I've never really understood the engineering decisions behind the older Crown amplifiers. There's always an odd mixing of good and forward thinking ideas with bass-ackwards 1970s technology. The CTs1200 is a good example- a relatively modern SMPS mixed with an ancient quasi-complementary power amplifier using TO-3 transistors
The cooling system in the Macro-Tech 3600VZ is also perplexing. Yes it's clever since it uses the fan motor as the low voltage transformer (at least that's what I remember), but it doesn't work all that well and it makes fan replacement really difficult if you can't buy an original part. It's also really loud, but doesn't move as much air as it probably could.
The cooling system in the Macro-Tech 3600VZ is also perplexing. Yes it's clever since it uses the fan motor as the low voltage transformer (at least that's what I remember), but it doesn't work all that well and it makes fan replacement really difficult if you can't buy an original part. It's also really loud, but doesn't move as much air as it probably could.
The bias circuit in those older Servos looks weird to me. The transistor around which it is built is not thermally connected to the main heat sink like in most other class B amplifiers and then there is a NTC for additional thermal compensation, which is not mounted to the heat sink either. Turn on the amplifier and the first minutes it draws > 100 W for just idling.
Until it warms up and power consumption decreases to a normal value. Setting the bias current is difficult, as removing the top cover influences transistor and NTC temps and the bias current goes with it. Also one of the adjustment pots increases bias current when turned clockwise, while it is counter-clockwise for the other pot.I 'fixed' mine by replacing the NTC by a regular resistor and mounting the transistor on the heat sink. Now the bias current is much more stable.
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Crest Audio CLh5000C
Some tests of the Crest Audio CLh5000C, at first I thought this was just an install version of the Peavy IPR2 5000 but it has better power output specs and its outputs are not bridgeable. This amp is not quiet but is also not so noisy as you hear its fans throughout the house only in the same room. This is quieter than classic PA amps with mains powered high output fans like the Cloud VTX1200. If you could put this amp in an equipment cupboard this would be OK. I now have a SPL meter but I only measured a small delta between the amp on and off so I am not certain of its accuracy.
SPL 1m from front grill amp off: 37.0 dBa (slow)
SPL 1m from front grill amp on: 41.4 dBa (slow)
To me 41.4dBa. seems plausible for how loud it is but perhaps the room is quieter than 37dBa as the low limit for the meter is 30dBa.
All voltages on scope screens are X10 as I used a 100x high voltage differential probe. The load is 4ohms on CH1.
CE2010 50Hz burst: 316.4Vpp = 3127W into 4ohms
After 100 cycles of 20Hz (~5s) = 312Vpp = 3041W into 4 ohms
There is an internal limiter that reduces gain to stop clipping.
So kind of weird I'm reading that this amp can do 110Vrms when the datasheet specifies it for 90Vrms. I'm also running off 240VAC not 120VAC as the datasheet specifies and perhaps they use a low distortion threshold? also there is quite a lot of switching hash which might be causing me to over read the voltage. Regardless this amp seems very strong with no significant reduction of output even after 5s so would be a good choice if you like sine wave bass lines (assuming you don't load it with 2*2ohms where the specs collapse a bit).
Some tests of the Crest Audio CLh5000C, at first I thought this was just an install version of the Peavy IPR2 5000 but it has better power output specs and its outputs are not bridgeable. This amp is not quiet but is also not so noisy as you hear its fans throughout the house only in the same room. This is quieter than classic PA amps with mains powered high output fans like the Cloud VTX1200. If you could put this amp in an equipment cupboard this would be OK. I now have a SPL meter but I only measured a small delta between the amp on and off so I am not certain of its accuracy.
SPL 1m from front grill amp off: 37.0 dBa (slow)
SPL 1m from front grill amp on: 41.4 dBa (slow)
To me 41.4dBa. seems plausible for how loud it is but perhaps the room is quieter than 37dBa as the low limit for the meter is 30dBa.
All voltages on scope screens are X10 as I used a 100x high voltage differential probe. The load is 4ohms on CH1.
CE2010 50Hz burst: 316.4Vpp = 3127W into 4ohms
After 100 cycles of 20Hz (~5s) = 312Vpp = 3041W into 4 ohms
There is an internal limiter that reduces gain to stop clipping.
So kind of weird I'm reading that this amp can do 110Vrms when the datasheet specifies it for 90Vrms. I'm also running off 240VAC not 120VAC as the datasheet specifies and perhaps they use a low distortion threshold? also there is quite a lot of switching hash which might be causing me to over read the voltage. Regardless this amp seems very strong with no significant reduction of output even after 5s so would be a good choice if you like sine wave bass lines (assuming you don't load it with 2*2ohms where the specs collapse a bit).
Attachments
Thanks, Chris.
What's a good source for silent fans?
I tried to look into this (for computers) decades ago, and everyone acted like it was a trade secret. Folks just wanted to resell fans to me rather than mention the brands that were made well.
I'm looking to replace the fan in my QSC RMX850a. I think it's an 80mm, but I've already put it back in the rack so it's out of reach for measurement. The OEM fan is SUPERRED DC24V 0.24A CHA8024EBN-K(8) CHENG HOME ELECTRONIC CO., LTD. MADE IN CHINA.
The RMX850a is for my sub, and even though it's advertised as a variable-speed fan, it's as loud as the TAPCO JUICE J-2500 that I had in service before. I can hear the QSC in the next room, so it's not workable. I agree with the top post listing the RMX as noisy. I wish I'd seen this thread before I made my purchase!
Meanwhile, QSC has these SPA2-* and SPA4-* half rack 1U amps. I should have bought one of those, but I'd already wired by sub with a SpeakON connector, and I'm too lazy to rewire for the SPA2-60 screw terminals. The SPA2-* do not have a fan, so I bet they'd be quiet. They even come with adapters for folks who need to mount them in a full-width rack.
I've heard good things about Noctua silent fans. 24v ones are a bit more difficult to find, but some searching around should get you there.
There are lots of people on AVS Forums which have done this sort of mod - they're mostly home-theatre enthusiasts, who find PA amps to be a good way of powering their monster subwoofers.
Easier to dismantle a SpeakOn connector than to replace a fan. YMMV.
Chris
Thanks. I'll look at Noctua.
I hadn't heard of AVS Forums, but I'll check them out.
That's hilarious, because you're absolutely right! It didn't take much time at all to convert the subwoofer cable connector from banana plugs to the SpeakON. It certainly shouldn't take much time to convert to something else.
I guess the full story is that I'm sold on the high-current connection style of the SpeakON, and don't really want to go back to banana or screw terminals.
SpeakONs really are great, but one thing that's slightly annoying is that there are multiple different wiring schemes. That is to say, some loudspeakers will have one SpeakON connector input, with pin 1+ / 1- for one driver and 2+ and 2- for another. That's how my TQ440s are wired.
Not all equipment is like that though.
Banana plugs (at least if you use the genuine Pomona MDP connectors) are great, but there are SO many pieces of consumer gear that don't use standard spacing.
Not all equipment is like that though.
Banana plugs (at least if you use the genuine Pomona MDP connectors) are great, but there are SO many pieces of consumer gear that don't use standard spacing.
Two more amps you can add are the Crest CA9 (the CA2, CA4 and CA6 should be about the same in this regard) and the QSC Powerlight 2 series. They fall under the "not a total racket" category. IMO, they're about the same volume level as the MC2 MC series. Not bad, not awesome.
What I will point out about the MC2 is that it's an amazing amplifier. My usage for these is more towards the near-field / mid-field monitoring application than strict PA.
I did a listening comparison between an MC450, a Crest CA9 and a Macro-Tech 3600VZ this week. Didn't have a chance to compare them to the Powerlight. I was expecting them all to sound about the same. After all, they all have pretty low distortion (below 0.03% across the spectrum) and all are far more powerful than needed. All three had needed minor repairs and I took the time to align them according to manufacturer specs. All of them were verified to meet their published THD specifications. I also set the gains approximately equal. Testing was done with a pair of Elac 510s (which have an AMT tweeter) and some Quested F11Ps. Obviously this is a relatively low-power test, probably not exceeding 20 watts or so on transients, so keep that in mind.
I was rather surprised that there was a noticeable difference. The MC450 came out on top, the Macro-Tech definitely lost, and the Crest was somewhere in the middle.
I would be happy to use either the MC2 or the Crest in my main system. I don't think I could put up with the Macro-Tech even without the fan noise. Higher frequencies are rather harsh, for lack of a better word. It's one of those things where at first it sounds like the rest, but after a couple minutes it really starts to get aggravating. It's especially bad with the Elacs. I really like the AMT tweeters in the Elacs, but they can be fatiguing in the wrong setup.
The Crest and the MC2 are both really pretty nice amplifiers that don't bother me. The MC2 is a traditional Class AB design and is biased pretty hot. The front end of the power amplifier stage is a 5532 with voltage rails that move with the output- a clever idea that works well. The Crest uses the same basic topology as the Pro series (4801, 6001, 7001, etc)- it's a well-implemented Class H design.
In a studio monitoring application I'd pick the MC2 over the Crest. Some of the subtleties in recordings tend to vanish a bit with the Crest in comparison. The newer S Series likely improves things even more.
A few more technical notes on the MC series:
-You CANNOT remove the fans in the MC series. It will run, but it WILL overheat and shut down even at idle. When biased according to the service manual (which recommends the use of a THD analyzer to do so) an MC650 will have ~200 mA of quiescent current flowing through the output devices, possibly more if biased using the THD analyzer method they recommend. I would expect most MC2 amplifiers to be the same in this regard.
-The heatsinks on the MC series are live. There will be sparks if you short one of them to the chassis (or to each other, for that matter. Each output module really has two isolated heatsinks).
-Quieter fans won't make the MC series silent, because the configuration generates quite a bit of turbulence, so it's not just the noise of the fans you're hearing.
What I will point out about the MC2 is that it's an amazing amplifier. My usage for these is more towards the near-field / mid-field monitoring application than strict PA.
I did a listening comparison between an MC450, a Crest CA9 and a Macro-Tech 3600VZ this week. Didn't have a chance to compare them to the Powerlight. I was expecting them all to sound about the same. After all, they all have pretty low distortion (below 0.03% across the spectrum) and all are far more powerful than needed. All three had needed minor repairs and I took the time to align them according to manufacturer specs. All of them were verified to meet their published THD specifications. I also set the gains approximately equal. Testing was done with a pair of Elac 510s (which have an AMT tweeter) and some Quested F11Ps. Obviously this is a relatively low-power test, probably not exceeding 20 watts or so on transients, so keep that in mind.
I was rather surprised that there was a noticeable difference. The MC450 came out on top, the Macro-Tech definitely lost, and the Crest was somewhere in the middle.
I would be happy to use either the MC2 or the Crest in my main system. I don't think I could put up with the Macro-Tech even without the fan noise. Higher frequencies are rather harsh, for lack of a better word. It's one of those things where at first it sounds like the rest, but after a couple minutes it really starts to get aggravating. It's especially bad with the Elacs. I really like the AMT tweeters in the Elacs, but they can be fatiguing in the wrong setup.
The Crest and the MC2 are both really pretty nice amplifiers that don't bother me. The MC2 is a traditional Class AB design and is biased pretty hot. The front end of the power amplifier stage is a 5532 with voltage rails that move with the output- a clever idea that works well. The Crest uses the same basic topology as the Pro series (4801, 6001, 7001, etc)- it's a well-implemented Class H design.
In a studio monitoring application I'd pick the MC2 over the Crest. Some of the subtleties in recordings tend to vanish a bit with the Crest in comparison. The newer S Series likely improves things even more.
A few more technical notes on the MC series:
-You CANNOT remove the fans in the MC series. It will run, but it WILL overheat and shut down even at idle. When biased according to the service manual (which recommends the use of a THD analyzer to do so) an MC650 will have ~200 mA of quiescent current flowing through the output devices, possibly more if biased using the THD analyzer method they recommend. I would expect most MC2 amplifiers to be the same in this regard.
-The heatsinks on the MC series are live. There will be sparks if you short one of them to the chassis (or to each other, for that matter. Each output module really has two isolated heatsinks).
-Quieter fans won't make the MC series silent, because the configuration generates quite a bit of turbulence, so it's not just the noise of the fans you're hearing.
Thanks for the info, could be related to crossover distortion if your listening at low level. Would be interesting to see the residual wave forms.
I'm not a fan (ha) of messing with the cooling systems of amplifiers as they are usually barley adequate or inadequate if your actually using the full output of the amp. E.G with the NU6000 most people report that its always running cool but when running PA subs off one I have got it blowing hot/warm air out the back so if I had put quiet fans in it, it would have blown. I quite like the approach of the P7000s where it has fans but only uses them if required (and starts them slow).
I'm not a fan (ha) of messing with the cooling systems of amplifiers as they are usually barley adequate or inadequate if your actually using the full output of the amp. E.G with the NU6000 most people report that its always running cool but when running PA subs off one I have got it blowing hot/warm air out the back so if I had put quiet fans in it, it would have blown. I quite like the approach of the P7000s where it has fans but only uses them if required (and starts them slow).
I didn't measure any crossover distortion on the Crown, but that doesn't mean that it doesn't have other nasty behavior at low power levels. Doesn't matter, that amp is going to be used for a physics experiment where distortion isn't a concern unless it's severe enough to make a flyback transformer unhappy.
If you aren't beating them to death, a lot of amps could have quieter fans fitted. That said, if you're planning to use an amp as a 3 kW signal generator, then I might go the other direction and install some server fans (being mindful of current drawn from the fan circuit).
If you aren't beating them to death, a lot of amps could have quieter fans fitted. That said, if you're planning to use an amp as a 3 kW signal generator, then I might go the other direction and install some server fans (being mindful of current drawn from the fan circuit).
I'd double-check that Crown amp. In my experience, they sound excellent if they're working properly. What often happens, though, is that if the output transistors blow, only the knackered ones are replaced, resulting in mis-matches.
I have a MA5002VZ here which works well as a HiFi amp. Very quiet fan at idle or low-power, and sounds great.
Chris
I have a MA5002VZ here which works well as a HiFi amp. Very quiet fan at idle or low-power, and sounds great.
Chris
I can confirm that this amplifier was in about the best condition it could have been. I actually got it from another research lab. It was never toured and was pretty well babied for its entire life. Knowing where it came from, if there ever was an issue it would have been sent back to Crown for repairs. Every one of the output devices appeared to be original.
From what I understand the "grounded bridge" idea used in the Crown is loosely based on the BSS EPC780, which does a similar thing (albeit in a slightly more complicated manner).
From what I understand the "grounded bridge" idea used in the Crown is loosely based on the BSS EPC780, which does a similar thing (albeit in a slightly more complicated manner).
I hear ya. The nice thing about TAPCO and QSC is that the SpeakON wiring info is right there on the back panel. Both would connect directly to your TQ440s.
They seem to like to wire the first SpeakON to carry both channels, and the second SpeakON to carry only channel two. That way you have options for how many cables you need between amp and cabinet. It's not helpful if you want to bi-amp with tweeters on one stereo amp and woofers on another stereo amp - that would require four cables. But there are a few configurations where the wiring would be really handy.
The bridged wiring just takes advantage of the fact that channels 1 and 2 are already connected on the first SpeakON.
Your advice is on the money, though, because I had to double-check that my old TAPCO wiring was the same as the QSC wiring before plugging in my sub.
When I bought this sub, it was recommended that I use cables with double wires ... as in four conductors. So, I had to squeeze two + and two - into the SpeakON screw terminals.
Yeah. My Pass Laboratories XA30.8 has weird spacing. I'm using one banana (in a paired connector that's only half utilized) and one bare wire. Looks bad, but it seems safe enough.
My To-Do list includes looking for a source for LINN brand banana plugs (they're individual) so I can swap out the pre-spaced banana pairs that I have.