Service Data Request: Kenwood KA-5700 Integrated Amp

[bob p]

I think you can still get schematics from Carver Pro.

Well, not any more, at least according to the folks at the Carver Forum. As I understand the situation, Carver Service is long gone, but the people at Sunfire (Bob Carver's new company) were providing service for Carver amps. As it turns out, Bob Carver just sold Sunfire to Elan, and Elan has begun downsizing Sunfire. The first thing to go was legacy support for Carver products, which Elan doesn't care about supporting the way Bob Carver did.

Sunfire sold off all of the old Carver parts and service data to a repair shop in the Pacific NW. This fellow now has a monopoly on Carver parts. Its not possible to buy a part from him. Your only option it so send your equipment for him to repair, and the pricing is steep. I had read a post where someone needed a drive belt for their Carver CD player, and he wouldn't sell it to them. They had to ship the unit to him so that he could install the drive belt for them.

As it turns out, all this just happened in the past couple of weeks. I guess I waited too long to start looking.

[bob p]

I think they aer great amps, but wouldn't be my choice for subwoofers, nor would they be my choice for touring.

As it turns out, I was thinking about using my M-1.5t to handle the low end of a biamp setup, with a big tube amp on top.

Is there any reason that you wouldn't choose a PM-1.5t for subs or for touring? Is it related to the availability of parts? What else would you consider in its place?

If you ever want a serious pain in the ass, take apart one of the original Carver CUbe amps. I forget the model, something 400 I think. It is a cube about 8" on a side and it kicks out 400 watts. No fan. No knobs. The Borg in stereo. Imagine a couple rack space amp folded up into a cube.

I remember the "Cube." It was the first Carver amp I had ever heard. I had actually thought it as one of the amps I might pick up, but if they're a huge PITA to work on, maybe I'll look for something else.

[bob p]

As to the normal/extended, just a guess, but with the resistor, the speaker puts out the "normal" amount of lows, while the removal of the resistor add to the power in the woofer to "extend" the lows. I am thinking a 1 ohm resistor and two 2 ohm drivers in series will have the resistor sucking up 20% of the power applied.

I guess that's as good an explanation as any. I had thought that the nomenclature had used the "normal" position for normal, girlie amps, and the "extended" position for amps that could handle the extended load. It would seem that the resistor is somewhat of a mixed blessing for the little amps -- although it provides a higher Z load that they might be more comfortable driving, it wastes an awful lot of their power. I keep the resistor switched out.

[Enzo]

Did we actually go to Carver Pro and talk to them directly? In the past they have been very helpful to me.

I would not look at the carvers for big bottom because that is harder on an amp. Longer wavelengths require the power supply to hold up longer, and we will be taxing that high voltage rail more and more. Full range music has large spaces between low freq peaks. In my view, subwoofer duty is pretty close to sine wave duty.

Rail switching - commutating, same thing. I would not use the term floating rails though. To me that is the same as "flying rails." I am sure you have seen some amps where the output emitters are grounded. Then the speaker is between ground and the filter cap and center tap common. In other words the rails are not referenced to ground, so the amp drags them up and down. They float.

Drive belt? Geez, I'd just buy one from the parts market - MCM or someone like them. Carver had two lines, the consumer stuff - like CD players - and the pro stuff. Are you sure this service guy is not just working on the consumer stuff?

I thought the cube was innovative and seemed to work OK, but I would hate to work on one. They look spiffy on the shelf, but frankly I think yet another rack width low profile thing to go with all the rest of the similarly shaped items in the stereo system might stack better on the shelf.

[bob p]

Did we actually go to Carver Pro and talk to them directly? In the past they have been very helpful to me.

Well, no. <blush>. CarverPro has an explicit warning on their web site NOT to call them with any questions about Carver consumer audio gear. I don't know if that warning is new or if it is old, but I took the explicit notice on the CarverPro Tech Support page to be a clear warning not to bother them with consumer audio questions. They redirect all consumer audio questions to CarverAudio.com. Unfortunately, CarverAudio.com does not appear to be anything more than a Carver fan site that behaves very much like an exclusive country club -- its not a very n00b-friendly place.

It seems like kind of a Catch-22: CarverPro.com redirects you to CarverAudio.com for consumer gear, and CarverAudio.com isn't interested in helping new users who are "looking for a handout." <sigh>.

Actually, I think that CarverPro is making a mistake in redirecting people to CarverAudio. It seems that CarverAudio has nothing to do with Carver Corporation, an never has had anything to do with them. Bob Carver has been invited to participate in their Carver fan club on several occasions, and even though he has been invited repeatedly he has never participated -- maybe that means something, maybe it doesn't. I don't know.

At any rate, I'm pretty surprised by how hard it is to get help on these amps. Carver seems to be one of those companies that would not let anyone other than their authorized shops have access to the service data. Now that the company has been split into pieces, pieces have gone through Chapter 11, etc., there's a clear rift between Pro and Consumer, and it seems that everyone likes to yell at you if they think you haven't read their support policy, or if you are bold enough to ask questions that are in violation of their published instructions. <sigh>

Maybe I'll call CarverPro tomorrow just to be a PITA to them. I won't do it today -- I've been called an asshole about this problem enough times today.

[bob p]

I would not look at the carvers for big bottom because that is harder on an amp. Longer wavelengths require the power supply to hold up longer, and we will be taxing that high voltage rail more and more. Full range music has large spaces between low freq peaks. In my view, subwoofer duty is pretty close to sine wave duty.

I understand your point about subwoofer duty being close to sine wave duty. Its interesting that a lot of the Carver users recommend exactly the opposite of what you're recommending -- they recommend putting the big Carver amps on the bottom of a bi-amped setup. Maybe they're just wrong, but good luck telling them that. They don't like new users as it is, and they certainly wouldn't like someone to come along and tell them that their babies aren't pretty -- even if he may be right!

I'm wondering why there would be a problem with the high voltage rail holding up. Does it suffer from wimpy little caps or something? I thought that the whole idea behind this kind of amp was to eliminate the need for the big caps. Maybe all this will be obvious once I get my hands on the schematic.

[bob p]

Drive belt? Geez, I'd just buy one from the parts market - MCM or someone like them. Carver had two lines, the consumer stuff - like CD players - and the pro stuff. Are you sure this service guy is not just working on the consumer stuff?

I have no personal knowledge. I am just relating a story that I had heard on the forum. The fellow's site is http://www.carveraudiorepair.com. His page states that he services both Carver pro and consumer stuff. He seems to claim that he is the "legacy" repair center now that the official Carver store is gone. His reputation on the forum is that he will not sell parts or information, and his service bills are prohibitive. Essentially, it sounds like your only option is to repair it yourself if you have parts and service manuals, or to pay him to do the repair if you don't.

[Enzo]

SO call Carverpro and ask for the PM1.5 rather than your M1.5. They don't have the consumer stuff, the other place doesn't want to give you the consumer stuff, so get the pro version of your consumer unit. Unless the input jack board is the problem, the difference won't matter. I might have the M1.5 version too, but again, my carver files are buried. If Carverpro doesn't support the consumer stuff, no point in asking them for it in spite of their warnings, just ask for the pro version.

I thought that the whole idea behind this kind of amp was to eliminate the need for the big caps.

Well, yeah. SInce in normal music ther are brief spikes of bottom every so often, with the rest of the music at far lower levels, if you make the main power supply able to handle everything, it has to be large. But if you make the low voltage rails robust for the all the time stuff, then the high voltage rails only have to power those brief spikes - like kick drum hits. But to power the subs, now it is like 50-60 kick drum hits per second. Or 30 in your case.

Look at it this way. If a 500 pound thing was holding your foot in place, you could probably jerk on it and get your foot out from under. Brief pulse of energy. But you could not just stand there holding it off the floor. Sustained energy.

All that having been said, I guess it matters just WHAT Carver model you have in mind and what the application is. Clearly the 2400 would be a lot happier pushing subs than my little PM600.

In fairness to mr. legacy there, I have some old parts for various things that I won't sell other than as repair parts. SOme old part is not only worth the parts price, it also enables me to make the repair. No part, no repair. SO a $5 might really be worth $65 to me if it represents the difference between making a repair or turning the customer away. So selling the part alone for the $5 is not worth it to me.

[bob p]

In fairness to mr. legacy there, I have some old parts for various things that I won't sell other than as repair parts. SOme old part is not only worth the parts price, it also enables me to make the repair. No part, no repair. SO a $5 might really be worth $65 to me if it represents the difference between making a repair or turning the customer away. So selling the part alone for the $5 is not worth it to me.

I can see why people are inclined to do that when they need the work. I guess parts are one thing, but I think refusing to sell tech info is somewhat odd. That makes it look like he's trying to force everyone into his shop. Not my favorite business model, but who am I to argue? He bought the inventory, he can do whatever he wants with it.

[Enzo]

I've bumped into that with Ensoniq. SOme guy bought all the legacy stuff of Ensoniq from EMU. WOn't sell parts boards or service literature. I use dto be a service center for them, but after EMU took over they closed us all down. And Ensoniq had never been open with its schemos even to us service centers. Frustrating.

I believe in professional courtesy. I share schematics with my competitors even.

[Steve Conner]

Hi Bob and Enzo,

The sine wave testing thing is interesting. I've attempted to design solid-state power amps before, and it gets obvious pretty quick that if you design it to put out continuous sine wave power indefinitely, it will end up considerably bigger and heavier than your competitors' designs.

The reason of course is not that your competitors have magic tricks that you don't. It's that no audio amp is designed to put out full rated sine wave power into a resistive load continuously. All audio amp makers derate things as far as they think they can get away with, according to the nature of music signals and speaker loads.

Personally, I like to design these things quite conservatively. The last one I did will drive continuous sine wave power into an 8 ohm load fine, but with 4 ohms, it will overheat after maybe 10 minutes. With 2 ohms it manages maybe 1/10 of its rated power and then shuts itself off. This is too conservative to be commercially competitive, but as a hobbyist I don't care.

About the Carver rail switching thing: It copes with sine waves of any size fine, as long as they are a low enough frequency that the rail switching can follow it. If you prodded around with your scope, you would see the amp toggling between its three sets of rails at the appropriate points in each half-cycle. High frequencies jam the rail switching system up, hence they are actually better suited for driving the subs in a PA setup, than the mids or horns. I don't think Carver's protection system even lets you drive full power at high frequencies.

If a Carver overheated on a low-frequency sine wave test, it's just because it's an audio amp, hence not rated for continuous sinewave duty. The rail-switching thing increases efficiency, but Carver probably decided to use that efficiency boost to lower the cost of the product by using smaller transformers and heatsinks, instead of keeping the amp big and heavy and letting it drive stuff *really* hard.

BTW: Bob, I can't see how even the crappiest hi-fi amp would die on you at 1/40 of its rated power! Are you sure you don't have an intermittent short somewhere?

Also, fuses are useless for transistor protection: a fuse has a much bigger SOA than a transistor The fuses are just to stop the cascade of failures after the output transistors have blown short.

[bob p]

The sine wave testing thing is interesting. I've attempted to design solid-state power amps before, and it gets obvious pretty quick that if you design it to put out continuous sine wave power indefinitely, it will end up considerably bigger and heavier than your competitors' designs.

Hi Steve.

Do you mean that it will end up looking something like a Threshold or a Mark Levinson, where the amp is essentially a 100-lb heatsink? Or even bigger? I've always wondered how those things would hold up to a sine wave test.

I've been going through lots of carver stuff lately, looking for answers. I remember spotting an actual sine wave specification, and I had planned on posting it here, but alas, I cannot find it now. IIRC the amp that gets rated as 350W RMS 8-ohms, 600W for "musically relevant" signals, had an FTC (US federal trade commission) sine wave rating of 200W at 8R.

[bob p]

BTW: Bob, I can't see how even the crappiest hi-fi amp would die on you at 1/40 of its rated power! Are you sure you don't have an intermittent short somewhere?

yeah, that's what i could never understand -- how one of those amps blew up at 1/40 of it rated power. i didn't think that they had an intermittent short, as i have been using those amps in my speaker break-in booth. i have been using those amps to drive 2x12 cabs at ear splitting levels for hours on end without any problems. if they had an intermittent short, i would have expected it to show up under those conditions. but as soon as they saw that 30 Hz sine wave... POOF!

when i opened them up, both of those little amps had blown the internal 2A fast blow fuses on the power rails. i replaced them and traced a low power sine wave, and the amps appeared to produce a signal on the outputs. i set them aside to work on something else, cleaned up, and then my signal generator test leads disappeared in the mess. i'll perform a more thorough test once they resurface. My gut inclination is that the 30 Hz sine wave that I was using to re-align the woofer just drew enough current to pop the fuses. that's what i'm hoping, anyway.

[bob p]

About the Carver rail switching thing: It copes with sine waves of any size fine, as long as they are a low enough frequency that the rail switching can follow it. If you prodded around with your scope, you would see the amp toggling between its three sets of rails at the appropriate points in each half-cycle. High frequencies jam the rail switching system up, hence they are actually better suited for driving the subs in a PA setup, than the mids or horns. I don't think Carver's protection system even lets you drive full power at high frequencies.

I have never actually gone inside of my M-1.5t. Its the amp that drives my Infinity speakers in my main audio system, and I'm reluctant to take it apart and use it as an educational guinea pig -- especially if the service docs are hard to come by. i don't want to do something stupid and kill something that i'm not prepared to fix -- espeically when my backups are already dead.

i would be really interested in scoping one of those amps to watch what happens as it switches power rails, though. what kind of test conditions do you recommend to see the artifacts you're talking about? i think that a display like the one shown in Fig 2 of the PM-1.5 Service Manaul would require an 8 channel scope. i've got two.

even in the absense of data, my ears are familiar with what i think you are describing. the amp sounds absolutely fabulous at low volume levels, but as the power gets turned up far enough for the ladder LEDs to indicate that its hitting peak power levels of 30 to 100 watts, i hear the tone becoming harsh and grainy in the top end. i never noticed that with my JBLs but its definitely noticable with the ribbon tweeters on my new speakers. i would be very interested in being able to demonstrate something with a scope that correlates with what i am hearing, and i think that you might have found the source. of course, the amp's published THD specs don't seem reflect this sort of thing. maybe this is just a case where the published specs don't measure what we're talking about.

The rail-switching thing increases efficiency, but Carver probably decided to use that efficiency boost to lower the cost of the product by using smaller transformers and heatsinks, instead of keeping the amp big and heavy and letting it drive stuff *really* hard.

i think you're right about that -- even the Carver Pro gear seems to be built to be light, without heatsinks, and has variable speed fans that turn on as needed.

[Steve Conner]

Hi Bob,

If you drive a sine wave test tone into a dummy load, and scope the output voltage, you should be able to see little glitches and spikes every time it commutates from one rail to another. The higher the frequency of the test tone, the more they'll stand out, but if you go too high the protection might shut it down. Or it might blow up ;-) 1-2KHz should be fine though.

I've never tried it before, but I've heard people on DIYAudio say it is clearly visible. You'll need to be driving considerable power to even hit the first switching point.

I would certainly not meddle with the guts of the M1.5 if it was my main amp If you accidentally let the mojo out of this complex design, you could have a hard time persuading it back in!