Carver Magnetic Field Power Amp -whazzit????

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#63
Hey Chris, yeah we've seen some innovative ways to blow up a cabinet. Mostly subs get damaged from being driven too hard. The amps have decent protection and the drivers are pretty stout, but if pushed hard enough you can hurt a Meyer product. It's usually the input board, which is mostly passive, the amp section when mosfets get shorted, or the power supply when input voltages are funky- many cabinets use 48v switching psu's. I either case we don't repair them. We bill for a new assembly and send the bad to Meyer to be rebuilt. I don't think they do component level repair either.

If I ever see a bid for Caribana I'll advice the bosses. Besides, there's a huge Meyer rentel house up there, I forget the name.

We actually don't recone. We bill for a new driver and the old ones go into the dumster. Diving in our dumpster can be a fruitful experience.
 
#64
Hey Chris, yeah we've seen some innovative ways to blow up a cabinet.
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One of my mates runs a small dealer/rental company for PA equipment.
He once sold an Audio Perforance PA to a small local music club. Audio Performance - a small Swiss manufacturer- used the same principles as early Meyer systems (the owner being a buddy of John Meyer).

So one of the guys at this venue once found out that there was a significant rise in bass at high loudness levels if certain links from the woofer box to the controller were removed. Well - they did indeed have more bass - but not for long (and not for cheap either). :hot:

Regards

Charles

Edit: Forgot to mention: It is impossible to make anything foolproof because fools are much too inventive.
 
#65
Hi Charles,
It is impossible to make anything foolproof because fools are much too inventive.
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😀
Yes, you learn that after a few years in the service business. Self proclaimed experts are the best at being stupid.

I had a policy of charging a$$hole tax to those people. I still didn't break even.

Hi mixi500,
Besides, there's a huge Meyer rentel house up there, I forget the name.
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Long & McQuade or Steve's?
Hey Chris, yeah we've seen some innovative ways to blow up a cabinet.
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I wish digital cameras were available way back when. What a gallery we could put together between all of us! 😀 Might be a good idea to start.

Hi Jason,
Oh, i thought these were switch mode PSU or somethng
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As djk mentioned, the triac controlled the amount of energy soming in - thus regulating the power supply rails. The transformer was a special type that liked chopped, partial sine waves. It was called a "mag coil" and will draw extremely high current if you apply a full sine wave all by itself. It was more of a current transformer I guess. We always had technicians short these triacs out (to force it on! 🙄 ). They would call to order a mag coil then try to tell us it was defective. I started refusing returns on these pretty quickly. We always tried to explain to these guys that that wasn't the problem.

I wonder how many unrepaired Carver amps there are due to these idiots. Must be a lot of them.

-Chris
 
#66
The weird pinout opamp referred to in this thread is most likely the old RC4136. It was a dual version more or less of the 4558, a cheapo workhore opamp from the '70s. TI made the TL075, a quad TL071-type opamp with the same pinout, but it was never very popular. The rest of the world instead standardized on the LM324 pinout for quad opamps, and left the 4136-type devices in a historical backwater.
 
#68
Nevertheless, despite their use in some circles, the 4136-pinout opamps went bye-bye. In their day, firms like Exar, Raytheon, and TI (among others) made them. I should have laid in a stock of TL075s when I had the chance. I still have some 4136s in my parts bin. They may still be there when they bury me....
 
#70
I have an "unrepaired" M1.0t glaring at me. When I first got it, it was intermittent turning on, although after a while it settled down. It was awesome for home use running a couple of NHT1259s. When I began doing parties, I found it wasn't quite so great. Running it off a generator, it ate fuses, until I had to give in and turn the volume down. After that I got a Peavey PV8.5C for the subs, and used the M1.0t for the mids/high cabinets. It still got very hot, so I made a cardboard shroud with a fan that duct-taped to the cover.

It finally gave up the ghost at a party where the generator voltage was unusually high. Nothing happens when it's switched on.

Any tips on what might have failed?
 
#71
Now this is an interesting case of bad timing. Some of you might remember that I've been looking for an M-1.5t Service Manual, just because I thought it would be good to have one around.

Well, today my amp started misbehaving. Its been playing fine without any audible symptoms or any warning lights, but when I powered it down today I ran into a status lights problem.

Normally, when I power down the amp (with the preamp turned all the way down) a soft "thump" is emitted from the speakers which is presumably a voltage transient. Then the red LEDs in the power bar slowly trickle upward and the amp goes to sleep. This is the way that the amp has worked for 20+ years since I bought it new.

Today when I powered down the amp things were different. As soon as I turned off the power, both yellow "Headroom Exhausted" LEDs came on and stayed on, and a whirring noise came out of the speakers. After a few intimidating seconds of yellow lights they finally went out, and I got the soft "thump." Then the red LEDs trickled upwards as normal and the amp went to sleep.

The new onset of the yellow LEDs at power down and the whirring noise coming out of the speakers scares me. The amp has never used the protection lights or made this sound before.
 
#72
Hi solderhead,
There is a thread where I posted some "go over" instructions. Read it again please. Reread this thread too. PM me please.

Hi dangus,
Read the threads where I've posted on Carvers. Everything you need to know is there. Including this thread. PM me if you can not service it yourself.

You did exactly everything in your power to blow up your Carver. It put up with a lot of abuse from you. I understand that you didn't intend to kill it, but you did a great job. 😉

Hey Jeff - Thank you for posting those.

-Chris
 
#74
Anatech wrote:
I still would be careful with the op amps.
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I had been thinking of someday substituting TL071s for the TLo81's in the M400. From the datasheet they look pretty compatible, almost like the TL07x's are TL08x's with better common mode rejection and better supply rejection. I wouldn't expect to hear much diiference except maybe a slightly lower noise floor.
 
#75
Hi sam9,
I wonder if the M400's were a little tougher.
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No. it's more a question of power output. The M 1.0t puts out a great deal more power, therefore the current demands are higher and the generated heat is much higher.

I had been thinking of someday substituting TL071s for the TLo81's in the M400.
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The TL071 is a superior part. You could try a more modern Fet type op amp, but you may run into stability problems. I'd just leave the originals in there unless you want to put newer ones of the same number. Processes are better today. If you feel really daring, try a new style Fet op amp. Might be fun and that might improve the performance, who knows?

-Chris
 
#76
mobyd said:
The cheesiest thing in the PM1.5 is the little $2 model shop motor that drives the fan (and whines like crazy when it whacks out its bearings).
M
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anatech said:
That motor isn't too bad. A lack of maintenance will allow the bearings to fail. I note that several other devices use a similar fan.

That thing is the easiest to replace. Small computer type fan without a speed regulator. The caps may go open in the fan supply. Don't forget how old these units are, they are allowed to fail.
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Chris, I have picked up a PM-1.5 that's got the noisy grinding bearings in the fan. What's the best solution, to buy a replacement fan from CarverPro? (if they're still available) Other sources?
 
#78
Hi solderhead,
First try to remove the fan and inspect it. Clean out all debris and clean the blades. Then run it with a variable power supply and listen to it. They draw a lot of current. Oil the front and rear sleeve bearings with a light, no additive machine oil. Sewing machine oil will not work over the long haul. 3-N-1 and WD-40 are not what you want to use either. Run it at low RPM to work the oil in. Then run it higher to see if it's still noisy.

I'm hoping you can save the bearings. Also check the caps and diodes for the fan supply.

Sometimes the brushes wear out. New motor time from Carver Pro.

Hi sam9,
There are some very qiet fans made for PC's that are extemely quiet such as those from Silenx. Can anny of those be adapted to this use?
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Sorry, no. Once you see one of these amps you will understand. They could have used a more efficient fan, but they didn't. Therefore we are stuck with these.

-Chris
 
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