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Posted: Thu Oct 04, 2007 6:16 pm
by bob p
MODS: I also did some mods to the fan PCB to fine-tune the fan's idle speed to my liking. Here are the results:

LOW Setting: The fan is quiet at idle, and speeds up appropriately when the amp is under load. This is a great setting for home use where the amp isn't always running full tilt.

HIGH Setting: The fan is kind of loud at idle, and speeds up appropriately when the amp is under load. This is the preferred setting for stage use where the amp is run pretty hard.

Safety Backup: If the amp ever gets hot, a thermal temp sensor on the center of the chassis will bypass the votlage dropping resistors on the fan board. This runs the fan at even higher speed. When the dropping resistors are bypassed the fan runs like a tornado until the amp is cool, and then goes back to your chosen Hi/Low setting. In safety mode it sounds like a Lockheed Constellation at take-off. (!)

The fan upgrade is really a great mod for old amps whose fans are old and turn too slowly at idle, and for those amps whose fan bearings are shot and make lots of squeaky noise.

The PCB mods allow you to adjust the range of fan speeds under idle/load conditions to suit your individual application.

BTW, since I had to buy a carton of them, I now have a boatload of fans if anyone needs one. O:)

Fans Now Available

Posted: Wed Apr 30, 2008 3:40 pm
by bob p
Fans are now available.

I had to turn away a handful of people who had sent me PMs and e-mails for fans because I had them stashed away in an inaccessible location. I'm happy to report that I've dug them out, so if anyone still needs them just let me know.

Re: Carver PM 1.5 amp Fan

Posted: Wed Apr 30, 2008 7:33 pm
by maddmaxxx
-BEAUTIFUL, mr bobp

-did'nt see your last years pics, post

-make sure you post 'em in the FS linky here too

Re: Carver PM 1.5 amp Fan

Posted: Fri May 23, 2008 4:45 pm
by bob p
Sorry for the late arrival to this thread. I haven't been subscribed to it. I guess I should change that. #-o

I've got the box of fans out, as more than one person has asked me about them. If you need a couple, send me a PM with your contact info and I'll figure out what it would cost to ship them for you.

Re: Carver PM 1.5 amp Fan

Posted: Sat May 24, 2008 1:46 am
by engtaz
Does this fan also work for the PM-1201?


Re: Carver PM 1.5 amp Fan

Posted: Sat May 24, 2008 2:17 am
by OBI56
engtaz wrote:Does this fan also work for the PM-1201?

Not sure about that engtaz; the PM-1.5A and PM-1201 have almost identical specs except the the 1201 was also designed to drive 16 ohm loads at 300WPC. Other than the difference in color and a different layout for the back panel they seem to be pretty much the same amp. Hard to tell without the service manuals or pictures of the inside though. Maybe chack the part number on the fan to make sure it is the same.

Re: Carver PM 1.5 amp Fan

Posted: Tue May 12, 2009 5:32 pm
by bob p
engtaz wrote:Does this fan also work for the PM-1201?

Sorry to be almost a year late in responding to your question. :shock: I wish that the board had a feature (like some of the other boards) where I could subscribe to e-mail notifications when this thread gets updated; then I would have known about your question a lot sooner. As it is, the only reason I found out about this question was because somebody e-mailed me to ask about buying an OEM replacement fan for their PM-1.5.

I've never been inside of a PM-1201, but I think the answer to your question is probably, "Yes."

My understanding is that the PM-1200 and PM-1201 are essentially later versions of the PM-1.5 where they added 70V line outputs and doubled the number of fans to facilitate cooling. My understanding of the situation is that just like in the PM-1.5, the fan speed is controlled by the amount of current that is passing through the power supply. This makes the fan run at a higher RPM as the demand on the amplifier increases.

Based upon the assumption that the power supply board & voltages are the same on these amps, and the fan control board's voltage dividers are the same on these amps, then the fan motors should also be the same. To get the definitive answer to this question, we'd really need to peek under the hood of a PM-1200 or a PM-1201 and compare the power supply and fan control circuitry to that of the PM-1.5. If the control circuits are the same, then its a short leap of faith to conclude that both amps can properly control the spin rate of the same fan motor.

A more forensic approach would be to remove the fan motors from both types of amps and place them in an external circuit that would allow us to measure the electrical properties of the fan motors themselves. The problem with this sort of reverse-engineering approach is that getting good data is entirely dependent upon the quality of the specimen being reverse-engineered; these types of measurements aren't that reliable with old, worn-out motors, so you have to base your forensic analysis on a good specimen.

Another option would be to look at the manuals, but I've never been able to lay my eyes on a PM-1200/1201 manual.

One thing that makes it particularly hard to source the proper OEM replacement parts from manufacturers like Carver is that like most electronics manufacturers that sold "authentic" repair parts as part of their business model, Carver's parts did not ever bear OEM part numbers. If the part bore any part number, then it was only an "in-house" part number. This locked you into buying parts from the manufacturer (Carver), and not from their supplier. If you're lucky, someone might have a crosswalk reference book that converts the "in-house" part numbers to "supplier" part numbers. That could allow you to source a generic replacement part if you couldn't get "in-house" parts.

Getting the right parts for Carver amps is particularly troublesome. Carver Parts is gone, and all of the leftover "in-house" parts inventory has been sold off. Sourcing the fan motors is particularly difficult as they don't bear any part numbers whatsoever -- there are no OEM numbers and no "in-house" numbers on the fan motors to help you. You literally have to know the specifications of the fan motor that you're looking for to find the right part.

Re: Carver PM 1.5 amp Fan

Posted: Tue May 12, 2009 9:33 pm
by birdyman
I just modified pm1.5 fan circuitry to use with 12v computer fan in dual speed. PM 1.5 uses ~40 v to run fan originally. you can remove most of parts from fan controller board then rewire them using 12v zener diod and any good npn output transistor to make 12v supply. Good reference diagram can be pm1.5's +12v supply circuit. You need to use heat sink for this then use 2X 30 ohm 2w resistors to make 15ohm 4w to step down fan speed. this will generate more CFM than original fan with much less noice and if fan goes bad again, you know where you can get the replacements( your son's junk computer!!). Good Luck

Re: Carver PM 1.5 amp Fan

Posted: Tue May 12, 2009 11:28 pm
by bob p
Hmm. E-mail notifications seem to be working now. I wonder why they weren't working before...

Birdy, I understand that a great many people have resorted to modifying the PM-1.5 using a computer fan mounted externally to replace the OEM fan that is mounted internally. Nobody makes the decision to externally modify the amp in this way because the mod is aesthetically pleasing -- hanging a computer fan on the outside of the amp creates an external obstruction and something that catches on cables. While this sort of mod would work OK for a home application where an amp is tucked into a rack and the installation remains static, I think that it would be a Royal PITA in a pro-audio application where cables are constantly being changed. I think that most people who choose to mod the amp to use a 12VDC computer fan choose this solution out of frustration from not being able to find the right part for the job. With no other options, they look for a creative solution.

Personally, I've never been willing to perform repairs that require me to compromise the cosmetic appearance of a Carver amp's exterior -- even on the back panel. Looking at the photos that I posted on page 1 of this thread, it should be obvious that I'm somewhat of a purist WRT maintaining the integrity of the aesthetics of the Carver amps, both internally and externally. I like the way Carver gear looks, and my personal preference is to keep it looking the way its supposed to look, both on the inside and on the outside. For example, I have an M-500t that I bought DOA off of eBay. It had 3 different circuits blown out due to a lightning strike. It required extensive internal repairs, including a new relay to isolate the output stage. Since the OEM part is unobtanium now, I had to use a generic relay mounted remotely from the PCB with jumper wires. For aesthetic reasons, I just can't bring myself to offer the amp for sale here. Its just not 100% right in my opinion and I wouldn't want anyone on the Carver Forum to own it because its not 100% original.

Back to aesthetics of the fan mod -- YES, the computer fan mod is cheap, but IMO the computer fan mod is butt-ugly and is a definite no-go because it violates the appearance of the amp. Just my opinion.

WRT modifying the fan control circuitry to accommodate a 12VDC computer fan, the modification would be simple enough, and wouldn't necessarily require any of the zener diodes, transistors, or heatsinks that you recommended. I'm not sure that I understand why you took that approach, so maybe you could explain it for me. To me it seems like an unnecessarily complex approach to a simple problem. To me, it doesn't make sense to gut the fan control circuitry and build a new 12VDC power supply for the fan. To me it would seem far simpler to just use the existing 40VDC supply tap and just re-scale the existing voltage divider circuitry on the fan control board to drive the fan at the desired speed. To me, it seems like you've chosen an unnecessarily complex solution to a simple problem.

Engatz, to clarify my previous answer, YES, the PM-1.5 fan will definitely work if you are willing to re-scale the voltage dividers. It may be necessary, but in all likelihood I would expect that it wouldn't be necessary as I suspect that Carver used the same fan motor in both amps.


Re: Carver PM 1.5 amp Fan

Posted: Thu May 14, 2009 11:57 am
by birdyman
If you use 3" fan, it will fit in to pm 1.5. You don't have to stick it out side. 12v cooling fan has come to long way thanks to abundunce of computers. They are cheaper and better in quallity than any other fans on the market. Some highend 12v fans have ball bearings rather than copper sleeves. It produce better CFM at low noice than original PM1.5 fan. IMHO, using resistor voltage divide can be little bit challenging because of wattage of resistors and heat. But either way is fine as far as it can supply 12v to fan. Cheers!

Re: Carver PM 1.5 amp Fan

Posted: Sun Nov 28, 2010 1:22 pm
by bob p
Hi Everyone. I'm bumping the thread because I've received a couple of emails recently about fan replacements.

It seems that once a month or so I get a bogus email request for a dozen fan motors from some ne'er do well from the other site. I guess people think it's funny to waste their time with these antics.

At any rate, the most recent fake fan request asked for a dozen fans, and as I packed them up and waited for the payment that never came, I realized that I don't have many fans left. Just so everyone knows, my stock of the original CarverPro fans is running out. I don't know how long the supply will last. I've been trying to find more, but nobody has them. We could be looking at the end of the supply of the OEM parts for the fan-cooled PM series amps.

Re: Carver PM 1.5 amp Fan

Posted: Sun Nov 28, 2010 2:15 pm
by TNRabbit
Bob, would you recommend any other replacement in particular?

Re: Carver PM 1.5 amp Fan

Posted: Sun Nov 28, 2010 3:52 pm
by bob p
No, I don't have an alternate solution. When the OEM Carver parts are gone, they're gone, and the world is going to have to go on turning without them. I hadn't realized that my supply was so low, so I've pulled a few fans out of the "for sale" box and set them aside, thinking that I'll have enough to get me through my lifetime. After doing that, I've only got a small number left to offer other people for restorations. I might have to limit how many fans any one individual can buy so that one person doesn't take them all.

When I was originally hunting for the fans, I was on a mission quest. I was willing to spend whatever time it took to find the right part so that I could repair my rack of PM amps, and I eventually found some. I bought a LOT of them, and this helped a lot of people over the years to restore their PM series amps. Now the supply of OEM fans in the market is gone. I've looked everywhere, but I haven't had any luck finding any more of them. The OEM fans are extinct / out of production, and without the proper parts, restoring vintage gear is going to become even more difficult.

What's unique about these amps is Bob Carver's very clever design of a demand-responsive ventilation system, where the amount of demand that was being placed on the amplifier output controlled the fan speed. The fan speed (and fan noise) changed in lock step with the volume coming out of the speakers. At low power output the fan was quiet, and at high power output the fan became quite loud, but the amp was so loud that you never really heard the fan working. It was a very ingenious design.

Every "mod" that I've seen people try to perform has amounted to bypassing Carver's original demand-responsive ventilation system, replacing it with a fixed-flow ventilation system. Having fixed flow (constant voltage and constant speed) means that if you have a fan that is adequate for high power conditions it will be far too loud for low power conditions. Or if it is quiet enough for low power conditions it will provide insufficient cooling for high power conditions.

It's important to remember that the PM amps don't have the same kind of ventilation system that the consumer amps have.

The consumer amps are open chassis, with passive ventilation to the ambient air. They have a thermal switch on the chassis that will shut them off if their temperature gets too high.

The pro amps are closed chassis, with no passive ventilation to the ambient air. They're rack mounted, and because they can't ventilate passively, they use motors to force air through the front and out of the back of the chassis. They also have a thermal switch on the chassis, but it won't shut the amp off if the amp gets too hot, because the amps are designed to operate continuously in live music applications. In the pro amps, the thermal switch runs the fan at the highest possible output in an "emergency" cooling mode.

If someone tried to use a different type of fan, like a fixed flow system, and took away the demand responsive cooling, then the pro amps would just burn themselves up under high load conditions. The popular mod of using a 12V computer fan is NOT a good solution.

When the supply of OEM fans is gone, the only other option is for someone to develop a new demand-responsive cooling circuit to retrofit into the amp. Paying an engineer to design that kind of a replacement circuit will be expensive -- more than the amps are worth.

Essentially, when supply of fans runs out, I think the amps will stop getting rebuilt and we'll see them going into the landfills.

Re: Carver PM 1.5 amp Fan

Posted: Sun Nov 28, 2010 4:30 pm
by F1nut
bob p wrote: It seems that once a month or so I get a bogus email request for a dozen fan motors from some ne'er do well from the other site. I guess people think it's funny to waste their time with these antics.
That's a despicable thing to do.

Re: Carver PM 1.5 amp Fan

Posted: Thu Mar 14, 2013 3:28 pm
by bob p
It seems that the photos from my old posts on fan replacement aren't available any more. Here they are again in case anyone needs them.
fan mod 1
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fan mod 2
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fan mod 3
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fan mod 4
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fan mod 5
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