Vintage M4.0t Silver Seven

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Robert R
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Re: Vintage M4.0t Silver Seven

Post by Robert R » Wed Aug 20, 2008 7:14 pm

Welcome CAM - sorry about your trouble

First thought is, it won't heal itself, new fuse not withstanding. Probably blew a transistor. Happens once in a while, not too often.

Next thought, it's worth fixing. Those amps sell for $350 plus on e-bray all the time. And what would you replace that amount of power with?

After those thoughts the Forum will want to know more details: Did it blow the replacement fuse? (You used the correct value and type, of course).
Does the noise come from the speakers or inside the unit itself?
What do the lights do, if anything?

As to repairs, what's your location? There are a few decent places scattered about the USA; the best, if you don't want to fool around, is in Oregon.

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Re: Vintage M4.0t Silver Seven

Post by frankieD » Wed Aug 20, 2008 7:39 pm

FOBofSC wrote:I have a M4.0t amp that has worked flawlessly for years. The other day, turned on pre-amp(other components are plugged into it) and nothing. Fuse in amp had gone bad. Replaced, no audio, only loud buzzing from amp. This happens whether amp power switch is on or off.

Any ideas? If not, any recommendations for repair tech that is qualified, competent, and honest. Thx. CAM

Hi, and welcome to the forum.

As for the amp, Send it to Roland at Hi-tech audio Ltd. He is by FAR the best. Check out the repair section you can get the phone number. He will talk to you about it before you send it.


Good luck, Frank.

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Re: Vintage M4.0t Silver Seven

Post by RichP714 » Wed Aug 20, 2008 8:19 pm

FOBofSC wrote:I have a M4.0t amp that has worked flawlessly for years. The other day, turned on pre-amp(other components are plugged into it) and nothing. Fuse in amp had gone bad. Replaced, no audio, only loud buzzing from amp. This happens whether amp power switch is on or off.

Any ideas? If not, any recommendations for repair tech that is qualified, competent, and honest. Thx. CAM
Hi there, and welcome! Others have already directed you to the guy with the most experience, Rolland at Hitech. The power switch doesn't make/break power to the primary of the coil, it enables a timing capacitor to start firing a triac, which sends a burst of line AC through the coil to start the startup sequence, and things go from there.

The number one thing to do is get somebody to repair it that has experience with Carver or other triac controlled power supplies. A 'normal' tech will often try to short across the triac in an effort to 'jump start' the coil, which sends full duty cycle AC through the coil primary. The coil cannot tolerate this, as a normal transformer does, and will self detruct.....none are available for replacement.....result a boat anchor.

If she hums loudly regardless of power switch position, and provided the power switch is working, there is most likely a problem in the triac control circuit. Simple thing to check, is the 115/220 switch in the right position?

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Re: Vintage M4.0t Silver Seven

Post by engtaz » Thu Aug 21, 2008 2:37 pm

Welcome FOBofSC. Glad you found us. Rich is the man when having info so what he says I would recommend. $350.00 is low ball price for a M4.0T. Average is $400.00 plus shipping. (and prayer that it arrives safely).

Good Luck,
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C 16, PT 2400, Slim Device, Carver TX-8, 490T and Rega TT w Grado Gold cart in the 2 channel setup
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Re: Vintage M4.0t Silver Seven

Post by TNRabbit » Thu Aug 21, 2008 3:27 pm

RichP714 wrote:
FOBofSC wrote:I have a M4.0t amp that has worked flawlessly for years. The other day, turned on pre-amp(other components are plugged into it) and nothing. Fuse in amp had gone bad. Replaced, no audio, only loud buzzing from amp. This happens whether amp power switch is on or off.

Any ideas? If not, any recommendations for repair tech that is qualified, competent, and honest. Thx. CAM
Hi there, and welcome! Others have already directed you to the guy with the most experience, Rolland at Hitech. The power switch doesn't make/break power to the primary of the coil, it enables a timing capacitor to start firing a triac, which sends a burst of line AC through the coil to start the startup sequence, and things go from there.

The number one thing to do is get somebody to repair it that has experience with Carver or other triac controlled power supplies. A 'normal' tech will often try to short across the triac in an effort to 'jump start' the coil, which sends full duty cycle AC through the coil primary. The coil cannot tolerate this, as a normal transformer does, and will self detruct.....none are available for replacement.....result a boat anchor.

If she hums loudly regardless of power switch position, and provided the power switch is working, there is most likely a problem in the triac control circuit. Simple thing to check, is the 115/220 switch in the right position?
Ditto...and WELCOME, FOBofSC!!
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Re: Vintage M4.0t Silver Seven

Post by gdb » Thu Aug 21, 2008 3:40 pm

Welcome, and sorry to hear about your problem, I can't speak for anyone else here but I never plug a "high draw" component into the recepticles on the back of a preamp. If anything at all, it's only something of 100watts or less,usually I just connect all pieces directly to a
power/surge supp. unit with a master off switch. Good Luck !! gdb

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Re: Vintage M4.0t Silver Seven

Post by OBI56 » Thu Aug 21, 2008 3:57 pm

gdb wrote:Welcome, and sorry to hear about your problem, I can't speak for anyone else here but I never plug a "high draw" component into the recepticles on the back of a preamp. If anything at all, it's only something of 100watts or less,usually I just connect all pieces directly to a
power/surge supp. unit with a master off switch. Good Luck !! gdb
SOME amps CAN be plugged into the switched power outlets on the back of a pre-amp IF and only if the switched power outlet has a sufficient rating. Among Carver preamps that have such a switched power outlet, the C-1 and C-2 are rated for 500W which will accomodate many Carver amps, but definitely NOT the M-4.0t (or the basicallyidentical TFM-4.0, TFM-42 and TFM-45) which require a switched power outlet rated at least for 1700W as per the owners manual. The consequences of this are usually a blown or burnt out power switch. The vast majority of non-Carver preamps can NOT handle a power amplifier connected to their switched power outlets. Your M-4.0t should be plugged directly into a dedicated 15A power outlet; even better a 20A dedicated circuit.
M-4-0t power requirements.JPG
M-4-0t power requirements.JPG (69.8 KiB) Viewed 2241 times
Now, all of this has nothng to do with the problem you are describing which relates to an internal problem with the power amp power supply (possibly the triac firing circuit).
Last edited by OBI56 on Thu Aug 21, 2008 10:21 pm, edited 1 time in total.
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Re: Vintage M4.0t Silver Seven

Post by engtaz » Thu Aug 21, 2008 4:56 pm

Nice read on the problem Obi.
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Carver M4.0T in front channels to Caver AL VI's in SACD & 2 Channel setup
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Re: Vintage M4.0t Silver Seven

Post by OBI56 » Thu Aug 21, 2008 5:12 pm

Weve had this discussion several times already engtaz. The C-1 and C-2 owners manuals as well as the manuals for several Carver amps do state that it is possible to hook them up to those specific Switched AC outlets on those Specific Preamps. This is because Bob designed those preamps with 2 seperate power switches connected to 1 outside button; 1 for the preamp itself, the other one with a higher amperage rating connected only to the switched AC outlets.
Equipement known to be safely used together:

C-1
C-2
C-4000
CT-7
M-400 (regular, a and t)
M-500 (regular and t)
M-1.5 (regular and t)
M-1.0t
M-0.5t
TFM-6 (regular and c)
TFM-15 (regular, c and cb)

Now, just to reiterate, this ONLY applies to those SPECIFIC preamps and amps mentionned and do not apply to other brands of equipment.
Why let facts or common sense get in the way of your opinions.

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Re: Vintage M4.0t Silver Seven

Post by Robert R » Thu Aug 21, 2008 8:16 pm

OBI, et.al:

On the plugging of big amps into the listed Carver preamps: For what it's worth, I'd advise against it, especially now that parts are practically unobtainable. I know the C-4000 book from 1981 says its OK, and doesn't even specify any upper number of watts. The C-1 manual says 500 watts total in the switched, 1000 in the unswitched. I'm not familiar with the C-2, but doubt that a lower end unit is any heftier. The M1.5 can deliver over 1200w peaks, so it obviously draws more than that, at least momentarily, and that's a lot of juice for those little wires such as you find inside a C-4000. Even if it didn't tend to fry the switch, you'd want to hook that amp directly to the wall, preferably a dedicated line, as you indicated, to maximize performance.

Otherwise, the switch runs hot and eventually gets brittle, then maybe crumbles or carbonizes and finally dies. I got one of my C-4000s that way. It smoked out, and wouldn't run, so the original owner peddled it as junk quickly, after about 20 years flawless service; he probably got something else very expensive and no better or not as good, and I got a steal. But those switches are special types, not available anywhere I can find. Incidentally, the dual deck design is NOT wired as stated, at least on mine. The AC, both to the preamp's power transformer and to rear switched outlets, is all handled by the one hefty switch deck, and the other section is just a mute switch on the same button, I believe to eliminate preamp shutdown thump. That part still functions, but not much use. Anyhow, when your switch fries and dies you just have to short the AC switch wires together to run the unit, but you have to pull the plug to shut it off. And of course all the outlets in the rear are now live until you do so.

Better to preserve these old things in original working order for use with tuners, players, processors, etc. that just draw modest watts. If you must have one-switch action to include the power amp, I suggest a good power strip, or better yet put a handy wall switch on that dedicated line.

Robert R
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Re: Vintage M4.0t Silver Seven

Post by OBI56 » Thu Aug 21, 2008 11:02 pm

My mistake Robert R, you are correct about the 500W rating (I have edited my post to correct this). I can't vouch personally for the C-4000 as this was reported/confirmed to me by another forum member. I can vouch however for the C-1 and C-2 as I own both and have opened them and physically tested them to ensure that what I said is accurate. Both the C-1 and C-2 have dedicated, heavy duty wire running from the AC input directly to the second power switch and back to the Switched power outlets; the C-1 even having these wires shielded. The dedicated power switches on both of these units have a 5A rating at 240V and 10A at 120V which should ensure at least a 500W capacity for the switched outlets.

As for the M-1.5t power requirements, I refer you to the Owners Manual excerpt below.
M-1-5t power needs.JPG
M-1-5t power needs.JPG (71.42 KiB) Viewed 2184 times
I have never suggested that these amps SHOULD be plugged into these SPECIFIC preamps, just that they COULD. You can check out all of my approx dozen posts on this subject and you will see that I have always had a consistent position on this subject. I have never even suggested that any other amp could be plugged into any other preamp, no matter what the brand and have always cautioned against doing so.

One last thing to remember about maximum power output VS power consumption on Carver Magnetic Field Amps. Musical peaks are of extremely short duration and are in no way related to the average power levels encountered in music reproduction. These Carver amps used multiple voltage rails and step between them as power levels increase. At most normal music listening levels the top voltage rail rarely gets used (percentagewise). Unless you are listening at extreme sound pressure levels with compressed music the power switch will almost never see more than its rated amperage rating for more thana fraction of a second every so often. Bob specifically designed his amps to have a low average power consumption and his preamps power switches to handle this. Later designs dropped this feature, probably due to cost considerations and the the inclusion of power switches on all amps.

My recommendations ONLY apply to those SPECIFIC amps and preamps. In ALL other cases, the general rule of NEVER plugging an amp into a switched AC outlet on the back of a preamp applies.
Why let facts or common sense get in the way of your opinions.

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Re: Vintage M4.0t Silver Seven

Post by BillD » Fri Aug 22, 2008 2:57 pm

The C-4000 manual states:
The C-4000 is equipped with three "switched" AC convenience outlets whose power is switched on and off by the C-4000's own front-panel power switch. These can be used to supply AC power to all-electronic products such as tuners and power amplifiers. The switch is a heavy-duty unit and can be safely be used to switch on power amplifiers of up to 1000 watts.
BTW, Marc, you can add the C-500 to the safe list on your amplifiers.
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Re: Vintage M4.0t Silver Seven

Post by OBI56 » Fri Aug 22, 2008 3:28 pm

OK, thanks Bill, will do!

Just thinking here about those C-4000s with bad power switches adn I'm wondering if there cound have been either a batch of bad switches or if they might have changed the design at one point to cut costs and substituted a different power switch. Might be worth looking into.
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Re: Vintage M4.0t Silver Seven

Post by Robert R » Fri Aug 22, 2008 3:37 pm

Seems I inadvertently stepped into an long-ongoing debate. On further reading, I see that the M-4000 does indeed have a rating number of 1000 watts, and of course I have no way of knowing what the burned up one I encountered was subjected to. I still think it ain't worth the risk to run a big amp off a preamp switch, because the return isn't worth the risk, at least to me.

Still, I must admit that I'm lazy enough to wish I had one-button shutdown myself. For a while I've had this idea kicking (well, twitching) around in my head that the whole thing would be easily solved with the right relay. I just don't know where to find it. It would be activated by 120VAC (from a "switched" convenience outlet, draw a very modest amount of current, and have the power capacity to handle your largest amp peak with ease. Well, such things are easy to find - there's one in about every home air conditioning system on the market, replaceable for maybe 20 bucks, + or-. BUT....there's a problem, right up front, before you worry about wiring, housing/containment, or reliability, or whatever - they are NOISY! All the ones I've seen (heard) sound like a slightly weary electric alarm clock; some worse than others, of course, but all unacceptable in a sound listening room.

So here's a case where maybe the power of the Forum can weigh in. Anybody out there know about power relays? Quiet ones?

Robert R

PS - If I knew how, I'd start a new thread concerning this switching business. We've left the M4.0t Silver Seven discussion long since.
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Re: Vintage M4.0t Silver Seven

Post by BillD » Fri Aug 22, 2008 3:46 pm

What you really need is a power center. I have one that has 6 switched, 6 unswitched and 2 special switched (high current) outlets. It can be triggered by either a power cord from a switched outlet on a preamp, or a 12v trigger. The high current outs come on last and off first (a 4 sec delay for one and 8 sec for the other) to avoid thumps. It's the ultimate in switched outlets (and it cleans up your power better than a $800 power cord)!
It should sound like it isn't there!
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Making life enjoyable through expensive electronics.
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