Crown D150 advice

MisterZ

MisterZ

Ouija - Mystifying Oracle
Hi all,

Over the weekend I came across a little hole-in-the-wall second hand shop not expecting to find anything in particular but you never know. This place looked like a store full of Garage sales with plenty of well-used furniture and "stuff", most of it pretty scruffy. On a shelf is something that catches my eye...a Crown D150. I've used a D75 in the distant past (and didn't care to know the specifics, only that it worked in the system I had access to) but the "Crown" script on this one is Old School. It's a straight up power amp and it's heavy as in 20+ lbs. It's sitting behind a pair of DIY Monkey Coffins that look like somebody's Home-brew version of Realistic Mach 1's.

The guy running the place says he knows what it is but can't test it AND he has no idea where it came from (I'm guessing it's a consignment arrangement at this place). It shows signs of being rack mounted - no faceplate but no rack mount ears either - only a drilled and tapped hole in an odd place nowhere near any components - so we work out an agreeable price ($50.00). I've got 24 hours to return it if it's dead. The apparent age of the thing has me a little concerned but I decide to give it a chance. looks just like this one:

BIG_CROWN_D150.jpg


I get it home,pop the covers and blow out what little dust is in the unit. No metal shavings...no burning smell I can detect. I get some adapters out and run an MP3 player to it, hook it up to a pair of Boston Acoustic a120's and I'm getting faint sound from one channel. I have a SAE PA-10 pre-amp and hook it up to switch/attenuate the player, some more fiddling and it sounds better. Just when I think I'm looking at am amp with one dead channel, I check the gain pots and after an adjustment, both channels clean and clear...I bring the volume up slowly and it sounds VERY nice...So I'm VERY Happy. I've only listened to it for a half an hour and I haven't noticed anything questionable at all. The heat sinks got maybe a few degree above room temperature and I was playing it maybe a bit loud for 10 minutes or so.

The questions I have are these:

1. Given the age of this amp (I'm assuming it's late 60's or early 70's vintage...no faceplate, though), is there anything I should be mindful of that is more likely to "go" in the area of capacitors?

2. The 75wpc this amp is stated to be capable of was enough to make one of the speakers have a loud "pop" at 1/2 volume (not trying THAT again). What loudspeakers would be a better pairing for this amp IF it were to be used at higher volumes for perhaps extended periods of time? My wife DOES have a "Drive it like you stole it" habit with gear occasionally...Wants to hear Concert recordings and Electronica/Trance LOUD. I have a pair of A/D/S L570's. Is this too much amp for them?

3. I'm a neophyte when it comes to amplifier "Class". The literature states that the D150 is a Class "A/B-B" and this is, from what I can tell this far something unique to Crown. What are the advantages of this type compared to Class "A", Class "D" and so forth? Can someone explain it in layman's terms? Is this amp better suited for Audio Reinforcement than HiFi?

4. As far as a Pre-Amp goes, I have that SAE PA-10 but I don't know if its "Consumer" nature plays well with this amp insofar as the strength of the signal it is outputting goes. I'm reading the amp should have 1.2 Volts fed to it and in my past experience with car audio I know some head units have 3 Volt outputs. What advantages/disadvantages are there to having a higher level fed to the amp (I'm assuming it's primarily to achieve higher SPL)? Is there some kind of standard level associated with commercial gear in this regard versus consumer home gear?

I apologize in advance for the long list of questions. I've read a fair amount about people's opinions of the D150 but most of the commentary has to do with later models having volume controls which I'm reading are built a bit differently than the one I have. Any and all pointers and help greatly appreciated...opinions as well.

Thanks
 
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These amps are from the period you mention, they came in 2 versions, an industrial with no faceplace and the home/studio version with the faceplate, same unit. Back then we had the industrial version in stock and kept a couple of faceplates. Our cost for the pair was less than the home/studio version so we ended up with more profit. Soundwise, a very good amp for home systems. I found the smaller the Crown amp, the better the sound, not untypical for amps of that period but seemed more pronounced with the Crowns.

The class configuration is typical of most amps of the era and after; low power is class A that turnsover to class AB at higher wattages. I think on balance the class is very good as a class A amp is very inefficient and except for a few usually not high powered. Never heard a class D I liked. From memory, the AR amp and receiver were class D. There are some other designs that have come out and most if not all have gone to the audio shelf in the sky.

As for the voltages, generally as long as the preamp can supply the necessary voltage to drive the amp to max power that is all you need to deal with. If the preamp output is insufficient to drive the amp to max output it simply means it will not have the gain to get the specified maximum power, not necessarily a bad thing. The impedence matching is usually more of a factor. The SAE/Crown should pose no problem. If the max voltage of the preamp is more than the max input for full output of the amp, then remember there are the gain controls on the amp to limit the input voltage or the preamp volume control. Each will limit the voltage in on the amp from the preamp..

Not sure of the pop on the speakers but, probably should track it down before putting a good set of speakers on it. Check the DC offset on the amp as a starting point. Also, the gain controls may be dirty, though it could be a cap or even a cold solder joint. I can not remember but I seem to remember the boards were plug in and it might be the connectors and pcd terminal stip need a healthy dose of cleaner.
 
This amp would be considered class AB by most folks, but there are a few nerds, myself included (as well as Douglas Self and apparently someone at Crown), who think the B designation is more appropriate. Bias current is so low that its class A operating region is microscopic -- just enough to overcome severe loss of transistor gain in the crossover region. The whole point is almost purely academic, but never forget that correct adjustment and stability of bias current is always a critical matter in this class.
 
It is actually a pretty good and nigh-on indestructible amplifier and well worth 50 smackers in working order. Assuming it is direct coupled (I honestly cannot remember) Brian's advice is good - don't hook it to any good loudspeakers until you check for DC on the outputs.

crownies.jpg


(found mine on the swap pile at our town dump)

EDIT: I wouldn't bother hunting down an IC-150 preamp,were I you...
 
The IC-150a is decent but as stated not the IC-150 without changing chips in it.

I am using a D-150 to drive a pair of MG-2.5/R speakers. It does a fine job. Mine is like yours, sans faceplate at this time. I was using it face down but now it is sitting there with the guts exposed facing the listener. I call this version the church amp because churches would buy this type for mounting to the rafters, podium or whatever and they did not need to spend money on a faceplate that was not needed.

The Crown site has info on this amp stating the faceplate was a 33 buck option or so.

Mine is a very good sounding amp or I would be using a McCormack DNA-1 instead. It is sitting between the speakers ready to go if needed for a bit more volume.
 
Thank you all for your very informative responses. The one thing I forgot to mention is that this particular item has no On/Off switch. That was another worrying point when I inspected it at the store as in “Did someone just plug this thing in sometime around 1968 and LEAVE it on…for a decade maybe?”. And there is always that question I find myself asking. “Why did someone get rid of it?”. Neither question is going to get answered, so I’m working with a blank slate. I do know one thing. In my workplace, except for a major blackout lasting 24 hours a few years ago, there are ten Crown D75’s that have been powered up since at least 1999. On average, I’d say they get MAYBE an hour of use a week apart from sitting idle. If what I have is similarly immune to deterioration from sitting idle over long periods, It will outlive me so I’m just it’s caretaker until then. It sure looks like it was installed, sat there for a LONG period, and was then removed. No scratches or scrapes indicating it being moved a lot or at all. Not even all that dusty considering. Someone DID bench test it at one time. I found a taped-on/taped over notation on the case with measurements in Hz over 50k if I recall correctly. When I have a chance this coming weekend, I’ll take a pic and post it. Don’t understand what was measured. The note isn’t dated but it isn’t recent judging from the paper used.

Brian,

Thanks for the advice on checking DC offset. I’ve downloaded the schematics, instructions and service manual from Crown. I’m glad that Harman Int’l has made these available. Some of the most clear instructions I’ve read and coupled with the info at: http://audiokarma.org/forums/showthread.php?t=5634 I’m there.

The speaker “Pop”? I think I know what caused it.

I was playing The Magnificent Seven by The Clash. It’s bass heavy and I pushed the speaker beyond its limits. The A120’s I have are 2-ways with a 10” Passive Radiator and a 6” Mid-woofer plus a dome tweeter. The mid-woofer has to work REAL hard with low frequency and the speakers are very efficient compared to most of the others I have…just not much there in the lower end. I’ve read a lot of people dislike the lack of bass from them. I think I just overdrove the mid-woofers. The gain pots on the amp were full open to their stops. I didn’t THINK it was playing as loud as it was. I was in a nearly empty room 40’ square. The wife confirmed that I WAS playing the music at high volume when it happened. I’ve only ever mated these speakers to a 40-watt Harmon-Kardon receiver before and I didn’t push them all that much.

Before I go and do something overenthusiastic again, I’ll really go through the unit and clean everything I can, perform the tests, follow the advice here and Crown’s instructions and correctly trim the gain pots.

BlueShadow, the faceplate is a nice to have but I gotta say I like the minimalist looks of the amp the way it is. I’m tempted to leave it face down. It will look “the Business next to my Technics RS1506. “Church Amp” sounds right. I could see it being installed in a school or some kind of commercial establishment…a theater. It’s anyone’s guess where it came from. The guy at the store was more informed on audio than I expected, just not on the provenance of this piece. Actually knew what and who Bozak was, said he got in “good stuff” every couple of weeks and he said he sold a pair of Magneplanar speakers (“Giant things” he says) the week previous for $100.00. I’ll be hitting that place in the future if only for the vinyl…he only had ~1.5k LP’s but claimed he had more “In the back room”. I’m moving to a new town and they have a “Electronics Recycle” drive and sale table for charity at the town’s waste management center, so I’ll take the hint mhardy and see if I can save something and do a financial good deed at the same time.
 
I was thinking that may be the case or they had it in a rack with a Master switch. I'm planning on a high quality Surge Protector for the easiest modular solution.
 
Check for DC on the outputs. This is a very good amplifier. And it is Crown Tough. Meaning Missionary Tough in the classic old Clarence Moore tradition. This is also a very good sounding amplifier to boot. Good enough for my discriminating taste.
 
I bought mine new sometime around 1968 and still have it. It took one trip back to Crown for a hum in one channel and hasn't failed since. No charge for the repair.

I bought mine without the front panel because back then it sat in the closet and the panel was more money than I wanted to spend. Great little amp and I have the McIntosh Clinic reports on mine over the years to verify its performance.
 
I've been highly impressed from the moment I removed the covers and the black front panel. Everything laid out and clear to see, nothing more than what needs to be there. I expect I will be learning a lot more about it as time goes on. It certainly sounds nice and clean from the limited time I've spent with it thus far.
 
I used to use those exact models in the mid-70s with then-new disco installations in bars across eastern North Carolina. I'd set them up in the manager's office with fans on them and run the wiring out to the dance floor for the speakers. In this nasty, smoky environment the Crowns just did their job. I _never_ had one fail on me throughout the 70s. That couldn't be said for the DJs who had too much to drink and tried to use the Rec-O-cut turntables......

At the same time, my weekend band used Crown DC-300s for much the same reason: they were bullet and idiot proof and would recover from dead shorts and other drug/alcohol infused studidity on band member parts without us having to default on a gig. This, IMHO, is what made Crown well-known in those circles as being reliable.

Later, I bought a Crown SX-724 tape deck for local recordings after lugging a 'portable' Magnecord around (it was a tube tape deck). The same build quality was inherent in those as well. I can still hear the solid 'thock!' sound as the pinch roller engaged the tape on one of those decks.

Congrats on the new amp, there. Its a slippery slope for good Crown gear!

Cheers,

David
 
Kinda reviving a long-dead thread here, but I wanted to clear up the class AB+B thing on these Crown amplifiers. This is a scheme in which the final output devices are operated entirely in class B (you'll notice in the service information that the quiescent base-emitter voltage on the output transistors is 330mV). The driver transistors are operating in class AB and are coupled to the output each via 5.6Ω resistors which also serve as the base-emitter shunts for the output devices.

For small output levels (anything beneath approximately 200mV peak) the output devices don't do anything. Once the output swings beyond this 200mV threshold the final output devices start conducting. Similar to the Current Dumping topology Quad used in the 405, albeit theirs operates the driver section in class A (with finals in class C).

A subtle truth is that both operate their outputs in the zone between class B and C, this is because the devices have finite exponential response and as such there is no hard threshold. Ideally the designs are set up such that under quiescent conditions the output devices are, for all intents, not conducting, but near enough to conduction that they will begin to add current into the output smoothly and rapidly without ever going into class AB.

For the most part, there is no substantial performance benefit over conventional topologies (if properly implemented), but these techniques do allow a great simplification in thermal design and choice of output devices (no need for adjustable bias, thermal tracking, etc.)
 
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