Carver M-1.5t THUMP at Power Off

[bob p]

I've got a Carver M-1.5t amp that I've had for 20+ years. The speakers always make a loud "THUMP" sound when the amp is powered on/off. In the past this has never bothered me too much (I learned to live with it), but its much more bothersome now with my new speakers.

I've thought of some kludge ways to fix the problem, like switching the speakers with a resistive load during power-up and power-down, but I'd prefer a cleaner, proper fix to a kludge work-around. I guess it would be possible to put a time delay relay in the circuit, but I was wondering if anyone has a better idea. I have never been inside of the amp and I have no idea what the circuit is like.

This is reportedly a pretty common problem with these amps. I think that the factory actually published a fix for the problem, though I haven't been able to obtain a schematic, service manual, or service bulletins. Of course, the Carver company is long gone, so direct support isn't an option.

[Mark Black]

I've only been in about one of those, but as I remember it is exactly a PM1.5 but with higher sensitivity RCA inputs. I think there are a few places where you can find the PM1.5 documentation online.

Or you could try contacting the re-born Carver at http://www.carverpro.com/2004/. They do a reasonable job of trying to support older pro product but don't have anything to do with the consumer hi-fi stuff, so if you ask for schematics on the M1.5 they may say no whereas they probably do have them for the PM1.5.

I am no help on the thump-at-turnoff problem, but I can tell you based on many repairs of PM1.5's that there are a few other issues you might want to address if you get inside:

1. Re-touch the solders at ALL output transistor sockets regardless of whether they look bad or not. This can be a bit tricky getting the iron in past the wiring & avoiding solder bridges but is well worth the effort.

2. Re-touch solders at all the hot-glued caps near the right (viewed from the front) end of the channel PCB's.

3. Squirt the bias and power supply trimmers with some DeOxit and work them back and forth (only if you plan to adjust them, otherwise probably best left alone).

Power supply trim is on the front-to-back PCB and should be set to +/- 124VDC measured at the large filter caps on the right side.

Bias is 3.4mVDC measured across the emitters of the two center output transistors on each channel (I find the transistor socket legs a handy place to clip on for that measurement).

Again, this info is only pertinent if my memory is correct on the M1.5 to PM1.5 relationship.

Good luck on the thump quest!

[Enzo]

I think the difference is minimal - input connectors, rack mounting, etc. The P in PM1.5 is for professional. BAsically they made models of the same amps for home stereo and for pro audio. I think the power supply and channel cards are the same.

If I get the chance, I'll dig out the files and look for a bulletin.

[bob p]

I've only been in about one of those, but as I remember it is exactly a PM1.5 but with higher sensitivity RCA inputs. I think there are a few places where you can find the PM1.5 documentation online.

Or you could try contacting the re-born Carver at http://www.carverpro.com/2004/. They do a reasonable job of trying to support older pro product but don't have anything to do with the consumer hi-fi stuff, so if you ask for schematics on the M1.5 they may say no whereas they probably do have them for the PM1.5.

Thanks for the link to CarverPro. I looked around on their website for manuals, and the most that I could find for the PM-1.5 on their download page was the PM-1.5 Owner's Manual. I couldn't find any schematics online, not even at their FTP site. I guess you have to buy the manuals. I don't have a problem with that, but I would be reluctant to buy the PM-1.5 manual, since I don't actually have the PM-1.5 amp and there are some differences in the inputs/outputs and the panel controls.

I did find something interesting in the PM-1.5 documentation, though. On Page 8 of the PM-1.5 manual, there's a section entitled, "Power-Up/Power-Down Procedure. The PM-1.5 OM states that voltage transients occur at power-on and power-off that could destroy speakers! To avoid blowing up drivers, they recommend turning the input volume down to zero at power-on and power-off. I'm thinking that there's got to be a more reliable way to protect your speakers -- sometimes people forget to turn the volume to zero before touching the power switch, and its not reasonable to expect the amp to blow up your speakers if you should forget.

I poked around the web site at CarverPro, and I found a disclaimer on their Tech Support page that states that they won't be able to help with consumer audio gear:

Carver Professional was purchased in November of 1995 by Phoenix Gold International, Inc. of Portland Oregon. Carver Professional, as a division of Phoenix Gold International, designs, sells and manufactures state-of-the-art, high quality amplifiers for the professional and commercial audio markets. Carver Professional continues to be responsible for the servicing of the professional amplifier products that were manufactured at Carver Corporation prior to the purchase by Phoenix Gold International.

We realize that you may own Carver consumer products manufactured or sold by Carver Corporation, and are having trouble finding support and service for those products. We would like to be able to help you, however, we do not have parts or documentation for the consumer electronic products sold under the "Carver" brand.

It would appear that when Bob Carver sold-off Carver Corporation, he split-off the Carver Professional division from the consumer products division, and they're now owned by two different companies.

The CarverAudio.com Forum reportedly has a large collection of Carver service documents. I have registered there and asked for help, and I've found that they won't release documents to new forum members, and this appears to be a sore spot with them. If you ask for help and you're a forum noob, you'll find people making posts that include little animations of people banging their head against a wall. Someone offered to put up a server to make it easy for people to access the manuals, and he was quickly shot down. As one member there said, "We want to smell your ass before we let you piss on our trees."

Alternatively, they will sell documents to you, but as I understand it, you can not buy copies of the original documentation that include the high res fold-out diagrams -- you can only buy scanned PDFs. I've bought printouts of scanned PDF service manuals on several occasions and I've always been disappointed. They're never as good as the original tech booklets.

[bob p]

I am no help on the thump-at-turnoff problem, but I can tell you based on many repairs of PM1.5's that there are a few other issues you might want to address if you get inside:

1. Re-touch the solders at ALL output transistor sockets regardless of whether they look bad or not. This can be a bit tricky getting the iron in past the wiring & avoiding solder bridges but is well worth the effort.

2. Re-touch solders at all the hot-glued caps near the right (viewed from the front) end of the channel PCB's.

3. Squirt the bias and power supply trimmers with some DeOxit and work them back and forth (only if you plan to adjust them, otherwise probably best left alone).

Power supply trim is on the front-to-back PCB and should be set to +/- 124VDC measured at the large filter caps on the right side.

Bias is 3.4mVDC measured across the emitters of the two center output transistors on each channel (I find the transistor socket legs a handy place to clip on for that measurement).

Thanks. At the Carver Forum I have read about people having problems with intermittent operation. I have also read threads about amps that went in for repair and were pronounced to have had cold solder joints, which I found surprising. Needless to say, 1+1=2. Thanks for the tips.

[Enzo]

Can I recommend CALLING CarverPro? Just because something is not sitting on their web site doesn't mean it is not available.

And did you download the owners manual to see if it included schematics or not?

If the Carver forum you have been on hates to help people they don't know, and they aer focused on the consumer goods, perhaps they are not the best place to look for advice.

[bob p]

Can I recommend CALLING CarverPro? Just because something is not sitting on their web site doesn't mean it is not available.

Just in case I wasn't clear, my amp is a CONSUMER amp, not a PRO amp. Enzo, I've seen you recommend calling the manufacturer directly on at least 1000 occasions (Crown comes to mind), so I know how important you think the direct approach is in solving problems like this. Yes, I know you think I'm stupid for not calling CarverPro. I have only hesitated to call them because their site disclaims any connection with consumer audio gear, and their site explicitly tells potential customers NOT to call them with ANY questions about consumer audio gear. They redirect all of their questions to the Carver Forum.

If the Carver forum you have been on hates to help people they don't know, and they aer focused on the consumer goods, perhaps they are not the best place to look for advice.

I am not too dense to understand that if the Carver Forum at CarverAudio.com isn't a friendly place, then its not the best place to look for help. But the Carver Forum at CarverAudio.com is the place that CarverPro tells you to go, then you don't have many other options.

There is NOWHERE else to go. There are 1200 people at the Carver Forum who are in the same position that I am in, and the consensus of opinion there is that there aren't any other options than the ones I've already cited in the other thread. The last bastion of hope was Bob Carver's daughter, who with two of the former Carver assembly techs, had been moonlighting out of their basements to repair old Carver gear by mail-order. They've closed their doors too.

I have been reluctant to call CaverPro because I have read and I understand their explicit instructions NOT to call them. But if you think it will be helpful, I will put on my Pestering Asshole hat and call them just to see how they respond. You never know -- I might just get something and then I could tell 1200 self-professed Carver experts that they were all wrong. That would give me immense joy... until the moment that I get banned from the forum.

And did you download the owners manual to see if it included schematics or not?

At the risk of giving a stupid answer, of course I downloaded the owner's manual. I couldn't have quoted the information in it if I hadn't downloaded the manual! I even provided a hyperlink to the manual so that anyone who was interested in looking at the manual could read it to see if there was a schematic.

I will give CarverPro a call and pester them just to see what happens. I've been working on this a long time, and the only stones that remain left unturned at this point are the ones that people have told me NOT to turn over.

If you decide to go through your archives and dig up your original Carver service data, let me know if you'd be interested in selling it rather than re-filing it.

[Enzo]

I am sorry if I have irritated you, my intent is not to call you stupid, but to make sure we have done everyting we could. And I am sorry If I do not have a 100% picture in my mind of your effort. Between all the threads here and on some other boards, not to mention the collection of efforts in my direct email every day, it can be a large task to keep it all organized in my mind. My concern for helping you is genuine, even if the result has made you uncomfortable with me.

The differences between your amp and the amps that Carver Pro concern them selves with are small. That is why I am trying to suggest calling them for the PM1.5. It will be a lot closer to your amp than nothing at all. Then you won't be an asshole to them. I don't mean for you to call them asking for what they specifically ask you not to.

To me part of being resourceful is getting close if exact is not at hand.

I have found my PM1.5 files, but it would be a lot to scan if I don't have to. I am looking for any M1.5 files I might have. I will be happy to scan them if that is what we need. I don't want to sell the files, nor do I want to charge anyone for scanning them.

SO far any M1.5 bulletins I have do not concern power down thumps.

I have several boxes of Carver files to open and look through yet. I think they are mostly consumer stuff like receivers and CD payers.

FOund the book for the Carver Amazing Loudspeakers though. They are huge, but boy do they sound good. And boy are they inefficient, you realldy do need several hundred watts per side to get any level going.

[bob p]

Enzo, I've never doubted your sincerity or your desire to help people, and if I'm coming across as irritated, its not because of you -- its because I've been yelled at by other people for asking questions that they think I should not be asking. It has been a frustrating experience.

In trying to find this information I'm going to keep looking until I have left no stone unturned. I'm willing to turn over all of the rocks that are necessary to solve the problem. Though I've been looking far and wide, I have been selective about which stones are getting turned over in what order; I'm trying to turn over the stones that are easiest to turn over first, and to save the stones that people tell me not to turn over until later, and to save the stones that amount to asking for big favors until last. You're right, something close is better than nothing, and the PM-1.5 manual would be better than not being able to get the M-1.5t manual.

I realize that copying odd sized documents is a real PITA, so I'm leaving a request for that sort of thing as the last stone to get turned over. I've even thought about the idea of borrowing original tech data from someone while I took it to Kinko's to make full size copies, and then returned the originals. But letting tech data out of their hands is an awfully big favor to ask of anyone.

If you've got a pretty big collection of Carver tech data and you're familiar with the line, do you have any interest in taking on more Carver repairs? If you're interested in the work, the people at the Carver Forum would probably like to have access to a good repair shop. Right now it seems that there's only one and he's got them by the balls.

Thanks again for all of your help.

[Enzo]

I just noticed yours is a M1.5t. I didn't notice the t before.

If I recall, and I might not, were the t versions the ones with an extra output xstr on each phase? Or is that the A versin I am thinning of?
If you ask for a PM1.5, you might check if there is a PM1.5t first.

I have some large fold out schemos for the PM1.5 that are like blueprints. But for the most part, the thing is all on letter size pages. The blueprints are duplicated on pafe size too. Ther is a lengthy tech discussion and adjustment and troubleshooting procedure. If I need to copy it, I'd almost rather go to Kinkos and stuff the pile in the batch copier and mail it.

So scanning would be whole pages, just lots of them.

[Enzo]

I have a couple boxes of them, and a reasonable collection of the PM series, but there are lots I don't have.

I do consumer repairs out of this shop mostly as a courtesy to the community, but not looking for more. They have few places to turn around here. And especially not looking for anything remotely resembling "audiophiles." ("No, man, my midrange is still grainy, and the soundstaging is off 3 degrees.")

[Steve Conner]

I think the "t" is for "Tube transfer function" - it has an artificially raised output impedance and some sweet-sounding distortion added.

Seeing the complexity of Carver's designs, I'd be sorely tempted to stuff in a relay-based anti-thump and DC offset protection board. Trying to modify the existing circuit could open such a can of worms.

I heard about the "Magnetic Field" power supply years ago and always wanted to know how in hell it worked. But from the literature you guys posted, it looks like it's just a triac lamp dimmer with a heavy coat of marketing BS. I still want to know more though, maybe I should be looking for a 2nd hand Carver to take apart

[bob p]

I just noticed yours is a M1.5t. I didn't notice the t before.

Yeah, all this alphabet soup with similar names for different models makes things confusing. I'm not sure whether there is a "t" model of the PM-1.5 or not -- I seem to remember seeing one named somewhere, but I haven't been able to find any "t" variations of the PM-1.5 amp name at the CarverPro site, or for sale on eBay. So maybe there aren't "t" versions of the Pro amp and we're just imagining them.

I think the "t" is for "Tube transfer function" - it has an artificially raised output impedance and some sweet-sounding distortion added.

Well, this is why the alphabet soup thing gets so confusing -- the meaning of the "t" designation changed over the course of the years as the Carver marketing program changed.

At first the "t" desingation meant that the amp was modified to emulate the transfer function of a specific high-end amp. Different Carver models with the "t" suffix emulated different amps, and they were not all tube or SS. Although the "t" did indicate a transfer function emulation, it never told you what amp was being emulated. You had to read the other marketing info and be "in the know" to figure it all out.

For example, the M-1.5t was designed to emulate the transfer function of the Mark Levinson ML-2, a Class A transistor amp. The M-1.0t amp was modified in response to Bob Carver's challenge for Stereophile in which he dared them to ask him to emulate any amp of their choice. Bob Carver bet them that he could do this not in his R&D lab, but in a hotel room near Stereophile's Arizona headquarters. The conditions of the test were that he would treat the target amp as a black box, that he could do it in 48 hours, and that Stereophile couldn't correctly identify the amps in a 48 hour blind test. The M-1.0t amp was modeled after a famous HiFi tube amp of the period, which was one of the Conrad Johnsons, IIRC. Carver won the bet and published the results in his ads. The Stereophile guys were so embarassed that it started a feud between Carver and Stereophile that went on for years, involved lawsuits, etc.

So in the beginning, the "t" designation meant that some famous High End amp was being emulated. It could have been either a SS or a tube amp, the "t" didn't indicate which.

Some time later on Bob Carver designed a tube amp that he called the "Silver Seven." Being a modest guy, he proclaimed it to be the best sounding tube amp ever, and then he designed a whole range of transistor amps that were designed to emulate the transfer function of THAT amp, gave them all "t" designations, and turned the marketing guys loose. After that there was a series of TFM-prefixed amps, and those all emulated some amp's transfer function and the alphabet soup gets even worse.

The only amps that I'm certain about are the M-1.5t and the M-1.0t, which were nulled against the Levinson ML-2 and the Conrad Johnson, respectively, to mimic their transfer functions.

[Steve Conner]

Awesome. I never heard of this before, and I can't believe he managed to pull that off even with those Class-G rail switcher output stages that generate huge HF transients. The commutating spikes are nasty distortion clearly visible on a scope, and I heard the M1.0 was Carver's first and nastiest Class-G attempt, but it still won the Stereophile blind test?

Bob Carver and his marketing team are my new heros.

[bob p]

I have some large fold out schemos for the PM1.5 that are like blueprints. But for the most part, the thing is all on letter size pages. The blueprints are duplicated on pafe size too. Ther is a lengthy tech discussion and adjustment and troubleshooting procedure. If I need to copy it, I'd almost rather go to Kinkos and stuff the pile in the batch copier and mail it.

So scanning would be whole pages, just lots of them.

I remember checking out the Amazing Loudspeaker when it was new, and it was a power hog like you mentioned earlier. When I was there I walked into the service dept and I saw a tech looking over a blueprint-sized schematic that had to be at least 36-inches wide. I asked him what it was, and he said it was a schem for the M-1.5t. Of course, I asked him if I could get a copy of it for my amp, and I was given the cold shoulder.

That big-ass schematic is just what I'm looking for, and that's why I'd like to buy a set of real Carver service data from someone, rather than relying on letter-sized paper printouts that are 1/10 the size. But tiny scans seem to be all that's available.

If copying is too inconvenient, I'd be happy to do the legwork so that you're not put to a whole lot of trouble. I have a scanner with an automatic document feeder that can handle both letter and legal pages and will scan to PDF. I'd be happy to make the trip to Kinko's to copy a big blueprint-sized schematic. If you'd be willing to send the original documents to me via registered mail I'd happily assume the responsibility for their safe return. If you prefer to not to do that sort of thing and you'd prefer to go to Kinko's, since you don't like to accept money for schematics I'd be happy to cover your costs and buy you lunch to show my appreciation.