negative phase of a balanced line. So it just depends how you connect it up.

 

Hmm, well with no fans at all and the lid back on ... too hot is the answer. I just ran it with the fans disconnected at reasonable volume and kept a wary eye on the red temperature indicator. The top got nice hot water bottle sort of hot and after about 20 minutes the red temp light started to flash.

Still its possible that they don't need to shift quite as much air. If they are as loud as they are now (with the noisy one quietened by virtue of tilting it a little) , then its quiet enough to get away with it for all but quiet listening. Unfortunately that's probably not quite quiet enough. if I shoved it in the cupboard way over there though, it would be fine.

Yes except that I want to keep my current pre if I can. Are there any decent off the shelf units that will convert unbalanced to balanced? Not bothered about the technology, am bothered that it will enable me to run a good long run from the pre to amp without fouling the signal up.

 

Well, this is the issue. You will have to pass it through either a transformer or an op-amp and doing that may have an audible effect. On the other hand it may be completely inaudible. Suck it and see.

I'd choose the passive transformer option since an op-amp will also require a power supply and the associated noise from that can get in to the signal. If its cheap, the PSU probably won't be very good. the transformer is more elegant if you ask me.

Having a quick look, the only two I can find right away are:

SONIFEX RB-UL2, which is a op-amp type interface and costs about £180. They usually make good stuff though.

There is another op-amp based converter I've never heard of 'MQ-S75' on ebay.com for $44 + P&P but I'd be wary of the quality at that price.

If you wanted, I could make a transformer based unit for around £120? I would use the same transformers I use in my Behringer mods, so I know they are good quality.

I'm sure I once saw a commercial transformer unit but I can't for the life of me remember who made it. It was around the >£100 mark though.

 

I'd be interested yes. Are there any downsides to that approach? I take it we are talking about a smallish box.

I've been running it the last hour or so with the fans off but the lid off as well - it hasn't lit the red light yet ... Hmm, maybe dropping the voltage in the fans wouldn't cause any issues.

 

Yeah quite small. You could fit it down the back of the rack. Not really any downside I can see. I could make it with a 1:1 ratio so it would have no effect on how easy the long cable run is to drive but the level will be the same. Or I could do it with a 2:1 ratio so there is more current available and the source impedance presented to the amp will be 1/4 (a good thing), but the level will go down 3dB.

You say it has 4 fans in the amp. Can you not just run it with 2, and make them low noise ones?

 

There lots of choice for 'quiet' PC fans these days. Most are pretty good too. But the best I've tried are from either Acousti Dustproof or Noctua. If you need a fan that is very quiet to start with and maintains a consistent noise level over its life span then go with the Acousti fans. They're very expensive for a fan but frankly I haven't used better and I had one for 2 years in old PC without issue... no noticeable increase in noise.

From 3 meters away the fans were completely silent when running at 7.5v (15.6dBA/1m).

http://www.quietpc.com/gb-en-gbp/products/acoustiproductsfans/afdp-12025b

 

Uncle,
It may be worth giving MC2 a ring re both fans and advice on using your unbalanced pre over long cable runs-they are incredibly helpful guys down there.
I've heard there was a company mod that kept the fans on all the time but steady slower speed as opposed to the full on cycling blast but haven't pursued it with them.
Cooky

 

Experiences lately lead me to the conclusion that the more power, the better. Reduced distortion and compression, more control, lack of strain all lead to a sound that is truer to whats on the recording to say nothing of much better performance by the speaker overall. Although I believe valves do fare better with lower power than SS, ie given the same power rating and quality design, the valve amp will generally sound more powerful than the equivalently powered SS amp.

 

I think I will give them a call yes, especially to ask about the fans. I ran it lid of all yesterday evening without fans and we played it fairly loud, and at no point did the temperature warning light flash. It really is a very fine sounding amp. Auntie loves the way it sounds, loathes the way it looks and declared that she can't/won't live the fan noise as it is. So if its to stay it will need to be hidden and I will need to do something about the fans.

The lid is solid with no vents, and there are smallish vents at the side of the case and a big one at the front. I'm assuming the amps natural environment is jammed into a rack with a bunch of other hot amps, so that arrangement would make some sense.

Experience so far would suggest that in a domestic environment, that lower speed low noise fans (or maybe fewer or no fans at all and a pair of larger heatsinks) with a ventilated lid may well work. It might be worth looking at some of the fancy heatsinks that are available for PC cololing perhaps. I'm also not sure that they thought too hard about airflow, all four fans are simply set to blow way from the heatsinks, I would have thought using at least one fan to draw cool air into the case and oiver the heatsinks would have made more sense.

I don't know if the "always on" mod hasn't actually been carried out ... the fans do seemt o stay on all the time when connected

Shinobiwan, yes those fans have been recommended to me elsewhere, sealed against dust, which gives them a much longer quiet life apparently. They are no 1 candidate, if the fiting arrangement allows for those soft rubber fixings as well, that will probably help.

Tenson, the 2 to 1 ratio sound like it might be the way to go, apart from losing a couple of dbs, are there any other potential pitfalls there?

 

Not that I can think of. In fact it will also 'float' the outputs, which means there is no physical electrical connection between the power amp and the rest of your kit. This means no noise can easily travel down the ground line as it usually will. Lower noise basically, and immunity to ground loops. Transformers have many advantages